MINISTRY OF SCIENCE AND EDUCATION OF THE REPUBLIC OF KAZAKHSTAN
STATE UNIVERSITY NAMED AFTER SHAKARIM, SEMEY
Document of 3 level by MQS
EMCD
Educational - methodical materials
for discipline «Chemistry of high
molecular compounds»
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EDUCATIONAL-METHODICAL COMPLEX OF DISCIPLINE
«Chemistry of high molecular compounds»
For the specialty
5B011200– «Chemistry»
Educational - methodical materials
Semey
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Content
1. Glossary of discipline
2. Brief synopsis of the lectures
3. Laboratory work
4. Self-study of students
5. Test and Measurement tools
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1 GLOSSARY OF THE COURSE «CHEMISTRY OF HIGH MOLECULAR
COMPOUNDS»
Alternating copolymer - a copolymer consisting of macromolecules comprising two
species of monomeric units in alternating sequence.
Anionic polymerization - an ionic polymerization in which the kinetic-chain carriers
are anions.
Atactic macromolecule - a regular macromolecule in which the configurational (base)
units are not all identical.
Atactic polymer - a substance composed of atactic macromolecules.
Bead-rod model - a model simulating the hydrodynamic properties of a chain
macromolecule consisting of a sequence of beads, each of which offers hydrodynamic
resistance to the flow of the surrounding medium and is connected to the next bead by a
rigid rod which does not. The mutual orientation of the rods is random. (IUPAC)
Bead-spring model - a model simulating the hydrodynamic properties of a chain
macromolecule consisting of a sequence of beads, each of which offers hydrodynamic
resistance to the flow of the surrounding medium and is connected to the next bead by a
spring which does not contribute to the frictional interaction but which is responsible for
the elastic and deformational properties of the chain. The mutual orientation of the
springs is random.
Block copolymer - a copolymer that is a block polymer. In a block copolymer, adjacent
blocks are constitutionally different, i.e., each of these blocks comprises constitutional
units derived from different characteristic species of monomer or with different
composition or sequence distribution of constitutional units.
Branch - an oligomeric or polymeric offshoot from a branched chain.
Branched polymer - a polymer, the molecules of which are branched chains.
Cationic polymerization - an ionic polymerization in which the kinetic-chain carriers
are cations.
Chain - the whole part of part of a macromolecule (or oligomer molecule or block)
comprising a sequence of constitutional units between two boundary constitutional
units, each of which may be either an end-group or a branch point. Except in linear
single-strand macromolecules, the definition of the chain may be somewhat arbitrary. A
cyclic macromolecule has no end groups but may nevertheless be regarded as chain.
Where appropriate, definitions relating to "macromolecule" may also be applied to
"chain".
Chain polymerization - a chain reaction in which the growth of a polymer chain
proceeds exclusively by reaction(s) between monomer(s) and reactive site(s) on the
polymer chain such that the reactive site(s) are regenerated on the same polymer chain
by the end of each growth step. A chain polymerization consists of initiation and
propagation reactions, and may also include termination and chain transfer reactions.
The adjective "chain" in "chain polymerization" denotes "chain reaction". In a chain
polymerization, the average degree of polymerization remains constant with monomer
conversion (e.g., in steady-state, radical polymerizations) or may increase with
monomer conversion (e.g., in the formation of living polymers).
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Chain transfer - a chemical reaction, usually occurring during chain polymerizations,
in which the activity of the kinetic-chain carrier is transferred from the growing
macromolecule or oligomer molecule to another molecule or another part of the same
molecule. Chain transfer to another part of the same molecule is often termed
backbiting.
Comb macromolecule - a macromolecule comprising a main chain from which long
chains emanate at approximately regular intervals.
Configurational base unit - a constitutional repeating unit in a regular macromolecule
(or oligomer or block), the configuration of which is defined at least at one site of
stereoisomerism in the main chain.
Co-Oligomer - an oligomer derived from more than one species of monomer.
Crosslink - a constitutional unit connecting two parts of a macromolecule that were
earlier separate molecules. Note: a network may be thought to consist of many "primary
chains" that are interconnected by a number of crosslinks. In the vast majority of cases,
the crosslink is a covalent bond but the term is also used to describe sites of weaker
chemical interactions, portions of crystallites, and even physical entanglements.
Degree of polymerization - the number of monomeric units in a macromolecule or
oligomer molecule.
End-group - a constitutional unit with only one attachment to a chain.
Gel-permeation chromatography - (recommended abbreviation: GPC ) A separation
technique in which separation mainly according to the hydrodynamic volume of the
molecules or particles takes place in porous non-adsorbing material with pores of
approximately the same size as the effective dimensions in solution of the molecules to
be separated.
Graft copolymer - a copolymer that is a graft polymer. In a graft copolymer, adjacent
blocks are constitutionally different, i.e., each of these blocks comprises constitutional
units derived from different characteristic species of monomer or with different
composition or sequence distribution of constitutional units.
Homopolymer - a polymer derived from one species of (real, implicit, or hypothetical)
monomer. Note: many polymers are made by mutual reaction of complementary
monomers. These monomers can readily be visualized as reacting to give an "implicit
monomer", the homopolymerization of which would give the actual product, which can
then be regarded as a homopolymer. Example: poly(ethylene terephthalate). Some
polymers are obtained by modification of other polymers such that the structure of the
macromolecules that constitute the resulting polymer can be thought of as having been
formed by homopolymerization of a "hypothetical monomer". These polymers can be
regarded as homopolymers. Example: poly(vinyl alcohol).
Inherent viscosity/logarithmic viscosity number - the ratio of the natural logarithm of
the relative viscosity to the mass concentration of the polymer.
Ionomer molecule - a polyelectrolyte in which a small but significant proportion of the
constitutional units carry charges.
Irregular macromolecule - a macromolecule in which the constitutional units are not
all identical.
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Isotactic macromolecule - a macromolecule comprising only one species of
configurational base unit (having chiral or prochiral atoms in the main chain) in a single
arrangement with respect to its adjacent constitutional units. Note: in an isotactic
macromolecule, the configurational repeating unit is identical with the configurational
base unit.
Linear chain - a chain with no branch points intermediate between the boundary units
(i.e. the end-groups or other branch points).
Living polymerization - a chain polymerization in which the concentration of kineticchain carriers, under the appropriate conditions for synthesis, remains constant for a
period many times longer than the duration of the synthetic procedure. Often, the
absence of chain transfer is implied in the term "living polymerization".
Macromolecule - a molecule of high relative molecular mass, the structure of which
essentially comprises the multiple repetition of a number of constitutional units.
Main chain / backbone - that chain to which all other chains (long or short or both)
may be regarded as being pendant.
Monomer - a substance, each of the molecules of which can, on polymerization,
contribute one or more constitutional units in the structure of the macromolecule.
Oligomer - a substance composed of oligomer molecules.
Pendent group - side group: an offshoot, neither oligomeric nor polymeric, from a
chain.
Periodic copolymer - a copolymer consisting of macromolecules comprising more than
two species of monomeric units in regular sequence.
Polyaddition a polymerization in which the growth of a polymer chain proceeds by
addition reactions between molecules of all degrees of polymerization, not accompanied
by the formation of low-molar-mass by-product(s).
Polycondensation - a polymerization in which the growth of a polymer chain proceeds
by condensation reactions between molecules of all degrees of polymerization
accompanied by the formation of low-molar-mass by-products(s). The growth steps are
expressed by P_x+P_y -> P_x+y + L {x} element of {1, 2, ... ∞}; {y} element of{1, 2,
...∞} where P_x and P_y denote chains of degree of polymerization x and y,
respectively, and L a low-molar-mass by-product. In a polycondensation where the total
amounts of the monomers are present from the beginning of the polymerization, the
average degree of polymerization increases with conversation of reactive groups.
Polymer-solvent interaction - The sum of the effects of all intermolecular interactions
between polymer and solvent molecules in solution that are reflected in the Gibbs and
Helmholtz energies of mixing.
Regular macromolecule - a macromolecule in which the constitutional units are all
identical with respect to both constitution and orientation.
Spiro chain - a chain that comprises constitutional units, joined so as to form an
uninterrupted sequence of rings through single common atoms between adjacent rings.
Star macromolecule - a macromolecule containing a constitutional unit from which
more than two chains (arms) emanate. A star macromolecule with n linear chains (arms)
attached to the central unit is termed an n-star, e.g., five-star.
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Statistical copolymer - a copolymer consisting of macromolecules in which the
sequential distribution of the monomeric units obeys known statistical laws. An
example for a statistical copolymer is one consisting of macromolecules in which the
sequential distribution of monomeric units follows Markovian statistics.
Stereorepeating unit - a configurational repeating unit having defined configuration at
all sites of stereoisomerism in the main chain of a regular macromolecule (or oligomer
molecule or block).
Syndiotactic macromolecule - a macromolecule comprising alternating enantiomeric
configurational base units. Note: in a syndiotactic macromolecule, the configurational
repeating unit consists of two configurational base units that are enantiomeric. (IUPAC)
syndiotactic polymer:
Telomer - a substance composed of macromolecules or oligomer molecules having few,
usually terminal, reactive functional groups enabling, under appropriate conditions, the
formation of larger macromolecules.
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2. BRIEF SYNOPSIS OF THE LECTURES
Lecture № 1-3. Chemical structure and properties of polymer molecules
Purpose: familiarize with the definition of polymer molecules by the general formula,
composition, classification of polymers
Key questions:
1.
2.
3.
4.
Basic concepts of polymer chemistry.
Nomenclature of polymers.
Classification of carbo-and hetero-polymers.
Characteristic properties of polymer molecules.
Summary:
1. Basic concepts of polymer chemistry.
A polymer in its simplest form can be regarded as comprising molecules of closely related
composition of molecular weight at least 2000, although in many cases typical properties do not
become obvious until the mean molecular weight is about 5000. There is virtually no upper end to the
molecular weight range of polymers since giant three-dimensional networks may produce crosslinked
polymers of a molecular weight of many millions. Polymers (macromolecules) are built up from basic
units, sometimes referred to as ‘mers’. These units can be extremely simple, as in addition
polymerisation, where a simple molecule adds on to itself or other simple molecules, by methods that
will be indicated subsequently. Thus ethylene CH2=CH2 can be converted into polyethylene, of which
the repeating unit is —CH2-CH2—, often written as (-CH2 - CH2-)n, where n is the number of repeating
units, the nature of the end groups being discussed later. The major alternative type of polymer is
formed by condensation polymerization in which a simple molecule is eliminated when two other
molecules condense. In most cases the simple molecule is water, but alternatives include ammonia, an
alcohol and a variety of simple substances. The formation of a condensation polymer can best be
illustrated by the condensation of hexamethylenediamine with adipic acid to form the polyamide best
known as nylon:
This formula has been written in order to show the elimination of water. The product of
condensation can continue to react through its end groups of hexamethylenediamine and adipic acid
and thus a high molecular weight polymer is prepared. Monomers such as adipic acid and
hexamethylenediamine are described as bifunctional because they have two reactive groups. As such
they can only form linear polymers. Similarly, the simple vinyl monomers such as ethylene CH2=CH2
and vinyl acetate CH2:CHOOCCH3 are considered to be bifunctional. If the functionality of a
monomer is greater than two, a branched structure may be formed. Thus the condensation of glycerol
HOCH2CH(OH)CH2OH with adipic acid HOOC(CH2)4COOH will give a branched structure. The
condensation is actually three dimensional, and ultimately a threedimensional structure is formed as
the various branches link up. Although this formula has been idealised, there is a statistical probability
of the various hydroxyl and carboxyl groups combining. This results in a network being built up, and
whilst it has to be illustrated on the plane of the paper, it will not necessarily be planar. As
functionality increases, the probability of such networks becoming interlinked increases, as does the
probability with increase in molecular weight. Thus a gigantic macromolecule will be formed which is
insoluble and infusible before decomposition. It is only comparatively recently that structural details of
these crosslinked or ‘reticulated’ polymers have been elucidated with some certainty. Addition
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polymers are normally formed from unsaturated carbon-to-carbon linkages. This is not necessarily the
case since other unsaturated linkages including only one carbon bond may be polymerised.
Addition polymerisation of a different type takes place through the opening of a ring,
especially the epoxide ring in ethylene oxide CH2-CH2. This opens as —CH2CH2O—; ethylene oxide
О
thus acts as a bifunctional monomer forming a polymer as H(CH2CH2O)n-CH2CH2OH, in this case a
terminal water molecule being added. A feature of this type of addition is that it is much easier to
control the degree of addition, especially at relatively low levels, than in the vinyl polymerisation
described above. Addition polymerisations from which polymer emulsions may be available occur
with the silicones and diisocyanates. These controlled addition polymerizations are sometimes referred
to as giving ‘stepwise’ addition polymers.
2. Nomenclature of polymers.
Source-Based Nomenclature For Homopolymers:
RULE 1
The source-based name of a homopolymer is made by combining the prefix “poly” with the name of
the monomer. When the latter consists of more than one word, or any ambiguity is anticipated, the
name of the monomer is parenthesized.
Example 1
Source-based name: polystyrene
Structure-based name: poly(1-phenylethylene)
Example 2
Source-based name: poly(vinyl chloride)
Structure-based name: poly(1-chloroethylene)
Generic Nomenclature
RULE 2
A generic source-based name of a polymer has two components in the following sequence: (1) a
polymer class (generic) name (polyG) followed by a colon and (2) the actual or hypothetical monomer
name(s) (A, B, etc.), always parenthesized in the case of a copolymer. In the case of a homopolymer,
parentheses are introduced when it is necessary to improve clarity.
PolyG:A
polyG:(B)
polyG:(A-co-B)
polyG:(A-alt-B)
Note 1 The polymer class name (generic name) describes the most appropriate type of functional
group or heterocyclic ring system.
Note 2 All the rules given in the two prior documents on source-based nomenclature can be applied to
the present nomenclature system, with the addition of the generic part of the name.
Note 3 A polymer may have more than one name; this usually occurs when it can be prepared in
more than one way.
Note 4 If a monomer or a pair of complementary monomers can give rise to more than one polymer,
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or if the polymer is obtained through a series of intermediate structures, the use of generic
nomenclature is essential.
Example 3
Generic source-based names - polyurethane:[butane-1,4-diol-alt-(hexane-1,6-diyl diisocyanate)]-blockpolyester: [(ethylene glycol)-alt-(terephthalic acid)]
Structure-based name: poly(oxybutane-1,4-diyloxycarbonyliminohexane-1,6-diyliminocarbonyl)block-poly(oxyethyleneoxyterephthaloyl)
Example 4
Generic source-based name: polyamide:[hexane-1,6-diamine-alt-(adipic acid)]-graftpolyether:(ethylene oxide)
RULE 5
In the case of carbon-chain polymers such as vinyl polymers or diene polymers, the generic name is to
be used only when different polymer structures may arise from a given monomeric system.
Example 5
Generic source-based name: polyalkylene:(buta-1,3-diene)
Source-based name: poly(buta-1,3-diene)
Structure-based name: poly(1-vinylethylene)
Example 6
Generic source-based name: polyalkenylene:buta-1,3-diene
Source-based name: poly(buta-1,3-diene)
Structure-based name: poly(but-1-ene-1,4-diyl)
Example 7
Generic source-based name: polyalkylene:acrylamide
Structure-based name: poly[1-(aminocarbonyl)ethylene]
Example 8
Generic source-based name: polyamide:acrylamide
Structure-based name: poly[imino(1-oxopropane-1,3-diyl)]
3. Classification of carbo-and hetero-polymers.
Homopolymers: one type of repeating units (but different architectures)
Copolymers: different types of repeating units (and microstructures)
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Polymers can be classified in several different ways-according to their structures, the types of
reactions by which they are prepared, their physical properties, or their technological uses. From the
standpoint of general physical properties, we usually recognize three types of solid polymers:
elastomers, thermoplastic polymers, and thermosetting polymers. Elastomers are rubbers or rubberlike
elastic materials. Thermoplastic polymers are hard at room temperature, but on heating become soft
and more or less fluid and can be molded. Thermosetting polymers can be molded at room temperature
or above, but when heated more strongly become hard and infusible. These categories overlap
considerably but are nonetheless helpful in defining general areas of utility and types of structures. The
structural characteristics that are most important to determining the properties of polymers are: the
degree of rigidity of the polymer molecules, the electrostatic and van der Waals attractive forces
between the chains, the degree to which the chains tend to form crystalline domains, and the degree of
cross-linking between the chains. Of these, cross-linking is perhaps the simplest and will be discussed
next. Consider a polymer made of a tangle of molecules with long linear chains of atoms. If the
intermolecular forces between the chains are small and the material is subjected to pressure, the
molecules will tend to move past one another in what is called plastic flow. Such a polymer usually is
soluble in solvents that will dissolve short-chain molecules with chemical structures similar to those of
the polymer. If the intermolecular forces between the chains are sufficiently strong to prevent motion
of the molecules past one another the polymer will be solid at room temperature, but will usually lose
strength and undergo plastic flow when heated. Such a polymer is thermoplastic. A crosslink is a
chemical bond between polymer chains other than at the ends. Crosslinks are extremely important in
determining physical properties because they increase the molecular weight and limit the translational
motions of the chains with respect to one another. Only two cross-links per polymer chain are required
to connect all the polymer molecules in a given sample to produce one gigantic molecule. Only a few
cross-links reduce greatly the solubility of a polymer and tend to produce what is called a gel polymer,
which, although insoluble, usually will absorb (be swelled by) solvents in which the uncross-linked
polymer is soluble. The tendency to absorb solvents decreases as the degree of cross-linking is
increased because the chains cannot move enough to allow the solvent molecules to penetrate between
the chains. Thermosetting polymers normally are made from relatively lowmolecular- weight, usually
semifluid substances, which when heated in a mold become highly cross-linked, thereby forming hard,
infusible, and insoluble products having a three-dimensional network of bonds interconnecting the
polymer chains. Polymers usually are prepared by two different types of polymerization reactionsaddition and condensation. In addition polymerization all of the atoms of the monomer molecules
become part of the polymer; in condensation polymerization some of the atoms of the monomer are
split off in the reaction as water, alcohol, ammonia, or carbon dioxide, and so on. Some polymers can
be formed either by addition or condensation reactions. An example is polyethylene glycol, which, in
principle, can form either by dehydration of 1,2- ethanediol (ethylene glycol), which is condensation,
or by addition polymerization of oxacyclopropane (ethylene oxide):
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4. Characteristic properties of polymer molecules.
Polymers are polydisperse. Polymer materials are
composed of a collection of chains with a distribution of
lengths/masses (and are typically characterized Mn by the
average mass and the breadth of the distribution).
Polymers often exhibit a continuous range of phase
behavior. (Are “viscoelastic”.) Polymers deform and flow
throughout this range but with different timescales.
Polymer properties are dictated almost entirely by
 Monomer structure;
 Average molecular weight; and
 Degree of crosslinking (to a lesser extent).
Polymers are produced on an industrial scale
primarily, although not exclusively, for use as
structural materials. Their physical properties are
particularly important in determining their
usefulness, be it as rubber tires, sidings for
buildings, or solid rocket fuels. Polymers that are
not highly cross-linked have properties that
depend greatly on the forces that act between the
chains. By way of example, considera polymer
such as polyethene which, in a normal
commercial sample, will be made up of
molecules having 1000 to 2000 CH, groups in
continuous chains. Because the material is a
mixture of different molecules, it is not expected to crystallize in a conventional way. Nonetheless, xray diffraction shows polyethene to have very considerable crystalline character, there being regions as
large as several hundred angstrom units in length, which have ordered chains of CH, groups oriented
with respect to one another like the chains in crystalline low- molecular-weight hydrocarbons. These
crystalline regions are called crystallites. Between the crystallites of polyethene are amorphous,
noncrystalline regions in which the polymer chains are essentially randomly ordered with respect to
one another. These regions constitute crystal defects. Quite good platelike crystals, about 100 A thick,
have been formed from dilute solutions of polyethene. In these crystals, CH, chains in the anti
conformation run between the large surfaces of the plates. However, the evidence is strong that when
the CH, chains reach the surface of the crystal they do not neatly fold over and run back down to the
other surface. Instead, the parts of a given chain that are in the crystalline segments appear to be
connected at the ends of the crystallites by random loops of disordered CH, sequences, something like
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an old-fashioned telephone switchboard. The forces between the chains in the crystallites of
polyethene are the so-called van der Waals or dispersion forces, which are the same forces acting
between hydrocarbon molecules in the liquid and solid states, and, to a lesser extent, in the vapor state.
These forces are relatively weak and arise through synchronization of the motions of the electrons in
the separate atoms as they approach one another. The attractive force that results is rapidly overcome
by repulsive forces when the atoms get very close to one another. The attractive intermolecular forces
between pairs of hydrogens in the crystallites of polyethene are only about 0.1-0.2 kcal per mole per
pair, but for a crystalline segment of 1000 CH, units, the sum of these interactions could well be
greater than the C-C bond strengths. Thus when a sample of the crystalline polymer is stressed to the
point at which it fractures, carbon-carbon bonds are broken and radicals that can be detected by esr
spectroscopy are generated. In other kinds of polymers, even stronger intermolecular forces can be
produced by hydrogen bonding. This is especially important in the polyamides, such as the nylons, of
which nylon 66 is most widely used.
The effect of temperature on the physical properties of polymers is very important to their
practical uses. At low temperatures, polymers become hard and glasslike because the motions of the
segments of the polymer chains with relation to each other are slow. The approximate temperature
below which glasslike behavior is apparent is called the glass temperature and is symbolized by Tg
When a polymer containing crystallites is heated, the crystallites ultimately melt, and this temperature
is usually called the melting temperature and is symbolized as Tm. Usually, the molding temperature
will be above Tm and the mechanical strength of the polymer will diminish rapidly as the temperature
approaches Tm. Another temperature of great importance in the practical use of polymers is the
temperature at which thermal breakdown of the polymer chains occurs. Decomposition temperatures
obviously will be sensitive to impurities, such as oxygen, and will be influenced strongly by the
presence of inhibitors, antioxidants, and so on. Nonetheless, there will be a temperature (usually rather
high, 2000 to 4000) at which uncntalyzed scission of the bonds in a chain will take place at an
appreciable rate and, in general, one cannot expect to prevent this type of reaction from causing
degradation of the polymer. Clearly, if this degradation temperature is comparable to Tm as it is for
polypropenenitrile (polyacrylonitrile), difficulties are to be expected in simple thermal molding of the
plastic. This difficulty is overcome in making polypropenenitrile (Orlon) fibers by dissolving the
polymer in N,N-dimethylmethanamide and forcing the solution through fine holes into a heated air
space where the solvent evaporates. Physical properties such as tensile strength, x-ray diffraction
pattern, resistance to plastic flow, softening point, and elasticity of most polymers can be understood in
a general way in terms of crystallites, amorphous regions, the degree of flexibility of the chains, crosslinks, and the strength of the forces acting between the chains (dispersion forces, hydrogen bonding,
etc.). A good way to appreciate the interaction between the physical properties and structure is to start
with a rough classification of properties of solid polymers according to the way the chains are disposed
in relation to each other.
1. An amorphous polymer is one with no crystallites. If the attractive forces between the chains are
weak and if the motions of the chain are not in some way severely restricted as by cross-linking or
large rotational barriers, such a polymer would be expected to have low tensile strength and when
stressed to undergo plastic flow in which the chains slip by one another.
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2. An unoriented crystalline polymer is one which is considerably crystallized but has the crystallites
essentially randomly oriented with respect to one another. When such polymers are heated they often
show rather sharp Tm points, which correspond to the melting of the crystallites. Above Tm these
polymers are amorphous and undergo plastic flow, which permits them to be molded. Other things
being the same, we expect Tm to be higher for polymers with stiff chains (high barriers to internal
rotation).
3. An oriented crystallline polymer is one in which the crystallites are oriented with respect to one
another, usually as the result of a cold-drawing process. Consider a polymer such as nylon, which has
strong intermolecular forces and, when first prepared, is in an unoriented state. When the material is
subjected to strong stress in one direction, usually above Tm, so that some plastic flow can occur, the
material elongates and the crystallites are drawn together and oriented along the direction of the
applied stress. An oriented crystalline polymer usually has a much higher tensile strength than the
unoriented polymer. Cold drawing is an important step in the production of synthetic fibers.
4. Elastomers usually are amorphous polymers. The key to elastic behavior is to have highly flexible
chains with either sufficiently weak forces between the chains or a sufficiently irregular structure to be
unstable in the crystalline state. The tendency for the chains to crystallize often can be considerably
reduced by random introduction of methyl groups, which by steric hindrance inhibit ordering of the
chains. A useful elastomer needs to have some kind of cross-linked regions to prevent plastic flow and
flexible enough chains to have a low Tm. The important difference between this elastomer and the
crystalline polymer is the size of the amorphous regions. When tension is applied and the material
elongates, the chains in the amorphous regions straighten out and become more nearly parallel. At the
elastic limit, a ~e~nicrystallinseta te is reached, which is different from the one produced by cold
drawing of a crystalline polymer in that it is stable only while under tension. The forces between the
chains are too weak to maintain the crystalline state in the absence of tension. Thus when tension is
released, contraction occurs and the original, amorphous polymer is produced. The entropy of the
chains is more favorable in the relaxed state than in the stretched state. A good elastomer should not
undergo plastic flow in either the stretched or relaxed state, and when stretched should have a
"memory" of its relaxed state. These conditions are best achieved with natural rubber (cis-poly-2methyl- 1,3-butadiene, cis-polyisoprene) by curing (vulcanizing) with sulfur. Natural rubber is tacky
and undergoes plastic flow rather readily, but when it is heated with 1-8% by weight of elemental
sulfur in the presence of an accelerator, sulfur cross-links are introduced between the chains. These
cross-links reduce plastic flow and provide a reference framework for the stretched polymer to return
to when it is allowed to relax. Too much sulfur completely destroys the elastic properties and produces
hard rubber of the kind used in cases for storage batteries. The chemistry of the vulcanization of rubber
is complex. The reaction of rubber with sulfur is markedly expedited by substances called accelerators,
of which those commonly known as mercaptobenzothiazole and tetramethylthiuram disulfide are
examples: Clearly, the double bonds in natural rubber are essential to vulcanization because
hydrogenated rubber ("hydrorubber") is not vulcanized by sulfur. The degree of unsaturation decreases
during vulcanization, although the decrease is much less than one double bond per atom of sulfur
introduced. There is evidence that attack occurs both at the double bond and at the adjacent hydrogen
(in a manner similar to some halogenations) giving crosslinks possibly of the following types:
The accelerators probably function by acting as sulfur carriers from the elemental sulfur to the
sites of the polymer where the cross-links are formed.
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Thus the simple linear polymers, polyethene -CH2CH2-, polymethanal -CH2-O-, and
polytetrafluoroethene - CF2-CF2 - , with regular chains and low barriers to rotation about the bonds in
the chain tend to be largely crystalline with rather high melting points and low glass temperatures. The
situation with polychloroethene (polyvinyl chloride), polyfluoroethene (polyvinyl fluoride), and
polyethenylbenzene (polystyrene) as usually prepared is quite different. These polymers are much less
crystalline and yet have rather high glass temperatures, which suggests that there is considerable
attractive force between the chains. The low degree of crystallinity of these polymers is the result of
their having a low degree of regularity of the stereochemical configuration of the chiral carbons in the
chain. The discovery by Natta in 1954 that the stereochemical configurations of chiral centers in
polymer chains could be crucial in determining their physical properties has had a profound impact on
both the practical and theoretical aspects of polymer chemistry. Natta's work was done primarily with
polypropene and this substance provides an excellent example of the importance of stereochemical
configurations. What properties would we expect for polypropene? If we extrapolate from the
properties of polyethene, -CH2-CH2-, Tm = 1300 and Tg = -120°, and poly-2 methylpropene - CH2C(CH3)2-, which is amorphous with Tg = -70°, we would expect that polypropene would have a low
melting point and possibly be an amorphous polymer. In fact, three distinct varieties of polypropene
have been prepared by polymerization of propene with Ziegler catalysts. Two are highly crystalline
and one is amorphous and elastic. These polymers are called, respectively, isotactic, syndiotactic, and
atactic polypropene. The differences between their configurations are shown in Figure:
If we could orient the carbons in the polymer chains in the extended zig-zag conformation of
Figure, we would find that the atactic form has the methyl groups randomly distributed on one side or
the other of the main chain. In contrast, isotactic polypropene has a regular structure with the methyl
groups all on the same side of the chain. Many other kinds of regular structures are possible and the
one of these that has been prepared, although not in quantity, is the syndiotactic form, which has the
methyl groups oriented alternately on one side or the other of the polymer chain. There are striking
differences in physical properties between the atactic and isotactic forms. The atactic material is soft,
elastic, somewhat sticky, and rather soluble in solvents such as 1,1,2,2-tetrachloroethane. Isotactic
polypropene is a hard, clear, strong crystalline polymer that melts at 1750. It is practically insoluble in
all organic solvents at room temperature, but will dissolve to the extent of a few percent in hot 1,1,2,2tetrachloroethane. Although both linear polyethene and isotactic polypropene are crystalline polymers,
ethene-propene copolymers prepared with the aid of Ziegler catalysts are excellent elastomers.
Apparently, a more or less random introduction of methyl groups along a polyethene chain reduces the
crystallinity sufficiently drastically to lead to an amorphous polymer. The ethene-propene copolymer
is an inexpensive elastomer, but having no double bonds, is not capable of vulcanization.
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Polymerization of ethene and propene in the presence of a small amount of dicyclopentadiene or 1,4hexadiene gives an unsaturated heteropolymer, which can be vulcanized with sulfur in the usual way.
dicyclopentadiene The rationale in using these particular dienes is that only the strained double bond
of dicyclopentadiene and the terminal double bond of 1,4-hexadiene undergo polymerization with
Ziegler catalysts. Consequently the polymer chains contain one double bond for each molecule of
dicyclopentadiene or 1,4-hexadiene that is incorporated. These double bonds later can be converted to
cross-links by vulcanization with sulfur. Polychloroethene (polyvinyl chloride), as usually prepared, is
atactic and not very crystalline. It is relatively brittle and glassy. The properties of polyvinyl chloride
can be improved by copolymerization, as with ethenyl ethanoate (vinyl acetate), which produces a
softer polymer ("Vinylite") with better molding properties. Polyvinyl chloride also can be plasticized
by blending it with substances of low volatility such as tris-(2-methylphenyl) phosphate (tricresyl
phosphate) and dibutyl benzene- l,2-dicarboxylate (dibutyl phthalate) which, when dissolved in the
polymer, tend to break down its glasslilce structure. Plasticized polyvinyl chloride is reasonably
flexible and is widely used as electrical insulation, plastic sheeting, and so on.
QUESTIONS FOR SELF-CONTROL:
1. Could we name molecule of oleic acid as a macromolecule of polymer:
CH3-(CH2)7-CH=CH-(CH2)7-COOH ?
2. Specify the structural unit of the macromolecule:
...-CH2-CH=CH-CH2-CH2-CH=CH-CH2-CH2-CH=CH-CH2-...
3. The degree of polymerization of the macromolecule is ...
4. What is the molecular weight of polypropylene macromolecule, if the degree of
polymerization n = 1000?
5. What is the average molecular weight of polyethylene, if 20% of macromolecules
have a molecular weight of 280000, 30% macromolecules – 18000, 50%
macromolecules - 2000?
REFERENCES:
1. “Nomenclature of regular single-strand organic polymers, 1975”, Pure Appl. Chem.
48, 373–385 (1976). Reprinted as chapter 5 in Ref. 7.
2. “Nomenclature of regular double-strand (ladder and spiro) organic polymers 1993”,
Pure Appl. Chem. 65, 1561–1580 (1993).
3. “Structure-based nomenclature for irregular single-strand organic polymers 1994”,
Pure Appl. Chem. 66, 873–889 (1994).
4. L. Mandelkern, An lntroduction to Macromolecules, Springer-Verlag, New York,
1992.
5. R. G. Treloar, lntroduction to Polymer Science, Springer-Verlag, New York, 1990.
An excellent and simple introduction to the relationship of polymer physical properties
to structure.
6. Шур А.М. Высокомолеклурные соединения, М., 1981г.
Lecture № 3-4. General characteristics of the processes of polymers.
Objective: To become familiar with the processes for producing polymers.
Key questions:
1. Basic ways of polymer synthesis.
2. General characteristics of the processes of polymers obtaining.
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3. Features of polymerization and polycondensation processes.
Summary:
1. Basic ways of polymer synthesis.
Types of reactions
Condensation
Addition
Ring opening
2. General characteristics of the processes of polymers obtaining.
There is a very wide variety of condensation reactions that, in principle, can be used to form high
polymers. However, as explained above, high polymers can be obtained only in high-yield reactions,
and this limitation severely restricts the number of condensation reactions having any practical
importance. A specific example of an impractical reaction is the formation of poly- 1,4-butanediol by
reaction of 1,4-dibromobutane with the disodium salt of the diol:
It is unlikely that this reaction would give useful yields of any very high polymer because E2
elimination, involving the dibromide, would give a doublebond end group and prevent the chain from
growing. A variety of polyester-condensation polymers are made commercially. Ester interchange
appears to be the most useful reaction for preparation of linear polymers:
Thermosetting space-network polymers can be prepared through the reaction of polybasic acid
anhydrides with polyhydric alcohols. A linear polymer is obtained with a bifunctional anhydride and a
bifunctional alcohol, but if either reactant has three or more reactive sites, then formation of a threedimensional polymer is possible. For example, 2 moles of 1,2,3-propanetrio1 (glycerol) can react with
3 moles of 1,2-benzenedicarboxylic anhydride (phthalic anhydride) to give a highly cross-linked resin,
which usually is called a glyptal:
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The first stage of the reaction involves preferential esterification of the primary hydroxyl groups with
the anhydride. In the next stage, in the formation of the resin, direct esterification occurs slowly,
particularly at the secondary hydroxyls. Normally, when the resin is used for surface coatings,
esterification is carried only to the point where the polymer is not so cross-linked as to be insoluble. It
then is applied to the surface in a solvent and baked until esterification is complete. The product is
hard, infusible, and insoluble, being cross-linked to the point of being essentially one large molecule.
A wide variety of thermosetting polyester (alkyd) resins can be made by similar procedures. The
following polybasic acids and anhydrides and polyhydric alcohols are among the other popular
ingredients in alkyd formulations:
Articles in which glass fibers are imbedded to improve impact strength often are made by mixing the
fibers with an ethenylbenzene (styrene) solution of a linear glycol (usually 1,2-propanedio1)butenedioic anhydride polyester and then producing a cross-linked polymer between the styrene and
the double bonds in the polyester chains by a peroxide-induced radical polymerization. A variety of
polyamides can be made by heating diamines with dicarboxylic acids. The most generally useful of
these is nylon 66, the designation 66 arising from the fact that it is made from the six-carbon diamine,
1,6-hexanediamine, and a six-carbon diacid, hexanedioic acid:
The polymer can be converted into fibers by extruding it above its melting point through spinnerettes,
then cooling and drawing the resulting filaments. It also is used to make molded articles. Nylon 66 is
exceptionally strong and abrasion resistant. The starting materials for nylon 66 can be made in many
ways. Apparently, the best route to hexanedioic acid is by air oxidation of cyclohexane by way of
cyclohexanone: 1,6-Hexanediamine can be prepared in many ways. One is from 1,3-butadiene by the
following steps: nylon 6 can be prepared by polymerization of 1-aza-2-cycloheptanone (Ecaprolactam), obtained through the Beckmann rearrangement of cyclohexanone oxime. One of the
oldest known thermosetting synthetic polymers is made by condensation of phenols with aldehydes
using basic catalysts. The resins that are formed are known as Bakelites.
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A very useful group of adhesives and plastics is based on condensation polymers of bisphenol A and
chloromethyloxacyclopropane (epichlorohydrin, CH2-CH – CH - Cl). The first step in the formation of
\O/
epoxy resins is to form a prepolymer by condensation polymerization of the sodium salt of bisphenol
A with the epoxide.
The formation of a prepolymer involves two different kinds of reactions. One
is an S2-type displacement, and the other is oxide-ring opening of the product by attack of more
bisphenol A. Usually, for practical purposes the degree of polymerization n of the prepolymer is small
(5 to 12 units). The epoxy prepolymer can be cured, that is, converted to a three-dimensional network,
in several different ways. A trifunctional amine, such as NH2CH2-CH2NHCH2CH2NH2, can be mixed
in and will extend the chain of the polymer and form cross-links by reacting with the oxide rings.
Alternatively, a polybasic acid anhydride can be used to link the chains through combination with the
secondary alcohol functions and then the oxide rings. The most important type of addition
polymerization is that of alkenes (usually called vinyl monomers) such as ethene, propene,
ethenylbenzene, and so on. In general, we recognize four basic kinds of mechanisms for
polymerization of vinyl monomers - radical, cationic, anionic, and coordination. The elements of the
first three of these have been outlined. The possibility, in fact the reality, of a fourth mechanism is
essentially forced on us by the discovery of the Ziegler and other (mostly heterogeneous) catalysts,
which apparently do not involve "free" radicals, cations, or anions, and which can and usually do lead
to highly stereoregular polymers. With titanium-aluminum Ziegler catalysts, the growing chain has a
C-Ti bond; further monomer units then are added to the growing chain by coordination with titanium,
followed by an intramolecular rearrangement to give a new growing-chain end and a new vacant site
on titanium where a new molecule of monomer can coordinate:
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In the coordination of the monomer with the titanium, the metal is probably behaving as an
electrophilic agent and the growing-chain end can be thought of as being transferred to the monomer
as an anion. Because this mechanism gives no explicit role to the aluminum, it is surely oversimplified.
Ziegler catalysts polymerize most monomers of the type RCH=CH2, provided the R group is one that
does not react with the organometallic compounds present in the catalyst. In contrast to coordination
polymerization, formation of vinyl polymers by radical chain mechanisms is reasonably well
understood- at least for the kinds of procedures used on the laboratory scale. The first step in the
reaction is the production of radicals; this can be achieved in a number of different ways, the most
common being the thermal decomposition of an initiator, usually a peroxide or an azo compound.
Many polymerizations are carried out on aqueous emulsions of monomers. For these, water-soluble
inorganic peroxides, such as ammonium peroxysulfate, often are employed. Other ways of obtaining
initiator radicals include high-temperature decomposition of the monomer and photochemical
processes, often involving a ketone as a photosensitizer. Addition of the initiator radicals to monomer
produces a growing-chain radical that combines with successive molecules of monomer until, in some
way, the chain is terminated.
3. Features of polymerization and polycondensation processes.
Addition
Condensation
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QUESTIONS FOR SELF-CONTROL:
1. Ozonizations of natural rubber and gutta-percha, which are both poly-2-methyl-l,3butadienes, give high yields of CH3COCH2CH2CH3 and no CH3COCH2CH2COCH3.
What are the structures of these polymers?
2. The radical polymerization of ethenylbenzene gives atactic polymer. Explain what
this means in terms of the mode of addition of monomer units to the growing-chain
radical.
REFERENCES:
1. L. Mandelkern, An lntroduction to Macromolecules, Springer-Verlag, New York,
1992.
2. R. G. Treloar, lntroduction to Polymer Science, Springer-Verlag, New York, 1990.
An excellent and simple introduction to the relationship of polymer physical properties
to structure.
3. Шур А.М. Высокомолеклурные соединения, М., 1981г.
Lecture #5. Radical polymerization
Purpose: familiarize with main steps of the radical polymerization, its mechanism and
means of implementing.
Key questions:
1. Main stages of radical polymerization
2. Initiation and its effectiveness
3. Propagation and termination reactions of macroradicals
4. Means of Polymerization implementing
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Summary:
1. Main stages of radical polymerization
In what is known as chain polymerization, the polymerization reaction requires the presence of
an initiator: a reactive species that serves to start the reaction. When we polymerize ethylene, we write
the reaction
nCH2=CH2 --> (-CH2-CH2-)n
but this begs the questions about what is at the end of the chains and how successive monomers are
added, i.e. the reaction mechanism. A major method to produce polyethylene is free radical
polymerization. The polymerization mechanism can be described in four stages:
1. Initiation
2. Propagation
3. Transfer
4. Termination
The term free radical describes what is formed when we break a single bond in any organic
molecule in such a way that we obtain two fragments, each of which had an unpaired electron, e.g.
CH3-CH2-CH2-CH2-CH2-CH3 --> CH3-CH2-CH2. + .CH2-CH2-CH3
where the periods represent unpaired electrons on the terminal carbons. Compounds with unpaired
electrons are free radicals: they are very reactive, just as atomic oxygen or fluorine would be. A stable
electronic structure is achieved for C, O and F when they have eight electrons in their outer shell, as is
achieved by sharing in covalent bond formation. If this structure is not present, then there is a
tremendous driving force to acquire a share of the necessary electrons, which is translated into high
reactivity. Thus free radicals are likely to react rapidly with any candidate that can supply the
additional necessary electrons, and the pi electrons of the double bond of ethylene are such a potential
source. Polymer initiation occurs when ethylene reacts with a free radical R. The latter acquires a share
one of the electrons involved in the double bond:
R. + CH2=CH2 ---> R-CH2-CH2.
2. Initiation and its effectiveness
A typical initiator for polymerization of ethylene is benzoyl peroxide, which breaks into two benzoyl
free radicals:
C6H5CO-O-O-CO-C6H5 ---> 2C6H5-COO.
We talked about peroxides in an earlier lecture, pointing out that they are unstable and tend to give up
oxygen. For example hydrogen peroxide H2O2 is used as a bleaching agent because it will give up an
oxygen to form the more stable H2O. This oxygen is acquired by colored unsaturated molecules, which
after reaction lose their color. Organic peroxides have the structure R-O-O-R' where the hydrogens of
H-O-O-H have been replaced by organic groups (which do not need to be identical). Organic peroxides
in general are unstable, and can detonate when subjected to shock. Benzoyl chloride is one of the more
stable, but even so it needs to be handled with care.
3. Propagation and termination reactions of macroradicals
The R. + CH2=CH2 ---> R-CH2-CH2. reaction simply transfers the "problem" of the unpaired electron
to the end of the attached ethylene unit, so the result is simply a larger free radical, which can then
react with another ethylene:
R-CH2-CH2. + -CH2=CH2 ---> R-CH2-CH2-CH2-CH2.
and so on:
R-CH2-CH2-CH2-CH2. + CH2=CH2 ---> R-CH2-CH2-CH2-CH2-CH2-CH2.
and eventually ---> R-(CH2-CH2)n-CH2-CH2.
This growth of the polymer chain is called propagation. It is a chain reaction, which can continue until
we run out of monomer, assuming of course that no other reactions are possible. The number of free
radicals does not change: they are not consumed in the reaction, except where termination occurs,
when two free radicals come together to form a covalent bond:
R-(CH2-CH2)n-CH2-CH2. + .CH2-CH2-(CH2-CH2)n'-R
---> R-(CH2-CH2)n+n'+2-R
Free radical polymerization as described here is used commercially to produce low density
poly(ethylene) (LDPE), and also poly(methylmethacrylate) (PMMA), poly(acrylonitrile) (PAN; -(CH221
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CH(CN)-)n) and poly(vinyl chloride) (PVC). In all four cases the polymerization involves opening a
double bond. Another peroxide initiator is t-butyl peroxide used for example to polymerize vinyl
chloride to produce PVC:
(CH3)3C-O-O-C(CH3)3 ---> 2(CH3)3C-O.
(CH3)3C-O. + CH2=CHCl ---> (CH3)3C-O-CH2-CHCl. ---> ---> (CH3)3C-O-(CH2-CHCl)n-CH2-CHCl.
To summarize so far, in the initiation stage we produce highly reactive free radicals:
Initiator ---> 2R.
and R. reacts with a monomer molecule
R. + M ---> R-M.
effectively creating a larger free radical. Propagation then proceeds by adding further monomer
molecules, which continually regenerates the terminal active site.
R-M. + M ---> R-M-M. ---> R-(M)2-M. ---> ---> R-(M)n-M.
The number of free radicals stays constant, and reaction continues until we run out of monomer,
unless termination occurs when two free radicals react with each other:
R-(M)n-M. + .M-(M)n'-R' ---> R-(M)n+n'+2-R'
Reaction will cease when all free radicals are disposed of in this manner, and this might occur before
all the monomer is polymerized. So one has to control the amount of initiator and the reaction
conditions to make sure complete polymerization occurs, but to avoid too much initiator, which can
lead to too many molecules and thus low molecular weight. One can see that there will be statistical
chance of reaction at the ends of growing molecules, and so we get a distribution of molecular weights.
But the reaction is more complex than described so far. Free radicals are very reactive, so the growing
polymer molecules R-(M)n-M. can also react with other polymer molecules, not only with the
monomer. These reactions are called transfer reactions:
R-(M)n-M. + A-B ---> R-Mn+1-A + B.
Here A-B is an existing polymer molecule prepared earlier in the synthesis; but it can also be an
impurity. We define this as transfer because the unpaired electron is effectively transferred to a new
species. The new free radical B. can react with monomer and grow into a polymer chain:
B. + M ---> B-M. ---> ----> B-Mn-M. and so on.
But the effect of the transfer reaction is that growth stops for the R-Mn+1-A species. So transfer
reactions have the effect of limiting molecular weight, as do the termination reactions.
Use of M for the monomer in the above equations is deceptive. It is important to realize that when an
existing polymer molecule reacts with a free radical the reaction does not necessarily occur at the M-M
monomer linkage bond. The monomer M is polyatomic and contains a number of bonds: in ethylene
we have the central C-C and four C-H bonds, and the free radical may react at any of these as well as
at the M-M linkage C-C bonds. Reaction at a C-H is common, so the free radical may take a hydrogen,
leaving an unpaired electron on the carbon, which may be other than at the chain end:
R-(M)n-CH2-CH2. + R'-Mn''-CH2-CH2-Mn"-R" ---> R-(M)n-CH2-CH3 + R'-Mn''-CH2-.CH-Mn"-R"
Here the unpaired electron is on a CH group away from the ends of the chain (this was a CH 2 that lost
the hydrogen atom to the original free radical) Reaction with an unreacted ethylene monomer can
now occur at this.CH group, resulting in a branched structure. There may also be rearrangement in a
linear polymer molecule where the free electron is moved from the last carbon to another back along
the chain, so that further addition occurs at that point, resulting in a branch. In free radical
polymerization we tend to get branched polymers, and in low density polyethylene (LDPE) there are
multiple branches per molecule. The number of branches depend on the probability of reaction with
the growing polymer molecules rather than with monomer, and this is controlled by adjusting the
temperature and pressure, and in recent years sophisticated catalysts have been developed for this
purpose, so as to have a tight control on properties. LDPE is synthesized from ethylene gas using the
free radical initiator benzoyl peroxide at high pressures (1000-3000 atm.) and temperatures (50300°C). Higher pressures and temperatures lead to better yields (more rapid reaction and higher
molecular weights) but the density and crystallinity decline progressively due to increasing numbers of
branching reactions. The densities are in the range 0.910-0.925 and crystallinities of 5060%.Remember that branching and lower density may be desirable. High density polyethylene HDPE
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has much less branching: the crystallinity may be as high as 90% and the densities 0.94-0.96 g/cm3.
Consequently HDPE and LDPE have very different properties, and different applications. HDPE is
produced by coordination polymerization, which will be the subject of the next lecture.
Besides the fact that free radical polymerization tends to produce branched chains, there is also
no control of tacticity. This is not a problem with polyethylene of course, but need to be considered
when we polymerize propylene and higher alkenes. For propylene:
R. + CH2=CH-CH3 ---> R-CH2-CH(CH3). ---> R-(CH2-CH(CH3))n-CH2-CH(CH3).
The reaction is such that the CH3 groups are attached to alternate carbons on the polymer
chain. We call this head-to-tail linkage of the monomers, rather than head-to-head/tail-totail, where we would have some CH3groups on adjacent backbone carbons. But there is
random spatial disposition of the CH3 groups, i.e. we have an atactic configuration (as we
discussed in an earlier lecture with reference to the structure of polystyrene).
4. Means of Polymerization implementing
Suspension polymerization:
 Water insoluble monomer.
 Water insoluble initiator.
 Suspending agent (optional).
 Droplets are 100 to 10-3 mm diameter.
 "Mini reactors."
Emulsion polymerization:
Water insoluble monomer.
Water soluble initiator.
Complicated mechanism.
Droplets are 10-5 to 10-6 mm diameter.
Advantages
Simple, few ingredients, cheap. Reaction medium is
mostly water, which absorbs the hear of
polymerization. Produces beads that have
Suspension
technological uses (xerographic toner, catalyst
carriers, ion exchange resins, substrates for
combinatorial synthesis, etc.)
Makes very high MW polymer quickly. Reaction
medium is mostly water, which absorbs the hear of
Emulsion polymerization. Creates very tiny particles of
polymer that have technological uses (paint,
coatings, drug delivery, etc.).
Disadvantages
Autoacceration will still occur.
Isolation of the polymer can be
laborious if you didn't want beads.
May need to purify polymer from
suspending agent.
Isolation of the polymer can be
laborious if you didn't want viny
particles. May need to purify
polymer from surfactant.
The mechanism is actually very complicated and continues to be studied to this day. The
reaction actually takes place in several stages, but, to a first approximation, the following description
suffices: the surfactant molecules surround small amounts of monomer molecules, creating micelles.
However, the usual recipe contains much more monomer than can be accomodated in micelles, so
there are also large droplets of monomer that are stabilized by small amounts of surfactant. Depending
on the monomer, there may also be a small amount of monomer dissolved in the water.
Initiator forms free radicals in the water, where they may find a few monomers to react with. In any
case, the radicals diffuse into the micelles, where they find lots of monomer but no other growing
chains to cause termination (at least, for a while). The growing chain is then protected from
termination until a second radical diffuses into the micelle. This is why the MW can be so high in
emulsion
polymerization
without
slowing
the
rate
of
conversion.
No polymerization seems to occur in the large monomer droplets. Why? The explanation lies in simple
statistics. Compared to the droplets, there are a large number of micelles, with much higher surface
area (estimated 1000 times more). It is simply more likely for a radical to diffuse into a micelle than a
droplet.
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QUESTIONS FOR SELF-CONTROL:
1. Write out the detailed mechanism for the radical chain polymerization of styrene
(vinylbenzene), designating the three stages of the chain mechanism, and giving the repeat
structure for the polymer. What is the significance of the subscript "n" in the repeat
structure? Why is this an average value? What term is used to describe the extent to which
a polymer product contains individual polymer molecules which have a wide or narrow
range of molecular weights?
2. Explain why the polymers obtained from the radical chain polymerization of vinyl
chloride, styrene, or acrylonitrile are unbranched.
3. Write out a mechanism for the radical chain polymerization of isoprene (2-methyl-1,3butadiene). Draw the repeat structures for both natural rubber and the polyisoprene which
results from radical polymerization.Then explain how these structures differ and why the
Ziegler-Natta catalytic system is able to polymerize isoprene to a polymer which is
identical to natural rubber.
4. In the radical chain polymerization of ethene, the polyethylene obtained is referred to as
"low density" polyethylene (LDPE). Explain, both in mechanistic/chemical terms,
including structural depictions, and in solid state/physical structural terms why this
polyethylene is "low density". What effect does this have on the physical properties of the
polymer?
REFERENCES:
1. L. Mandelkern, An lntroduction to Macromolecules, Springer-Verlag, New York,
1992.
2. R. G. Treloar, lntroduction to Polymer Science, Springer-Verlag, New York, 1990.
An excellent and simple introduction to the relationship of polymer physical properties
to structure.
3. Шур А.М. Высокомолеклурные соединения, М., 1981г.
4. http://research.cm.utexas.edu/nbauld/hmwkpolym.html
Lecture № 6-7. Ion coordination polymerisation.
Objective: To become familiar with the mechanism of ion-coordination polymerization
Key questions:
1. Ionic polymerization mechanism,
2. Cationic polymerization
3. Anionic polymerization.
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Summary:
1. Ionic polymerization mechanism,
Ionic vinyl polymerizations are very similar to free radical vinyl polymerizations. The only difference
is the "flow" of the electrons during propagation.
Recall that a double bond equals a single bond plus two more electrons.
In free radical vinyl polymerization, the electrons in the pi bond split up. One combines with the
unpaired electron in the initiator (or growing chain end) to form the new bond, and the second ends up
on the chain end, reproducing the attacking species.
In anionic vinyl polymerization, the electrons in the pi bond more together instead of separately. The
initiator (or growing chain end) attacks with a pair of electrons, used to form the new bond. The pibond electron pair "flows" away from the attacking species, reproducing the anion at the chain end.
Cationic vinyl polymerization is exactly the same mechanism, except that the initiator (or chain end)
lacks a pair of electrons. The electron "flow" is simply in the oposite direction, leaving behind a
positive charge at the chain end to continue the process. One important difference: ionic
polymerizations necessarily carry along a counterion, and their rates are much more sensitive to
reaction conditions (e.g., solvent polarity, temperature).
2. Cationic polymerization
Initiation and Propagation
The mechanism of cationic polymerization is a kind of repetitive alkylation reaction.
Electron donating groups are needed as the R groups because these can stabilize the propagating
species by resonance. Examples:
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Propagation is usually very fast. Therefore, cationic vinyl polymerizations must often be run at low
temperatures. Unfortunately, cooling large reactors is difficult and expensive. Also, the reaction can be
inhibited by water if present in more than trace amounts, so careful drying of ingredients is necessary
(another expense). Cationic Initiators:
 Proton acids with unreactive counterions
Lewis acid + other reactive compound:
Chain Transfer Reactions
Cationic vinyl polymerization
is plagued by numerous side
reactions, most of which lead
to chain transfer. It is difficult
to achieve high MW because
each initiator can give rise to
many separate chains because of chain transfer. These side reactions can be minimized but not
eliminated by running the reaction at low temperature. Here are a few examples:
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Examples of Commercial Cationic Polymers
3. Anionic polymerization.
In general, we expect that anionic polymerization will be favorable when the monomer carries
substituents that will stabilize the anion formed when a basic initiator such as amide ion adds to the
double bond of the monomer:
Cyano and alkoxycarbonyl groups are favorable in this respect and propenenitrile and methyl 2methylpropenoate can be polymerized with sodium amide in liquid ammonia. Ethenylbenzene and 2methyl- l,3-butadiene undergo anionic polymerization under the influence of organolithium and
organosodium compounds, such as butyllithium and phenylsodium. An important development in
anionic polymerization has been provided by M. Szwarc's "living polymers." The radical anion,
sodium naphthalenide, transfers an electron reversibly to ethenylbenzene to form a new radical anion,
1, in solvents such as 1,2-dimethoxyethane or oxacyclopentane:
Dimerization of the sodium naphthalenide radical anion would result in a loss of aromatic stabilization,
but this is not true for 1, which can form a C-C bond and a resonance-stabilized bis-phenylmethyl
dianion, 2.
The anionic ends of 2 are equivalent and can add ethenylbenzene molecules to form a long-chain
polymer with anionic end groups, 3 :
If moisture and oxygen are rigorously excluded, the anionic groups are stable indefinitely, and if more
monomer is added polymerization will continue. Hence the name "living polymer," in contrast to a
radical-induced polymerization, which only can be restarted with fresh monomer and fresh initiator,
and even then not by growth on the ends of the existing chains. The beauty of the Szwarc procedure is
that the chains can be terminated by hydrolysis, oxidation, carboxylation with CO2 and so on, to give
polymer with the same kind of groups on each end of the chain. Also, it is possible to form chains in
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which different monomers are present in blocks. The only requirements are that the different
monomers polymerize well by the anion mechanism and contain no groups or impurities that will
destroy the active ends. Thus one can start with ethenylbenzene (S), and when the reaction is complete,
add methyl 2-methylpropenoate (M) to obtain a block copolymer of the type
QUESTIONS FOR SELF-CONTROL:
1. Write an equation for the dimerization of sodium naphthalenide analogous to dimerization of the
ethenylbenzene radical anion 1 to give 2. Show why you may expect that this dimerization would not
be as energetically favorable as the dimerization of 1.
2. Formulate the complete mechanism of the anionic polymerization of styrene using sec-BuLi as the
initiator and water as the quenching reagent
3. Compare the anionic polymerization of styrene, 2-vinyl pyridine, and methyl methacrylate by
drawing the active species at the chain end! Which one is more reactive and why?
REFERENCES:
1. L. Mandelkern, An lntroduction to Macromolecules, Springer-Verlag, New York, 1992.
2. R. G. Treloar, lntroduction to Polymer Science, Springer-Verlag, New York, 1990. An excellent
and simple introduction to the relationship of polymer physical properties to structure.
3. Шур А.М. Высокомолеклурные соединения, М., 1981г.
4. http://chem.chem.rochester.edu/~chem421/classes.htm
Lecture # 8. Polycondensation.
Objective: To become familiar with the mechanism of polycondensation
Key questions:
1. Polycondensation mechanism
2. Conditions of process
3. Hardware design of process
Summary:
1. Polycondensation mechanism
In condensation reaction (or step-growth polymerization), two reactants with degree of polymerization,
m and n, combine to form their respective polymer. Step-Growth Polymerization applies to monomers
with functional groups such as -COOH, -COOR, -COOOC-, -COCl, -OH, -NH2, -CHO, -NCO, epoxy.
Polymers such as polyamides and polyesters can be prepared by condensation polymerization where
small molecules are eliminated as polymer chains are formed. Condensation polymerization of this
type is called polycondensation polymerization. General formula are shown below.
m (X-A-X) + n (Y-B-Y) = -[A-B]-m+n + 2nXY
Functionality
2 = Linear molecule: thermoplastics
>2 = Crosslinkable: gel, thermosets
Characteristics
 Repeat unit often not same as monomer structure
 Release of small molecules (H2O, HCl, etc)
 Gradual growth of molecular weight. The step-growth reaction proceeds through formation of
dimers, trimers, tetramers, etc, by reactions that are identical in rate and mechanism.
 Successive condensation reactions,”coupling”
 Relatively slow reactions. Since these reactions are equilibrium reactions, high molecular weight
polymer chains will be obtained if the equilibrium is displaced towards the formation of products. This
can be achieved by stripping through distillation the low molecular weight condensation products that
may form during the reaction (H2O, CH3OH, etc.).
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Stoichiometric concerns. W.H. Carothers determined a relationship between xn the number average
chain length (number of repeat units) and the extent of reaction, p for step-growth polymerization
reactions. Consider the polymerization of A-X-B, assuming N0 molecules at t = 0, then the extent of
reaction at time t is defined by: p = (N0-N)/ N0, where N is the number of molecules at time t.
Since xn is given by xn = N0/N (number of monomers per molecule), then the Carother’s equation is
written as: xn = 1/(1-p) and Mn = M0 xn.
In step-growth polymerization, a linear chain results from the stepwise condensation or
addition of reactive groups of bifunctional monomers.
• Polyesters: D = -COOA, = -COOH, -COCl, -COOR, -COOOC- and B = -OH
• Polyamides: D = -CONHA, = -COOH, -COCl, -COOR, -COOOC- and B = -NH2
• Polyurethanes: D = -NHCOOA, = -NCO and B = -OH
Thermosetting Polymers: one of the monomers has a functionality higher than 2.
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QUESTIONS FOR SELF-CONTROL:
1. Specify features of the polymerization reaction:
а) substitution reaction;
e) step-stage process;
f) different elemental composition of the polymer and
b) elimination reaction;
monomer;
c) addition reaction;
g) the same elemental composition of the polymer and
monomer.
d) chain process;
2. What type of reactions is polycondensation related?
3. Select compounds that can be used as monomers in the polymerization:
а) HOOC-CH=CH-COOH
d) C2H5-C6H4-COOH
b) CH2=CCl2
e) H2N-(CH2)5-COOH
c) HO-CH2CH2-OH
f) HO-CH2CH2CH2-COOH
4. Select compounds that can be used as monomers in the polycondensation:
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а) CH3(CH2)3COOH
d) CH2=CH-COOH
b) NH2(CH2)2COOH
e) HOOC-CH=CH-COOH
c) HO(CH2)3COOH
f) HOCH2CH2OH
5. What is the monomer used to produce the polymer:
6. What is the formula of the monomer, if at its polymerization formed macromolecule has following
structure: ...-CH2-CCl=CH-CH2-CH2-CCl=CH-CH2-... ?
7. What is the formula corresponding Capron?
REFERENCES:
1. L. Mandelkern, An lntroduction to Macromolecules, Springer-Verlag, New York, 1992.
2. R. G. Treloar, lntroduction to Polymer Science, Springer-Verlag, New York, 1990. An excellent
and simple introduction to the relationship of polymer physical properties to structure.
3. Some features of non-equilibrium polycondensation, V.V. Korshak, Institute of Element-Organic
Comppounds
4. Шур А.М. Высокомолеклурные соединения, М., 1981г.
Lecture № 9-12. The structure and properties of polymers
Objective: To study the features of the structure and properties of macromolecular compounds
Key questions:
1. Block, graft, and ladder polymers
2. Naturally occurring polymers
Summary:
1. Block, graft, and ladder polymers
When polymerization occurs in a mixture of monomers there will be competition between the
different kinds of monomers to add to the growing chain and produce a copolymer. Such a polymer
will be expected to have physical properties quite different from those of a mixture of the separate
homopolymers. Many copolymers, such as GRS, ethene-propene, Viton rubbers, and Vinyon plastics
are of considerable commercial importance. The rates of incorporation of various monomers into
growing radical chains have been studied in considerable detail. The rates depend markedly on the
nature of the monomer being added and on the character of the radical at the end of the chain. Thus a
1-phenylethyl-type radical on the growing chain reacts about twice as readily with methyl 2methylpropenoate as it does with ethenylbenzene; a methyl 2-methylpropenoate end shows the reverse
behavior, being twice as reactive toward ethenylbenzene as toward methyl 2-methylpropenoate. This
kind of behavior favors alternation of the monomers in the chain and reaches an extreme in the case of
2-methylpropene and butenedioic anhydride. Neither of these monomers separately will polymerize
well with radical initiators. Nonetheless, a mixture polymerizes very well with perfect alternation of
the monomer units. It is possible that, in this case, a 1: 1 complex of the two monomers is what
polymerizes. In genera1 however, in a mixture of two monomers one is considerably more reactive
than the other and the propagation reaction tends to favor incorporation of the more reactive monomer,
although there usually is some bias toward alternation. Ethenylbenzene and 2-methyl-1,3-butadiene
mixtures are almost unique in having a considerable bias toward forming the separate homopolymers.
One of the more amazing copolymerizations is that of ethenylbenzene and oxygen gas, which at one
atmosphere oxygen pressure gives a peroxide with an average molecular weight of 3000 to 4000 and a
composition approaching C8H802:
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When heated rapidly in small portions the product undergoes a mild explosion and gives high yields
(80% to 95%) of methanai and benzenecarbaldehyde. The mechanism may be a kind of unzipping
process, starting from a break in the chain and spreading toward each end:
A variation on the usual variety of copolymerization is the preparation of polymer chains made of
rather long blocks of different kinds of monomers. A number of ingenious systems have been devised
for making such polymers. Another scheme, which will work with monomers that polymerize well by
radical chains but not with anion chains, is to irradiate a stream of a particular monomer, flowing
through a glass tube, with sufficient light to get polymerization well underway. The stream then is run
into a dark flask containing a large excess of a second monomer. The growing chains started in the
light-induced polymerization then add the second monomer to give a two-block polymer if termination
is by disproportionation, or a three-block polymer if by combination. Thus, with A and B being the
two different monomers,
Block polymers also can be made easily by condensation reactions. Thus block polymers can be made
by esterification:
The very widely used polyurethane foams can be considered to be either block polymers or
copolymers. The essential ingredients are a diisocyanate and a diol. The diisocyanate most used is 2,4diisocyano-1-methylbenzene and the diol can be a polyether or a polyester with hydroxyl end groups.
The isocyano-groups react with the hydroxyl end groups to form initially an addition polymer, which
has polycarbamate (polyurethane) links, and isocyano end groups:
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A foam is formed by addition of the proper amount of water. The water reacts with the isocyanate end
groups to form carbamic acids which decarboxylate to give amine groups:
The carbon dioxide evolved is the foaming agent, and the amino groups formed at the same time
extend the polymer chains by reacting with the residual isocyano end groups to form urea linkages:
Graft polymers can be made in great profusion by attaching chains of one kind of polymer to the
middle of another. A particularly simple but uncontrollable way of doing this is to knock groups off a
polymer chain with x-ray or y radiation in the presence of a monomer. The polymer radicals so
produced then can grow side chains made of the new monomer. A more elegant procedure is to use a
photochemical reaction to dissociate groups from the polymer chains and form radicals capable of
polymerization with an added monomer. Modern technology has many uses for very strong and very
heat-resistant polymers. The logical approach to preparing such polymers is to increase the rigidity of
the chains, the strengths of the bonds in the chains, and the intermolecular forces. All of these should
be possible if one were to make the polymer molecules in the form of a rigid ribbon rather than a more
or less flexible chain. Many so-called ladder polymers with basic structures of the following type
have been prepared for this purpose:
A With the proper structures, such polymers can be very rigid and have strong intermolecular
interactions. Appropriate syntheses of true ladder polymers in high yield usually employ difficultly
obtainable starting materials. An example is
Although there seem to be no true ladder polymers in large-scale commercial production, several
semi-ladder polymers that have rather rigid structures are employed where high-temperature strength
is important. Among these are
2. Naturally occurring polymers
There are a number of naturally occurring polymeric substances that have a high degree of
technical importance. Some of these, such as natural rubber, cellulose, and starch, have regular
structures and can be regarded as being made up of single monomer units. Others, such as wool, silk,
and deoxyribonucleic acid are copolymers. The difference between the properties of the cis- and transisomers is apparent for naturally-occurring polyisoprenes
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NaturalRubber(cis-1,4-polyisoprene)
Cellulose is a long chain of linked sugar molecules that gives wood its remarkable strength. It is
the main component of plant cell walls, and the basic building block for many textiles and for paper.
Cotton is the purest natural form of cellulose. In the laboratory, ashless filter paper is a source of
nearly pure cellulose. Cellulose is a natural polymer, a long chain made by the linking of smaller
molecules. The links in the cellulose chain are a type of sugar: ß-D-glucose. Two unlinked molecules
of ß-D-glucose are pictured at right. The sugar units are linked when water is eliminated by combining
the -OH group and H highlighted in gray. Linking just two of these sugars produces
a disaccharide called cellobiose. Cellulose is a polysaccharide produced by linking additional sugars in
exactly the same way. The length of the chain varies greatly, from a few hundred sugar units in wood
pulp
to
over
6000
for
cotton.
The cellulose chain bristles with polar -OH groups. These groups form many hydrogen bonds with OH
groups on adjacent chains, bundling the chains together. The chains also pack regularly in places to
form hard, stable crystalline regions that give the bundled chains even more stability and strength.
Cellulose is a major component of wood. Cellulose fibers in wood are bound in lignin, a complex
polymer. Paper-making involves treating wood pulp with alkalis or bisulfites to disintegrate the lignin,
and then pressing the pulp to matte the cellulose fibers together. Cellulose is found in large amounts in
nearly all plants, and is potentially a major food source.
Plants store glucose as the polysaccharide starch. The cereal grains (wheat, rice, corn, oats, barley)
as well as tubers such as potatoes are rich in starch. Starch can be separated into two fractions-amylose
and amylopectin. Natural starches are mixtures of amylose (10-20%) and amylopectin (80-90%).
Amylose forms a colloidal dispersion in hot water whereas amylopectin is completely insoluble.
The structure of amylose consists of long polymer chains of glucose units connected by an alpha
acetal linkage. The graphic on the left shows a very small portion of an amylose chain. All of the
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monomer units are alpha -D-glucose, and all the alpha acetal links connect C1 of one glucose to C4 of
the next glucose. As a result of the bond angles in the alpha acetal linkage, amylose actually forms a
spiral much like a coiled spring. Amylose is responsible for the formation of a deep blue color in the
presence of iodine. The iodine molecule slips inside of the amylose coil. The graphic shows very small
portion of an amylopectin-type structure showing two branch points [drawn closer together than they
should be]. The acetal linkages are alpha connecting C1 of one glucose to C4 of the next glucose. The
branches are formed by linking C1 to a C6 through an acetal linkages. Amylopectin has 12-20 glucose
units between the branches. Natural starches are mixtures of amylose and amylopectin. In glycogen,
the branches occur at intervals of 8-10 glucose units, while in amylopectin the branches are separated
by 10-12 glucose units.
Spider silk is composed of complex protein molecules. This, coupled with the isolation stemming
from the spider's predatory nature, has made the study and replication of the substance quite
challenging. In 2005, independent researchers in the University of Wyoming (Tian and
Lewis), University of the Pacific (Hu and Vierra), the University of California at Riverside (Garb and
Hayashi) and Shinshu University (Zhao and Nakagaki) have uncovered the molecular structure of the
gene for the protein that various female spider species use to make their silken egg cases.
Although different species of spider, and different types of silk, have different protein sequences, a
general trend in spider silk structure is a sequence of aminoacids (usually alternating glycine and
alanine, or alanine alone) that self-assemble into a beta sheet conformation. These "Ala rich" blocks
are separated by segments of amino acids with bulky side-groups. The beta sheets stack to form
crystals, whereas the other segments form amorphous domains. It is the interplay between the hard
crystalline segments, and the elastic semi amorphous regions, that gives spider silk its extraordinary
properties.
The Structure and Function of deoxyribonucleic acid (DNA)
Biologists in the 1940s had difficulty in accepting DNA as
the genetic material because of the apparent simplicity of
its chemistry. DNA was known to be a
long polymer composed of only four types of subunits,
which resemble one another chemically. Early in the
1950s, DNA was first examined by x-ray diffraction
analysis, a technique for determining the threedimensional atomic structure of a molecule . The early xray diffraction results indicated that DNA was composed
of two strands of the polymer wound into a helix. The
observation that DNA was double-stranded was of crucial
significance and provided one of the major clues that led
to the Watson-Crick structure of DNA. Only when this
model was proposed did DNA's potential for replication
and
information
encoding
become
apparent.
A DNA molecule consists of two long polynucleotide
chains composed of four types of nucleotide subunits.
Each of these chains is known as a DNA chain, or a DNA
strand. Hydrogen bonds between the base portions of the
nucleotides hold the two chains together. Nucleotides are composed of a five-carbon sugar to which
are attached one or more phosphate groups and a nitrogen-containing base. In the case of the
nucleotides in DNA, the sugar is deoxyribose attached to a single phosphate group (hence the
name deoxyribonucleic acid), and the base may be either adenine (A), cytosine (C), guanine
(G), or thymine (T). The nucleotides are covalently linked together in a chain through the sugars and
phosphates, which thus form a “backbone” of alternating sugar-phosphate-sugar-phosphate.
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Because only the base differs in each of the four types of subunits, each polynucleotide chain in DNA
is analogous to a necklace (the backbone) strung with four types of beads (the four bases A, C, G, and
T). These same symbols (A, C, G, and T) are also commonly used to denote the four different
nucleotides—that is, the bases with their attached sugar and phosphate groups. The way in which
the nucleotide subunits are lined together gives a DNA strand a chemical polarity. If we think of
each sugar as a block with a protruding knob (the 5′ phosphate) on one side and a hole (the
3′ hydroxyl) on the other, each completed chain, formed by interlocking knobs with holes, will have all
of its subunits lined up in the same orientation. Moreover, the two ends of the chain will be easily
distinguishable, as one has a hole (the 3′ hydroxyl) and the other a knob (the 5′ phosphate) at its
terminus. This polarity in a DNA chain is indicated by referring to one end as the 3′ end and the other
as the 5′ end. The three-dimensional structure of DNA—the double helix—arises from the chemical
and structural features of its two polynucleotide chains. Because these two chains are held together by
hydrogen bonding between the bases on the different strands, all the bases are on the inside of the
double helix, and the sugar-phosphate backbones are on the outside. In each case, a bulkier tworing base (a purine) is paired with a single-ring base (a pyrimidine); A always pairs with T, and G with
C. This complementary base-pairing enables the base pairs to be packed in the energetically most
favorable arrangement in the interior of the double helix. In this arrangement, each base pair is of
similar width, thus holding the sugar-phosphate backbones an equal distance apart along the
DNA molecule. To maximize the efficiency of base-pair packing, the two sugar-phosphate backbones
wind around each other to form a double helix, with one complete turn every ten base.
Because we already have considered the chemistry of most of these substances, we shall confine
our attention here to wool and collagen, which have properties related to topics discussed previously in
this chapter. The structure of wool is more complicated than that of silk fibroin because wool, like
insulin and lysozyme, contains a considerable quantity of cystine, which provides -S-S- (disulfide)
cross-links between the peptide chains. These disulfide linkages play an important part in determining
the mechanical properties of wool fibers because if the disulfide linkages are reduced, as with
ammonium mercaptoethanoate solution, the fibers become much more pliable. Advantage is taken of
this reaction in the curling of hair, the reduction and curling being followed by restoration of the
disulfide linkages through treatment with a mild oxidizing agent.
The principal protein sf skin and connective tissue is called collagen and is primarily
constituted of glycine, proline, and hydroxyproline. Collagen is made up of tropocollagen, a substance
with very long and thin molecules (14 x 2900 A, MW about 300,000). Each tropocollagen molecule
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consists of three twisted polypeptide strands. When collagen is boiled with water, the strands come
apart and the product is ordinary cooking gelatin. Connective tissue and skin are made up of fibrils,
200 A to 1000 A wide, which are indicated by x-ray diffraction photographs to be composed of
tropocollagen molecules running parallel to the long axis. Electron micrographs show regular bands,
640 A apart, across the fibrils, and it is believed that these correspond to tropocollagen molecules, all
heading in the same direction but regularly staggered by about a fourth of their length. The conversion
of collagen fibrils to leather presumably involves formation of cross-links between the tropocollagen
molecules. Various substances can be used for the purpose, but chromium salts act particularly rapidly.
QUESTIONS FOR SELF-CONTROL:
1. If you make a block copolymer from isoprene, methyl methacrylate, and styrene, in which
order do you have to add the monomers (and what is the obtained block copolymer)?
2. How would you make: (i) poly(styrene-block-isoprene‐block-vinyl pyridine); (ii) poly(vinyl
pyridine‐block-styrene-block-vinyl pyridine); (iii) poly(styrene-block‐vinyl pyridine‐block‐styrene)?
3. What would be the expected structure of a copolymer of ethenylbenzene and propene made by
a Ziegler catalyst if the growing chain is transferred to the monomer as a radical? As an anion?
4. Devise a synthesis of a block polymer with poly-1,2-ethanediol and nylon 66 segments. What
kind of physical properties would you expect such a polymer to have?
5. Suppose one were to synthesize two block copolymers with the following structures:
What difference in physical properties would you expect for these two materials?
REFERENCES:
1. Alberts B, Johnson A, Lewis J, et al., Molecular Biology of the Cell. 4th edition, New
York: Garland Science; 2002.
2. L. Mandelkern, An lntroduction to Macromolecules, Springer-Verlag, New York, 1992.
3. R. G. Treloar, lntroduction to Polymer Science, Springer-Verlag, New York, 1990. An excellent
and simple introduction to the relationship of polymer physical properties to structure.
4. Шур А.М. Высокомолеклурные соединения, М., 1981г.
Lecture № 13-15. Processing of polymers
Objective: To learn the basic methods of processing materials in products
Key questions:
1. Classification of methods of polymer processing
2. Crystallization, melting and glass transition
3. Mechanical behavior of polymers
4. Characteristics and typical applications of few plastic materials.
Summary:
1. Classification of methods of polymer processing.
Polymers play a very important role in human life. In fact, our body is made of lot of polymers,
e.g. Proteins, enzymes, etc. Other naturally occurring polymers like wood, rubber, leather and silk are
serving the humankind for many centuries now. Modern scientific tools revolutionized the processing
of polymers thus available synthetic polymers like useful plastics, rubbers and fiber materials. As with
other engineering materials (metals and ceramics), the properties of polymers are related their
constituent structural elements and their arrangement. Polymers are classified in several ways – by
how the molecules are synthesized, by their molecular structure, or by their chemical family. For
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example, linear polymers consist of long molecular chains, while the branched polymers consist of
primary long chains and secondary chains that stem from these main chains. However, linear does not
mean straight lines. The better way to classify polymers is according to their mechanical and thermal
behavior. Industrially polymers are classified into two main classes – plastics and elastomers. Plastics
are moldable organic resins. These are either natural or synthetic, and are processed by forming or
molding into shapes. Plastics are important engineering materials for many reasons. They have a wide
range of properties, some of which are unattainable from any other materials, and in most cases they
are relatively low in cost. Following is the brief list of properties of plastics: light weight, wide range
of colors, low thermal and electrical conductivity, less brittle, good toughness, good resistance to
acids, bases and moisture, high dielectric strength (use in electrical insulation), etc. Plastics are again
classified in two groups depending on their mechanical and thermal behavior as thermoplasts
(thermoplastic polymers) and thermosets (thermosetting polymers). Thermoplasts: These plastics
soften when heated and harden when cooled – processes that are totally reversible and may be
repeated. These materials are normally fabricated by the simultaneous application of heat and pressure.
They are linear polymers without any cross-linking in structure where long molecular chains are
bonded to each other by secondary bonds and/or inter-wined. They have the property of increasing
plasticity with increasing temperature which breaks the secondary bonds between individual chains.
Common thermoplasts are: acrylics, PVC, nylons, polypropylene, polystyrene, polymethyl
methacrylate (plastic lenses or perspex), etc. Thermosets: These plastics require heat and pressure to
mold them into shape. They are formed into a permanent shape and cured or ‘set’ by chemical
reactions such as extensive cross-linking. They cannot be re-melted or reformed into another shape but
decompose upon being heated to too high a temperature. Thus thermosets cannot be recycled, whereas
thermoplasts can be recycled. The term thermoset implies that heat is required to permanently set the
plastic. Most thermosets composed of long chains that are strongly cross-linked (and/or covalently
bonded) to one another to form 3-D network structures to form a rigid solid. Thermosets are generally
stronger, but more brittle than thermoplasts. Advantages of thermosets for engineering design
applications include one or more of the following: high thermal stability, high dimensional stability,
high rigidity, light weight, high electrical and thermal insulating properties and resistance to creep and
deformation under load. There are two methods whereby cross-linking reaction can be initiated –
cross-linking can be accomplished by heating the resin in a suitable mold (e.g. bakelite), or resins such
as epoxies (araldite) are cured at low temperature by the addition of a suitable cross-linking agent, an
amine. Epoxies, vulcanized rubbers, phenolics, unsaturated polyester resins, and amino resins (ureas
and melamines) are examples of thermosets. Elastomers: Also known as rubbers, these are polymers
which can undergo large elongations under load, at room temperature, and return to their original
shape when the load is released. There are number of man-made elastomers in addition to natural
rubber. These consist of coil-like polymer chains those can reversibly stretch by applying a force.
Processing of polymers mainly involves preparing a particular polymer by synthesis of
available raw materials, followed by forming into various shapes. Raw materials for polymerization
are usually derived from coal and petroleum products. The large molecules of many commercially
useful polymers must be synthesized from substances having smaller molecules. The synthesis of the
large molecule polymers is known as polymerization in which monomer units are joined over and over
to become a large molecule. More upon, properties of a polymer can be enhanced or modified with the
addition of special materials. This is followed by forming operation. Addition polymerization and
condensation polymerization are the two main ways of polymerization. Most of polymer properties are
intrinsic i.e. characteristic of a specific polymer. Foreign substances called additives are intentionally
introduced to enhance or modify these properties. These include – fillers, plasticizers, stabilizers,
colorants, and flame retardants. Fillers are used to improve tensile and compressive strength, abrasion
resistance, dimensional stability etc. wood flour, sand, clay, talc etc are example for fillers. Plasticizers
aid in improving flexibility, ductility and toughness of polymers by lowering glass transition
temperature of a polymer. These are generally liquids of low molecular weight. Stabilizers are
additives which counteract deteriorative processes such as oxidation, radiation, and environmental
deterioration. Colorants impart a specific color to a polymer, added in form of either dyes (dissolves)
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or pigments (remains as a separate phase). Flame retardants are used to enhance flammability
resistance of combustible polymers. They serve the purpose by interfering with the combustion
through the gas phase or chemical reaction.
Polymeric materials are formed by quite many different techniques depending on (a) whether the
material is thermoplast or thermoset, (b) melting/degradation temperature, (c) atmospheric stability,
and (d) shape and intricacy of the product. Polymers are often formed at elevated temperatures under
pressure. Thermoplasts are formed above their glass transition temperatures while applied pressure
ensures that the product retain its shape. Thermosets are formed in two stages – making liquid
polymer, then molding it. Different molding techniques are employed in fabrication of polymers.
Compression molding involves placing appropriate amount of polymer with additives between heated
male and female mold parts. After pouring polymer, mold is closed, and heat and pressure are applied,
causing viscous plastic to attain the mold shape. Figure shows a typical mould employed for
compression molding.
Transfer molding differs from compression molding in how the materials is introduced into the mold
cavities. In transfer molding the plastic resin is not fed directly into the mold cavity but into a chamber
outside the mold cavities. When the mold is closed, a plunger forces the plastic resin into the mold cavities,
where and molded material cures. In injection molding, palletized materials is fed with use of hopper into a
cylinder where charge is pushed towards heating chamber where plastic material melts, and then molten
plastic is impelled through nozzle into the enclosed mold cavity where product attains its shape. Most
outstanding characteristic of this process is the cycle time which is very short. The schematic diagram of
injection-molding machine is shown in figure.
Extrusion is another kind of injection molding, in which a thermoplastic material is forced through a die
orifice, similar to the extrusion of metals. This technique is especially adapted to produce continuous
lengths with constant cross-section. The schematic diagram of a simple extrusion machine is shown in
figure:
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Blow molding of plastics is similar to blowing of glass bottles. Polymeric materials may be cast similar to
metals and ceramics.
2. Crystallization, melting and glass transition
Polymers are known by their high sensitivity of mechanical and/or thermal properties. This
section explains their thermal behavior. During processing of polymers, they are cooled with/without
presence of presence from liquid state to form final product. During cooling, an ordered solid phase
may be formed having a highly random molecular structure. This process is called crystallization. The
melting occurs when a polymer is heated. If the polymer during cooling retains amorphous or noncrystalline state i.e. disordered molecular structure, rigid solid may be considered as frozen liquid
resulting from glass transition. Thus, enhancement of either mechanical and/or thermal properties
needs to consider crystallization, melting, and the glass transition. Crystallization and the mechanism
involved play an important role as it influences the properties of plastics. As in solidification of metals,
polymer crystallization involves nucleation and growth. Near to solidification temperature at favorable
places, nuclei forms, and then nuclei grow by the continued ordering and alignment of additional
molecular segments. Extent of crystallization is measured by volume change as there will be a
considerable change in volume during solidification of a polymer. Crystallization rate is dependent on
crystallization temperature and also on the molecular weight of the polymer. Crystallization rate
decreases with increasing molecular weight. Melting of polymer involves transformation of solid
polymer to viscous liquid upon heating at melting temperature, T . Polymer melting is distinctive from
m
that of metals in many respects – melting takes place over a temperature range; melting behavior
depends on history of the polymer; melting behavior is a function of rate of heating, where increasing
rate results in an elevation of melting temperature. During melting there occurs rearrangement of the
molecules from ordered state to disordered state. This is influenced by molecular chemistry and
structure (degree of branching) along with chain stiffness and molecular weight. Glass transition
occurs in amorphous and semi-crystalline polymers. Upon cooling, this transformation corresponds to
gradual change of liquid to rubbery material, and then rigid solid. The temperature range at which the
transition from rubbery to rigid state occurs is termed as glass transition temperature, Tg. This
temperature has its significance as abrupt changes in other physical properties occur at this
temperature. Glass transition temperature is also influenced by molecular weight, with increase of
which glass transition temperature increases. Degree of cross-linking also influences the glass
transition such that polymers with very high degree of cross-linking do not experience a glass
transition. The glass transition temperature is typically 0.5 to 0.75 times the absolute melting
temperature. Above the glass transition, non-crystalline polymers show viscous behavior, and below
the glass transition they show glass-brittle behavior (as chain motion is very restricted), hence the
name glass transition. Melting involves breaking of the inter-chain bonds, so the glass- and meltingtemperatures depend on:
• chain stiffness (e.g., single vs. double bonds)
• size, shape of side groups
• size of molecule
• side branches, defects
• cross-linking
3. Mechanical behavior of polymers
Polymer mechanical properties can be specified with many of the same parameters that are used for metals
such as modulus of elasticity, tensile/impact/fatigue strengths, etc. However, polymers are, in many
respects, mechanically dissimilar to metals. To a much greater extent than either metals or ceramics, both
thermal and mechanical properties of polymers show a marked dependence on parameters namely
temperature, strain rate, and morphology. In addition, molecular weight and temperature relative to the
glass transition play an important role that are absent for other type of materials. A simple stress- strain
curve can describe different mechanical behavior of various polymers. As shown in figure – 11.4, the
stress-strain behavior can be brittle, plastic and highly elastic (elastomeric or rubber-like). Mechanical
properties of polymers change dramatically with temperature, going from glass-like brittle behavior at low
temperatures to a rubber-like behavior at high temperatures. Highly crystalline polymers behave in a brittle
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manner, whereas amorphous polymers can exhibit plastic deformation. These phenomena are highly
temperature dependent, even more so with polymers than they are with metals and ceramics. Due to unique
structures of cross-linked polymers, recoverable deformations up to very high strains / point of rupture are
also observed with polymers (elastomers). Tensile modulus (modulus) and tensile strengths are orders of
magnitude smaller than those of metals, but elongation can be up to 1000 % in some cases. The tensile
strength is defined at the fracture point and can be lower than the yield strength.
As the temperature increases, both the rigidity and the yield strength decrease, while the elongation
increases. Thus, if high rigidity and toughness are the requirements, the temperature consideration is
important. In general, decreasing the strain rate has the same influence on the strain-strength characteristics
as increasing the temperature: the material becomes softer and more ductile. Despite the similarities in
yield behavior with temperature and strain rate between polymers, metals, and ceramics, the mechanisms
are quite different. Specifically, the necking of polymers is affected by two physical factors that are not
significant in metals: dissipation of mechanical energy as heat, causing softening magnitude of which
increases with strain rate; deformation resistance of the neck, resulting in strain-rate dependence of yield
strength. The relative importance of these two factors depends on materials, specimen dimensions and
strain rate. The effect of temperature relative to the glass transition is depicted in terms of decline in
modulus values. Shallow decline of modulus is attributed to thermal expansion, whereas abrupt changes are
attributable to viscoelastic relaxation processes. Together molecular weight and crystallinity influence a
great number of mechanical properties of polymers including hardness, fatigue resistance, elongation at
neck, and even impact strength. The chance of brittle failure is reduced by raising molecular weight, which
increases brittle strength, and by reducing crystallinity. As the degree of crystallinity decreases with
temperature close to melting point, stiffness, hardness and yield strength decrease. These factors often set
limits on the temperature at which a polymer is useful for mechanical purposes. Elastomers, however,
exhibit some unique mechanical behavior when compared to conventional plastics. The most notable
characteristics are the low modulus and high deformations as elastomers exhibit large, reversible
elongations under small applied stresses. Elastomers exhibit this behavior due to their unique, cross-linked
structure. Elastic modulus of elastomers (resistance to the uncoiling of randomly orientated chains)
increases as with increase in temperature. Unlike non-cross-linked polymers, elastomers exhibit an increase
inelastic modulus with cross-link density.
4. Characteristics and typical applications of few plastic materials.
a) Thermo plastics
1. Acrylonitrile-butadiene-styrene (ABS):
Characteristics: Outstanding strength and toughness, resistance to heat distortion; good electrical
properties; flammable and soluble in some organic solvents.
Application: Refrigerator lining, lawn and garden equipment, toys, highway safety devices.
2. Acrylics (poly-methyl-methacrylate)
Characteristics: Outstanding light transmission and resistance to weathering; only fair mechanical
properties.
Application: Lenses, transparent aircraft enclosures, drafting equipment, outdoor signs
3. Fluorocarbons (PTFE or TFE)
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Characteristics: Chemically inert in almost all environments, excellent electrical properties; low
o
coefficient of friction; may be used to 260 C; relatively weak and poor cold-flow properties.
Application: Anticorrosive seals, chemical pipes and valves, bearings, anti adhesive coatings, high
temperature electronic parts.
4. Polyamides (nylons)
Characteristics: Good mechanical strength, abrasion resistance, and toughness; low coefficient of
friction; absorbs water and some other liquids.
Application: Bearings, gears, cams, bushings, handles, and jacketing for wires and cables
5. Polycarbonates
Characteristics: Dimensionally stable: low water absorption; transparent; very good impact resistance
and ductility.
Application: Safety helmets, lenses light globes, base for photographic film
6. Polyethylene
Characteristics: Chemically resistant and electrically insulating; tough and relatively low coefficient of
friction; low strength and poor resistance to weathering.
Application: Flexible bottles, toys, tumblers, battery parts, ice trays, film wrapping materials.
7. Polypropylene
Characteristics: Resistant to heat distortion; excellent electrical properties and fatigue strength;
chemically inert; relatively inexpensive; poor resistance to UV light.
Application: Sterilizable bottles, packaging film, TV cabinets, luggage
8. Polystyrene
Characteristics: Excellent electrical properties and optical clarity; good thermal and dimensional
stability; relatively inexpensive
Application: Wall tile, battery cases, toys, indoor lighting panels, appliance housings.
9. Polyester (PET or PETE)
Characteristics: One of the toughest of plastic films; excellent fatigue and tear strength, and resistance
to humidity acids, greases, oils and solvents
Application: Magnetic recording tapes, clothing, automotive tire cords, beverage containers.
b) Thermo setting polymers
1. Epoxies
Characteristics: Excellent combination of mechanical properties and corrosion resistance;
dimensionally stable; good adhesion; relatively inexpensive; good electrical properties.
Application: Electrical moldings, sinks, adhesives, protective coatings, used with fiberglass laminates.
2. Phenolics
o
Characteristics: Excellent thermal stability to over 150 C; may be compounded with a large number of
resins, fillers, etc.; inexpensive.
Application: Motor housing, telephones, auto distributors, electrical fixtures.
QUESTIONS FOR SELF-CONTROL:
1. Determine the geometric shape of the macromolecule:
2. What is the geometric shape of the macromolecules of polymers A and B?
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3. During the processing of polymers in products often are used method of casting a
polymer melt into the prepared mold. Which polymers may be used at this stage of
processing?
4. What signs are distinguished polymers from low molecular compounds:
a) poor solubility;
f) flexibleness;
b) swelling during dissolution;
g) low friability;
c) low viscosity of solutions;
h) thermoplasticity;
d) high viscosity of solutions;
i) thermoset;
e) inability to crystallize;
j) conductivity?
5. Compare the flexibility of macromolecules:
А. [-СО-(CH2)5-NН-]n;
B. [-CH2-CH(CH3)-]n.
REFERENCES:
1. V. R. Gowariker, N. V. Viswanathan, and Jayadev Sreedhar, Polymer Science, New
Age International (P) Limited publishers, Bangalore, 2001
2. C. A. Harper, Handbook of Plastics Elastomers and Composites, Third Edition,
McGrawHill Professional Book Group, New York, 1996.
3. William D. Callister, Jr, Materials Science and Engineering – An introduction, sixth
edition, John Wiley & Sons, Inc. 2004.
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LABORATORY WORKS
Methodical recommendations for conducting laboratory works
Laboratory studies promotes knowledge of the physical methods of chemical
research, the student develops independence and instills the skills of the experiment. In
order to work in the laboratory took place successfully, you must first explore the
theoretical material from textbooks, lecture notes and the benefits of chemical
workshops. This produces a conscious attitude to the implementation of experimental
techniques, the work itself will be understood, and, therefore, and understood. Working
in the chemistry lab should strictly observe the safety rules and regulations of the
chemical utensils and appliances. We must learn to use chemical agents, chemical
equipment, which are listed in the guidelines for the work on the chemical workshop.
Guidelines should not be a straitjacket, and to deprive independence, but rather follow
the orders of speeds up, prevents possible damage to equipment, glassware and
reagents. The success of the experimental work depends not only on the correctness of
the choice of working methods, the sequence of measurement, weight measurements,
but also on the correct systematic recording of results. By the implementation of the
laboratory work allowed students with admission after verification of a teacher of
theoretical knowledge on the subject, knowledge of laboratory methods of work and
prepared to conduct lab journal entries on the topic. After completing the laboratory
work the student must bring order to your workplace and deliver them on duty or
technician. After processing the results in the lab book the student must submit the
report teacher.
Thematic plan of laboratory work
1.
2.
3.
4.
Name of the theme
Number
of hours
Manual
Laboratory work № 1-2. Identification of physical
and chemical parameters of polymers
Laboratory work № 3-4. Determination of the
molecular weight of the polymer by viscometric
method
Laboratory work № 5-6. Determination of the
resin and filler in the polymer samples.
Laboratory work № 7-8. Synthesis of the polymer
by polycondensation and study of its properties
Laboratory work № 9-10. Determination of the
isoelectric point of the protein
Laboratory work № 11-12. Identification of
natural, artificial and synthetic fibers.
Laboratory work № 13-15. Polymeranalogous
conversion of polymers
2
Methodical instructions
2
Methodical instructions
2
Methodical instructions
2
Methodical instructions
2
Methodical instructions
2
Methodical instructions
3
Methodical instructions
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Methodical instructions
Laboratory work № 1-2. Identification of physical and chemical parameters of
polymers
Purpose: To determine the content of volatile substances and moisture, moisture
absorption of the test polymer.
1. Determination of moisture and volatiles.
Equipment and instruments: weighing bottles, desiccators, analytical balance.
Test materials: nylon pellets
Stages of the work:
Moisture and volatile content is determined by the difference between specific weights of the initial
plastic sample before and after drying in a thermostat at the installed temperature and time. In a 40 mm
diameter weighing bottle about 5 g of the polymer is weighed up to 0.001 g on the analytical balance
and is placed in an incubator. Drying temperature and time of the plastics specified in technological
instructions. Then open weighing bottle is cooled in a desiccator, then you must close lid and re-weigh.
Volatile content and moisture content are expressed in percentage.
Allowable moisture and volatile components in the powdered phenoplast are 2-4.5% and
aminoplast are 3.5 - 4%, in fibrous and layered phenoplast are 0.8-3% and 0.2% in polyamides.
Data processing:
The content of volatile substances and moisture in percentage (x) is calculated by the formula:
(а  а )  100
х 2 1
а2  а
where a2 is the weight of weighing bottle with the sample before drying, g;
a1 - the weight of weighing bottle with the sample after drying, g;
a - the weight of the empty sample bottle, g
For the calculation you must take the average value between two determinations.
2. Determination of water absorption of the polymer material
Objective: To determine the mass of water absorbed by the specimen as a result of their staying in the
water for a well established time at a certain temperature.
Test materials: 3 Discs of 2 polymeric materials with diameters of 100 mm.
Equipment and appliances: drying cupboard, water baths, electric cooker, analytical balances.
Stages of the work:
A) Determination of water absorption in cold water.
Samples is weighed and quickly immersed in distilled water and kept at 232 С during 241 hour.
Thereafter, the samples removed from water, wiped with dry and clean cloth or filter paper no more
than 1 minute, and weighed.
Processing of the results:
The mass of water absorbed by the sample is calculated in milligrams according to the formula:
Х1 = m2 – m1,, g
where m1 - mass of the sample before immersion in water, g
m2 - mass of the sample after removal of the water, g
Weight of water absorbed by the sample per unit of area:
X2 
(m2  m1 )
, where
A
А — sample surface, mm
А
 d 2
4
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X3 
Mass fraction of water absorbed by the sample in percentage:
m2  m1
 100%
m1
Laboratory work № 3-4. Determination of molecular weight polymers by viscosimetry
Objective: To determine the molecular weight.
Equipment and devices: Oswald viscosimeter, flasks with ground glass stoppers on 25
ml, 5 ml graduated pipette with scale interval 0.2 ml, stopwatch
Test materials: polystyrene solution in benzene
Preparing for the determination.
Preparing viscometer
The viscometer is thoroughly washed with the chromic mixture, then a large amount of hot water, rinse
with distilled water, alcohol, ether and dried.
Preparation of polymer solution
The milled and dried polymer is dissolved in a suitable solvent. A portion of the polymer is selected so
that for the initial solution at a measurement temperature ηspecific = 1.5. The solution should not contain
particulate matter that can clog the capillary. This solution was filtered through a glass filter number 1
or number 2.
Taking measurements
First, measure the flow time of the pure solvent. To do this, 10 ml of solvent is poured into the wide
knee of viscometer. Through a rubber tube with a blower the solvent is sucked above the upper mark
on the ball-shaped extension. Suction is stopped. As soon as the liquid level drops to the upper mark,
the stopwatch is started and flow time of the solvent from the top to the bottom mark is noted. When
the liquid drops to the bottom mark, turn off the stopwatch and record the result. Flow time is
determined at least 5 times and take the average. After determining the flow time (τ0) of the solvent
viscometer is removed from the oven, the solvent is poured through the wide knee and viscometer is
dried. In a dry viscometer poured with graduated pipette 10 ml of polymer solution and again set
viscometer in a thermostat. After incubation during 15 minutes flow time of solution is measured at
least 5 times (τ) as described above. Thereafter viscometer is thoroughly washed with solvent and
dried. Then 10 ml of solution with another concentration, which obtained by adding 5 ml of pure
solvent to the initial solution, is poured into viscometer and it’s flow time is measured. Of all, you
must perform at least three dilutions and measurements for dilute solutions. After all measurements
viscometer must be washed several times with solvent and dried.
Obtained data are recorded in Table 1.
Solution Concentration
Flow
volume,
of the solution, time of
reduced
specific
rel
ml
g/100 ml
solution
( t), s



Processing of the results:
The relative viscosity (ηrel) is the ratio of the solution flow time to the solvent flow time:
 rel 
t solution
t 0 solvent
Specific viscosity (ηSpecific) is the ratio of the difference between the solution and the solvent
viscosity to the viscosity of the solvent:
 specific 
t  t0
  rel  1
t0
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The reduced viscosity (η reduced) is the ratio of the specific viscosity of the polymer solution to
its concentration:
 reduced 
 specific
С
Intrinsic viscosity [η] is called as the limiting value of ηspecific / C (or ln η relative / C) at a concentration
of the solution tends to zero.
To determine the molecular weight, the Mark-Houwink equation, which expresses the
dependence of the intrinsic viscosity from the molecular weight, are used.

   KM
M
[ ]
K
K = 1,1 • 10-4
α = 0,725
where K and a - constants for the system polymer - solvent at a given temperature.
Polymer
Solvent
T, K
K*10-4
α
polystyrene
toluene
25
1.18
0.72
polymethacrylate
chloroform
25
0.47
0.78
polymethacrylate
acetone
25
0.96
0.69
cellulose acetate
acetone
25
1,6
0,82
polyacrylonitrile
dimethylformamide 25
3,35
0,72
Polyvinyl alcohol
water
25
5,95
0,63
polyvinylpyrrolidone water
25
1,4
0,7
Based on the retrieved data, curve is constructed as a function ηspecific / C from C, after that you
must continue its to intersection with the y-axis and by the point of intersection as the resulting value
of [η] determined the value of the molecular weight by taking the value of "K" and "α" from the tables
for the corresponding pair "polymer-solvent system".
ηуд/С
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0 0,10,20,30,40,50,60,70,80,91,01,11,21,31,41,51,61,71,81,92,02,12,22,32,4
Laboratory work № 5-6. Determination of the resin and filler
Objective: To determine the amount of resin and filler in the sample by extraction.
Test material: press powder.
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Reagents, instruments and equipment: Acetone, boxing for taking the sample, the
conical flask with refinished stopper to 250 ml, the thermostat.
Stages of the work:
Press powder of about 5 g is weighed, taken up with 0.01 grams, and placed in a conical flask to 250
ml with stopper. To press powder 40 - 50 ml of acetone is added, flask is closed by stopper and
vigorously stirred for about 10 min. Then the slurry is filtered and the residue of filler on the filter is
dried in a thermostat at 800C to constant weight.
Processing of the results:
The amount of filler in the percentage is calculated by the formula:
X = (A1 / A) * 100, where
a - the mass of the press powder, g
a1 - weight of residue, g
The resin content percentage calculated by the formula:
Х1 = 100 – Х
Laboratory work № 7-8. The synthesis of polymer by polycondensation and studying
its properties
Exp 1. Obtaining polyether based on glycerine and phthalic anhydride
Reagents: glycerol, phthalic anhydride, acetone, alcoholic solution of potassium
hydroxide 0.5N, 1% phenolphthalein solution
Equipment: a porcelain cup (crucible), burette, thermometer to 3500C, 50ml conical
flasks, cylinder or graduated tube, analytical balance, stove.
Stages of the work:
In a porcelain beaker 5.5 g phthalic anhydride and 3.35 g of glycerol are placed and covered by
porcelain cup. Mixture is heated to 1800C with maintaining this temperature for one hour. During the
synthesis of the polyester, phthalic anhydride is sublimated under heating and crystallized on the cold
walls of the beaker and the cup. It periodically is scraped into a beaker and the reaction mixture is
thoroughly stirred. After synthesis the molecular weight of the polymer is determined.
Exp 2. Determination molecular weight of polyester
a) Determination of the acid number.
In a pre-weighed on an analytical balance flask 0.1-0.3 g of sample with accurate to 0.0002 g is placed,
then 5-7ml of acetone is added and after dissolution of sample, solution is titrated with an alkali in the
presence of phenolphthalein until the appearance of pink color. Parallel with, control experiment is
carried out with the same amount of solvent.
Acid Number (AN), indicating the number of mg KOH required to neutralize the carboxyl
groups contained in 1 g of the analyte, is calculated by the formula:
, mg of KOH/g of polymer
where V1 - volume of 0.1 N solution of alkali, who had gone on a working sample titration, ml; V2 volume of 0.1 N solution of alkali, who had gone on a control sample, in ml; F - amendment to the titer
of 0.1 N solution of KOH; 0.00561 - titer 0.1N solution of alkali, g / ml; q - the weight of substance, g.
Molecular weight of polyester is calculated by the formula:
Make a conclusion with reaction equations according to the results of experiments.
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Laboratory work № 9-10. Determination of the isoelectric point of the protein
State of swelling characterized by the degree of the swelling α, which is defined as the amount
of liquid absorbed per unit mass or volume of the polymer:
Where m0 and V0 - weight and volume of the initial polymer, mt and Vt - weight and volume of the
swollen polymer at time t. Thus, the process of swelling can be observed periodically weighing the
swelling agent (gravimetric method) or by measuring the volume of liquid remaining after swelling
(volumetric method).
Reagents - food gelatin, gelatin treated with 40% aqueous formaldehyde, 0.2 M
solutions of acetic acid and sodium acetate.
Equipment - pipette on 5 and 10 ml, weighing bottles, a glass, a watch glass, a pH
meter, analytical scales.
Studying the influence of pH on the swelling of gelatin is carried out in solutions of the
following compositions:
Table 1.
Volume of 0.2 M Volume of 0.2 M Approximate pH Weight of gelatin Weight of gelatin
acetic acid
sodium acetate
before swelling,
after swelling, m,
solution, ml
solution, ml
m0, g
g
0
0
7.0
1
9
5.7
3
7
5.1
4
6
4.9
5
5
4.8
7
3
4.4
9
1
3.8
10
0
2.7
The pH is accurately measured using a pH meter. Weighing gelatine (weighing about 50 mg) is
must be bring in the weighing bottles or glasses with a prior prepared solutions. After 60 minutes,
removed from the sample bottle gelatin, gently dried between sheets of filter paper and weighed on a
watch glass.
Then you must take a small amount of swollen gelatin from each sample, transfer to tubes, pour
5 ml of distilled water and heat on a steam bath until complete dissolution of the polymer in one of the
tubes.
Make a conclusion with calculating the degree of swelling of gelatin α and the graph of
depending the degree of swelling from the pH value and finding the IEP. Explain differences in the
degree of swelling and solubility of usual gelatin and gelatin processed with formalin.
Laboratory work № 11-12. Identification of natural, artificial and synthetic fibers.
Exp 1. Behavior of fibers during combustion
Reagents and equipment: fiber samples, dry fuel or spiritlamp
Reaction of the burning is a preliminary test of textile fibers. Test is carried out in a flame of a spirit
lamp or a match. Fiber is pre-rolled in the flagellum with length of 1.5-2 cm and is carefully it
introduced with tweezers into the flame. After the start of the combustion fiber is immediately
removed from the flame. You should note the behavior of the fiber at the approaching to the flame,
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introducing into the flame and removing from it; the kind of residue (ash) after burning and smell at
the burning of fiber. The results are recorded in the table.
Fiber
Ability to
ignite
Color of
the flame
Burning
behavior
Smell
View of
residue
Reaction
of steam
By the nature of combustion all the fibers can be divided into four groups:
1- At the approaching to fire they do not melt and do not change shape, burn without melting, after
removing from the flame they continue to burn without melting; burning residue - light ash-gray color;
burning smell is burnt paper (cotton, linen, viscose, copper and ammonia, polynosic fibers).
2- At the approaching to flame they melt and twist in the direction of the opposite to flame, burn
slowly with melting, after removing from the flames they damp by themselves; burning residue fragile black ball or a fluffy black ash; during combustion they emit a smell of burning feathers (silk,
wool).
3- At the approaching to flame they melt, after removing from the flame they continue to burn with a
bright flame; melting residue – is a solid black bead with irregular shape, a certain burning smell is
absence (diacetate, triacetate fibers, the fibers of polyacrylonitrile).
4- At the approaching to flame they melt, burn slowly with melting, at the combustion they give
white smoke (nylon, Anid) or black smoke with soot (polyester), after removing from the flame they
damp by themselves (except lavsan), the residue after burning - solid round ball, a certain burning
smell is absence (polyamide fibers - nylon, Anid, Enanth, polyester - polyester, perchlorovinyl chlorine).
Exp 2. Testing solubility in acids.
The fibers are boiled with concentrated hydrochloric acid for 5-10 minutes, stirring
occasionally with a glass stick.
soluble in boiling hydrochloric acid,
broken or deformed: natural fibers
(cotton, linen, wool, silk), synthetic
fibers (acetate, copper-ammonia,
viscose), a synthetic polyamide fiber
are not soluble in boiling hydrochloric
acid: synthetic fibers, excepting
polyamide fiber (polyester,
perchlorovinyl, polyacrylonitrile)
Determine the reaction of the
decomposition products
(at heating dry fibers in a test tube
strip of pH paper, soaking in water,
is brought to the outlet of tube and
the reaction of the vapors of
decomposition products is noted)
1. Benzene at the cold - dissolves
(perchlorovinyl fiber)
2. Insoluble – act with nitric acid
without heating – dissolves
(polyacrylonitrile fiber)
3. Insoluble – act with nitric acid
at the heating - dissolves
(polyester fiber – lavsan)
A) Acid reaction
cellulose fibers (cotton, linen,
acetate, copper-ammonia,
viscose staple)
A1 Glacial acetic acid – dissolves
B) Base reaction
protein fibers (wool, silk), polyamide fiber
B1 Glacial acetic acid at the heating dissolves (polyamide fiber)
B2 Insoluble (wool, silk) - act with
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(acetate fiber)
A2 Insoluble – act with concentrated
hydrochloric acid without heating –
dissolves (copper-ammonia, viscose)
A3 Insoluble – act with concentrated
sulfuric acid without heating –
dissolves (cotton), insoluble (linen)
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concentrated hydrochloric acid
without heating – dissolves (silk)
B3 Insoluble (wool) act with
concentrated sulfuric acid at
heating – dissolves rapidly (wool),
dissolves slowly (protein fibers)
Exp 3. Qualitative reactions for textile fibers
a) Qualitative reactions for wool, silk
A1 In concentrated nitric acid they swell and stain in yellow
A2 With an alkaline solution of lead salts wool gives dark brown coloration
A3 At heating with a 1% solution of ninhydrin they are painted in blue color
b) Qualitative reactions for cellulose fibers - copper-ammonia, viscose, acetate fiber
B1 At the treatment with concentrated solution of zinc chloride (2-3ml), to which is added 3 drops of a
solution of iodine in potassium iodine, the fibers is colored in blue
B2 Viscose fiber in concentrated sulfuric acid dissolves with formation a red-brown solution
c) Qualitative reactions for acetate fiber – in 0.5% solution of potassium permanganate they are
colored in dark brown, viscose in a dark gray color
d) Qualitative reactions for polyamide fiber
D1 At boiling for 1 minute in 0.2% solution of ninhydrin they give a blue color
D2 At boiling for 2-3 minute in a mixed solution of rhodamine C (0.3-0.4g per liter) and cationic blue
(0.1-0.2 g per liter), followed by washing with cold water, they are painted in bright reddish-purple
color
e) Qualitative reactions for polyacrylonitrile fiber
E1 At boiling in a concentrated solution of sodium hydroxide they are painted in orange or reddishbrown color
E2 At boiling for 2-3 minute in a mixed solution of rhodamine C (0.3-0.4g per liter) and cationic blue
(0.1-0.2 g per liter), followed by washing with cold water, they are painted in bright the blue color
f) Qualitative reactions for chlorine-containing fibers – perchlorovinyl (chlorine),
polyvinylchloride)
Fiber sample is placed in a dry tube and heated to decomposition. When plentiful vapors start to
allocation you must tray moistened iodine-starch paper to the hole tube. It’s bluish indicates the
presence of free chlorine in the vapor. Iodine-starch paper is paper, impregnated with starch solution to
which is added potassium iodide.
g) Qualitative reactions for polyester fiber – lavsan
G1 At boiling in dry tube to decomposition yellow ring – sublimate of terephthalic acid - is formed on
the walls of the tube.
G2 At boiling for 2-3 minute in a mixed solution of rhodamine C (0.3-0.4g per liter) and cationic blue
(0.1-0.2 g per liter), followed by washing with cold water, they are painted in light pink color
Make a conclusion with reaction equations according to the results of experiments.
Laboratory work № 13-15. Polymer conversion
Exp 1. Dissolving cellulose in copper-ammonia solution (reagent Schweitzer)
Reagents and equipment: copper-ammonia solution (reagent Schweitzer) – (10g
of anhydrous copper sulfate is dissolved in 200ml of water and poured 100ml 2M
sodium hydroxide solution. Precipitate of copper hydroxide is washed with water for
removing sulfate ions and then sucked through a Buchner funnel. The resulting
precipitate is dissolved in 25% ammonia solution. Ammonia is slowly poured under
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continuous stirring of the flask contents; at the bottom of the flask a little precipitate
must remain. The solution is allowed to stand, then it is drained by decantation or
filtration. Reactive should be stored in a tightly closed bottle.); Concentrated
hydrochloric acid, absorbent cotton wool, tubes, rods.
Stages of the work:
Into tube 4-5ml cuprammonium solution are poured, then are dipped a small piece of cotton
(cellulose). All mixture thoroughly stirred with wand to completely dissolve. There are formatted a
viscous clear solution with bright blue color. To this solution 10-15 drops of concentrated
hydrochloric acid is added. Cellulose stands out (compare with the structure of the original). The
ability to dissolve cellulose in Schweitzer's reagent is used in the production of cuprammonium
artificial silk.
Exp 2. Preparation and properties of cellulose acetate
Reagents and equipment: sulfuric and acetic acid, concentrated; absorbent
wadding, acetone, 50 ml conical flask, porcelain cup, test tube with a ground glass neck,
reflux condenser, a glass slide.
Stages of the work:
A small piece of cotton wool is well wetted with water and placed in a 50 ml conical flask,
which is filled before with 5ml glacial acetic acid and 1-2 drops of concentrated sulfuric acid
(catalyst). After cooling the mixture is heated in a boiling water bath with constant stirring with a glass
rod to dissolve the cellulose. The resulting solution is poured as a thin stream to the glass with 250300ml of ice water. Precipitated flakes is filtered and dried in a porcelain dish on a boiling water bath.
Obtained cellulose acetate is placed into the tube with 1-2 ml of acetone and heated on the steam bath
with reflux condenser for 2-3 minutes. The resulting solution is poured onto a glass slide and allowed
to acetone evaporating. The resulting film is removed and applied to the flame. You should compare
the ability to burn the original cellulose and its acetate.
Exp 3. Interaction cellulose with the alkali (mercerization)
Reagents and equipment: 40% sodium hydroxide solution, 10% hydrochloric acid
solution, the filter paper.
Stages of the work:
In the glass with concentrated sodium hydroxide strip of filter paper is lowered. In another
glass with distilled water a strip of paper of the same size is dipped (sample for comparison). After 5-7
minutes the paper is extracted from liquid. The sample from the first glass is washed with water,
neutralized with 10% hydrochloric acid solution, rinsed again with water and dried between sheets of
filter paper. You must compare appearance of the samples, water wetting ability and strength at break.
Exp 4. Reacting cellulose with sulfuric acid
Reagents and equipment: concentrated sulfuric acid, sulfuric acid solution (in
porcelain cup to 20ml of water is added 30ml of concentrated sulfuric acid, after that the
solution should be cool to 5°C), 10% ammonia solution, the filter paper, porcelain cup.
Stages of the work:
In porcelain dish with half filled solution of sulfuric acid filtration paper strip with 1 cm of
wide is immersed for 5, 10, 15, 20, 25, and 30 second. There after, the paper is quickly transferred
into a large glass of water, to which added a small amount of ammonia solution. After some time the
paper strips is removed, dried between sheets of filter paper and then in airing cupboard.
You must compare appearance of the samples, water wetting ability and strength at break.
Make a conclusion with reaction equations according to the results of experiments.
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4 STUDENT’S SELF-STUDY (SSS)
Guidelines for performing tasks of individual work
The purpose of self-study is to master the fundamental knowledge, skills and
abilities in the field of macromolecular chemistry. Independent student work includes
preparation to current lectures and laboratory work, studing material imposed on
independent study. This kind of work promotes the development of independence,
responsibility and organization of students, the development of creative approach to
solving problems on educational and professional levels.
One of the self-study forms is the writing and defensing the essay on one of the
suggested topics. The abstract should contain necessary:
1. Title page (you can see the pattern on chair)
2. Table of contents - this essay plan in which each section must comply with the
page number on which it is located.
3. Introduction - a section of the essay, devoted to justifying the choice of topic
and formulating the problem, which will be presented.
4. Main part - part of the essay, which consistently revealed major aspects of
problem in accordance with some logic (chronological, thematic).
5. Conclusion - summarizing, a brief analysis - justification of the benefits of that
point of view with which you agree.
6. List of literature sources - at least 8-10 literature sources
Length of an abstract should be no less than 8 and no more than 12 pages. Work
must be done with 14 font, sizes of fields - top, bottom, left - 25mm, right - 15mm; line
spacing - 1.5. Pages must be numbered. Indention - 1cm.
Thematic plan of the SSS
The kind of work
The contents
Referen
ces
The preparing for Consolidate
the 1, 3, 4
lectures
obtained knowledge
by participating in
office
hour, studying the
scientific
and
journalistic periodic
press
The preparation to Activate self study
1, 3, 4
laboratory works
Consolidate the
obtained knowledge
by participating in
office
Hour.
Mastering by the
elementary
techniques
of
researches of objects
Fulfillment
period
1-15 weeks
Quantity of
hours
20
Form
of control
Orally,
written
tasks
1-15
weeks
20
Written
work
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Total
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Check the obtained
knowledge through
examinations
and
tests
7, 15 week
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5
Orally
45
Individual tasks for checking progress
3 week
1. Demonstrate a possible mechanism of chain termination in the polymerization of
ethylene as a result of disproportionation and recombination.
2. Show a scheme of chain polymerization reaction of propylene. Write a radical
mechanism of this reaction (three stages) with acetyl peroxide.
3. Locate hydrocarbons below in order of increasing lightness to chain polymerization:
1) ethylene, 2) propylene, 3) 2,3-Dimethyl-2-butene, 4) 2-butene.
6 week
1. Show the mezanizm of chain polymerization of butene-1 in the presence of benzoyl
peroxide.
2. Write schemes of chain polymerization for the following compounds: styrene,
acrylonitrile, methyl acrylate. Please give a mechanism of cationic polymerization for
the styrene in the presence of boron fluoride.
3. Teflon - highly stable polymer prepared by polymerization of tetrafluoroethylene.
Make a chart of the reaction.
10 week
1. For produsing viscose silk the cellulose is treated with sodium hydroxide. After this
to the formed alkyl cellulose is added carbon disulfide and in this conditions cellulose
xanthate (viscose) are obtained. Viscose silk is a hydrolysis product of the cellulose
xanthate in an acidic medium. Write the equation of all these reactions. What is
cellophane?
2. Write the fragment of xylan molecule formula, if it is known that it consists of
residues of β-1,5-D-xylose linked by β-1,4 glycosidic bonds.
3. A.M. Butlerov first realized the dimerization of isobutylene at heating with 60%
sulfuric acid. Obtained dimer is a mixture of two isomers: 2,4,4-trimethylpentene-1 and
2,4,4-trimethylpentene-2. Write the reaction of producing diisobutylenes. Explain the
mechanism of this reaction, taking into account that it proceeds via carbocation.
4. Make a chart of step polymerization reaction with three molecules of propylene.
Explain the mechanism of this reaction (with the formation of carbocations). Call
trimers obtained by systematic nomenclature.
5. By the polymerization in the presence of sulfuric acid diisobutylene was obtained
from 140g. isobutylene. Unreacted isobutylene was evaporated and diisobutylene was
mixed with bromine, and 120g of bromine was expended. Determine the percentage
yield of diisobutylene.
14 week
Topics of abstract
1. Thermoplastics - the current state of the industry
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2. Thermosets - the current state of the industry
3. Main components of the polymeric compositions
4. Rubber and tire
5. Polymers of natural origin and their derivatives
6. The structure and general properties of polymers
7. Using of polymers in medicine
8. Natural fibers
9. Synthetic fibers
10. Artificial fibers
11. Polymer films
12. Ion exchange resin
13. Plastics based on natural and petroleum asphalts
Criteria for evaluating all forms of Student’s Self-Study
Points/
100
Criteria
The ability to
+
use theoretical
knowledge in
solving
practical tasks
Level of
+
mastering of
theoretical
material
Reasonableness
+
and clarity of
response
Quality of
+
reporting
material
Completeness
+
of
representations
the
knowledges
and skills by
the subject
90
85
80
75
70
65
60
55
50
<50
+
+
+
+
-
-
-
-
-
-
+
+
+
+
+
+
+
+
+
-
+
+
+
+
+
+
-
-
-
-
+
+
+
+
+
+
+
+
+
-
+
+
+
+
+
+
+
+
+
-
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Test and Measurement tools
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
Basic concepts of polymer chemistry
The unique properties of polymers
Starting materials for synthesis of polymers
Molecular weight and polydispersity of the polymer molecules
Differences between low molecular weight substances and macromolecules
Number average molecular weight characterization and methods of determination.
Weight average molecular weight characteristics and methods of its determination.
Curves of the molecular weight distribution
Chemical method of establishing the molecular weight
classification of polymers by origin
Classification of synthetic polymers on the structure of the main chain
Classification of synthetic polymers by chemical composition
Classification of carbon-chain polymers
Classification of hetero polymers
Thermoplastic and thermosetting polymers
Structure of polymers
Classification of polymers in the form of molecules and stereoisomers
Intermolecular forces in macromolecules - orientation effect, hydrogen bonds, etc.
Globular and fibrillar structure
The additive polymerization - main stage
Mechanisms of chain termination - recombination
Mechanisms of chain termination - disproportionation
Chain termination mechanisms - transfer to the monomer, the polymer, the solvent
Polymerization inhibitors or stabilizers
Cationic polymerization mechanism - the main stage, the conditions of conducting
Anionic polymerization mechanism - the main stage, the conditions of conducting
Coordination polymerization based on ziegler-natta catalysts
Polycondensation process, the main characteristics
Functionality of monomer and its value
Equilibrium polycondensation
Nonequilibrium polycondensation
Influence of various factors on the rate of polycondensation and polymer molecular weight
Modification of polymers without changing the length macrochain
Modification of polymers with increasing chain length
Destruction of polymers
Methods for polymer processing into articles. Forming fibers.
Methods for polymer processing into articles. Forming films.
Methods for polymer processing into articles. Plastics molding
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Vocabulary
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