POLYMER CHEMISTRY
1.1
INTRODUCTION
The term ‘polymer’ derived from the Greek words, polys—many and meros—parts
or units. Thus, polymer is a large molecule, formed by repeated linking of small
molecules called ‘monomers’. Therefore, a substance made up of long molecules which
are characterized by many repeating molecular units in linear sequence is called a
polymer. Polymers are made by sequential addition of many monomer molecules to
each other.
nA → A—A—A—A— . . . —
— A—(A)n–2—A
monomers
polymer
For example, polyethylene; a polymer is formed by repeated leakage of simple ethylene
molecules (monomers):
nCH2—CH2

→
ethylene
(—CH2—CH2—)n
Polyethylene
In many polymers, the fundamental units are not all the same but are two or more
similar molecules. Such substances are called ‘copolymers’ to distinguish them from
homopolymers, which contain only one kind of fundamental unit.

→
nA + mB
—(A—B—A—B—A—B—A)n+m—
comonomers
copolymers

→
nA
A—A—A—A— . . . —
— A—(A)n–2—A
monomers
homopolymer
The products of linking only small number of monomer units are designated by the use
of Greek prefixes:
Monomer
A
Dimer
A—A
Trimer
A—A—A
1
2
ENGINEERING CHEMISTRY
Tetramer
A—A—A—A
Pentamer
A—A—A—A—A
etc.
The above are short chain polymers, also known as oligomers. The monomeric units
may combine with each other into a macromolecule to form polymers of linear, branched
or cross linked (three dimensional) structures.
Polymers which possess only long sequential strands are called linear polymers, e.g.,
A—A—A—A— . . . Homopolymers
or
A—B—A—B—A— . . . Copolymers
Linear copolymers in which the units of each type form fairly long continuous
sequences (blocks) are called ‘block copolymers’ e.g.,
A—A—A—A— . . . — . . . —A—A—B—B—B— . . .
In copolymer molecules, the monomers may be arranged in the chain at random or
regularly. Copolymers of the former group are called ‘statistical’ or ‘irregular’, whereas
those of the latter group are called ‘regular’.
If the main chain is made up of same species of atoms, the polymer is called homochain
polymer, and if the main chain is made up of different atoms is called heterochain polymer
e.g.,
. . . A—A—A—A—A— . . . Homochain Polymer
. . . A—A—A—B—A—A—A—B—A—A— . . . Heterochain Polymer
Branched polymers are of following structures:
M
A
Branching of same monomers
A
. . . A—A—A—A—A—A— . . .
A
A
A
A
M
M
Branched chain homopolymer
POLYMER CHEMISTRY
3
M
B
Branching of comonomers
A
A—B—A—B—A—B—A—B—A—B—A—
B
B
A
A
:
:
Branched copolymer
Branched copolymers with one kind of monomers in their main chain and another kind
of monomers in their side chains are called ‘graft copolymers’. e.g.,
. . . —A—A—A —A—A—A—-A—A— . . .
B
B
B
B
:
:
It is also possible, with three functional groups (or two different monomers at least one
of which is trifunctional), to have long linkage sequences in two (or three) dimensions and
such polymers are distinguished as cross linked polymers, e.g.,
—A—A—A —A—
—A—A
A —A
← Homo cross linked polymers
A—A—A —A—
Trifunctional monomers
A—B—A —B—A— . . .
A
A
← Copolymers
A—A—A— B—A— . . .
Linear polymers are commonly relatively soft, often rubbery substances, and often
likely to soften (or melt) on heating and to dissolve in certain solvent, whereas cross linked
polymers are hard and do not melt, soften or dissolve in most cases.
4
ENGINEERING CHEMISTRY
The number of repeating units in the chain so formed is called the ‘degree of polymerization’ (DP). Polymers with a high degree of polymerization are called ‘high polymers’ and
those with low degree of polymerization are called ‘oligopolymers’. High polymers have
very high molecular weights (104 to 106) and hence are called as ‘macromolecules’.
The orientation of monomeric units in a macromolecule can take an orderly or disorderly fashion with respect to the chain. If the monomers have entered the chain in a random
fashion, it is called an ‘atactic’ polymer. If all the side groups lie on the same side of the
chain (cis arrangement), it is called an ‘isotactic’ polymer. If the arrangement of side groups
is in alternating fashion (trans arrangement), it is called a ‘syndiotactic’ polymer, e.g.,
Atactic polymer: Polypropylene
Isotactic polymer: Natural rubber
Syndiotactic polymer: Guttapercha
H— H
H— R
H— H
H— R
H— H
H— R
H— H
H— R
H— H
H— R
H— H
H— R
H— H
H— R
H— H
R— H
H— H
R— H
H— H
H— R
H— H
R— H
H— H
H— R
R— H
R— H
H
H
H
R
H
R
H
R
H
H
H
H
H
H
H
H H
H H
A ta ctic P o lym er
H
H
H
R
Iso ta ctic p olym e r
H
H
H
H
H
H
R
H
R
H
H
R
H
R
R
H
H
H
R
H
H
H
H
R
H
S ynd io tactic po lym er
The importance of polymers in our life is almost breathtaking. Proteins and carbohydrates, which constitute two of the three principal classes of human foodstuffs, are natural
polymers of high molecular weight. Nucleic acids are responsible for transmission of genetic
characteristics in living organisms. Natural rubber, synthetic elastomers (synthetic rubbers),
plastics, synthetic fibers, and resins are all polymers having uses that reach into every part
of our lives. The tonnage of polymers marketed by the American chemical industries exceeds
by a wide margin the volume of all other synthetic organic chemicals. Most of the structural
tissues of living things are composed of polymers. In plants these are chiefly cellulose
POLYMER CHEMISTRY
5
(a polysaccharide) and lignins. In animals the main structural polymers are proteins, which
take different forms as skin, hair, muscle, etc.
1.2
CHARACTERISTICS OF POLYMER STRUCTURE AND PROPERTIES OF
POLYMERS
Following are the main characteristics of the structure and properties of polymers:
(i) The major structural features of polymeric compounds is the presence of chain
molecules in which a large number of atoms are combined successively. They have
two types of bonds, chemical and inter-molecular, which greatly differ in energy and
length. The atoms in the chain are joined to each other by strong chemical bonds,
about 1–1.5 Å in length. Much weaker intermolecular forces interact between the
chains at distances of about 3–4 Å. Crossed linked or three dimensional polymers
have chemical bonds (cross-links) between their chains.
(ii) The presence of large molecular and two types of bonds predetermines all properties which are typical of polymers.
(iii) Polymeric substances exhibit wide varieties of physical and chemical properties.
This is naturally expected because of the many possible kinds of macro-molecular
composition and arrangement. The broad range of fibrous, adhesive, plastic, foamy,
filmy and rubbery polymeric materials so readily available attested to this
macromolecular versatility.
(iv) The chemical nature of the monomeric unit is the primary factor which determines
the properties of the polymer. Differences in the thermal stability and mechanical
strength of different polymers are related to difference in bonding and structure of
the monomer as well. The chemical reactivity of a polymer is mostly due to the
reactivity of its molecular components, e.g., natural rubber undergoes deterioration
when ozone attacks the double bonds of the polymer chain whereas a saturated
hydrocarbon chain like polyethylene resists such attack.
(v) Cellulosic polymers offer their free hydroxyl groups to a variety of reagents and
thus make it possible to incorporate useful modifications of properties, e.g., reaction with nitric acid produces nitro-cellulose, from which propellant (gun cotton)
and plastic (celluloid) are formed. On the other hand, reaction with acetic acid
produces cellulose acetate, which can be fabricated into films, sheets and other useful
forms. Both the above reactions alter the free hydroxyl group of cellulose. There are
extensive possibilities for chemical modification and fabrication into products.
(vi) More drastic chemical differences are capable of yielding wider differences in chemical
properties, e.g., silicone polymers, in which the macromolecular chains contain
Si—O— linkages. The great thermal stability of the O—Si bonds, mainly due to the
p-dπ bonding (this refers to the π bonding between p and d orbitals) of O to Si,
renders the solicone products to be used at high temperature. The hydrocarbon
side chains contribute oily or lubricating properties.
(vii) The properties of a polymer also depend upon the form and arrangement of its
macromolecules. The critical factors are the molecular weight (which depends on
6
ENGINEERING CHEMISTRY
the degree of polymerization), the extent of branching, cross-linking or network
structure, the stereotic disposition of the monomeric units, the degree and the
kinds of crystallinity of the macromolecules. Several variations can be brought
about even without alteration of chemical functional groups.
(viii) Stereo-regularity facilitates crystallinity which enhance all the properties related to
crystallinity, e.g., stereo-regularity strengthens polyethylene.
(ix) Mechanical deformation also changes the properties of a polymer. Stretching of
rubber offers an example. In the unstretched form, rubber molecules undergo
random motion. When rubber is stretched, this motion is restricted, the molecules
assume a linear crystalline arrangement and the entropy is reduced. The consequent release of energy in the form of heat is a familiar observation.
1.3
CLASSIFICATION OF POLYMERS
On the basis of different chemical structures, physical properties, mechanical behaviour, thermal characteristics, stereochemistry, polymers can be classified into following
ways:
1.3.1 Natural and Synthetic Polymers
Depending on their origin, polymers can be grouped as natural or synthetic. Those
isolated from natural materials are called natural polymers, e.g., cotton, silk, wool and
rubber. Cellophane, cellulose rayon, leather and so on are, in fact, chemical modification of
natural polymers.
Polymers synthesized from low molecular weight compounds are called synthetic polymers, e.g., polyethylene, PVC, nylon and terylene.
1.3.2 Organic and Inorganic Polymers
A polymer whose backbone chain is essentially made of carbon atoms is termed as
organic polymer. The atoms attached to the side valencies of the backbone carbon atoms are,
however, usually those of hydrogen, oxygen, nitrogen, etc. The majority of synthetic polymers is organic. In fact, the number and variety of polymers are so large thats why we refer
to ‘polymers’ on the other hand, generally contains no carbon atom in their chain backbone.
Glass and silicone rubber are examples of inorganic polymers.
1.3.3 Thermoplastic and Thermosetting Polymers
Some polymers soften on heating and can be converted into any shape that they can
retain on cooling. The process of heating, reshaping and retaining the same on cooling can
be repeated several times. Such polymers, that soften on heating and stiffen on cooling, are
termed ‘thermoplastics’. Polyethylene, PVC, nylon and sealing wax are examples of thermoplastic polymers. Some polymers, on the other hand, undergo some chemical change on
heating and convert themselves into an infusible mass. They are like the yolk of egg, which
on heating sets into a mass, and, once set, cannot be reshaped. Such polymers, that become
infusible and insoluble mass on heating, are called ‘thermosetting” polymers.
POLYMER CHEMISTRY
7
1.3.4 Plastics, Elastomers, Fibres and Liquid Resins
Depending on its ultimate form and use, a polymer can be classified as plastic, elastomers,
fibre or liquid resins. When, e.g., a polymer is shaped into hard and tough utility articles
by the application of heat and pressure, it is used as a ‘plastic’. Typical examples are
polystyrene, PVC and polymethyl methacrylate.
When vulcanised into rubbery products exhibiting good strength and elongation, polymers
are used as ‘elastomers’. Typical examples are natural rubber, synthetic rubber, silicone
rubber.
If drawn into long filament like material whose length is at least 100 times its diameter,
polymers are said to have been converted into ‘fibre’ e.g. nylon and terylene.
Polymers used as adhesives, potting compound sealants, etc. in a liquid form are
described liquid resins. Commercially available epoxy adhesives and polysulphide sealants
are typical examples.
1.3.5 Atactic, Isotactic and Syndiotactic Polymers
On the basis of the configurations, (stereochemistry) polymers can be classified into
three categories viz., atactic, isotactic (cis-arrangement) and syndiotactic (trans-arrangement).
Those polymers in which arrangement of side groups is at random around the main
chain, are termed as atactic polymers.
Those polymers in which the arrangement of side groups are all on the same side are
known as isotactic polymers.
Whereas, those polymers in which the arrangement of side groups is in alternating
fashion is termed as syndiotactic polymers.
1.4
TYPES OF POLYMERS
There are two types of polymers; viz. (i) addition polymer, and (ii) condensation polymer.
1.4.1 Addition Polymers
The addition polymer is one in which the monomers are molecules with multiple bonds
which undergo true addition reactions with each other, e.g.,
n(R—CH —
— CH—R)

→
R
R
Vinyl polymer
nCH2 —
— O

→
Polystyrene, PVC, polyethylene, polychlorostyrene etc. are the examples of addition
polymers.
8
ENGINEERING CHEMISTRY
1.4.2 Condensation Polymers
The condensation polymer is one in which a small molecule (usually water) is eliminated in the condensation of any two monomer units. It is clear, therefore, the monomers
for condensation polymers must be (at least) bifunctional molecules in which one function
on one monomer molecule reacts with the other function on another molecule, e.g.,
nH O
COOH
(n - 1 ) H 2 O + H O (
C O — O )n H
P o lyester
(n - 1 ) H 2 O + H 2 N (
H 2N
COOH
nHO
O H + nH O C O
C O — N H )n H
C O OH
(2 n – 1 ) H 2 O + H O (
O— CO
C O — O )n H
P o lyester cop o lym e r
The last example implies a variant in which two bifunctional units are present on each
of two kinds of monomers to create a condensation polymer.
Polymers which possess only long sequential strands like those listed are called linear
polymers.
Nylon is the main example of condensation polymer
1.5
STRUCTURE OF POLYMERS
1.5.1 Elastomers or Rubbers
An elastomer is a linear polymer which exhibits elasticity and other rubber-like properties. Rubbers are of two types:
(i) Natural rubber, and
(ii) Synthetic rubber.
1.5.1.1 Natural Rubber
Natural rubber is obtained in the form of latex from rubber trees (Hevea brasiliensis).
The latex normally contains 30-60% rubber. It can be used, as such, in the latex form or the
solid rubber can be coagulated from the latex using 1% acetic acid solution. Natural rubber
is a highly soft and elastic material.
Natural rubber is a polymerized form of isoprene (2, Methyl-1,3-butadiene):
CH2 —
— C—CH —
— CH2
CH3
POLYMER CHEMISTRY
9
Isoprene is synthesized from propylene, as follows:
→ CH2 = C—CH2—CH2—CH3
CH2 —
— CH 
CH3

→
CH3
Isomerization
CH3—C —
— CH—CH2—CH3
CH3

→
Pyrolysis
CH2 —
— C—CH —
— CH2 + CH4
CH3
Isoprence
Polymerization of isoprene yields polymers containing varying degrees of cis-1,4- and
trans-1, 4 as well as 1, 2 or 3, 4-vinyl units in the molecule, depending upon the initiator
and the solvent systems employed. Under controlled conditions, polyisoprene containing
upto 96% cis-configuration can be obtained by using a lithium alkyl initiator and anhydrous
oxygen free aliphatic hydrocarbon solvents.
H
H
H— C
H H H H
C— H
C
C
C— C
n
H— C
H
C
C
H
H— C
H
H H
H
cis-po lyiso pre ne
(N a tu ral rub b er)
Isop re ne
H
H
H
H
H— C— H H H— C— H H H— C— H H H— C— H H
H C H C H C H C H C H C H C H C
C H
C H C
C H C
C
C H C
H
H
H
H
Isop re ne
U n it
Isop re ne
U n it
Isop re ne
U n it
Isop re ne
U n it
P o ly (cis) iso pren e (N atu ra l ru bb er)
The general structure of polyisoprene is as follows:
10
ENGINEERING CHEMISTRY
Gutta Percha
It is obtained from the mature leaves of dichopsis gutta and palagum gutta trees. Gutta
percha may be recovered by solvent extraction, when insoluble resins and gums are separated. Alternatively the mature leaves are ground carefully; treated with water at about 70°C
for half an hour and then poured into cold water. When gutta percha floats on water surface
and is removed. The structure of gutta is as follows:
H
H
H
H— C— H
H
C
C
C
C
H
H
H
H
H— C— H
H C
C
C
H
H
H
H— C— H
H
C
H
H
C
C
C
C
H
H
C
Both the cis- as well as trans-varieties occur in nature as natural rubber and gutta
percha, respectively. Natural rubber is a highly soft and elastic material. It is soluble in
carbon disulphide and petrol. Whereas Gutta-percha is a hard thermoplastic solid and dissolves in petrol only on heating and is thrown out of solution when cooled. Structurally,
gutta-pereha is trans-polyisoprene; whereas natural rubber is cis-polyisoprene
1.5.1.2 Synthetic Rubbers
It is also known as artificial rubber. Synthetic rubbers are of following types:
(i)
Styrene rubber
(GR-S or Buna-S)
(ii)
Nitrile rubber
(GR-A or Buna-N)
(iii)
Neoprene
(GR-M)
(iv)
Butyl rubber
(GR-I)
(v)
Polysulphide rubber
(GR-P or Thiocol)
(vi)
Polyurethane rubber
(isocyanate rubber)
(vii)
Chlorosulphonated Polyethylene rubber
(Haplon)
(viii)
Silicone rubber.
(i) Styrene Rubber (Buna-S)
Styrene butadine rubber (SBR) is prepared by the copolymerization of butadine (75%)
and sytrene (25%) in an emulsion system at 50°C in the presences of catalyst such as cumene
hydroperoxide.
SBR is also known as Buna-S or GR-S. Styrene rubber have high abrasion resistance,
high load bearing capacity, low oxidation resistance, swells in oil and solvents, like natural
rubber SBR also vulcanised and produce cold rubber, which has greater tensile strength and
greater abrasion resistance.
nx
H
H
H
H
C
C
C
C
H
H
B u tad ie ne
+n
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
H
Styren e
H
H
x
H
n
P o lybu tad ie ne -co-styre ne
(styren e bu tad ie ne ru bb er, S B R )
POLYMER CHEMISTRY
11
SBR is used in motor tyres, shoes soles, footwear components, insulation of wire and
cables, carpet backing, gaskets, adhesives, etc.
(ii) Nitrile Rubber (Buna-N/NBR)
It is a copolymer of acrylonitrile and butadiene. It is prepared by the copolymerization
of acrylonitrile and butadiene in emulsion systems.
— CH—CH —
— CH2 + n(CH2 —
— CHCN)
CH2 —
acrylonitrile
1,3-butadiene
copolymerization
[CH2—CH —
— CH—CH2—CH—CH2]n
CN
Nitrile rubber
Nitrile rubber (GR-A) has low swelling, low solubility, goods tensile strength and abrasion resistance even after imersion in gasoline or oils. It has good heat resistance.
It is used in fuel tanks, gasoline hoses, as an adhesive and in the form of latex for
impregnating paper, teather and textiles.
(iii) Neoprene (GR-M)
Neoprene, also known as polychloroprene, has the following structure:
— CH—CH2 ]n
[CH2—C —
Cl
It is prepared by the free radical polymerization of chloroprene (2-chloro-l, 3-butadiene)
in an emulsion system.
CH2 —
— C— CH —
— CH2
P o ly m e riz a tio n
[ C H 2— C —
— C H — C H 2 ]n
Cl
Cl
N eo pre ne
or
H
CH2
— CH2
C H 2—
H
C—
—C
C—
— C
Cl
CH2
Cl
Tra ns-1,4-p oly chlorop re ne
Neoprene can be vulcanised to a considerable extent by heat alone. Its physical properties are enhanced by compounding it with metallic oxides, such as ZnO or MgO. They have
a higher oil resistance than many rubbers including nitrile rubbers. Due to the Trans-1, 4,structure, it is therefore, an easily crystallisable elastomer. The vulcanized products are
found to have excellent tensile strength.
This elastomer is principally used for providing oil resistant insulation coatings to wires
and cables and for producing shoe soles, solid tyres, gloves and industrial hoses, tubing for
carrying corrosive gases and oils.
12
ENGINEERING CHEMISTRY
(iv) Butyl Rubber (GR-I)
Butyl rubber, also known as polyisobutylene, is prepared by the copolymerization of
isobutene with isoprene and methylchloride as solvent.
C H2
—
— C — C H3
C H2
n
+
—
—
CH3
C — CH
—
— C H2
CH3
Is obutene
Is oprene
C H3
— C H 2 — C — CH 2 — C
C H3
—
— C H — C H2 —
C H3
n
P o ly is obu tylene
Butyl rubber is amorphous under normal conditions but gets crystallized on stretching.
It has excellent resistance to heat, abrasion, ageing, chemicals (such as H2SO4, HNO3, HCl
or HF), polar solvents (like alcohol and acetone) but is soluble in hydrocarbon solvents like
benzene.
Butyl rubber is used as inner tubes because its superior impermeability to gases. It is
used for wire and insulation. It is used in the production of tyres.
(v) Polysulphide Rubber (GR-P)
Polysulphide rubber, also known as Thiocol, is prepared by the reaction between sodium
polysulphide (Na2S) and ethylene dichloride (CH2Cl—CH2Cl).
C l— C H 2 — C H 2 C l
+
N a2 S x + C l C H 2— C H2 C l
— C H 2— C H2 — S— S— C H 2— C H2 —
S
S
T hioko l rubb er
Thiokols are those elastomers in which sulphur forms a part of the polymer chain. It
has extremely good resistance to mineral oils, fuel oxygen, ozone and sunlight. It is also
impermeable to gases. It cannot be vulcanized and hence does not form hard rubber. It has
poor strength and abrasion resistance.
Polysulphide rubbers are mainly used to make sealants, gaskets, balloons, fabric coatings
and gasoline hoses. Polysulphides form excellent fuel material and, upon mixing with inorganic
oxidisers such as ammonium perchlorate, they become solid propellants for rockets.
1.5.2 Polyacrylonitrile (PAN)
Polyacrylonitrile (PAN), also known as Polyvinyl cyanide, has the following structure:
[ C H 2— C H ] n
CN
POLYMER CHEMISTRY
13
Acrylonitrile can be made either by the direct catalytic addition of HCN to acetylene,
or by the addition of HCN to ethylene oxide to give ethylene cyanohydrin, followed by
dehydration.
→ CH3—CH—CN
CH3CHO + HCH 
|
OH
CH2 —
— CH—CN + H2O
It can also be produced by ammonoxidation of propylene:
CH2 —
— CH—CH3 + NH3 +
3
2
500°C
O2 
— CH—CN + 3H2O

→ 2CH2 —
Catalyst
PAN has a remarkable resistance to heat upto around 220°C and exhibits very good
mechanical properties. PAN is used to produce fibres known as PAN fibres. The copolymers
of PAN with butadiene (nitrile rubber) is a material of great industrial importance.
1.5.3 Polystyrene (PS)
Polystyrene, also known as polyvenyl benzene has the following structure:
[ C H 2 — C H ]n
Polystyrene is prepared by the free radical addition polymerization of styrene monomer
(dissolved in ethyl benzene) in the presence of benzoyl peroxide as a catalyst.
H
nC
H
C
P o ly m e riz a tio n
H
H
C
C
H
H
Sty re ne
n
PS
It is a transparent, light, excellent moisture resistant. It can be nitrated and sulphonated
by fuming nitric acid and cone. H2SO4 respectively. It yields water soluble emulsion at
100°C. It is highly electric insulating, highly resistant to acids and goods and is chemical
resistant. It has low softening range (90-100°C) and brittle. However, it has the unique
property to transmitting light through curred sections.
It is used in moulding of articles like comb, toys, buttons, buckels, radio and television
parts, refrigerator parts, battery cases, high frequency electric insulators, lenses, etc.
1.5.4 Polymethyl Methacrylate (PMMA)
Polymethyl Methacrylate, also known as Lucite or Plexiglass has the following structure:
CH3
C H 2— C
COOCH3
n
PMMA is prepared by radical polymerization (in bulk or suspension) of methyl
methacrylate in the presence of acetyl peroxide or H2O2 as catalyst.
14
ENGINEERING CHEMISTRY
CH3
CH3
P o ly m eriza tio n
C
n C H2
C H 2— C
C O O C H3
COOCH3
M e thyl m e thac rylate
(M M A )
n
PM M A
PMMA is a hard, fairly rigid material with a high softening point of about 130-140°C,
but it becomes rubber like at a temperature above 65°C. It has high optical transparency,
high resistance to sunlight and ability of transmitting light accurately. However, it has low
chemical resistance to hot acids and alkalis and has low scratch resistance.
It is used to make attractive signboards and durable lenses for automobile lighting, TV
screens, artificial eyes, paints, adhesives, etc.
1.5.5 Polyamides
Polyamides are prepared by the melt polycondensation between dicarboxylic acids and
diamines. They have the general structure as follows:
[ N — (R)x — N — (R )y — C ] n
H
where
H
O
R is —CH2— or
The aliphatic polyamides are generally known as NYLONS. There are different types
of nylons and are usually indicated by a numbering system. This number gives the number
of carbon atoms present in the monomer molecules. Aliphatic Nylon have M.P. of
250-300°C.
Nylon-6:6
It is obtained by the polymerization of adipic acid with hexamethylene diamine.
H
H
N
C
H
H
H
HO
+
N
H
6
C
O
H
OH
C
C
H
4
H
P o lym eriza tion
— H 2O
H
N
C
H
H
H
6
N
C
C
H
O
H
C
4
O
n
or
( N H — (C H 2 )6 — N HC O (C H 2 ) 4 CO )n
P o ly h exa m e thy len e a d ipa te (N y lo n -6 .6)
POLYMER CHEMISTRY
15
Nylon-6
It is prepared by the self condensation of ε-amino caproic acids.
O
— N H — (C H 2 ) 5 — C —
N H 2 — (C H 2 ) 5 — C O O H
P o ly ca p ro la ctu m (N y lo n -6 )
Nylon-6:10
It is prepared by the reaction between hexamethylene diamine and sebacic acid. The
product formed is hexamethylene diammonium sebacate (Nylon-6:10) which on further
polymerization forms ribbon of Nylon-6:10. This is not used as a fibre. It is used in brushes,
bristles, sports equipment, etc.
N H 2 — (C H 2 ) 6 — N H 2 + H O O C — (C H 2 ) 8 — C O O H
H ex am e thy lene d iam ine
S e bac ic ac id
[ N H (C H 2 ) 6 — N H C O (C H 2 ) 8 C O ]n
N y lon -6 :10
Nylon-11
It is produced by the self condensation of ω-aminoundecanoic acid.
O
H
— N — (C H 2 ) 1 0 — C —
N H 2 — (C H 2 ) 10 — C O O H
N y lo n -11
(P o ly - ω-a m in o u n d e ca n o ic a cid )
Nylon-11 is less water sensitive than other nylons because of its greater hydrocarbon
character. It is used as textile fibre.
Nylon-6:6 is used as plastic as well as a fibre. It has good tensile strength, abrasion
resistance and toughness upto 150°C. Also, it offers resistance to many solvents. However,
formic acid, cresols and phenols dissolve this polymer. It is used to produce tyre cord,
monofilament of ropes, substitute of metal in gears and bearings.
Kelvar
It is a aromatic polyamide similar to nylons, but in benzene rings rather than aliphatic
chains linked to the amide groups —CONH—.
It is prepared by the condensation polymerization of terephthalic acid dichloride and
1, 4-diaminobenzene
n [C lO C
C O C l]
+ n [H 2 N
Terephtha lic a cid
dichlorid e
N H2]
p-am inoa niline
(1, 3-diam inobe nze ne)
O
O
H
H
—C
C
N
N
n
K e lv ar
Kelvar is exceptionally strong. This is due to the stronger intermolecular forces between
neighbouring chains. It also has high heat stability.
16
ENGINEERING CHEMISTRY
Kelvar is used in tyres, brakes, clutches linging and other car parts, bullet proof vests,
motor cycle helmets, aerospace and aircraft industries.
1.5.6 Polyester Resins
Polysters have the structure with ester linkages as follows:
(O (R ) O — C (R ′) C ) n
O
O
where R and R′ are aliphatic.
They are prepared by a polycondensation reaction between a dicarboxylic acid and a
diol. Aliphatic polysters were not of much industrial importance, mainly because of their low
M.P. e.g., the polyster with a degree of polymerization comparable to the commercial
polyethylene melts somewhere in the range of 50-80°C, whereas the M.P. of polyethylene is
around 120°C. This problem of low M.P. was overcome by introducing aromatic rings into
the polyster chain. This is evident from the following examples:
(O — (C H 2 ) 2 — O — C — (C H 2 ) 6 — C ) n
(M .P. 65 °C )
O
O — (C H 2 ) 2 — O — C
C
O
O
(M .P. 26 5°C )
n
Polyster (e.g., terene or terelene or dacron) is prepared by the condensation polymerization
of dicarboxylic acid with dihydroxy alcohols.
HO
H O — (C H 2 )2 — O H +
E thylene gly c ol
HO
C
C
O
O
Terephth alic a cid
P o ly m erization
O — (C H 2 ) 2 — O — C
C
n
O
O
P o lyster (Tere le ne o r D a cro n)
Polyster is a good fibre forming material. This is due to the presence of numerous polar
groups and symmetrical structures. Such fibres have high stretch resistance. Polyethylene
terephthalate (PET) is highly resistant to mineral and organic acids but is less resistant to
alkalis.
It is used in making synthetic fibres like terelene, dacron etc., for blending, with wool
to provide better crease and wrinkle resistance. It is also used as glass reinforcement
material in safety helmets, battery boxes, etc.
1.6
CONDUCTING POLYMERS AND THEIR APPLICATIONS
Ordinary polymers are purely insulators. Conducting polymers (CP) are long chain
having current flowing properties. To make the polymer materials conductive they are doped
with atoms that donate negative or positive charges (oxidizing or reducing agents) to each
unit, enabling curent to travel down the chain. Depending on the dopant, conductive polymers exhibit either p-type or n-type conductivity.
POLYMER CHEMISTRY
17
Conducting polymers can be classified into the following types:
C o nd ucting p olym ers
In trinsically con d uctin g
p olym e rs
C .P. ha vin g
con ju ga tio n
E xtrinsica lly co nd ucting
p olym e rs
C o nd ucting e lem e nt
fille d po lym ers
D o pe d co nd ucting
p olym e rs
B len de d C .P.
These are briefly discussed below :
1.6.1 Intrinsically Conducting Polymers
(a) C.P. having conjugated π–electrons in the backbone :
Such polymers contains conjugated π–electron in the back bone which increases their
conductivity to a large extent. This is because overlapping of conjugated π–electrons over
the entire backbone results in the form of valence bonds as well as conduction bonds, which
extends over the entire polymer molecule.
For example—Polypyrrole: It is obtained by electropolymerization of pyrrole
H
N
P o lym eriza tion
n
N
N
H
P yrro le
H
N
H
P o lypyrro le
n
Polypyrrole is an inherently conducting polymer due to inter chain dopping of electrons.
It can be easily prepared by oxidative polymerization of the monomer pyrrole.
Mechanism
H
H
H
N
N
–e
–
N
H
N
N
H
H
M on om e r
N
H
H
N
N
H
–e
–
N
–
–e
– 2H +
N
N
H
H
H
H
N
N
D im e r
N
H
H
H
N
N
N
H
Trim e r
+
18
ENGINEERING CHEMISTRY
Polythiophene
Polythiophenes consist of a chain of alternating double and single-bonds like poly acetylene, however, each first and fourth carbon atom are connected by a sulphur atom forming
a thionyl ring.
S
n
S
S
S
S
S
n
Therefore, bond between the second and the third carbon atom get more single bond
character than other C–C bonds and consequently also the bonds connecting the thionyl
rings are more of single-bond character.
Due to this weaker mesomerization than in polyacetylene the band gaps of polythiophenes
are shifted to the blue and UV. Beside of their structure defining function the sulphur atoms
will have also a direct influence on the electronic and optical properties of a polythiophene.
(b) Doped Conducting Polymers: It is of two types
(i) p–doping (oxidative doping).
(ii) n–doping (reductive doping).
p–doping
It is done by oxidation process. (i.e., removal of e– from the polymer pi – back bone).
This formation is known as polaron. A second oxidation of this polaron, followed by radical
recombination yields two positive charge carriers on each chain which are mobile.
+
(CH) x
A
Lewis acid
Polyacetylene
+ −
ˆˆˆ
†
‡ˆˆ
ˆ (CH) x A
[Oxidation process]
p-doped
polyacetylene
(1 )
VB
P o lyace tylen e
– e – (o xida tion )
I 2/C C l 4
(2 )
+
P o la ron (R a dica l ca tion )
–
(3 )
+
+
B ipo la ron
+
S o liton p air
(p -do pe d po lyace tylen e )
CB
VB
S e gre ga tion o f cation
+
CB
VB
I 2/C C l 4
– e o xida tion
CB
(4 )
CB
VB
POLYMER CHEMISTRY
19
n–doping
It is done by reduction process (addition of an e– to the polymer).
(CH) x
Polyacetylene
+
B
Lewis acid
ˆˆˆ
†
‡ˆˆ
ˆ
(CH)−x
B+
n-doped
polyacetylene
It forms polaron and bipolaron in two steps. This followed by recombinaton of radicals
yields two negative charge carriers on each chain of polyacetylene which are responsible for
conduction.
(1 )
VB
P o lyace tylen e
–
+
+e (R e du ctio n)
CB
N a ( C 10H 8)
–
–
(2 )
CB
P o la ron (ra dical an io n)
VB
+e
+
–
N a ( C 10H 8)
–
–
(3 )
CB
–
B ipo la ron
VB
S e gre ga tion o f anion
–
(4 )
CB
–
S o liton pa ir
(p -do pe d po lyace tylen e )
[Here VB = Valence bond, CB = Conduction bond,
VB
= Donal level].
1.6.2 Extrinsically Conducting Polymers
It is of two types
(a) Conductive Element filled polymers.
(b) Blanded conducting polymers.
(a) Conductive Element Filled Polymer: In this, the polymers act as the binder to
hold the conducting element (such as carbon black, metallic fibers, metallic oxides etc.)
together in the solid entity.
Minimum concentration of conductive filler which should be added so that polymer
starts conducting is known as percolation threshold. Carbon black is very used as filler
which has very high surface area (1000m2/gm) more porosity and more of a filamentous
properties. It bears good conductive properties and low in cost, light in weight, as well as
durable.
It is used in hospital operating theatres where it was essential that static charges did
not build up leading to explosion involving on aesthetics.
(b) Blended Conducting Polymers: It obtained by blending a conventional polymer
with a conducting polymer. Such polymers possess better physical, chemical, electrical and
mechanical properties and they can be easily processed.
20
ENGINEERING CHEMISTRY
For example: up to 40% of polypyrrole will have little effect on tensile strength and also
give a much higher impact strength than obtained with a carbon-black filled compound at
only 10% loading. Such compounds are used in electromagnetic shielding.
A polymer which conduct electricity is termed as ‘conducting polymer’. Most polymeric
materials are poor conductor of electricity, because of the non-availability of large number
of free electrons in the conduction process. Although no commercial products are yet known,
there is considerable interest in polymers with a wide range of electrical conductive properties,
produced for the most part by doping with inorganics such as arsenic, pentafluoride or
iodine, polymers such as polyacetylene and the polyphenylene sulfide, e.g.,
— CH=CH— CH=CH—
P o ly ace tylene
P o ly -p -ph eny len
N
P o ly pyrrole
Electrical conductivity of some important polymers are as given below in Table 1.1.
Table 1.1
Sl. No.
Polymers
Electrical conductivity in Ohm–1 m–1
1
Nylon 6, 6
10–12 – 10–13
2
Polystyrene
< 10–14
3
Phenol formaldehyde
10–9 – 10–10
4
Polyethylene
10–15 – 10–17
5
Polytetrafluoroethylene
< 10–17
6
Poly-methyl methacrylate
< 10–12
The phenomenon of conduction is observed in a number of polymers such as polypyrrole,
polythiophene, polyacetylene, polyparaphenylene and polyaniline which have been doped
with appropriate impurities. These polymers may be made either n-type, i.e., free electrons
dominant or p-type, i.e., holes dominant, depending upon the type of dopant used. However,
unlike semiconductors, the dopant atoms or molecules do not substitute or replace any of
the polymer atoms, n and p doping polymers are produced in the following ways :
→ (Polymer)n– An+ where A is Na, Li etc.
n-doping : Polymer + A 
→ (Polymer)n+ Bn– where B is I2, Br2, AsF5 etc.
p-doping : Polymer + B 
Since π electrons can easily be removed or added to the polymeric chains, so unsaturated
polymers with π electrons are mostly employed for producing high conducting polymers by
the process of doping. In general, the polymer can be made conductive in the following ways:
(i) Conductivity by doping
(ii) Conductive element filled polymer
POLYMER CHEMISTRY
21
(iii) Conjugated π electron conducting polymer
(iv) Blended conducting polymer
(v) Decreasing in band gap
(vi) Coordination conducting polymer
(vii) Photoconductive polymers.
1.6.3 Applications of Conducting Polymers
(1) Polythiophene is marketed under the trade name Baytron. It can be used to make
plastics paintable by adding the conductive agent first, and also in the electrodes
of small, high performances tantalum capacitors found in telecommunications,
computer and automobile products.
(2) Contex, a fiber is coated with a conductive polymer polypyrrole can be woven to
create an antistatic fabric which can be used in carpet industry.
(3) These can be used in producing photovoltaic devices, e.g., in Al/polymer Au photovoltaic cells.
(4) It used in making button type batteries. These batteries are long lasting, rechargeable and can produce current density up to 50 mA/cm2.
(5) Used as conductive paints.
(6) Used as electro-chemical accumulators.
(7) An emerging application for electrically conductive polymeric materials is biosensors
and chemical sensors, which can convert chemical information into measurable
electrical response.
(Aptech has developed a range of enzyme biosensors.)
(8) Used for making sensors for pH, O2, NOx, SO2, NH3 and glucose as analytical
sensors.
(9) Used in rechargeable lead-acid battery in automotive.
(10) Used in optically display devices based on polythiophene.
(11) Used in solar cells.
(12) Used in photovoltaic systems.
(13) Used in electronic devices such as transistors and diodes.
(14) Used in telecommunication systems.
(15) Used in the wiring in aircraft and aerospace components.
(16) Used in antistating coatings for clothing.
(17) Used in variable transmission (smart) windows etc.
22
1.7
ENGINEERING CHEMISTRY
ZEIGLER-NATA CATALYSTS
These are a special type of coordination catalysts, comprising two components, which
are generally referred to as the catalyst and the cocatalyst. The catalyst component consists
of halides of IV-VIII group elements having transition valence and the cocatalysts are
organometallic compound such as alkyls, aryls and hydrides of group I-IV metals (ZeiglerNata Catalysts). Although there are organo aluminium compounds such as triethyl aluminium
(AlEt 3 ) or diethyl aluminium chloride (AlEt 2 Cl) in combination with titanium
chlorides—both tri and tetra (TiCl3 and TiCl4)—are, by far, the most commonly used.
Aluminium alkyls act as the electron acceptor whereas the electron donor is titanium
halides and the combination, therefore, readily forms coordination complexes. The complex
formed is insoluble in the solvent and is, hence, heterogeneous in nature. Many structures
have been proposed for these complexes are:
Cl
R
R
Al
R
Cl
Ti
Ti
Cl
Cl
R
δ⊕
R
δ
Cl
Al
Cl
C l— Ti— R
Cl
Cl
Cl Cl
The active centres, from where the polymer chain growth propagates are formed at the
surface of the solid phase of the catalyst complex, and the monomer is complexed with the
metal ion of the active centre before its insertion into the growing chain.
The complex formed, now acts as the active centre. The monomers then attached
towards the Ti—C bond (C from the alkyl group R) in the active centre, when it forms a π
complex with the Ti ion.
R
Al
Ti
+ CH2
R
—
— CHCH3
Al
Cl
Ti
Cl
CH2 —
— CHCH3
The bonds between R and Ti opens up producing an electron deficient Ti and a carbanion
at R.
CH3
CH
R
CH2
Al
Ti
Cl
The Ti ion attracts the π electrons pair or the monomer and forms σ bond
CH3
CH
R
C H2
Al
Ti
Cl
Tra nsitio n state
This transition state now gives rise to the chain growth at the metal carbon bond,
regenerating the active centre:
POLYMER CHEMISTRY
23
R
CH3
CH
CH2
Al
Ti
Cl
Repeating the whole sequence, with the addition of second monomer molecule, we will
get the structure of the resultant chain growth as:
CH3
CH
CH3
CH2
R
CH2
CH2
Al
Ti
Cl
The five coordinated titanium ions on the surface of the catalyst is assumed to have a
vacant orbitals as shown at 6 in the following structure:
6
Cl
4
Cl
Cl
1
Ti
2
Cl
5
Cl
3
After the chemisorption of aluminium alkyl on the TiCl3 crystal, Ti3+ is alkylated by
an exchange mechanism, as follows:
Et
Et
Cl
Cl
Cl
Ti
C l + A l[E t] 3
Cl
Cl
Cl
Ti
Al
Cl
Cl
Et
Cl
Et
Cl
Cl
Cl
Ti
+ C lA I[E t]2
Cl
ac tiv e c ata ly st
Once the active catalyst is formed, the monomer is attached towards the vacant orbital
which then forms a transition π complex with the Ti.
Et
Cl
Cl
Ti
Cl
Et
Cl
+
CH 2 —
— CH
X
Cl
Cl
Cl
CHX
Ti
CH2
Cl
Et
Cl
Cl
Cl
Ti
Cl
X
CH
CH2
trans ition s tate
24
ENGINEERING CHEMISTRY
The transition state quickly gives rise to the growth of the polymer chain by the
monomeric insertion at the Ti-Et bond.
X
Cl
Et
X
Cl
Ti
Cl
C H 2— C H — Et
Cl
Ti
Cl
CH
Cl
OR
Cl
Cl
CH2
Cl
CH2
Ti
Cl
Cl
Et
CH
X
Cl
Therefore, on the basis of the above, polymerization is characterised by the initiation
propagation and termination reaction as follows:
(i) Initiation
M t— R
a ctive c e n tre
+ C H2 —
— CH
M tC H 2 C H R
X
(ii) Propagation
X
M t C H 2C H R + n C H2 —
— CH
X
M t C H2 C H — C H2 — C H — R
X
X
n
(iii) Termination
By an active hydrogen compound
M t C H 2C H R + n C H2 —
— CH
X
M t C H2 C H — C H2 — C H — R
X
X
n
By Transfer with monomer
M tC H 2 C H — C H 2 — C H — R + C H 2 — C H
X
X
n
M tC H 2 — C H 2 +
X
X
CH2 —
— C H — C H 2 CH — R
X
n
X
By spontaneous internal transfer
M tC H 2 C H — C H 2 — C H — R
X
X
n
M tH + C H 2 —
— C — C H 2— C H — R
X
X
n
Here Mt denotes transition metals such as Ti, Mo, Cr, V, Ni, or Rh Zeigler Natta
polymerization is used to prepare polypropylene, polyethylene polydiene, etc.
POLYMER CHEMISTRY
25
PROBLEMS
1. Identify the repeating unit in the following and determine the structure of the monomer.
CH3
CH3
CH3
(i) — C H 2 — C — C H 2 — C — C H 2 — C —
CH3
CH3
CH3
(ii) — C H 2 — C H — C H 2 — C H — C H 2 — C H —
CN
CH3
CN
CN
CH3
CH3
(iii) — C H 2 — C — C H 2 — C — C H 2 — C —
COOCH3 COOCH3 COOCH3
CH2
CH2
— H 2C
C—
— CH
(iv)
CH —
— CH
CH2
CH3
CH2
CH2
(v) — C H 2 — C H — C H 2 — C H — C H 2 — C H — C H 2 — C H —
C 6H 5
C 6H 5
C 6H 5
C 6H 5
2. If 20 gm of polyethylene were completely burnt in the presence of excess of air, how many
moles of CO2 will be produced?
3. What are addition polymers? Give five examples.
4. Write four units for the polymers obtained from the following monomers (assuming head
to tail structure), and name the monomeric units.
CH— CH2
(i)
N
(ii)
O
(iii) C H 2 —
— C— CN
(iv)
CH2 —
— CF2
COOCH3
(v) C H 2 —
— C— C H —
— C H 2—
CH3
5. What is the difference between a monomer and a polymer? Classify polymers on the basis
of occurrence and chemical nature.
6. What are graft and block copolymers? Give their examples?
7. Give the structure of following polymers:
(i) Nylon 66
(iii) Orlon
(ii)
Terylene
(iv)
Chloroprene.
26
ENGINEERING CHEMISTRY
8. What are organic polymers? Give the structure of five organic polymers.
9. What are vinyl monomers? Give four examples.
10. Give the mechanism of free radical polymerization of vinyl monomers.
11. What are initiators? Name four free radical initiators.
12. What are inhibitors? Give examples.
13. What is Zieglar Natta catalyst? Give two examples. What is the significance of a catalyst
in polymerization?
14. What are condensation polymers? Give four examples of condensation polymers.
15. What are bio-polymers? Give three examples.
16. Classify the polymers on the basis of stereochemistry.
17. If average degree of polymerization of polymethyl methacrylate is 103, calculate its average
molecular weight.
18. State the differences between addition and condensation polymerization.
19. Write two uses of the following polymers; low density polyethylene; polystyrene,
polymethylmethacrylare, Nylon 66, epoxy resins.
20. State the differences between RNA and DNA,
21. What are proteins? Write any three tests for proteins.
22. What are polysaccharides? Write examples and their building unit.
23. What is a copolymer? Write structure of Buna—N, Buna—S. Classify the copolymers on the
basis of arrangement of two monomer units?
24. What are the characteristics of polymer? Why do polymers have an average molecular
weight.
25. State the differences between free radical and ionic polymerization.
26. Write structure of phenol formaldehyde resin, urea formaldehyde resin, polymides,
polycarbonate and polyurethanes.
27.
(i) If two polymers of molecular weight 10,000 and 1,00,000 are mixed together in equal
parts by weight, determine the number average and weight average molecular weights.
(ii) If the above polymers are mixed so that equal number of molecules are added, determine
Mn and Mw.
28. A sample of polystyrene is composed of a series of fractions of different sized molecules.
Fraction
Weight/fraction
Molecular weight
A
0.10
12,000
B
0.19
21,000
C
0.24
35,000
D
0.18
49,000
E
0.11
73,000
F
0.08
1,02,000
G
0.06
1,22,000
H
0.04
1,46,000
POLYMER CHEMISTRY
27
Calculate the number average and weight average molecular weights of this polymer
sample.
29. Fractions of a polymer when dissolved in an organic solvent gave the following intrinsic
viscosity values at 25°C.
M(g mol–1):
34,000
61,000
1,30,000
[η]:
1.02
1.60
2.73
30. What is polydispersity index? Give its importance. Write expressions for calculation of
Mw , Mv, and M z for polymers. Name the techniques to determine the above average molecular
weight(s).
31. State whether true or false. If false, give the correct statement:
(i) Polyvinyl alcohol can be prepared by polymerization of vinyl alonol.
(ii) CH4 can be polymerised.
(iii) C2H2 and aniline cannot be polymerised.
(iv) Polymers have sharp melting point.
(v) Ziegler-Natta catalyst is used for the preparation of syndiotactic polymer.
32. Explain in details about conducting polymers.
33. What are adhesives? Explain the synthesis and application of epoxy resin.
[VTU 2006-07]
34. What are elastomers? Discuss the advantages of synthetic elastomers.
[VTU 2006-07]
35. Give the synthesis and applications of butyl rubber.
[VTU 2006-07]
36. Discuss the mechanism of conductance in polyacetylene.
[VTU 2006-07]
SOLVED NUMERICALS
1. Calculate the number average degree of polymerization of an equimolecular mixture
of hexamethylenediamine and adipic acid for the extent of reaction 0.500, 0.800, 0.900, 0.950,
0.970, 0.990 and 0.995.
Solution.
Dp
Then putting the value of p
If
p = 0.500,
=
1
1− p
then Dp = 2
p = 0.800,
then Dp =
p = 0.900,
then Dp =
p = 0.950,
p = 0.970,
1
=5
1 − 0.800
1
= 10
1 − 0.900
then Dp = 1/1–0.950 = 20
p = 0.990,
then Dp = 1/1–0.970 = 33.3
then Dp = 1/1–0.990 = 100
p = 0.995,
then Dp = 1/1–0.995 = 200
28
ENGINEERING CHEMISTRY
2. If two polymers of molecular weights 10,000 and 100,000 are mixed together in equal
parts by weight, determine the number average and weights average molecular weights; and
if the above polymers are mixed so that equal number of molecules are added,
determine M n and M w .
Solution. If equal parts of the two polymers of molecular weight M = 10,000 and
1,00,000 are mixed
(10,000 × 10) + (1,00,000 × 1)
= 18181 ≈ 18,200
1 + 10
10 × 108 + 1 × 1010
= 91819 ≈ 92,000.
Mw =
104 + 105
3. What is the percentage of sulphur present in vulcanised rubber? (Isoprene M.wt = 68).
Then
Mn =
Solution. 2 monomer units of isoprene require 2 atoms for cross links
Hence 2 × 68 gm of isoprene requires 2 × 32 gm of sulphur
68 gm of isoprene requires 32 gm of sulphur
The vulcanised rubber (68 + 32) contains 32 gm of sulphur
Thus, 1 gm of vulcanised rubber contains =
32
gm
100
32
× 100 = 32%
100
4. A polymer sample consists of 10% by weight of macromolecules of molecular wt 19000
and 90% by wt of macromolecules with M.wt 1,00,000. Calculate the M n and M w .
and 100 gm of vulcanised rubber contains =
Solution. Mn =
ΣNiMi ΣWi
=
ΣNi
ΣNi
As given
W1 = 10 gm and W2 = 90 gm
Thus,
ΣW1 = W1 + W2 = 10 + 90 = 100 gm
Wi
Mi
= 10/10,000 and N2 = 90/1,00,000
Since
Ni =
Hence
N1
Therefore,
and
Mn =
Mw =
=
W1 + W2
10 + 90
ΣWi
= N + N = 10 / 10,000 + 90 / 1,00,000 = 5.26
ΣNi
1
2
N1 M 12 + N 2 M 22
N M2 + N2M2
ΣNiM 2i
= 1 1
=
N1 M1 + N 2 M 2
W1 + W2
Σ NiMi
10 /10,000 × (10,000)2 + 90 /1,00,000 × (1, 00,000)2
= 9.1 × 104
10 + 90
5. The M n of a polystyrene is 105 gm/mole. Find its Dpn .
Solution. As we know that Dpn =
Mn
Mo
POLYMER CHEMISTRY
Mo for polystyrene,
29
per unit is 12 × 8 + 1 × 8 = 104
( C H 2— C H )
C 6H 5
Hence,
n
Dpn =
Mn 105
=
= 961.54
Mo 104
6. Find M w for polypropene, given its degree of polymerization (DP) as 10,000.
Solution.
Since
DPw =
∴
Mw
Mo
Mw = DPw × Mo
Mo = Molecular weight of repeat unit of pp =
( C H 2— C H )
CH3
= 12 × 3 + 6 × 1 = 42
Mw = 10,000 × 42 = 42 × 104 gm/mole.
Hence,
7. 42 gm of propene was polymerized by radical polymerization process and Dp was
found to be 100. Calculate the number of molecules of pp produced.
Solution.
As
Dp of pp
=
Number of propene molecules
Number of pp molecules formed
Hence, number of pp molecules formed
=
=
Number of propene molecules
Dp of pp
42 gm × (6.023 × 1023 molecules/42 gm)
1,000
= 6.023 × 1020 molecules.
8. 216 gm butadiene is copolymerized with 104 gm of sytrene. What is the molecular
formula of the copolymer?
Solution. 216 gm of butadiene = 216 g/54 gm mole–1 = 4 mole.
104 g of styrene = 104 g/104 g mole–1 = 1 mole
∴ Molecular formula of copolymer is:
9. What is the molecular mass of polypropylene molecule containing 4,000 monomer
units?
Ans. 168000 amu.
n n n