POLYMERS
Polymer:
Polymers are macromolecules formed by the repeated linking of large no. of small
molecules called monomers.
nCH2=CH2 → (-CH2-CH2-) n
Ethylene
Polyethylene
Monomer:
Monomer is a micromolecule which combines with each other to form a polymer.
EX: CH2=CH2 (Monomer) -CH2-CH2- (repeating unit)
Polymerization
Polymerization is a process in which large no. of small molecules combine to form
a big molecule with (or) with out elimination of small molecules like water.
Degree of polymerization:
The no .of repeating unit in a polymer chain is known as degree of
polymerization.
3CH2=CH2
→
-CH2-CH2-CH2-CH2-CH2-CH2-
Tacticity:
The orientation of monomeric units (or) functional groups in polymer molecule
can take place in a orderly (or) disorderly manner with respect to the main chain is
known as tacticity.
Functionality:
The no.of bonding sites (or) functional groups present in a monomer is
known as its functionality.
1. Bifunctional monomer
2. Trifunctional monomer
3. Polyfunctional monomer
Ex: poly ethylene, poly propylene
..-M-M-M-M-M-M-M-M-M-M-M….
Copolymer (Heteropolymer):
A polymer containing more than one type of monomer is known as copolymer.
Ex: Nylon, Terylene.
-M1-M2-M1-M2-M1-M2-M1-
Hetero chain polymer:
If the main chain of a polymer is made up of different atoms.
Ex: nylon 6:6
....C-C-O-C-C-O -C-C …
Addition(or)chain growth polymerization :
It is a reaction that yields a polymer, which is an exact multiple of the original
monomeric molecule contains one (or) more double bond in addition polymerization
there is no elimination of any molecule.
Ex:polyethylene is produced from ethylene
Condensation polymerization
It is a reaction between simple polar groups containing monomer with the
formation of polymer and elimination of small molecule like H2O
Hexamethylene diamine react with adipic acid condense to form of nylon6:6
nH2N – (CH2)6 –NH2 +n HOOC – (CH2)4 -COOH→[HN-(CH2)6 –NH–CO –CH2-CO -]n
(Nylon 6:6)
Co polymerization
It is the joint polymerization in which 2 (or) more different monomers
combine to give a polymer.
n(CH2=CH –CH =CH2 +n CH2= CH) → -(CH2-CH=-CH-CH2-CH2-CH-)n
C6H5
C6H5
Butadiene styrene
polybutadiene costyrene
Classification of polymers
Classification based on source of availability
1. Naturally occurring polymers
These occur in plants and animals and are very essential for life. These include starch
cellulose, proteins, nucleic acids and natural rubber. Starch is a polymer of glucose,
cellulose is also a polymer of glucose, proteins are polymers of amino acids. Natural
rubber consists of repeat units of isoprene (2-Methyl-1,3-Butadiene).
2. Semi synthetic polymers
These are mostly derived from naturally occurring polymers by chemical
modifications. Cellulose on acetylation with acetic anhydride in presence of sulphuric
acid forms cellulose diacetate used in making threads and materials like films, glasses
etc. Vulcanised rubber has much improved properties and is used in making tyres etc.
Gun-cotton , which is cellulose nitrate, is used in making explosives.
3. Synthetic polymers
The polymers which are prepared in the laboratory are called synthetic polymers.
These are also called man made polymers . These include fibres, plastics and synthetic
rubbers and find diverse uses as clothing, electric fittings, eye lenses, substitute for wood
and metals.
nCH2=CH2
→ n….CH2-CH2 ….→ - (CH 2-CH2-) n
Ethylene
Ex: PVC is produced from vinyl chloride
polyethylene
PLASTICS
Plastics are high molecular organic material that can be moulded into any desired
shape by the application of heat and pressure in the presence in the presence of a catalyst.
Classification of plastics:
1. Thermoplastics ex: PVC, polyethylene
2. Thermosetting plastics ex: Bakelite, polyester
Thermoplastic resin:
Thermoplastic can be softened on heating and hardened on cooling. They are
generally soluble in organic solvent.
Ex: PVC, polyethylene
Thermosetting resin
Thermosetting plastics are prepared by condensation polymerization.
These plastics get harden on heating and once harden cannot be softened again.
Ex;Bakelite,polyester.
S.No
1
Thermoplastic resins
Thermosetting resins
They are formed by addition
They are formed by Condensation
polymerization
polymerization.
2
3
4
5
The consist of linear long chain
They consist of three dimensional network
polymer.
structure.
They are weak, softened less brittle.
They are strong, hard and more brittle.
They can be remoulded
They can not be remoulded.
They soften on heating and harden on
cooling.
They do not soften on heating.
MECHANISM OF ADDITION POLYMERISATION
The mechanism of addition polymerisation can be explained by any one of the
following three types.
1.
2.
3.
4.
Free radical mechanism.
Ionic mechanism.
Co-ordination mechanism.
Free radical mechanism
Free radical mechanism occurs in three major steps namely,
(i) Initiation
(ii) Propagation, and
(iii) Termination
Initiators are compounds which produce free radicals by the homolytic
dissociation (decomposition). These free radicalsinitiate the polymer chain growth.
(i) Initiation
It is considered to involve two reactions.
(a) First reaction involves production of free radicals by homolytic dissociation of an
initiator (or catalyst) to yield a pair of free radicals (R•).
(ii) Propagation
It involves the growth of chain initiating species by successive addition of large
number of monomers.
The growing chain of the polymer is known as living polymer.
(iii) Termination
Termination of the growing chain of polymer may occur either by coupling
reaction or disproportionation.
(a) Coupling (or) Combination
It involves coupling of free radical of one chain end to another free radical
forming a macro molecule.
Disproportionation
It involves transfer of a hydrogen atom of one radical centre to another radical
centre, forming two macromolecules, one saturated and another unsaturated.
The product of addition polymerisation is known as Dead polymer.
1) Ionic polymerisation: The Addition polymerisation that takes place due to Ionic
intermediate is called Ionic Addition polymerisation.
Based on the nature of ions used for the initiation process Ionic polymerisation
classified into 2 types
i) Cationic polymerisation
ii) Anionic polymerisation
i) Cataionic polymerisation: Cationic polymerisation is initiated by an acid (Lewis
Acids such as BF3, AlCl3, FeCl3, SnCl4, H2SO4, HF in presence of small amount
of
H2O.
E.g. Isobutylene – Butyl rubber, polystyrene. Polyvinyl ether
ii) Anionic polymersation: Anionic polymerisation is initiated by anion (may be base
(or) nucleophiles such as n-butyl lithium (or) Potassium amide)
Monomer, containing e– withdrawing groups like phenyl (–C6H5). Nitrile (–CN) etc.
undergo anionic addition polymerisation.
E.g. Polystyrene, Poly acylonitrile
Ionic polymerisation:
The Addition polymerisation that takes place due to Ionic intermediate is called Ionic
Addition polymerisation.
Based on the nature of ions used for the initiation process Ionic polymerisation classified
into 2 types
a) Cationic polymerisation
b) Anionic polymerisation
a) Cationic polymerisation: Cationic polymerisation is initiated by an acid (Lewis acids
such as BF3, AlCl3, FeCl3, SnCl4, H2SO4, HF in presence of small amount of
H2O.
E.g. Isobutylene – Butyl rubber, polystyrene. Polyvinyl ether.
H2SO4 → H+ + HSO−4
HF → H+ + F–
BF3 + H2O → H+ + BF3(OH–)
1) Chain initiation: Proton (H+) add to C – C double bond of alkene to form stable
carbocation.
CH 2 → CH − CH3
G
G
|
vinyl monomer
(G = e– donating group, + I effect)
2) Chain propagation: Carbocation add to the C – C double bond of another monomer
molecule to from new carbocation.
⊕
⊕
→ CH3
− CH− CH2
CH3 −
− CH
|
|
|
|
CH3
G
G
− CH− CH2
|
G
⊕
−
|
G
G
G
Reapeated
→
|
G
⊕
CH3 − CH− CH2 − CH− CH2 − CH
|
G
G
G
3) Termination: Reaction is terminated by combination of carbocation with negative
ion (or) by loss of proton
⊕
CH − CH(−CH − CH− ) CH − CH
3
2
n 2
|
|
G
G
CH3
−
→
4
|
G
− CH(−CH2
|
− CH)n − CH
|
|
G
G
G
b) Anionic Polymerization: Anionic polymerisation is initiated by anion (may be
base (or) nucleophiles such as n-butyl lithium (or) Potassium amide)
Monomer, containing e– withdrawing groups like phenyl (–C6H5). Nitrile (–CN) etc.
undergo anionic addition polymerisation.
E.g. Polystyrene, Poly acylonitrile
1) Chain initiation:
K⊕NH2−
2) Chain propagation:
−
H2N − CH2 −
→ H2N − CH2 − CH−
|
W
→
|
W
|
W
CH2
|
W
H2N − CH2 − CH− CH2 − CH →
|
|
W
W
H N − CH − CH− (CH − CH − ) − CH − CH−
2 2
2
2
|
|
|
W
W
W
Anionic polymerisation has no chain termination reaction.
GLASS TRANSITION TEMPERATURE
The glass–liquid transition (or glass transition for short) is the reversible transition
in amorphous materials (or in amorphous regions within semicrystalline materials) from a
hard and relatively brittle state into a molten or rubber-like state.[1] An amorphous solid
that exhibits a glass transition is called a glass. Supercooling a viscous liquid into the
glass state is called vitrification, from the Latin vitreum, "glass" via French vitrifier.
Despite the massive change in the physical properties of a material through its
glass transition, the transition is not itself a phase transition of any kind; rather it is a
laboratory phenomenon extending over a range of temperature and defined by one of
several conventions.[2][3] Such conventions include a constant cooling rate (20
K/min)[1] and a viscosity threshold of 1012 Pa·s, among others. Upon cooling or heating
through this glass-transition range, the material also exhibits a smooth step in the
thermal-expansion coefficient and in the specific heat, with the location of these effects
again being dependent on the history of the material.[4] However, the question of
whether some phase transition underlies the glass transition is a matter of continuing
research.[2][3][5]
The glass-transition temperature Tg is always lower than the melting temperature,
Tm, of the crystalline state of the material, if one exists
FACTORS INFLUCING Tg
1. The value of Tg depends on chainlength, extent of cross-linking , the berrier
which hinders the internal rotation of the chainlinks.
2. the value of Tg ofagiven polymer varies with the rate of heating andcooling.
3. below Tgthe polymer is hard and brittle.
4. Increase in cross-linking decreases mobility leads to decrease in free volume and
increase in Tg.
5. As length of side group increases the polymer chains move apart from each other
and that increases free volume in the molecule resulting in decreased Tg.
TACTACITY
Isotactic polymers
Isotactic polymers are composed of isotactic macromolecules (IUPAC
definition).[3] In isotactic macromolecules all the substituents are located on the same
side of the macromolecular backbone. An isotactic macromolecule consists of 100%
meso diads. Polypropylene formed by Ziegler-Natta catalysis is an isotactic polymer.[4]
Isotactic polymers are usually semi crystalline and often form a helix configuration.
Syndiotactic polymers
In syndiotactic or syntactic macromolecules the substituents have alternate
positions along the chain. The macromolecule consists 100% of racemo diads.
Syndiotactic polystyrene, made by metallocene catalysis polymerization, is crystalline
with a melting point of 161 °C. gutta percha is also an example for Syndiotactic
polymer.[5]
Atactic polymers
In atactic macromolecules the substituents are placed randomly along the chain.
The percentage of meso diads is between 1 and 99%. With the aid of spectroscopic
techniques such as NMR it is possible to pinpoint the composition of a polymer in terms
of the percentages for each triad.[citation needed]
MOLECULAR MASS OFPOLYMER
In linear polymers the individual polymer chains rarely have exactly the same
degree of polymerization and molar mass, and there is always a distribution around an
average value. The molar mass distribution (or molecular weight distribution) in a
polymer describes the relationship between the number of moles of each polymer species
(Ni) and the molar mass (Mi) of that species.[1] The molar mass distribution of a polymer
may be modified by polymer fractionation.
Contents
Different average values can be defined depending on the statistical method that is
applied. The weighted mean can be taken with the weight fraction, the mole fraction or
the volume fraction:




Number average molar mass or Mn
Mass average molar mass or Mm
Viscosity average molar mass or Mv
Z average molar mass or Mz
[2]
Here is the exponent in the Mark-Houwink equation that relates the intrinsic viscosity to
molar mass.
Measurement
These different definitions have true physical meaning because different
techniques in physical polymer chemistry often measure just one of them. For instance,
osmometry measures number average molar mass and small-angle laser light scattering
measures mass average molar mass. Mv is obtained from viscosimetry and Mz by
sedimentation in an analytical ultracentrifuge. The quantity a in the expression for the
viscosity average molar mass varies from 0.5 to 0.8 and depends on the interaction
between solvent and polymer in a dilute solution. In a typical distribution curve, the
average values are related to each other as follows: Mn < Mv < Mm < Mz. Polydispersity
of a sample is defined as Mm divided by Mn and gives an indication just how narrow a
distribution is.
The most common technique for measuring molecular mass used in modern times
is a variant of high-pressure liquid chromatography (HPLC) known by the
interchangeable terms of size exclusion chromatography (SEC) and gel permeation
chromatography (GPC). These techniques involve forcing a polymer solution through a
matrix of cross-linked polymer particles at a pressure of up to several hunderd Bar. The
limited accessibility of stationary phase pore volume for the polymer molecules results in
shorter elution times for high-molecular-mass species. The use of low polydispersity
standards allows the user to correlate retention time with molecular mass, although the
actual correlation is with the Hydrodynamic volume. If the relationship between molar
mass and the hydrodynamic volume changes (i.e., the polymer is not exactly the same
shape as the standard) then the calibration for mass is in error.
The most common detectors used for size exclusion chromatography include
online methods similar to the bench methods used above. By far the most common is the
differential refractive index detector that measures the change in refractive index of the
solvent. This detector is concentration-sensitive and very molecular-mass-insensitive, so
it is ideal for a single-detector GPC system, as it allows the generation of mass v's
molecular mass curves. Less common but more accurate and reliable is a molecularmass-sensitive detector using multi-angle laser-light scattering - see Static Light
Scattering. These detectors directly measure the molecular mass of the polymer and are
most often used in conjunction with differental refractive index detectors. A further
alternative is either low-angle light scattering, which uses a single low angle to determine
the molar mass, or Right-Angle-Light Laser scattering in combination with a viscometer,
although this latter technique does not give an absolute measure of molar mass but one
relative to the structural model used.
The molar mass distribution of a polymer sample depends on factors such as
chemical kinetics and work-up procedure. Ideal step-growth polymerization gives a
polymer with polydispersity of 2. Ideal living polymerization results in a polydispersity
of 1. By dissolving a polymer an insoluble high molar mass fraction may be filtered off
resulting in a large reduction in Mm and a small reduction in Mn thus reducing
polydispersity.
Number average molecular mass
The number average molecular mass is a way of determining the molecular mass
of a polymer. Polymer molecules, even ones of the same type, come in different sizes
(chain lengths, for linear polymers), so the average molecular mass will depend on the
method of averaging. The number average molecular mass is the ordinary arithmetic
mean or average of the molecular masses of the individual macromolecules. It is
determined by measuring the molecular mass of n polymer molecules, summing the
masses, and dividing by n.
The number average molecular mass of a polymer can be determined by gel
permeation chromatography, viscometry via the (Mark-Houwink equation), colligative
methods such as vapor pressure osmometry, end-group determination or proton NMR.[3]
An alternative measure of the molecular mass of a polymer is the mass average
molecular mass. The ratio of the mass average to the number average is called the
polydispersity index.
High Number-Average Molecular Mass Polymers may be obtained only with a
high fractional monomer conversion in the case of step-growth polymerization, as per the
Carothers' equation.
Mass average molecular mass
The mass average molecular mass is a way of describing the molecular mass of a
polymer. Polymer molecules, even if of the same type, come in different sizes (chain
lengths, for linear polymers), so we have to take an average of some kind. For the mass
average molecular mass, this is calculated by
where
is the number of molecules of molecular mass
.
If the mass average molecular mass is m, and one chooses a random monomer,
then the polymer it belongs to will have a mass of m on average (for a homopolymer).
The mass average molecular mass can be determined by static light scattering,
small angle neutron scattering, X-ray scattering, and sedimentation velocity.
The ratio of the mass average to the number average is called the polydispersity index.
The mass-average molecular mass, Mw, is also related to the fractional monomer
conversion, p, in step-growth polymerization as per Carothers' equation:
, where Mo is the molecular mass of the
repeating unit.
Polydispersity Index
The ratio of weight average molecular mass to the number average molecular
mass is calledpolydispersity index, PDI.
PDI = MW/Mn
This gives an idea about the homogeneity of a polymer.
(i) The polymers whose molecules have nearly same molecular masses are
called monodisperse polymers. For these molecules, MW = MN and therefore, PDI is
one.
(ii) The polymers whose molecules have wide range of molecular masses are
called polydisperse polymers. For these polymers, MW > MN and therefore, their PDI is
greater than one.
Polymerization
1. Bulk Polymerization
2. Solution Polymerization
3. Suspension Polymerization
4. Emulsion Polymerization
BULK POLYMERISATION
Bulk polymerization or mass polymerization is carried out by adding a soluble
initiator to pure monomer in liquid state. The initiator should dissolve in the monomer.
The reaction is initiated by heating or exposing to radiation. As the reaction proceeds the
mixture becomes more viscous. The reaction is exothermic and a wide range of molecular
masses are produced.
Bulk polymerization has several advantages over other methods, these advantages
are[citation needed





The system is simple and requires thermal insulation.
The polymer is obtained pure.
Large castings may be prepared directly.
Molecular weight distribution can be easily changed with the use of a chain
transfer agent.
The product obtained has high optical clarity
Disadvantages




Heat transfer and mixing become difficult as the viscosity of reaction mass
increases.
The problem of heat transfer is compounded by the highly exothermic nature of
free radical addition polymerization.
The polymerization is obtained with a broad molecular weight distribution due to
the high viscosity and lack of good heat transfer.
Very low molecular weights are obtained.
Emulsion polymerization is a type of radical polymerization that usually starts with
an emulsion incorporating water, monomer, and surfactant. The most common type of
emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer (the
oil) are emulsified (with surfactants) in a continuous phase of water. Water-soluble
polymers, such as certain polyvinyl alcohols or hydroxyethyl celluloses, can also be used
to act as emulsifiers/stabilizers.
Emulsion polymerization is used to manufacture several commercially important
polymers. Many of these polymers are used as solid materials and must be isolated from
the aqueous dispersion after polymerization. In other cases the dispersion itself is the end
product. A dispersion resulting from emulsion polymerization is often called a latex
(especially if derived from a synthetic rubber) or an emulsion (even though "emulsion"
strictly speaking refers to a dispersion of an immiscible liquid in water). These emulsions
find applications in adhesives, paints, paper coating and textile coatings.
Advantages of emulsion polymerization include:




High molecular weight polymers can be made at fast polymerization rates. By
contrast, in bulk and solution free radical polymerization, there is a tradeoff
between molecular weight and polymerization rate.
The continuous water phase is an excellent conductor of heat and allows the heat
to be removed from the system, allowing many reaction methods to increase their
rate.
Since polymer molecules are contained within the particles, the viscosity of the
reaction medium remains close to that of water and is not dependent on molecular
weight.
The final product can be used as is and does not generally need to be altered or
processed.
Disadvantages of emulsion polymerization include:




Surfactants and other polymerization adjuvants remain in the polymer or are
difficult to remove
For dry (isolated) polymers, water removal is an energy-intensive process
Emulsion polymerizations are usually designed to operate at high conversion of
monomer to polymer. This can result in significant chain transfer to polymer.
Can not be used for condensation, ionic or Ziegler-Natta polymerization, although
some exceptions are known.
Suspension polymerization is a heterogeneous radical polymerization process that
uses mechanical agitation to mix a monomer or mixture of monomers in a liquid phase,
such as water, while the monomers polymerize, forming spheres of polymer.
This process is used in the production of many commercial resins, including
polyvinyl chloride (PVC), a widely used plastic, styrene resins including polystyrene,
expanded polystyrene, and high-impact polystyrene, as well as poly(styrene-acrylonitrile)
and poly(methyl methacrylate). Solution polymerization is a method of industrial
polymerization. In this procedure, a monomer is dissolved in a non-reactive solvent that
contains a catalyst.
The reaction results in a polymer which is also soluble in the chosen solvent. Heat
released by the reaction is absorbed by the solvent, and so the reaction rate is reduced.
Moreover the viscosity of the reaction mixture is reduced, not allowing autoacceleration
at high monomer concentrations. Once the maximum or desired conversion is reached,
excess solvent has to be removed in order to obtain the pure polymer. Hence, solution
polymerization is mainly used for applications where the presence of a solvent is desired
anyway, as is the case for varnish and adhesives. It is not useful for the production of dry
polymers because of the difficulty of complete solvent removal.
This process is one of two used in the production of sodium polyacrylate, a
superabsorbent polymer used in disposable diapers.
Notable polymers produced using this method are polyacrylonitrile (PAN) and
polyacrylic acid (PAA).
Nylon (Polyamides)
Nylon - 6:6
Nylon - 6.6 is obtained by the polymerisation of adipic acid with
hexamethylene diamine.
Nylon - 6
It is prepared by self-polymerization of caprolactam.
Nylon - 11
It is prepared by self-condensation of ω-amino undecanoic acid.
Among the different nylons, nylon 6:6 and nylon-6 are important for fibre.
The number indicates, number of carbon atoms in the material from which it is
made.
Properties
1. Nylons are translucent, whitest, horny and high melting polymers.
2. They possess high temperature stability and good abrasion-resistance.
3. They are insoluble in common organic solvents and soluble in phenol and formic
acid.
Uses
1. Nylons are used for making filaments for ropes,bristles for tooth-brushes and
films, etc.
2. Nylon - 6 and Nylon - 11 are mainly used for moulding purposes for gears,
bearings, etc.
3. Nylon 6:6 is used for fibres, which is used in making socks, dresses, carpets, etc.
EPOXY RESIN
Epoxy is both the basic component and the cured end product of epoxy resins,
as well as a colloquial name for the epoxide functional group. Epoxy resins, also known
as polyepoxides are a class of reactive prepolymers and polymers which contain
epoxide groups. Epoxy resins may be reacted (cross-linked) either with themselves
through catalytic homopolymerisation, or with a wide range of co-reactants including
polyfunctional amines, acids (and acid anhydrides), phenols, alcohols, and thiols.
APPLICATIONS
Polyester epoxies are used as powder coatings for washers, driers and other
"white goods". Fusion Bonded Epoxy Powder Coatings (FBE) are extensively used for
corrosion protection of steel pipes and fittings used in the oil and gas industry, potable
water transmission pipelines (steel), and concrete reinforcing rebar. Epoxy coatings are
also widely used as primers to improve the adhesion of automotive and marine paints
especially on metal surfaces where corrosion (rusting) resistance is important. Metal
cans and containers are often coated with epoxy to prevent rusting, especially for foods
like tomatoes that are acidic. Epoxy resins are also used for decorative flooring
applications such as terrazzo flooring, chip flooring, and colored aggregate flooring.
Epoxy flooring has been proven to be an environmentally friendly alternate to other
types of flooring, reducing the facility's impact on the environment through less water
consumption and less pesticides needed