Polymers

Polymers
V.S.SARAVANA MANI
HEAD AND ASSOCIATE PROFESSOR,
DEPARTMENT OF CHEMISTRY
ANNAPOORANA ENGINEERING COLLEGE, SALEM

Introduction
 Polymers (derived from the Greek words, poly or many and
mer means units or parts) are
 macro molecules formed by the combination of a large number of small
molecules known as monomers. Polymers can be classified as plastics (resins),
elastomers (rubber) and fibres (nylon, terylene)
 The properties of polymer depend on their molecular configuration, the degree of
polymerization, branching and cross linking.
2
V.S.Saravana Mani, Head& Asso.Prof, Dept. of Chemistry.

Definition
3
 Polymers are high molecular weight compounds whose structures are
composed of a large number of simple repeating units. The repeating units
are usually obtained from low molecular weight simple compounds referred
to as monomers.

Monomer
Monomer is a micromolecule (smaller molecule) which combines with each other
to form a polymer.
Eg.
Ethylene, vinyl chloride, styrene, butadiene, acrylonitrile etc.,
4

Classification of Polymers
(Based on Source)
5
Natural polymers: These polymers are found in plants and animals. Examples are proteins,
cellulose, starch, resins and rubber.
Semi-synthetic polymers: Cellulose derivatives as cellulose acetate (rayon) and cellulose nitrate,
etc. are the usual examples of this sub category.
Synthetic polymers: A variety of synthetic polymers as plastic (polythene), synthetic fibres (nylon
6,6) and synthetic rubbers (Buna - S) are examples of manmade polymers extensively used in daily
life as well as in industry.

Classification of Polymers
(Based on Structure)
Linear polymers
6
These polymers consist of long and straight chains. The examples are high density
polythene, polyvinyl chloride, etc. These are represented as:

Branched chain polymers
These polymers contain linear chains having some branches, e.g., low density polythene.
These are depicted as follows:
7

Cross linked or Network polymers
8
These are usually formed from bi-functional and tri-functional monomers and contain strong
covalent bonds between various linear polymer chains, e.g. bakelite, melamine, etc. These
polymers are depicted as follows:

Polymerization
9
 Polymerization is a process in which large number of small molecules (called
monomers) combine to form a big molecule (called a polymer) with or without
elimination of small molecules like H2O, CH3OH etc.,

Degree of polymerization
The Degree of polymerization (n or N) is defined as
10
the number of monomeric units in a macromolecule or polymer or oligomer
molecule. (Because in reality polymers consists of chains of different length,
the average value is used.)

Types of polymerization:
There are three types of polymerization processes:
 Addition polymerization (or) chain growth polymerization
 Condensation polymerization (or) stepwise polymerization
 Copolymerization
11

Addition polymerization (or)
chain growth polymerization
12
An addition polymer is a polymer which is formed by an addition reaction, where
many monomers bond together via rearrangement of bonds without the loss of any
atom or molecule.

Some Common Addition Polymers
13

Condensation polymerization (or)
stepwise polymerization
Condensation polymers are any kind of polymers formed through a condensation
reaction--where molecules join together--losing small molecules as by-products
such as water or methanol, as opposed to addition polymers which involve the
reaction of unsaturated monomers.
(CH2 )
+ HOOC ( ) COOH
H2N NH2 CH2
6
(NH CH2 NH CO
( ) ( CH2 )
CO )
6 4 n 4
+ H2O
14

Copolymerization
16
Copolymerization is defined as the process of combining two polymers that are
different

COPOLYMERS
Polymers which are formed by combining two different
monomers in alternating fashion are called copolymers.
A + B + A + B A B A B
butadiene
styrene
styrene-butadiene
rubber (SBR)
17

S.
No.
Addition /
chain polymerization
Condensation /
step polymerization
1 The monomer must have at least one multiple
bond. Examples:
Ethylene: CH2 = CH2, Acetylene
The monomer must have at least two
identical (or) different functional
groups. Glycol, Nylon(6,6)
2 Monomers add on to give a polymer and no other
byproduct is formed.
Monomers condense to give a polymer and by
products such as H2O, CH3OH are formed.
3 Number of monomeric units decreases steadily
throughout the reaction.
Monomers disappear at the early stage of reaction.
4 Molecular weight of the polymer is an integral
multiple of molecular weight of monomer.
Molecular weight of the polymer need not be an
integral multiple of monomer.
5 High molecular weight polymer
is formed at once.
Molecular weight of the polymer rises
steadily throughout the reaction.
6 Longer reaction times give higher yield, but have
a little effect on molecular weight.
Longer reaction times are essential to
obtain high molecular weight.
7 Thermoplastics are produced.
Example: Polyethylene, PVC
etc.,
Thermosetting plastics are produced.
Example: Bakelite, urea-formaldehyde
8 Homo-chain polymer is obtained Hetero-chain polymer is obtained.
18

S. No. Thermoplastic Resins Thermosetting Resins
1.
They are formed by addition
polymerisation.
They are formed by
condensation polymerisation.
2. They consist of linear long chain polymers.
19
They consist of three dimensional network
structure.
3.
All the polymer chains are held together by
weak vanderwaals forces.
All the polymer chains are linked by strong
covalent bonds.
4. They are weak, soft and less brittle. They are strong, hard and more brittle.
5.
They soften on heating and harden on
cooling.
They do not soften on heating.
6. They can be remoulded. They cannot be remoulded.
7. They have low molecular weights. They have high molecular weights.
8 They are soluble in organic solvents. They are insoluble in organic solvents.

20
PREPARATION OF ADDITION POLYMERS
FREE RADICAL MECHANISM

21

22

23

24
CATIONIC MECHANISM

C C
C C
+
POLYMERIZATION
+
H2O
H2SO4
C C
H
OSO3H
C C
H
conc. 0o C
conc. OSO3H
C CH2
(CH2CH2)n
H
Polymerization
C C + H2SO4
concentrated,
smaller amount,
not cold
polymer
A cationic polymerization catalyst (Ziegler Catalyst)
can be used instead of H2SO4.
25

CATIONIC MECHANISM
Catalyst
+
H2SO4 or
cationic
catalyst
R
+
R
+ etc.
Polystyrene
styrene could be as simple
as a proton from
sulfuric acid
resonance
stabilized
(+) (+)
(+)
Catalyst
+
(Markovnikoff)
26

POLYSTYRENE
n
repeating
unit
R
27

28
ANIONIC MECHANISM

Anionic Polymerization
General Scheme
B-Z + CH2=CHX B-CH2-CH- Z+
X
Initiation:
Propagation:
M- Z+ + M MM- Z+
Termination:
M- Z+ + HT MH + ZT
29

Styrene Polymerization
CH CH Li 3CH2
CH3
CH2 CH CH CH 3CH2
CH3
CH2 CH Li
CH2 CH Li CH2 CH CH2 CH CH2
CH Li
CH2 CH Li H OH CH2 CH2 Li OH
Initiation:
Propagation:
Termination:
+
+
+ +
30

31

Properties of Polymers
 The glass transition temperature
 Tacticity
 Molecular Weight
32

The glass transition temperature
33
 The glass transition temperature is the temperature at which an
amorphous solid becomes soft upon heating or brittle upon cooling.
The glass transition temperature is lower than the melting point of
its crystalline form, if it has one.

“
”
Tacticity
34

Polyolefins with side chains have stereocenters on every other carbon
Polymer Microstructure
CH3
n
CH3 CH3 CH3 CH3 CH3 CH3 CH3
With so many stereocenters, the stereochemistry can be complex. There are three main
stereochemical classifications for polymers.
Atactic: random orientation
Isotactic: All stereocenters have same orientation
Syndiotactic: Alternating stereochemistry
35

STEREOISOMERIC POLYPROPYLENE POLYMERS
CH3 CH3 CH3 CH3 CH3 CH3
ISOTACTIC all methyl groups on the same side
H CH3 H CH3 H CH3
SYNDIOTACTIC methyl groups alternate sides
ATACTIC methyl groups randomly oreinted
stereoregular
polymers
not regular
C
C
C
C
C
C
C
C
C
C
C
C
H H H H H H
H H H H H H H H H H H H
C
C
C
C
C
C
C
C
C
C
C
C
CH3 H CH3 H CH3 H
H H H H H H H H H H H H
36

Tacticity – stereoregularity of chain
H
C C
H
H
H
C C
H
R H
R
H
C C
H
R
H
H
C C
H
R
H
H
C C
H
H
R
R H
R
C C
H
H
R
H
C C
H
H
C C
H
H
H
H
C C
H
H
H
C C
H
R H
R
R
C C
H
H
H
H
C C
H
R
H
isotactic – all R groups on
same side of chain
syndiotactic – R groups
alternate sides
atactic – R groups random
37

Molecular weight: a few definitions
Synthetic polymers are polydisperse, i.e. a given polymer sample exhibits
Mi
wi
Mi molecular weight of the ith polymer chain
Ni number of polymer chains with molecular weight Mi
wi weight fraction of polymer chains with molecular weight Mi


M N

i
i
i
i i
__
n N
M
Mn number average molecular weight


N M

i
i i
i
i i
w N M
M
2
__
Mw weight average molecular weight


M 2

i
N M
i i
i
i i
z
N M
3
__
Mz or Z-average molecular weight
Mn
Mw
Mz
Ð = Mw /Mn
푷푫푰 =
푴풘
푴풏
dispersity (1 – 10)
 
 

1
2
1
__











N M

i
i i
i
i i
N M
M M  viscosity average molecular weight
(0 <  < 1)
distribution of molecular weights
38

Number Average Molecular Weight (Mn)
39
The weight of polymer divided by the number of polymer molecules. This
average molecular weight follows the conventional definition for the mean
value of any statistical quantity. In polymer science, it is called the number
average molecular weight (Mn). The total weight of the molecules present
divided by the total number of molecules.

Weight Average Molecular Weight (Mw)
40
The probability factor in a weight-average considers the mass of the molecules so
that the heavier molecules of the polymer segment are more important. Consider of
polymer property which depends not just on the number of polymer molecules but
on the size or weight of each polymer molecule.
Mw > Mn

41
MOLECULAR WEIGHT DISTRIBUTION
M x M
 
n i i
M w M
 
w i i
__
Mn = the number average molecular weight (mass)
Mi = mean (middle) molecular weight of size range i
xi = number fraction of chains in size range i
wi = weight fraction of chains in size range i

Molecular weight: characterization techniques
Mn  techniques related to colligative properties (dependence on the number of molecules)
 membrane osmometry (> 25 000 g/mol)
 vapor pressure osmometry (< 25 000 g/mol)
 mass spectrometry
 electrospray ionization mass spectrometry (ESI-MS)
 matrix-assisted laser desorption/ionization (MALDI)
 size exclusion chromatography
Mw
 static laser light scattering
 analytical ultracentrifuge
Mz
 static laser light scattering
 analytical ultracentrifuge
M
 viscometry
Mi
wi
Mn
Mw
Mz
42

Polydispersity Ratio or Index:
Mw/Mn is a measure of polydispersity; it is 2.0 for condensation polymers.
For a polymer mixture which is heterogeneous with respect to molecular weight
distributions, Mz> Mz >Mn with decrease in heterogeneity the various molecular
weights will converge, Finally, Mz = Mz =Mn Criterion for homogeneous polymer
mixtures.
푃퐷퐼 =
푀푤
푀푛
≥ 1
43

Nylon (6,6)
 Nylon comes from a family of synthetic polymers known as polyamide. It was first
introduced by Wallace Carothers on 28th February 1935. Nylon 6,6 is a polyamide made by
poly-condensation of adipic acid methylenediamine , and contains a total of 12 carbon
atoms in each repeating unit . The properties which make Polyamides suitable for plastic
applications are resistance to toughness, thermal stability, good appearance, resistance to
chemicals etc
44

Chemical
structure:
Nylon 6,6 o PA-66
Hexamethylene diamine + Adipic acid
(CH2 )
+ HOOC ( ) COOH
H2N NH2 CH2
6
(NH CH2 NH CO
( ) ( CH2 )
CO )
6 4 n 4
+ H2O
45

Properties
 Nylon 6,6 peruses excellent abrasion resistance and a high melting point .
 Nylon 6,6 has high tensile strength and exhibits only half of shrinkage in steam .
 It also provides a very good resistance to photo degradation.
 Nylon 6,6 also has good advantage over industrial products because it reduces moisture
sensitivity in raw products and has a high dimensional stability and melting point .
46

 Nylon 6,6 has a repeat unit with molecular weight of is 226.32 g/mol and crystalline density of 1.24
g/(cm)^3 .
 Nylon 6,6 has long molecular chains resulting in more hydrogen bonds , creating chemical springs and
making it very resilient .
 Nylon 6,6 is an amorphous solid so it has a large elastic property and is slightly soluble in boiling water .
 Nylon 6,6 is very stable in nature.
 Nylon 6,6 is very difficult to dye but once it is dyed it has a high colorfastness and is less susceptible to
fading .
 Its chemical properties does not allow it to be affected by solvents such as water , alcohol etc .
47

Applications
 Nylon is a light material , it is used in parachutes .
 Nylon 6,6 is waterproof in nature so it is also used to make swimwear.
48
 Nylon 6,6 having a high melting point make it more resistant to heat and friction so it is suitable to
be used in in airports , offices and other places which are more liable to wear and tear .
 Nylon 6,6 being waterproof in nature is used to make machine parts. It is also used in the following
like airbags , carpets , ropes . hoses etc . Hence Nylon 6 6 is a very useful creation by mankind .

Epoxy Resin
49

Properties
 High chemical resistance to water, acids, alkalis, solvents and other
chemicals
 Flexible, tough and possess very good heat resisting property
 Excellent adhesion quality
50

Uses
 Surface coatings (provide a hard, durable and rustproof surface)
o Paint for ships and other marine uses
o Primers for cars
o Steel pipes
Electrical insulation materials (to prevent conduction of electricity)
o Enclosing transformers, condensers, capacitors and other electrical components
51
Adhesives and glues
Widely used across many industries for its strong bonding properties, e.g. aircraft, flooring, road
and bridge surfacing, concrete bonding, automobile manufacturers

 Epoxies are used in paint industry as it dries quickly and provides protective layers that are highly
52
tough
 Epoxies are used as structural or engineering adhesives used in the construction of aircrafts,
automobiles, boats and other such applications
 These are an integral part of the electronic industry and used in over-molding transistors, integrated
circuits, PCB’s, and hybrid circuits
 As an imperative part of aerospace industry, epoxies are used as structural matrix material
 In a highly technical application, epoxy resin is used for embedding samples for their use under
electron microscope
 Not limited just to technical applications, artists have also used epoxies as a painting medium by
mixing it with pigments to obtain colors
 As brilliant composites, epoxies are used in the manufacturing of various casts and molds laminates,
plastic toolings, and similar other fixture V.S.Saravana Mani, Head& Asso.Prof, Dept. of Chemistry.

Bulk polymerization
53
 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 is carried out in the absence of any solvent or dispersant and is thus the simplest in
terms of formulation. It is used for most step-growth polymers and many types of chain-growth
polymers. In the case of chain-growth reactions, which are generally exothermic, the heat evolved may
cause the reaction to become too vigorous and difficult to control unless efficient cooling...

Bulk polymerization
 The simplest method of polymerization where the reaction mixture contains
only the monomer and a monomer soluble initiator.
 Example
 PMMA
54

55

Advantages
 The system is simple and requires thermal insulation.
 The polymer obtained is 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
 High rates of polymerization
 High degree of polymerization
 High purity of product
 High molar mass polymer are produce
58

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.
 Increase in the reaction viscosity with conversion.
 *difficulty in removing heat.
 *auto-acceleration
 *if the polymer formed is insoluble in the monomer (such as acrylonitrile, vinyl chloride) ==>
precipitating of the polymer and we can not apply the kinetics.
59

Solution polymerization
60
 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 auto-acceleration 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.

61
 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).
 This method is used to solve the problems associated with the bulk polymerization because the
solvent is employed to lower the viscosity of the reaction, thus help in the heat transfer and
reduce auto-acceleration.

62

Disadvantage
 Reduce monomer concentration which results in decreasing the rate of the
reaction and the degree of polymerization.
 Solvent may cause chain transfer.
 Clean up the product with a non solvent or evaporation of solvent.
65

Suspension polymerization
66
 This method is used also to solve the problem of heat transfer. It is similar to bulk polymerization
where the reaction mixture is suspended as droplets in an inert medium. Monomer, initiator and
polymer must be insoluble in the suspension media such as water.
 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).

67
 This is one of procedure used to induce radical polymerization with a vinyl group
monomer. A polymerization process in which an insoluble monomer is dispersed and
suspended by continuous strong agitation in a liquid phase, usually water, and it
became monomer droplet with the size of 0.01～1mm. In addition, the polymerization
in which soluble initiator
 (for example: benzoyl peroxide or azobisisobutyronitrile) is added in the monomer.
Poly-addition reaction such as polyurethane may also performed in a suspended form.

68
 Suspension polymerization most commonly used as industrial manufacturing
method in order to get polymer for forming material such as polystyrene,
polymethylmethacrylate, polyvinyl acetate, polyvinyl chloride, because a
polymer with a high degree polymerization is obtained with the polymerization
and generated polymer isolation is easy.

69

Emulsion polymerization
 This is similar to suspension polymerization except that the initiation
is soluble in suspension media and insoluble in the monomer.
 The reaction product is colloidally stable dispersion known as latex.
 The polymer particles have diameter in the range of (0.05 - 1  m)
smaller than suspension.
71

Emulsion polymerization
72
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. The name
"emulsion polymerization" is a misnomer that arises from a historical misconception. Rather than occurring in emulsion
droplets, polymerization takes place in the latex particles that form spontaneously in the first few minutes of the process.
These latex particles are typically 100 nm in size, and are made of many individual polymer chains. The particles are
stopped from coagulating with each other because each particle is surrounded by the surfactant ('soap'); the charge on the
surfactant repels other particles electrostatically. When water-soluble polymers are used as stabilizers instead of soap, the
repulsion between particles arises because these water-soluble polymers form a 'hairy layer' around a particle that repels
other particles, because pushing particles together would involve compressing these chains.

73
 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. They are often preferred over solvent-based products in these applications due to the
absence of VOCs (Volatile Organic Compounds) in them.

74

75

Advantages
76
 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, enabling fast polymerization rates
without loss of temperature control.
 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
 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.
 Cannot be used for condensation, ionic or Ziegler-Natta polymerization, although some
exceptions are known.
77

 Advantages  Disadvantages
 High molecular weight polymers
 fast polymerization rates.
 allows removal of heat from the system.
 viscosity remains close to that of water
and is not dependent on molecular
weight.
 The final product can be used as such
,does not need to be altered or processed
 Surfactants and polymerization
adjuvants -difficult to remove
 For dry (isolated) polymers, water
removal is an energy-intensive process
 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.
78

Plastic Recycling Symbols 79
In 1988 the Society of the Plastics Industry developed a numeric code to
provide a uniform convention for different types of plastic containers.
These numbers can be found on the underside of containers.
1. PET; PETE (polyethylene terephthalate): plastic water and soda bottles.
2. HDPE (high density polyethylene): laundry/dish detergent
3. V (Vinyl) or PVC: Pipes, shower curtains
4. LDPE (low density polyethylene): grocery bags, sandwich bags
5. PP (polypropylene): Tupperware®, syrup bottles, yogurt cups,
6. PS (polystyrene): Coffee cups, disposable cutlery
7. Miscellaneous: any combination of 1-6 plastics

Polymers

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