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Unit-5
Polymers
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A polymer is a large molecule or a macromolecule which essentially is a combination of
many subunits called monomers
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Polymers can be found all around us, from the strand of our DNA which is a naturally
occurring biopolymer to polypropylene which is used throughout the world as plastic
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Classification of Polymers
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I
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Natural Polymers:
They occur naturally and are found in plants and animals
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To add up, we also have biodegradable polymers which are called
biopolymers
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Semi-synthetic Polymers:
They are derived from naturally occurring polymers and undergo further chemical modification
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3
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Plastic is the most common and widely used synthetic polymer
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For example, nylon-6, 6, polyether’s etc
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Classification Based on Polymerization

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In this, small monomer units join to form a giant polymer
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For example, Polymerization of ethane in the presence of Peroxides

Example-poly ethane, Teflon, Polyvinyl chloride (PVC)
2
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Generally, organic compounds containing bifunctional groups such as idols, -dials,
diamines, dicarboxylic acids undergo this type of polymerization reaction
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Example, Nylon -6, 6, terylene, polyesters
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Classification Based on Monomers
1
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For example, Polyethene
2
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For
example, nylon -6, 6
IV
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Elastomers: These are rubber-like solids; weak interaction forces are present
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2
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For example, nylon -6, 6
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Thermoplastics: These have intermediate forces of attraction
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4
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It provides enhanced chemical and heat resistance
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Vulcanization of Rubber
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Vulcanization is a chemical process in which the rubber is heated with sulphur,
accelerator and activator at 140–160°C
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On vulcanization, Sulphur forms cross-links at the reactive sites of double bonds and
thus the rubber gets stiffened
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CONDUCTING POLYMERS
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Polymers which can conduct electricity are called conducting polymers
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The cause of conducting current by a polymer is presence of conjugated π electrons in
the backbone chain
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Intrinsically conducting polymers:
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These types of polymers have a solid backbone made up of extensive conjugated system,
which is responsible for conductance
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The presence of conjugated π -electrons in polymers increases its conductivity, e
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Polypyrrole, polyacetylene,polythiophene
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Doping is the process by which conductivity of the polymers may be increased by
creating negative or positive charge on the polymer backbone by oxidation or reduction
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In this process, the conducting polymer is
treated with a Lewis acid
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In this process, the conducting polymer is
treated with a Lewis base
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Extrinsically conducting polymers:
Those conducting polymers which owe their conductivity due to the presence of externally
added ingredients in them are called extrinsically conducting polymers
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(ii) Blended conducting polymers: These types of polymers are obtained by blending a
conventional polymer with a conducting polymer either physically or chemically
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Applications of Conducting Polymers:
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3
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6
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Biodegradable polymers
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These are those polymers which get decomposed under aerobic or anaerobic conditions,
as a result of the action of microorganism/enzymes
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Aliphatic polyesters are the most commonly used polymers of this type
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Poly β-hydroxybutyrate – co-β-hydroxy valerate (PHBV)
2
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Polyhydroxybutyrate (PHB)
Properties of Biodegradable Polymers
1
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Hydrophilic end groups
3
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More porous
5
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Applications of Biodegradable Polymers
1
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2
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3
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5
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Preparation and Applications of some Important Polymers
1
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It is produced by copolymerization of butadiene (about 75% by weight) and styrene
(25% by weight)
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It possesses high abrasion-resistance, high load-bearing capacity and resilience
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Moreover, it swells in oils and solvents
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It can be vulcanized in the same way as natural rubber either by sulphur or sulphur
monochloride (S2Cl2)
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Mainly used for the manufacture of motor tyres
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Other uses of these elastomers are floor tiles, shoe soles, gaskets, foot-wear
components
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wire and cable insulations, carpet backing, adhesives, tank-linings, etc
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Nitrile Rubber or GR-A or Buna – N or NBR
Preparation: It is prepared by the copolymerization of butadiene and acrylonitrile in
emulsion system
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Excellent resistance to oils, chemicals, aging (sun light)
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Compared to natural rubber, nitrile rubber (vulcanized) has more heat resistance and it
may be exposed to high temperatures
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It has good abrasion resistance, even after immersion in gasoline or oils
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For making Conveyor belts, Lining of tanks, Gaskets

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2
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Automobile parts and high altitude air-craft components Hoses and adhesives
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NEOPRENE
Neoprene: It was the first synthetic rubber manufactured on large scale
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Its monomer chloroprene (chlorobutadiene) is prepared from acetylene
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PROPERTIES:
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3
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USES:

1
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4
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Properties:
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2
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Applications:
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3
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6
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It is obtained by condensation polymerization
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•translucent, whitish, high melting (160ºC – 264ºC) polymers
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• high temperature stability and good abrasion resistance
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• insoluble in common organic solvents (methylated spirit, benzene and acetone) and
soluble in phenol and formic acid
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• mouldings and extrusions have good physical strengths (especially high impact
strength) and self-lubricating properties
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• absorb little moisture, and are thus drip – dry in nature
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• very flexible and retain original shape after use

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