POLYMER CHEMISTRY
Overview
Introduction to Polymers
Introduction to Polymers
POLYMERS
Polymers are high molecular mass substances consisting of a large number of repeating structural units.
INTRODUCTION TO POLYMERS
polymers are single, giant molecules, i.e. large size molecules, they are also called macromolecules.
Simple molecules which combine to form polymers are called monomers.
The process of formation of polymers from respective monomers is called polymerisation.
CLASSIFICATION OF POLYMERS
No. | Classification | Types | Examples | |||||||
based on | ||||||||||
∙ | Natural polymers: Polymers | Cellulose, starch | ||||||||
obtained from nature, mostly plants | etc. | |||||||||
and animals. | ||||||||||
1. | Source of | |||||||||
∙ | Synthetic polymers: Polymers | Teflon, | ||||||||
availability | prepared in the laboratory. | Nylon 6,6, | ||||||||
Synthetic rubber | ||||||||||
(Buna - S) etc. | ||||||||||
∙ | Semi-synthetic polymers: Polymers | Rayon (cellulose | ||||||||
derived from naturally occurring | acetate), | |||||||||
polymers by carrying out chemical | cellulose nitrate | |||||||||
modifications. | etc. | |||||||||
2. | Structure of | ∙ | Linear polymers: Polymers | High-density | ||||||
polymer | consisting of long and straight | polythene, | ||||||||
chains. | polyvinyl | |||||||||
chloride etc. | ||||||||||
∙ | Branched chain polymers: | |||||||||
Polymers containing linear chains | Low-density | |||||||||
with some branches. | polythene | |||||||||
∙ Cross-linked or network polymers: | ||||||||||
Polymers in which monomer units | Bakelite, | |||||||||
are cross linked together to form 3- | melamine etc. | |||||||||
dimensional network polymers. | ||||||||||
3. | Mode of | ∙ | Addition | ∙ | Homopolymers: | |||||
polymerisation | polymers: | Polymers | ||||||||
Polymers are | formed by the | Polythene, | ||||||||
formed by | polymerisation | Polystyrene | ||||||||
the repeated | of a single | |||||||||
addition of | monomeric | |||||||||
monomers | species. | |||||||||
with double | ||||||||||
∙ | Copolymers: | |||||||||
and triple | Polymers | |||||||||
bonds. | formed by | Buna - S, | ||||||||
addition | Buna - N | |||||||||
polymerisation | ||||||||||
of two different | ||||||||||
monomers. | ||||||||||
∙ | Condensation polymers: Polymers | |||
formed by repeated condensation | Nylon 6, 6, | |||
reactions between two different bi- | Nylon 6 | |||
functional or tri-functional | ||||
monomeric units with elimination of | ||||
simple molecules. | ||||
4. | Molecular | ∙ | Elastomers: Polymer chains are | Buna – S, |
forces | held together by weakest | Buna – N, | ||
intermolecular forces. Polymers | Neoprene | |||
are rubber-like solids with elastic | ||||
properties. | ||||
∙ Fibre: Polymers have strong | Nylon 6, 6, | |||
intermolecular force such as | Polyesters | |||
hydrogen bonding. Fibres are | ||||
thread-forming solids which | ||||
possess high tensile strength and | ||||
high modulus. | ||||
∙ | Thermoplastic polymers: Polymers | Polythene, | ||
are held by intermolecular forces | Polystyrene | |||
which are in between those of | ||||
elastomers and fibres. These | ||||
polymers are capable of repeated | ||||
softening on heating and | ||||
hardening on cooling. | ||||
∙ | Thermosetting polymers: Polymers | Bakelite, | ||
are cross linked or heavily | Urea- | |||
branched molecules, which on | Formaldelyde | |||
heating undergo extensive cross | Resins | |||
linking in moulds and again | ||||
become infusible. | ||||
IMPORTANT ADDITION POLYMERS
No | Name of | Polymerisation Reaction and Uses | ||||
. | polymer | |||||
1 | Low | |||||
density | ||||||
polythene | ||||||
(LDP) | ||||||
Uses: It is used in the insulation of electricity-carrying wires and the | ||||||
manufacture of squeeze bottles, toys and flexible pipes. | ||||||
2 | High | |||||
density | ||||||
polythene | ||||||
(HDP) | ||||||
Uses: It is used for manufacturing buckets, dustbins, bottles, pipes etc. | ||||||
3 | Polytetrafl | |||||
u- | ||||||
oroethene | ||||||
(Teflon) | ||||||
Uses: It is used in making oil seals and gaskets and also used for non-stick | ||||||
surface-coated utensils. | ||||||
4 | Polyacry | |||||
lon-itrile | ||||||
Uses: It is used as a substitute for wool in making | ||||||
commercial fibres as orlon or acrilan. | ||||||
Condensation polymerisation or step-growth polymerisation: Polymerisation generally involves a repetitive condensation reaction between two bi-functional monomers. In condensation reactions, the product of each step is again a bi-functional species and the sequence of condensation goes on. Because each step produces a distinct functionalised species and is independent of each other, this process is also called step-growth polymerisation.
IMPORTANT CONDENSATION POLYMERS
Polyamides: Polymers possess amide linkage (-CONH-) in the chain. These polymers are popularly known as nylons.
Examples:
Nylon 6, 6: It is prepared by condensation polymerisation of hexamethylenediamine with adipic acid under high pressure and at high temperature.
Uses: Nylon 6, 6 is used in making sheets, bristles for brushes and in the textile industry.
Nylon 6: It is obtained by heating caprolactam with water at a high temperature.
Uses: Nylon 6 is used for the manufacture of tyre cords, fabrics and ropes.
POLYESTERS: These are polycondensation products of dicarboxylic acids and diols. Example: Terylene or Dacron
Terylene or Dacron: It is manufactured by heating a mixture of ethylene glycol and terephthalic acid at 420 to 460 K in the presence of zinc acetate–antimony trioxide catalyst.
Uses: Dacron fibre (Terylene) is crease resistant and is used in blending with cotton and wool fibres. It is also used as glass-reinforcing material in safety helmets.