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Polymers: They are macro-sized, high molecular mass compounds, formed by the combination of a large number of simple molecules or repeating units.
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Monomers: These simple molecules or repeating units which combine to give polymers are called monomers.
The process of joining together of a large number of the monomers is termed as polymerization.
A polymer formed from one type of monomers is called a homopolymer, e.g., polyethylene, PVC, polyacrylonitrile, etc.
A polymer formed from two or more different monomers is called copolymer e.g., Nylon-6,6, polyester, bakelite, etc.
The number of times a monomer unit is repeated in a polymer is called its degree of polymerization.
Classification of Polymers:
Natural polymers: These are substances of natural origin and are mainly found in plants and animals, e.g., starch, cellulose, proteins, etc.
Synthetic polymers: These polymers are prepared in the laboratories, they are also called man-made polymers, e.g., te_on, terylene, synthetic rubber, etc.
Semi-synthetic polymers: They have mostly derived from naturally occurring polymers by chemical modi_cations, e.g., vulcanized rubber, cellulose nitrate, etc.
Linear polymers: In these polymers monomers are linked together to form linear chains, e.g., polyethylene, polyester, nylon, etc.
Branched-chain polymers: In these polymers the monomers are joined to form long chains or branches of different lengths, e.g., glycogen, starch, etc.
Cross-linked polymers: In these polymers, the monomer units are cross-linked together to form a three-dimensional network polymer, e.g., bakelite, melamine, etc.
Elastomers: These are the polymers having very weak intermolecular forces between the polymer chains. The weak forces permit the polymer to be stretched. Elastomers, thus, possess elastic character, e.g., vulcanized rubber.
Fibers: These are the polymers which have strong intermolecular forces between the chains. These are either hydrogen bonds or dipole-dipole interactions, e.g., Nylon-6,6.
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Thermoplastics: These are the polymers in which the intermolecular forces of attraction are intermediate between those of elastomers and fibers. These polymers do not have any cross-links between the chains, they can be easily mouled on heating, i.e., thermoplastics so_en on heating and become hard on cooling, e.g., polythene, polystyrene, PVC, etc.
Thermosetting polymers: They have extensive cross-links formed between polymer chains on heating. They undergo a permanent change on heating, e.g., bakelite, melamine, etc.
Addition polymerization: A polymer formed by direct addition of repeated monomers without the elimination of by-product molecules is called addition polymer and the phenomenon is known as addition polymerization, e.g., polythene.
Condensation polymerization: A polymer formed by the condensation of two or more than two monomers with the elimination of simple molecules like water, ammonia, alcohol, etc. is called condensation polymer and The phenomenon is known as condensation polymerization, e.g., Terylene.