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Classification based on the Molecular Forces:, Based on this, polymers are of 4 types:, , 1. Elastomers:, • These are rubber – like solids with elastic properties. In, these polymers, the polymer chains are held together by, the weakest intermolecular forces (van der Waal’s force)., So they can be stretched., • A few ‘cross links’ are formed in between the chains, which, help the polymer to regain to its original position after the, force is released., • E.g. buna-S, buna-N, neoprene, etc.
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2. Fibres:, •Fibres are the thread forming solids which possess high tensile strength, and high modulus., •Here the different polymer chains are held together by strong, intermolecular force they have close packed structure and are crystalline, , in nature., •Eg: Nylon6,6, Nylon-6, terylene etc.
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Addition polymers:, These are polymers formed by addition polymerisation reaction. Here the monomer, molecules are unsaturated (i.e they contain double or triple bonds). Addition polymers, , are now known as chain growth polymers. E.g. polythene, polypropene, polystyrene,, polyvinyl chloride etc., , Polythene (Polyethene): It is obtained by the polymerisation of ethene, , There are two types of polythene – Low density polythene and high, density polythene
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Low density polythene (LDP): It is obtained by the polymerisation of ethene under, high pressure of 1000 to 2000 atmospheres at a temperature of 350 to 570 K in the, , presence of an organic peroxide (catalyst)., •It is used in the insulation of electricity carrying wires and manufacture of squeeze, bottles, toys and flexible pipes., High density polythene (HDP):, , •It is formed when the polymerisation of ethene takes place in the presence, of a catalyst such as triethylaluminium and titanium tetrachloride (ZieglerNatta catalyst) at a temperature of 333 K to 343 K and under a pressure of 67 atmospheres., •It is used for manufacturing buckets, dustbins, bottles, pipes, etc.
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•Teflon:, •It is manufactured by heating tetrafluoroethene in presence of a catalyst, at high pressures., , It is used in making oil seals and gaskets and also for making non –, stick cooking pans. It is used for making pipes, rain coat, vinyl, flooring etc.
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Condensation polymers:, These are polymers formed by condensation polymerisation reaction. In this, polymerisation reaction, the elimination of small molecules such as water,, , alcohol, hydrogen chloride, etc take place. Here the monomers should be, bifunctional or polyfunctional. Condensation polymers are now known as step, growth polymers., , E.g. Nylon- 6,6, Nylon- 6, terylene, glyptal etc., , •Nylon 6,6: It is prepared by the condensation polymerisation of, hexamethylenediamine with adipic acid under high pressure and at high, , temperature.
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It is used in making sheets, bristles for brushes and in textile industry., , •Nylon 6: It is obtained by heating caprolactum with water at a high, temperature., , It is used for the manufacture of tyre cords, fabrics and ropes
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Natural rubber:, •It is a linear polymer of isoprene (2-methyl-1, 3-butadiene) and is also called as, cis-1, 4 -polyisoprene., , •The various cis-polyisoprene chains are held together by weak van der Waals, forces and has a coiled structure., , •Thus, it can be stretched like a spring and exhibits elastic properties.
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Vulcanisation of rubber :, •To improve the physical properties of natural rubber, it is heated with, , sulphur and an appropriate additive at a temperature of 373 to 415 K., This process is called vulcanisation., •On vulcanisation, sulphur forms cross links between the different, , polyisoprene units and thus the rubber gets stiffened.
