Polymers are defined as high molecular mass macromolecules, which consist of repeating structural units derived from the corresponding monomers.Polymers occur in nature also. Cotton, for example, is a polymer called cellulose.Cellulose is made up of a large number of glucose units.
On the basis of intermolecular forces Polymers are classified as:
1.Elastomers– rubber, buna-S, buna-N, neoprene etc.
2.Fibres – polyamides(nylon 6, 6), polyesters (terylene), etc.
3.Thermoplastic polymers – Such plastic which gets deformed easily on heating and can be bent easily are known as thermoplastics. Polythene, polystyrene, polyvinyls, etc.
4.Thermosetting polymers – some plastics which when moulded once, can not be softened by heating. These are called thermosetting plastics.eg: bakelite, melamine etc.
(i)Low-density polythene-polymerisation of ethene under high pressure in the presence of traces of dioxygen or a peroxide initiator (catalyst).
(ii)High-density Polythene – polymerisation of ethene in the presence of a catalyst such as triethylaluminium and titanium tetrachloride (Ziegler-Natta catalyst).
(b)Polytetrafluoroethene (Teflon) – Teflon is manufactured by heating tetrafluoroethene with a free radical or persulphate catalyst at high pressures.
(c)Polyacrylonitrile – Polymer of acrylonitrile in presence of a peroxide catalyst.
(a)Polyamides – It possess amide linkages.
(i) Nylon 6,6 – prepared by the condensation polymerization of hexamethylenediamine with adipic acid under high pressure and at high temperature.
ii) Nylon 6 – obtained by heating caprolactum with water at a high temperature.
(b)Polyesters – It is Polycondensation products of dicarboxylic acids and diols. It is prepared by ethylene glycol and terephthalic acid.
Terylene is the best-known example of polyesters.It can be drawn into very fine fibres that can be woven like any other yarn.
(c)Phenol – Formaldehyde polymer (Bakelite and related polymers).It is prepared by the condensation reaction of phenol with formaldehyde in the presence of either an acid or a base catalyst.
The initial product could be a linear product which is Novolac and is used in paints.Novolac on heating with formaldehyde undergoes cross-linking to form an infusible solid mass called bakelite. It is used for making combs, phonograph records, electrical switches and handles of various utensils.
(d)Melamine – It is a formaldehyde polymer.
Melamine formaldehyde polymer is formed by the condensation polymerization of melamine and formaldehyde.
Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. It is used for making floor tiles, kitchenware and fabrics which resist fire.It is used in the manufacture of unbreakable crockery.
(i)Natural rubber – Natural rubber may be considered as a linear polymer of isoprene (2-methyl-1, 3-butadiene) and is also called as cis – 1, 4 – polyisoprene.
Vulcanisation of rubber-This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373 K to 415 K so that rubber gets stiffened.
(ii)Synthetic Rubbers –
Neoprene – It is prepared by the free radical polymerisation of chloroprene.
Rayon – Rayon or artificial silk. Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre.
Nylon – Nylon is also used for making parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.
You may also like to Read: Western Ghats, Buddhism, Advent of The Europeans, Soils in India, Clouds, Alloys and their composition, Grasslands of World, Light and its phenomena(Part1), Light and its phenomena (Part 2)