Polymers and their all types-
Polymers: – Polymers are high molecular mass substances which is formed by combination of large number of simple molecules or monomer. And these monomers are combined to form polymer and the process is known as polymerization. In the other words, by the process of polymerization monomers are combine to form polymers.
Polymers are of two types:-
(i) Homopolymers: – When same monomers units are combined to form polymer is called homopolymer. For example; polythene.
n (CH2=CH2) ————————>(CH2-CH2) n (polythene)
(ii) Copolymers: – When different monomer units are combined to form polymer is called copolymer. For example; nylon 6, 6.
H2N(CH2 )6-NH2 + HOOC-(CH2)4-COOH——> ( N-(CH2)6-N-C-(CH2)4-C) n
Classification of polymers:-
Based on sources:-
(i) Natural polymer: – The polymers which are obtained from nature. These are found in plants and animals. Example are protein, starch, rubber and cellulose etc.
(ii)Semi- Synthetic polymer: – The polymers which are prepared artificially from natural polymers. For example; Cellulose derivatives as cellulose acetate (rayon), cellulose nitrate.
(iii) Synthetic polymer: – These polymers are prepared in laboratory. These are also called manmade polymers. Example; a variety of synthetic polymers as plastic (polythene), nylon 6, 6.
Based on structure:-
(i) Linear polymer: – These polymers consist of long and straight chains. These are well packed and therefore have high density, high melting and boiling point and high tensile strength. Example; polythene and polyvinyl.
(ii) Branched chain polymer: – These polymers contain linear chains having some branches. These polymers are not well packed, therefore have low density, low tensile strength and low melting and boiling point. Example; starch and low density polythene.
(iii)Cross-linked or network polymers: – These are polymers in which monomers units are crossed linked with each other to form three dimensional network structure. These are hard and rigid polymers. These are usually formed from bi-functional and tri-functional monomers. Example; Bakelite and Melamine.
Based on mode of polymer:-
(i) Addition polymers: – The addition polymers are formed by repeated addition of monomers molecules possessing double and triple bonds.
n (CH2=CH2)———————> (CH2-CH2) n (polythene)
(ii)Condensation polymer: – These polymers are formed by addition of two or more monomers units but by the removal of small compounds like water, ammonia, alcohol etc.
(CH2 )6-NH2 + HOOC-(CH2)4-COOH————-> ( N-(CH2)6-N-C-(CH2)4-C) n
Based on molecular force:-
(i) Elastomer: – These are rubber like solids with elastic properties. In these elastomer polymers, the polymer chain are held together by the weakest intermolecular forces. These weak binding forces permits the polymers to be stretched.
(ii) Fibers: – Fibers are the thread forming solids which posses’ high tensile strength and high modulus. These characteristics can be attributes to be strong intermolecular forces like hydrogen bonding.
(iii) Thermoplastic polymers: – These polymers can be easily softened on heating and hard when cooled with little change in properties. There is no cross linked between chain and can be modulated into any shape.
(iv)Thermosetting: – These are undergo permanent change on heating. There are cross linked between chains. Thermosetting polymers cannot be reused.