Polymers-Basic Concept

Polymer: A Polymer is a macro molecule(high molecular weight) formed by the repeated union of simple, small chemical unit called monomer. The monomer units are linked together in a macro molecule by a covalent bond. The physical and chemical nature (properties) of macromolecules are totally different from which it is formed (monomers). In general the molecular weight of macromolecules varies from 1000 to 10000000.

Eg. 1. Polythene is the addition polymer formed by the repeated union of simple unit ethene

Eg. 2. Nylon 6,6 is an example for condensation polymer formed by the condensation reaction between adipic acid and hexamethylene diamine.

Monomer: Monomer is defined as a small unit which has two or more bonding sites through which it forms a covalent bonds with the other monomer units to form a giant molecule with high molecular mass. All chemical simple units cannot act as a monomers but only those simple units with minimum two bonding sites can behave as monomers. Example for simple units which behaves as monomers are alkenes (ethene), vinyl chloride, adipic acid, glycol, hexamethylene diamine etc.

Eg. Vinyl chloride(chloroethene) is the monomer having two bonding sites. Two functionality results in the formation of giant molecule of poly vinyl chloride (PVC).

Polymerization: The chemical reaction of obtaining high molecular weight macro molecule(polymer) from a low molecular weight, simple molecule (monomer) in presence of initiator is called polymerization.

Monomer ---- Polymer

Eg1. Vinyl chloride----PVC

Eg2. Styrene ----Polystyrene

Functionality: It is the number of bonding sites present in a molecule of the monomer. Compounds containing double bonds like ethene, propene,vinyl chloride etc have two bonding sites. Therefore their functionality is two or bifunctional. Phenol has three active centres at 2,4 and 6 positions. There fore its functionality is three.