How are polymers classified on the basis of structure?

Polymers are classified based on structure, into 3 types:

i) Linear Polymer: They have a long and straight chain of molecules. Ex: high-density Polythene, Polyvinyl chloride

ii) Branched-chain Polymers: They have linear molecular chains along with some branches. Ex: less density polythene.

iii) Cross-linked or network Polymers: In these polymers, strong covalent bonds are between the linear chains. Generally, they contain 2 or 3 types of functional groups. Ex: Bakelite, melamine