Polymers are classified on the basis of the structure as follows: 

1. Linear polymers: These polymers are formed of long straight chains. They can be depicted as: 

For e.g., high-density polythene (HDP), polyvinyl chloride, etc. 

2. Branched-chain polymers: 

These polymers are basically linear chain polymers with some branches. These polymers are represented as: 

For e.g., low-density polythene (LDP), amylopectin, etc. 

3. Cross-linked or Network polymers:

These polymers have many cross-linking bonds that give rise to a network-like structure. These polymers contain bi-functional and tri-functional monomers and strong covalent bonds between various linear polymer chains. Examples of such polymers include bakelite and Melmac.