( iii ) Semisynthetic polymers : Polymers obtained by making some modification in natural polymers by artificial means , are known as semi synthetic polymers , e . g ., cellulose acetate ( rayon ), vulcanised rubber etc .
Classification of Polymers Based on Structure
( i ) Linear polymers These are the polymers in which the monomer units are linked to one another to form long linear chains . These linear chains are closely packed in space . The close packing results in high densities , tensile strength and high melting and boiling points . e . g ., high density polyethene , nylon and polyesters are linear polymers .
( ii ) Branched chain polymers In such polymers , the monomer units are linked to form long chains with some branched chains of different lengths with source . As a result of branching , these polymers are not closely packed in space . Thus , they have low densities , low tensile strength as well as low melting and boiling points . Some common examples of such polymers are low density polyethene , starch , glycogen etc .
( iii ) Cross-linked polymers or network polymers In such polymers , the monomer units are linked together to form three dimensional network . These are expected to be quite hard , rigid and brittle . Examples of cross linked polymers are bakelite , glyptal , melamine-formaldehyde polymer etc .