Copolymers are polymers bearing two or more different repeat units in the same macromolecule, as opposed to homopolymers where only one repeat unit is used.
Copolymers are essential to plastics industry as they allow to combine the properties of different polymers to create new polymers with unique properties. Many relevant commercial polymers are indeed copolymers.
Copolymers can be classified based on the alternation of the repeat units in random, alternating, block and graft copolymers. In random copolymers, the repeat units are linked together in a random manner. In alternating copolymers two species of repeat units are distributed in alternating sequence. Block copolymers feature blocks of the same repeat unit, whereas graft copolymers feature branches of different repeat units.
Figure 1: Classification of copolymers.