Copolymer

A macromolecule in which two or more types of monomer are incorporated into the polymer chain. This contrasts with a homopolymer, which consists of only one type of monomer. Copolymerization offers the ability to alter the properties of a homopolymer by introducing an appropriately chosen second repeating unit, or to combine the desirable properties of two different homopolymers in a single molecule. The properties of a copolymer depend on the nature of the monomers and their distribution in the chain. Thus, monomers A and B can polymerize randomly (e.g. as ABBAABA); they can alternate (ABAB); they can form blocks (AAABBB); or one polymer can be grafted onto a polymer of the other (see Figure 1). Copolymers can be prepared by all the known methods of polymerization: addition polymerization of vinyl monomers (by conventional or living free-radical, anionic, cationic, or coordination catalysis), ring-opening polymerization, or condensation polymerization. Copolymers can also be formed by the chemical reaction of functional groups (usually endgroups) on the constituent polymer chains.