2 Copolymerization

Copolymerization permits the synthesis of an almost unlimited range of polymers and is often used, therefore, to obtain a better balance of properties for the commercial application of polymeric materials. Copolymers may be synthesized by chain growth and step growth condensation polymerization processes. This section deals exclusively with chain growth copolymerization, in which one or more types of monomer add to an active center located on a growing (or live) polymer chain. The term ‘copolymerization’ includes the simultaneous polymerization of two or more types of monomer; however, the terms terpolymerization and multicomponent polymerization are often used to indicate polymerization of three types of monomer and three or more types of monomer, respectively. Chain growth copolymerizations may be done using various active centers, including free radical, ionic and Ziegler–Natta processes. There are four basic copolymer structures: random, alternating, block and graft. Random copolymers have relatively random distributions of the two monomer units along the polymer chain. Alternating copolymers have the two monomer units, MA and MB, occurring in an alternating fashion (MAMBMAMBMAMB). A block copolymer is a linear copolymer with one or more long uninterrupted sequences of each type of monomer unit (MAMAMAMAMAMBMBMBMBMB). A graft copolymer is a branched copolymer with the main chain and branches having different compositions. This section deals exclusively with random and alternating copolymers.