Copolymers

Copolymer is a polymer derived from two or more chemically distinct monomer species. By incorporating different monomers, copolymers can combine properties of the constituent homopolymers and exhibit new behavior not present in a single monomer polymer. Copolymers may be homogeneously mixed on the macromolecular level and can be designed to tune properties such as glass transition temperature, strength, toughness, and chemical resistance.

Structural architectures include random copolymers, where monomers are distributed randomly along the chain; alternating copolymers, where the two monomer units alternate; block copolymers, consisting of blocks of one monomer followed by blocks of another; and graft copolymers, in which side chains of a second monomer are grafted onto a backbone polymer. The arrangement is influenced by monomer reactivity ratios and polymerization conditions.

Copolymer synthesis is achieved mainly by free-radical polymerization, or by controlled/living polymerization techniques such as RAFT, ATRP, or anionic polymerization, which provide better control of sequence and architecture. The composition can be adjusted by feed ratio, monomer reactivity, and reaction conditions to tailor properties and phase behavior.

Properties depend on composition and architecture; copolymers can improve compatibility between different materials, reduce crystallinity, or create phase-separated morphologies that enhance toughness, impact resistance, or barrier properties. Applications include elastomers and plastics, adhesives and coatings, packaging materials, automotive parts, and medical devices. Copolymers also serve as compatibilizers in polymer blends and as functional materials in membranes and electronics.

Common examples include styrene-butadiene copolymers used as synthetic rubber, acrylonitrile-butadiene-styrene (ABS) plastics, ethylene-vinyl acetate (EVA) copolymers used in packaging and adhesives, and vinyl chloride copolymers such as vinyl chloride–vinyl acetate copolymers.