Copolymerization

Copolymerization is a polymerization process in which two or more different monomer species react to form a polymer chain containing two or more types of repeat units. This approach broadens the range of achievable properties beyond those of homopolymers, enabling tuning of thermal behavior, mechanical strength, chemical resistance, and processing characteristics.

Copolymer sequences can be categorized by arrangement. Random copolymers have monomer units distributed statistically along the chain. Alternating copolymers display a regular alternation of the two monomer units. Block copolymers consist of contiguous blocks of one monomer followed by blocks of another, while graft copolymers have side chains of one monomer grafted onto a backbone formed from another monomer.

The composition and sequence distribution in a copolymer are influenced by monomer reactivity ratios, feed ratios, and reaction conditions. Reactivity ratios describe the tendency of each monomer to add to chains terminated by either monomer. When r1 and r2 are close to one, random copolymers are favored; significant disparity can lead to more blocky or phase-separated structures. Process parameters, solvents, temperature, and catalysts also affect the outcome.

Common methods include free-radical copolymerization in solution, bulk, emulsion, or suspension; anionic or cationic polymerization for specialized systems; and coordination polymerization using catalysts such as metallocenes or Ziegler–Natta systems. Living or controlled polymerization techniques (e.g., RAFT, ATRP) enable more precise block and graft architectures.

Applications span plastics, elastomers, adhesives, and coatings. Examples include acrylonitrile-butadiene-styrene (ABS), styrene-butadiene rubber, ethylene-vinyl acetate (EVA), and various graft or block copolymers designed for tailored toughness, processability, or chemical resistance. Copolymerization remains a central strategy for material design and performance optimization.