copolymerisation

Copolymerisation is a polymerization process in which two or more different monomer species are linked into a single polymer chain, creating a copolymer whose properties differ from those of homopolymers derived from the individual monomers. By combining monomers with complementary chemical and physical traits, copolymers can be engineered to exhibit enhanced processability, strength, toughness, chemical resistance, or tailored glass transition temperatures.

Architectures: Random copolymers have monomer units distributed statistically along the chain; alternating copolymers feature successive units of the two monomers; block copolymers consist of large blocks of one monomer followed by blocks of another; graft copolymers have side chains of one monomer grafted onto a backbone of another. Copolymers may contain two or more distinct comonomers and can be linear or branched or crosslinked.

Synthesis and control: Free-radical polymerization is widely used for copolymers and can produce various architectures depending on monomer reactivity and feed ratios. Living or controlled radical polymerization methods, such as RAFT, ATRP, and ROMP, allow precise block and graft architectures. Ionic and coordination polymerizations (for example Ziegler–Natta and metallocene systems) provide stereoregular copolymers. Reactivity ratios describe the relative tendency of each monomer to add to the growing chain and influence microstructure and sequence distribution.

Properties and applications: Copolymers enable tuning of properties such as Tg, crystallinity, tensile strength, impact resistance, and chemical resistance. They are widely used in packaging, automotive parts, elastomers, adhesives, electronics, and consumer goods. Common commercial examples include ethylene–vinyl acetate copolymers (EVA), styrene–butadiene rubber (SBR), and acrylonitrile–butadiene–styrene (ABS) terpolymers.

Challenges and considerations: Copolymer composition control, phase behavior, and compatibility of monomer units affect material performance. Synthesis costs, catalyst residues, and environmental impact are also considered in material selection.