polydienes

Polydienes are polymers derived from diene monomers, molecules that contain two carbon–carbon double bonds. They form a broad class of elastomeric or semi-elastic polymers whose repeating units include carbon–carbon double bonds. The best known examples are polyisoprene (the main component of natural rubber) and polybutadiene, as well as copolymers such as styrene–butadiene rubber (SBR) and acrylonitrile–butadiene rubber (NBR).

Monomers commonly used include isoprene and butadiene. Polydienes can be homopolymers or copolymers, and their microstructure—such as the pattern of 1,4- versus 1,2-additions, and the cis/trans stereochemistry in certain backbones—significantly affects properties like elasticity, glass transition temperature, and processability.

Polymerization methods vary. Anionic polymerization, often used for polybutadiene and polyisoprene, can yield living polymers with controlled architecture and high cis content. Coordination polymerization with transition metal catalysts (including metallocenes) allows precise control over tacticity and microstructure. Free-radical polymerization is widely used for copolymers such as SBR and NBR, offering scalable production but less microstructural control.

Polydienes are typically unsaturated, enabling vulcanization (crosslinking with sulfur or peroxides) to form three-dimensional networks that enhance strength, elasticity, and heat resistance. The degree of crosslinking, along with composition and microstructure, determines final properties.

Applications include tires and other elastomeric components such as belts, seals, hoses, and vibration dampers. Polydienes are valued for their resilience, abrasion resistance, and aging behavior, with performance tunable by copolymerization, composition, and vulcanization chemistry.