What is copolymerisation?
Copolymerisation is a polymer chemistry process in which two or more different monomers are polymerised together to produce a polymer with tailored properties. In contrast to homopolymerisation (in which only one monomer reacts), copolymerisation makes it possible to combine the advantages of different monomers in one material and tailor them specifically to the requirements of an application.
Principle & reaction types of copolymerisation
During copolymerisation, the monomers are reacted together in a defined ratio in the reactor. Depending on the mechanism, the reaction is initiated by radical or ionic initiators or, in the case of coordination polymerisation, by catalysts (e.g. Ziegler-Natta systems). This results in polymer chains with different structures:
- Alternating copolymers: individual monomers alternate in the polymer chain
- Statistical copolymers: The monomers are randomly distributed, as in styrene-butadiene rubber (SBR)
- Block copolymers: Longer sequences of one monomer alternate with sequences of the other, which often leads to phase separation and special material properties
- Graft copolymers: The main chain consists of a main chain of a specific monomer, while the side chains are formed by another monomer. One example is acrylonitrile-butadiene-styrene (ABS) in which a polybutadiene backbone is grafted with styrene and acrylonitrile side chains for impact modification
Factors influencing copolymerisation
By selecting the monomers and their mixing ratio, it is possible to Hardness, elasticity, chemical resistance, temperature behaviour or transparency. Acrylonitrile in NBR the material a high Oil resistance, while butadiene increases flexibility. In elastomer production, copolymerisation is a key tool for optimising the balance between various properties such as mechanical strength and media resistance.
Industrial significance of copolymerisation
Copolymers can be found in almost all technical areas: from tyres (SBR, EPDM) to technical seals (NBR, HNBR) through to high-performance plastics (ABS, PBT/ASA). In many cases, copolymerisation is the only way to produce materials that meet both the mechanical and chemical requirements of modern applications.