A polymer that is formed from more than one type of monomer. Copolymers are often confused with blends. A blend is a mixture. In a copolymer, the different types of monomer are chemically bonded to one another. ABS Is one of the most well known copolymers. Nylon-6,6 can be thought of as an alternating copolymer.

The Types of Copolymer
Each letter represents a different monomer.

Block Copolymers

AAAABBBBAAAABBBBAAAABBBB

Branch Copolymers

   B        B
   B        B
   B        B
   B        B
AAAAAAAAAAAAAAAAAAAAAAAAA
                   B
                   B
                   B
                   B

Random Copolymers

ABBABAAAAAAABABAABABBBBBA

Alternating

ABABABABABABABABABABABABA

Why Make and Use Copolymers?

These materials often have properties that are not found in any homopolymers, polymers made from only one type of monomer. It is sometimes possible to create custom copolymers that have exactly the right properties for a certain job. In the case of ABS plastic, the styrene component makes it stiff, while the butadiene makes it rubbery and thus crack resistant. Some of them, like nylon-6,6 are easy to make. Many others are no harder to make than their homopolymer counterparts.

Applications
  • Teflon is not actually pure polytetrafluoroethyene, it has some propylene or ethylene copolymerized with it to make it less stiff. It would be too difficult to process, and too brittle to use, without those add-in molecules.
  • ABS is a very stiff but crack resistant plastic. It is used in everything from car dashboards to drain pipes.
  • Tissue engineering may call for peptide copolymers to act as scaffolds on which cells can grow.

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