Types of Copolymers
Since a copolymer consists of at least two types of constituent units (also structural units), copolymers can be classified based on how these units are arranged along the chain. These include:
- Alternating copolymers with regular alternating A and B units (2)
- Periodic copolymers with A and B units arranged in a repeating sequence (e.g. (A-B-A-B-B-A-A-A-A-B-B-B)n)
- Statistical copolymers are copolymers in which the sequence of monomer residues follows a statistical rule. If the probability of finding a given type monomer residue at a particular point in the chain is equal to the mole fraction of that monomer residue in the chain, then the polymer may be referred to as a truly random copolymer (3).
- Block copolymers comprise two or more homopolymer subunits linked by covalent bonds (4). The union of the homopolymer subunits may require an intermediate non-repeating subunit, known as a junction block. Block copolymers with two or three distinct blocks are called diblock copolymers and triblock copolymers, respectively.
Copolymers may also be described in terms of the existence of or arrangement of branches in the polymer structure. Linear copolymers consist of a single main chain whereas branched copolymers consist of a single main chain with one or more polymeric side chains.
Other special types of branched copolymers include star copolymers, brush copolymers, and comb copolymers. In gradient copolymers the monomer composition changes gradually along the chain.
A terpolymer is a copolymer consisting of three distinct monomers. The term is derived from ter (Latin), meaning thrice, and polymer.
- Stereoblock copolymers
A special structure can be formed from one monomer where now the distinguishing feature is the tacticity of each block.
Read more about this topic: Copolymer
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