Homopolymer vs copolymer

In general, polymers such as PVC are referred to as "homopolymers", as they consist of repeated long chains or structures of the same monomer unit, whereas polymers that consist of more than one monomer unit are referred to as copolymers (or co-polymers).

But frequently all polymers having one repeating unit are considered homopolymers. So homopolymers can include polymers with more than one monomer species. It violates the above definition.

Let we stick to the first definition.

Homopolymers and copolymers (examples)
Homopolymer polystyrene	Homopolymer polydimethylsiloxane, a silicone. The main chain is formed of silicon and oxygen atoms.	The homopolymer polyethylene terephthalate has only one repeat unit.	Copolymer styrene-butadiene rubber: The repeat units based on styrene and 1,3-butadiene form two repeating units, which can alternate in any order in the macromolecule, making the polymer thus a random copolymer.

Homopolymers $A+A+A+...\rightarrow AAAA...$ Copolymers $A+B+A+B...\rightarrow ABAB...$

Note

Copolymers also can be categorized into,

1. Random copolymer
2. Alternating copolymer
3. Block copolymer
4. Graft copolymer

In the schematic figure below, Ⓐ and Ⓑ symbolize the two repeat units.

Random copolymer	Gradient copolymer	Graft copolymer
Alternating copolymer	Block copolymer

Q&A

1. Do homopolymers have multiple species of monomers?
2. can we make a copolymer with a one species of monomer?

Answer

1. No, if it has more monomer types then it will be a copolymer. According to the first definition.
2. No, by definition copolymer must have more than one monomer species. But one species can be chemically changed to many species and copolymer can be made by it.

Summary

• homopolymer - one species of monomer
• copolymer - more than one species of monomers

Activities

• search in internet for copolymer types and their definitions.