When two different types of monomers are joined in the same polymer chain, the polymer is called a copolymer.

Polypropylene copolymer (PPC) is a bit softer but have better impact strength, is tougher and more durable than homopolymer polypropylene. Copolymer polypropylene tends to have better stress crack resistance and low temperature toughness than homopolymer at the expense of quite small reductions in other properties.

There are three important types of copolymers. A random copolymer contains a random arrangement of the multiple monomers. A block copolymer contains blocks of monomers of the same type. Finally, a graft copolymer contains a main chain polymer consisting of one type of monomer with branches made up of other monomers.

When the two monomers are arranged randomly in any random order, the polymer is called random copolymer.

In a block copolymer, all of one type of monomer are grouped together, and all of the other are grouped together. A block copolymer can be thought of as two homopolymers joined together at the ends.

Graft copolymers are a special type of branched copolymer in which the side chains are structurally distinct from the main chain where the main chain and side chains are composed of distinct homopolymers. However, the individual chains of a graft copolymer may be homopolymers or copolymers.