This is a chain-growth polymerization.

The basic difference between chain growth and step-growth polymerization is as follows:

In step-growth polymerisation, bifunctional or trifunctional monomers in the growing chains further react with each other to form longer chains. But in the case of chain-growth polymerization, only monomers react with each other to continue the growing chain.

In this diagram, two monomers simply and combine to form the polymer by chain- growth polymerization reaction.