Compared to chain-growth polymerization, where the production of the growing chaingrowth is based on the reaction between polymer with active center and monomer, step-growth polymerization doesn’t have initiator or termination. The monomer in step-growth polymerization will be consumed very quickly to dimer, trimer or oligomer. The degree of polymerization will increase steady during the whole polymerization process. On the other hand, in chain-growth polymerization, the monomer consumed steadily but the degree of polymerization could be increased very quickly after chain initiation.