Chain-growth polymerization (AE) or chain-growth polymerisation (BE) is a polymerization technique where unsaturated monomer molecules add onto the active site on a growing polymer chain one at a time. There are a limited number of these active sites at any moment during the polymerization which gives this method its key characteristics.
Chain-growth polymerization involves 3 types of reactions : 
# Initiation: An active species I* is formed by some decomposition of an initiator molecule I
# Propagation: The initiator fragment reacts with a monomer M to begin the conversion to the polymer; the center of activity is retained in the adduct. Monomers continue to add in the same way until polymers P* are formed with the degree of polymerization i
# Termination: By some reaction generally involving two polymers containing active centers, the growth center is deactivated, resulting in dead polymer