Final answer:
Addition polymerization is catalyzed by a free radical, which is a chemical species with an unpaired electron. The free radical initiator begins the polymerization process by attacking a monomer and starting the chain reaction that leads to the formation of the polymer.
Step-by-step explanation:
Addition polymerization is often catalyzed by a free radical, that is, a chemical species with an unpaired electron. During the initiation phase of free radical polymerization, a free radical initiator, such as hydrogen peroxide, can split to form two radicals which each have an unpaired electron. This free radical then attacks a carbon-carbon double bond of a monomer, forming a new radical that can react with another monomer, thereby propagating the polymer chain.Free radicals, due to their unpaired electron, are highly reactive. They are keen to pair up this unpaired electron, making them potent initiators for polymerization reactions. The whole process, including initiation, propagation, and termination steps, results in the transformation of monomers into a long-chain polymer.