Types of Polymerization Reactions
Addition Reactions and Condensation Reactions
The two general classes of polymerizations are addition reactions and condensation reactions. In addition reactions, also described as chain growth polymerizations, the intact monomer links together to form linear or branched chains.
In addition polymerizations (a.), the entire monomer molecule becomes a segment of the polymer. Addition polymers form via several different mechanisms including free radical polymerizations, anionic polymerizations, cationic polymerizations, etc. Common polymers formed by addition polymerizations include polyolefins such as c, polystyrene and polyvinylchloride. Another type of addition reaction is ring-opening polymerization used in the preparation of polymers, such as polycaprolactam, as well as highly tailored siloxane polymers.
In condensation reactions (b.), both polymer and a by-product molecule such as water or HCl are formed when monomers join. If the monomers have two or more reactive functional groups, then more branched polymers form. Condensation reactions are commonly described as step-growth polymerizations because initially dimers are formed, then trimers, eventually leading up to longer chain oligomers. Common polymers formed by condensation reactions include polyamides, polyester and polycarbonate.