Stepwise condensation of monomers to form polymers is known as step-growth polymerization. In this polymerization process, the monomers react to form the dimers first, which then form trimers or tetramers, followed by the formation of oligomers and eventually polymers. Since each polymerization step is associated with the loss of small molecules in the form of water or HCl, it is also known as condensation polymerization. Monomers involved in step-growth polymerization must have two functional groups for bonding. Depending on the type of functional groups present at each end, monomers can be of A-A type, B-B type, or A-B type. A-A and B-B type monomers condense to give (A-A-B-B)n type polymer. A-B type monomers have two different functional groups at each end. These monomers undergo self-condensation to form an (A-B)n type polymer.