Polycondensation

Polycondensation is step-growth polymer formation in which monomers or growing chains react while releasing small molecules such as water or methanol.

Step-growth polymerization: A polymerization process in which molecules of any size react through functional groups to form larger molecules. Polycondensation is a step-growth process whose coupling reactions also release small molecules.
Bifunctional monomer: A monomer with two reactive functional groups capable of forming bonds during polymerization. Two reactive ends allow linear chains to grow through repeated condensation.
Polyester: A polymer whose backbone contains ester linkages. Many polyesters form when diols and dicarboxylic acids condense with water elimination.
Addition polymerization: Polymer formation by adding monomers without eliminating small-molecule byproducts. Unlike polycondensation, its defining chain-forming additions release no small molecule.
Condensation reaction: A chemical reaction that joins molecules while eliminating a small molecule, often water. The bond-forming steps in polycondensation eliminate small-molecule byproducts.
Dicarboxylic acid: An organic compound containing two carboxyl groups. Dicarboxylic acids supply one common pair of condensation sites for polyester and polyamide synthesis.
Polyamide: A polymer whose backbone contains repeating amide linkages. Polyamides can form by condensation of diamines with dicarboxylic acids.
Chain-growth polymerization: Polymerization in which monomers add successively to an active chain end. Polycondensation grows through reactions among molecules of many sizes, not only active chain ends.
Functional group: A specific group of atoms in a molecule that determines characteristic chemical reactions. Complementary functional groups on monomers provide the reactive sites for chain growth.
Diol: An organic compound containing two hydroxyl groups. Diols react with dicarboxylic acids to form polyester chains and water.

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