polykondensering

Polykondensering is a type of step-growth polymerization process where monomers react to form a polymer with the elimination of a small molecule, such as water, methanol, or hydrochloric acid. This process differs from chain-growth polymerization where monomers add sequentially to a growing chain. In polykondensering, the molecular weight of the polymer increases gradually as monomer units react, forming dimers, trimers, and eventually long polymer chains.

The reaction typically involves monomers with at least two functional groups that can react with each other. Common examples of functional groups involved include hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), and ester (-COO-). The reaction proceeds through a series of reversible steps, where the equilibrium often needs to be shifted towards product formation by removing the small molecule byproduct.

Key characteristics of polykondensering include the formation of a byproduct and the requirement for monomers with multiple reactive sites. The rate of polymerization is often slow, and high molecular weights are achieved only when the reaction goes to high conversion. Examples of polymers formed by polykondensering include polyesters (like PET), polyamides (like nylon), polycarbonates, and polyurethanes. The properties of the resulting polymers are influenced by the choice of monomers and the reaction conditions.