polycondensationiksi

Polycondensation is a type of step-growth polymerization in which monomers react to form a polymer and a small molecule byproduct. This byproduct is typically water, but can also be methanol, hydrochloric acid, or other simple compounds. Unlike addition polymerization, which involves the addition of monomers without the loss of any atoms, polycondensation reactions involve the elimination of a small molecule with each repeating unit formed. The monomers involved in polycondensation generally possess two or more functional groups that can react with each other. Common examples of functional groups that participate in polycondensation include hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), and ester (-COO-) groups.

The process of polycondensation occurs in stages. Initially, monomers react to form dimers, trimers, and longer oligomers. As the reaction proceeds, these oligomers combine to form longer polymer chains. The molecular weight of the polymer increases gradually throughout the reaction. This step-growth nature means that high molecular weights are typically achieved only at high conversions of the monomers. The type of polymer formed depends on the specific monomers used. For instance, the reaction between a diol and a dicarboxylic acid yields a polyester, while the reaction between a diamine and a dicarboxylic acid produces a polyamide. Other important polymers formed through polycondensation include polycarbonates and polyurethanes. The byproduct formed during the reaction often needs to be removed to drive the equilibrium towards polymer formation and achieve higher molecular weights.