polikondensatsiooni

Polikondensatsioon is a type of step-growth polymerization process where monomers react to form a polymer chain, releasing a small molecule as a byproduct. This distinguishes it from addition polymerization, which does not produce byproducts. The reaction typically involves monomers with at least two functional groups that can react with each other, such as hydroxyl (-OH), carboxyl (-COOH), or amino (-NH2) groups. As the reaction proceeds, these functional groups react and eliminate a small molecule, commonly water (H2O), but also methanol (CH3OH) or hydrogen chloride (HCl).

The process of polikondensatsioon occurs in steps. Initially, monomers react to form dimers, then trimers, and so on, gradually increasing the chain length. At each step, a new monomer or oligomer reacts with the growing polymer chain, and a small molecule is eliminated. The molecular weight of the polymer increases throughout the reaction, and high molecular weights are achieved only at high conversions. This step-growth mechanism means that the polymer chains grow at different rates and are of varying lengths.

Common examples of polymers produced by polikondensatsioon include polyesters, polyamides (like nylon), polycarbonates, and phenolic resins. For instance, the formation of polyester involves the reaction between a diol and a dicarboxylic acid, with the elimination of water. Similarly, polyamides are formed from the reaction of diamines with dicarboxylic acids, also releasing water. The ability to control the type of monomers and their functional groups allows for the synthesis of polymers with a wide range of properties, making polikondensatsioon a versatile and important method in polymer chemistry.