porrasreaktiopolymerisaatio

Porrasreaktiopolymerisaatio, also known as step-growth polymerization, is a type of polymerization mechanism where polymer chains grow by the reaction of monomers with functional groups. Unlike chain-growth polymerization, where monomers add sequentially to a growing chain end, step-growth polymerization involves reactions between any two molecules, whether they are monomers, oligomers, or polymer chains. This means that the molecular weight of the polymer increases gradually throughout the reaction.

The process typically involves monomers with at least two reactive functional groups. These groups react with each other, forming a new bond and releasing a small molecule, such as water or alcohol, as a byproduct. Common examples of step-growth polymerization include polyesterification, polyamidation, and polyurethanization. For instance, the formation of polyester involves the reaction between a diol and a dicarboxylic acid.

Step-growth polymerization can occur via several mechanisms, including condensation polymerization (where a small molecule is eliminated) and addition polymerization (where no small molecule is eliminated, but the monomers add directly to each other, often involving ring-opening mechanisms). The reaction rate generally slows down as the polymer grows and the concentration of reactive functional groups decreases. The final molecular weight is dependent on the extent of reaction and the stoichiometry of the monomers.