Porrasaskelpolymerisaatio

Porrasaskelpolymerisaatio, also known as step-growth polymerization, is a type of polymerization mechanism where monomers containing two or more reactive functional groups react with each other to form larger molecules. This process occurs in discrete steps, with each step involving the reaction of a monomer with another monomer or a growing polymer chain. Unlike chain-growth polymerization, where a single chain grows rapidly, porrasaskelpolymerisaatio involves the gradual increase in molecular weight as more monomers are added.

The key characteristic of porrasaskelpolymerisaatio is that the reaction can occur between any two reactive species present, whether they are monomers, dimers, trimers, or longer oligomers. This leads to a distribution of molecular weights throughout the reaction mixture. Common functional groups involved include hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), and isocyanate (-NCO) groups.

Polymers formed through porrasaskelpolymerisaatio include polyesters, polyamides (like nylon), polyurethanes, and polycarbonates. The reaction typically proceeds through condensation, where a small molecule, such as water or methanol, is eliminated during each step. The rate of polymerization is often slow at the beginning when the concentration of reactive groups is high, but it accelerates as longer chains with more reactive ends are formed. The final molecular weight achieved is highly dependent on the extent of reaction.