Steppolycondensation

Step-polycondensation is a polymerization technique where monomers react in a stepwise fashion to form a polymer chain. Unlike chain-growth polymerization, where monomers add sequentially to a growing chain end, step-polycondensation involves reactions between functional groups on the monomers or oligomers. These reactions typically result in the formation of a small molecule byproduct, such as water or methanol, for each bond formed between monomers.

The process can occur between monomers with two different functional groups (A-B type) or between monomers with two identical functional groups that can react with each other (A-A + B-B type). Key characteristics include the fact that high molecular weight polymers are only achieved at high conversions of monomers, and that the molecular weight distribution is typically broad. The reaction rate is generally slower than chain-growth polymerization, and the process can be influenced by factors such as temperature, catalyst presence, and reactant concentration. Common examples of polymers formed via step-polycondensation include polyesters, polyamides (like nylon), and polycarbonates. The mechanism involves the gradual increase in molecular weight as more functional groups react, leading to the formation of longer polymer chains.