Polymérisations

Polymérisations refers to the chemical process by which small molecules, called monomers, react together to form very large molecules, called polymers. These polymers consist of repeating structural units derived from the monomers. The process can occur through various mechanisms, leading to different types of polymers.

One primary type of polymerization is addition polymerization. In this process, monomers add to one another in such a way that the polymer contains all the atoms of the monomer. This often involves unsaturated monomers, such as alkenes. Common examples include the formation of polyethylene from ethylene monomers and polyvinyl chloride from vinyl chloride monomers. This type of polymerization typically proceeds via free radical, cationic, or anionic mechanisms.

Another major category is condensation polymerization. In this type, monomers react to form a polymer with the elimination of a small molecule, such as water or methanol. The resulting polymer does not contain all the atoms of the original monomers. Examples include the formation of polyesters from diols and dicarboxylic acids, and polyamides (like nylon) from diamines and dicarboxylic acids.

Chain-growth polymerization and step-growth polymerization are broader classifications that encompass addition and condensation reactions, respectively, based on the mechanism of polymer chain formation. Chain-growth involves the rapid addition of monomers to an active growing chain end, while step-growth involves reactions between monomer molecules or oligomers that slowly build up the polymer chain. The understanding and control of polymerization processes are fundamental to the synthesis of a vast array of materials with diverse properties, including plastics, fibers, and elastomers.