polymerisations

Polymerisation is a chemical process that links monomer units to form polymer chains. It encompasses several mechanisms, the two broad classes being chain-growth (addition) polymerisation and step-growth (condensation) polymerisation. In chain-growth processes, an active center such as a free radical or an ion adds successive monomer units to grow a chain, with most polymerisation occurring after initiation, through propagation, and ending by termination or chain transfer.

Monomers include ethylene, propylene, styrene, vinyl chloride, and acrylates. Common products are polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polymethyl methacrylate.

Step-growth polymerisation proceeds by reaction between functional groups on bifunctional monomers, often with small molecule elimination such as water or methanol. It requires high conversion to achieve high molecular weight. Examples are polyesters from diols and dicarboxylic acids, polyamides such as nylon, and polyurethanes formed from diisocyanates and polyols.

The molecular weight and polymer architecture depend on stoichiometry, functionality, purity, temperature, and catalysts. Chain-growth often reaches high molecular weights rapidly at high initiator efficiency, while step-growth builds molecular weight gradually.

Industrial polymerisations occur in bulk, solution, suspension, or emulsion. They may produce linear, branched, or crosslinked networks; process conditions influence morphology, crystallinity, and mechanical properties. Safety and environmental considerations include heat management and handling of reactive intermediates.

Polymers underpin packaging, construction, textiles, electronics, and automotive parts. Recyclability and life-cycle impacts are active research areas.