polyadditioon

Polyadditioon, often referred to as polyaddition in English, is a class of polymerization reactions in which polymers form by the successive addition of monomer units without the elimination of small molecules. This is distinct from polycondensation, where each coupling step releases a by-product such as water or methanol. Polyadditions can proceed through various mechanisms, including step‑growth and chain‑growth processes, and they rely on the presence of complementary reactive groups on the monomers.

Common examples include the formation of polyurethanes from diisocyanates and polyols, polyureas from diisocyanates and diamines, and epoxy resins cured with amines or anhydrides. Thiol‑ene systems and ring‑opening polymerizations of epoxides and other cyclic monomers are also described as polyadditions when no small molecule is released during the growth of the chain. The resulting materials can be linear, branched, or densely crosslinked networks depending on monomer functionality and stoichiometry.

Key features of polyadditions are the absence of volatile by‑products and the possibility of high conversion without distillation or removal of by‑products. Reaction control typically requires careful stoichiometry, effective catalysts or initiators, and sometimes moisture exclusion. Molecular weight and architecture are determined by monomer functionality and the polymerization conditions.

Applications include coatings, adhesives, foams, elastomers, and composite matrices. The approach offers material designs with predictable properties and straightforward purification, though network defects, residual functional groups, and processing challenges can arise with highly crosslinked systems.