Monomeeraddition

Monomeeraddition, in English often called addition polymerization or chain-growth polymerization, is a polymerization mechanism in which polymer chains grow by the successive addition of monomer units to active sites at the ends of the growing chains. In this mechanism, no low-molecular-weight byproducts are produced during the main growth step, distinguishing it from condensation polymerizations where small molecules are released.

The process generally proceeds through initiation, propagation, and termination (or chain transfer). Initiation forms reactive centers via free radicals, cations, anions, or coordination complexes. Propagation adds monomer units to the active center, extending the chain without eliminating byproducts. Termination stops growth, by combination, disproportionation, or chain transfer to solvent or monomer, although some systems can be designed as living polymerizations where termination and transfer are minimized.

Typical systems include radical polymerization of vinyl monomers (for example, ethylene, styrene, acrylates), ionic polymerization (anionic polymerization of styrene or acrylates; cationic polymerization of vinyl ethers), and coordination polymerization of olefins using transition-metal catalysts (for example, Ziegler–Natta or metallocene catalysts). Living versions of these processes enable precise control of molecular weight and architecture, including block copolymers.

Compared with step-growth polymerization, monomeeraddition polymerization often yields polymers with high degrees of polymerization and high molecular weights, with the structure depending on monomer reactivity, initiation efficiency, and termination or transfer reactions. Applications span plastics, elastomers, adhesives, and coatings.