additiopolymerisaatioon

Additiopolymerisaatioon, or addition polymerization, is a type of polymerization in which monomer units with unsaturated bonds, typically vinyl groups, add to a growing polymer chain without the loss of small molecules. The process contrasts with condensation polymerization, where by-products such as water or methanol are released.

There are several mechanisms for addition polymerization. The most common are free-radical, ionic (cationic or anionic), and coordination polymerizations. In free-radical polymerization, an initiator generates reactive radicals that add to monomer units, creating a propagating radical that continues to add more monomers. Termination occurs by combination or disproportionation of radical chain ends, and chain-transfer reactions can alter molecular weight or cause branching. Ionic polymerizations proceed via charged active centers, with cationic and anionic processes differing in sensitivity to impurities and solvents. Coordination polymerization, often used for olefins, involves metal catalysts that coordinate monomers before insertion into a growing chain.

Kinetics and properties in addition polymerization are governed by the balance of initiation, propagation, and termination steps. The rate of polymerization depends on monomer and initiator concentrations, temperature, and solvent. Molecular weight and dispersity are influenced by chain-transfer and termination events; living or controlled methods (such as RAFT, ATRP, or NMP) can yield predetermined molecular weights and narrow dispersities.

Stereochemistry plays a role for certain monomers, affecting tacticity (isotactic, syndiotactic, atactic) and crystallinity, which in turn influence material properties. Crosslinking or multifunctional monomers can produce networks or thermosets.

Industrially, addition polymerization produces polymers such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, poly(methyl methacrylate), and polyacrylates. These processes span gas-phase, bulk, emulsion, and solution polymerizations and are central to plastics, coatings, and adhesives industries. Safety and heat management are important due to exothermic reactions and radical intermediates.