initiatorfamilies

Initiatorfamilies is a term used in polymer chemistry to classify chemical initiators that start polymerization reactions. The concept groups initiators by their mechanism for radical generation and by the energy source required for activation. The main subfamilies are thermal initiators, photoinitiators, redox initiators, and ionic initiators, each with characteristic decomposition pathways, typical monomer scopes, and common handling considerations.

Thermal initiators, activated by heat, include peroxide and azo compounds. Peroxide initiators such as benzoyl peroxide and di-tert-butyl peroxide decompose upon heating to yield radicals that begin chain growth. Azo initiators, notably 2,2'-azobis(2-methylpropionitrile) (AIBN), generate radicals when heated. Thermal initiation is widely used in bulk, solvent, and emulsion polymerizations where temperature control is practical.

Photoinitiators rely on light to produce reactive species. Type I photoinitiators cleave upon illumination to form radicals, with examples including benzoin ethers and α-hydroxy ketones. Type II photoinitiators require a co-initiator, typically an amine, to generate radicals under UV or visible light. Photoinitiators underpin many UV-curing coatings, inks, and 3D-printed resins.

Redox initiators generate radicals through rapid redox pairs, such as persulfates with reducing agents or metal-catalyzed systems, enabling polymerization at ambient temperatures. Ionic initiators, used in certain cationic polymerizations, involve strong Lewis acids or related catalysts to activate monomers.

Safety and handling vary by subfamily; peroxides can be shock-sensitive and oxidizing, photoinitiators may pose exposure hazards, and redox/ionic systems require careful control of byproducts and moisture. The initiatorfamilies framework helps practitioners balance reactivity, monomer compatibility, processing conditions, and safety.