fotoinitiated

Photoinitiated, or photoinitiation, refers to chemical reactions that are started by light exposure using a photoinitiator. This approach is widely used to cure polymers, coatings, inks, adhesives, and dental materials.

In a photoinitiated process, a photoinitiator absorbs photons and converts light energy into reactive species such as radicals or ions that drive polymerization or crosslinking. Two main mechanisms exist: Type I photoinitiators undergo cleavage upon excitation to form reactive radicals directly; Type II photoinitiators form radicals only in the presence of a co-initiator, typically an amine, through energy or electron transfer.

Examples of photoinitiators include Type I compounds such as benzoin ethers and hydroxyalkyl ketones (for instance, 2-hydroxy-2-methylpropiophenone), which generate radicals upon light absorption. Type II systems commonly use camphorquinone with a tertiary amine co-initiator. Modern visible-light systems employ acylphosphine oxides and related photoinitiators that respond efficiently to blue or green light, expanding applications beyond traditional UV curing.

Applications span dental resins, ultraviolet- and visible-light–curable coatings, inks, adhesives, and 3D-printing resins. The choice of photoinitiator depends on the desired wavelength, curing speed, depth of cure, and material compatibility. Key operational factors include matching the light source wavelength to the initiator’s absorption, light intensity and exposure time, initiator concentration, and oxygen inhibition effects, which can limit polymerization at surfaces or in thin films.

Safety and environmental considerations encompass potential photoinitiator residues and light hazard. Proper handling and formulation are essential to minimize toxicity and optimize performance.