fotoiniciátor

A fotoiniciátor, also known as a photoinitiator, is a substance that, upon absorption of light, produces a chemical species (typically radicals or cations) that initiates a polymerization reaction. These initiators are crucial components in photopolymerization processes, which are widely used in applications such as coatings, inks, adhesives, and 3D printing.

The mechanism involves the photoinitiator molecule absorbing photons in the ultraviolet (UV) or visible light spectrum. This absorption leads to an electronic excitation of the molecule. Following excitation, the photoinitiator undergoes a chemical transformation, often fragmentation or hydrogen abstraction, to generate reactive species. These reactive species then interact with monomers, initiating a chain reaction that leads to the formation of a polymer network.

Photoinitiators are broadly classified into two main types: free radical photoinitiators and cationic photoinitiators. Free radical photoinitiators generate free radicals, which then initiate the polymerization of monomers containing vinyl groups. Cationic photoinitiators, on the other hand, generate strong Brønsted or Lewis acids, which initiate the ring-opening polymerization of monomers like epoxides and vinyl ethers.

The choice of photoinitiator depends on several factors, including the light source, the wavelength of light used, the type of monomer, the desired curing speed, and the application's requirements for properties like yellowing resistance and migration. Efficiency, solubility, and cost are also important considerations. The development of photoinitiators that absorb light in the visible spectrum has opened up new possibilities for photopolymerization, allowing for deeper penetration of light and enabling the curing of thicker materials or those containing pigments that absorb UV light.