Photoinitiators-Light Absorbing Amines

This type of photoinitiating system has been studied carefully using a series of 6-alkoxy-2,4-diiodo-3-fluorones and 2-acyl- or 7-alkyl-2,4,5-triiodo-3-fluorones [117-120] as the primary light absorbers. The systems have been further evaluated as initiators for photopolymerization in the presence of a tertiary aromatic amine. Photoinitiated polymerization was triggered with an argon-ion (514.5 nm line) or He-Ne (632 nm line) laser. 

When composite resins were first introduced, their polymerization involved free radical initiation by a combination of benzoyl peroxide with tertiary amine activator, de-hvered in two different pastes, known respectively as base and catalyst. Contemporary composites are visible light-activated one-paste systems and the principal photoinitiator used is camphorquinone [70,80], It is used in conjunction with a co-initiator, typically an amine [81], This latter compound does not absorb hght, but is necessary to react with the fight-activated camphorquinone molecule to generate free radicals and hence initiate the chain polymerization. 

Keywords photooxidation, UV absorbers (UVA), outdoor performance, weathering, accelerated weathering, kinetic chain length, photoinitiator, Norrish reactions, peroxide decomposer, hindered amine light stabilizers (HALS), photosensitizer, transition metal complex, UV stabilizer, time-controlled stabilization, reactive antioxidants, polymeric antioxidants. 

Benzil and quinones, such as 9,10-anthraquinone and camphorquinone, also function as PI2 photoinitiators by intramolecular abstraction from tertiary amines. Since these dicarbonyl compounds absorb light at wavelengths longer than 400 nm, they may be used with visible light sources. 

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