Photoinitiator 2-hydroxy-acetophenones

In the photopolymerization of methacrylamide by benzoin methyl ether, chain-transfer to monomer has been found to be important, and benzalde-hyde is reported to be an inefficient photoinitiator of methyl methacrylate polymerization unless benzophenone and triethylamine are present. Acetophenone has been found to sensitize the cycloaddition of maleic anhydride to 7-oxabicyclo[2.2.1]heptan-5-one-2,3-dicarboxylic anhydride, , a-hydroxy-acetophenone derivatives have been found to be non-yellowing initiators, and h.p.l.c. has been used to determine residual carbonyl photoinitiators in u.v.-cured resins. In the emulsion-polymerization of methyl methacrylate using an aromatic ketone and a continuous or intermittent laser, the former conditions were found to be similar to those under continuous u.v. irradiation. The dependence of the polymerization rate and average chain-length on the absorbance of the initiator used in the photoinitiated polymerization of vinyl monomers has been studied. Interestingly, irrespective of all conditions, maximum conversion is observed when initiator absorbance is 2.51. "... 

This compound is also called hydroxy-cyclbhexyl phenyl ketone (HCPK). The mixed aliphatic/aromatic initiators are reported to cause less yellowing of the photopolymers. The efficiencies of the last three photoinitiators have been compared using laser irradiation of solutions of trimethylolpropane triacrylate in 2-propanol . In air, the rates were found to be equivalent but imder nitrogen the ai-hydroxy-acetophenone derivatives were somewhat faster. 

Phan X.T. (1986) Photochemical a-cleavage of 2,2-dimethoxy-2-phenyl-acetophenone and 1-hydroxy-cyclohexyl-phenyl ketone photoinitiators. Effect of molecular oxygen on free radical reaction in solution. J. Radiation Curing, 13, 18-25. 

Several UV applications require good weatherability, i.e., nonyellowing. Photoinitiators based on alpha-substituted acetophenone show good performance in these applications. Hydroxy cyclohexyl phenyl ketone is a popular commercial product of this type. 

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