Iodonium butyltriphenylborate salts (AI+Ar′Ph3B−R), (Bu) were found to be more efficient than iodonium tetraphenylborate salts (RPh) when used as photoinitiators for the polymerization of acrylates. Relative photodecomposition rates were also different. It was found from a study of the photoreaction of iodonium borate salts with a model monomer, methyl methacrylate, that iodonium butyltriphenylborate salts simultaneously produce a butyl radical from the borate anion and an aryl radical from the iodonium cation upon irradiation. Both radicals initiate polymerization. Iodonium tetraphenylborate salts were found to release an aryl radical, but only from the iodonium cation. Iodonium borate salts exhibit strong absorption below 300 nm with a tail absorption above 400 nm. Thus, iodonium butyltriphenyl borate salts are efficient photoinitiators even when used with visible light. When a photosensitizer such as 5,7‐diiodo‐3‐butoxy‐6‐fluorone is employed, iodonium butyltriphenylborate salts are rendered much more efficient for visible light photopolymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1667–1677, 1998

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Several new 4-benzoylbenzylammonium borates were prepared in order to study their photochemical properties. It was found that a quantitative yield of biphenyl and a small amount of benzene are formed from photolysis of the title compounds as tetraphenylborates in the absence of oxygen. In addition, amines and methylbenzophenone were detected after the steady-state photolysis. The quantum yields of the photolysis of the title compounds and the formation of biphenyl, amines, and methylbenzophenone were determined. Radical trapping experiments showed that the photogenerated amine is converted to an R-aminoalkyl radical, which is an important initiating species for the polymerization of acrylates when tetraphenylborate is chosen as a counteranion. It was found that even 1-(4-benzoylbenzyl)pyridinium tetraphenylborate is an active photoinitiator, however, indicating that R-aminoalkyl radical is not the only initiating species formed from 4-benzoylbenzylammonium tetraphenylborates. The effect of structure on initiating activity was determined and discussed.