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Sulfonium, iodonium or ferrocenium hexafluoro phosphates or antimonate
salts are well known to be highly efficient as photoinitiators for
polymerization of organic or silicone epoxides . The presence of heavy
metal like antimony still present after curing is a major drawback for many
applications involving food contact coatings . The replacement by
phosphates is an alternative but Bronsted acid generated under UV
light is not so powerful in this case. The result is a lower activity.
As presented in the recent publications C.PRIOU and coil . (1-2) developed the
concept of new bulky borate anions associated with sulfonium, iodonium or
ferrocenium cations which can be used as a photoinitiator. The borate anion linked
to an oxonium cation during the polymerization process is a very soft
basis. it is partly due to the bulkiness of the anion and the electronic effect of
fluorine substituants. Tetrakis (pentafluorophenyl) borate diaryliodonium or triaryisuifonium
exhibit a high activity and solubility in organics . As opposed to hexafluorophosphate, this
photoinitiator is not hydrolysable, non hygroscopic and has a high thermal stability.
