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An industrial tolylcumyliodonium- tetrakis pentafluorophenylborate , commercially named
Rhodorsil ® Photoinitiator 2074 , was developed by Rhodia 1] The objective was to give an
alternative to solventless release silicone coatings . .J.CRIVELLO and other company 2] had
already introduced cationic commercial systems in the mid-eighties.
Cationic polymers do not require nitrogen inertization in comparison to free radical polymerization of silicones which represents a cost saving process The photoinitiator can be used without inertizing under both UV and e.beam processes The exceptional solubility in different media of Rhodorsil photoinitiator 2074 due to its very poor ionic character is also an advantage in comparison to conventional antimonate or phosphate photoinitiators . It can be directly handled in epoxysilicones or epoxy organic polymers and monomers 3] The mechanism involving iodonium salts has been widely described in the literature. The first step of the process is the degradation under UV of the cationic part of the photoinitiator by homolytic cleavage of a C-I bond. The strong acid generated reacts with a first epoxy group and thus forms an oxonium ion. Polymerization then takes place by reaction of the epoxy with this reactive ion. Polymerization is fast, and stops when nucleophilic species meet the oxonium ion or when all the epoxy functions have reacted.
