A new visible-light sensitive photoinitiator

bis (diphenyl-iodonium) salt of eosin

is reported. This system has good thermal stabi ity in ground state. When excited

it can undergo intra-ion-pair electron transfer

leading to the bleaching of the dye and the decomposition of the onium salt. The later results in the formation of initiating radical species. This system can be used as a photoinitiator in radical polymerization of conventional vinyl monomers

especially for acrylates. When methyl methacrylate (MMA) is chosen as the monomer

the polymeri-zation satisfeis the following kinetic equation. The activation energy of polymerization was obtained to be Ea=7.00kcal/mol. In the poly-merization system

oxygen acted not only as the inhibitor of polymerization

but also as the quencher of the triplet of the initiator.