riphenylalkyl borates (ph

RB) are a new.class of activator for visiblelight induced polymerization of vinyl monomers sensitized by photoreducible dyes

such as methylene blue(MB) used in this paper. Under irradiation (MBph3RB)

theborate cleaves rapidly via electron transfer to give an alkyl radical that is capableof initiating the polymerization of acrylates. The results obtained show that therate of electron transfer reaction for MB borate in the tight ion pair form (ket1012s-1) is far faster than that observed in the solvated free ion form whose proper-ty strongly depends on the solvent polarity and concentration. The polymerization can not take place in acetonitrile with MB borate alone but readily occurs by MB borate(MBph3RB)/TEA borate (Et4Nph3RB) combination and polymerization rate inc-reases with increasing TEA borate. The rate inhancement was also observed by ad-dition of methanol to the system.