A novel intra-ion-pair electron transfer sensitization system for visible photopolymerization

Mono- and di- iodonium salts of eosin dye, EoEt( Ph2 I) and Eo( Ph2 I)2, as a novel sensitization system for visible photopolymerization were synthesized and studied in comparison with the corresponding bimocular systems (EoNa2/Ph2 ICl). The photochemical activity of unimolecular system is much higher than that of bimolecular system. Photobleaching rate obtained decreases in the order Eo(Ph2 I)2> EoNa2/2 (Ph2 ICl)> EoEtNa/2 (Ph2 ICl). The same results for radical polymerization were also obtained. The kinetic results of polymerization with Eo(Ph2 I)2 as initiator show that the polymerization rate is directly proportional to the concentration of MMA and Eo (Ph2 I)2 with exponent of 1.0 and 0.46 respectively. The overall activation energy of polymerization was measured to be 7.0 (kcal.mol-1). The photopolymerization rate is affected significantly by solvent polarity as a results of variance in absorption spectrum. Multiacrylate photocrosslinking rates obtained in the dry film indicate that the disalt Eo(Ph2 I)2 is more efficient than mono salt EoEt(Ph2 I) and essentially, no reaction occures in the case of bimolecular system (EoNa2/Ph2 ICl)