FREE-RADICAL PRODUCTION UPON PHOTOINDUCED ELECTRON-TRANSFER REACTIONSIN THE PRESENCE OF VINYL MONOMERS, EFFECT OF WATER ADDITION

Free radical fragments produced in the photoinduced electron transfer from triethylamine (TEA) to excited pyrenebutyltrimethylammonium (PyB u+) lead to 1-vinyl-2-pyrrolidinone (VP) and a-hydroxyethyl methacryla te (HEMA) polymerization, Experiments carried out in water/acetonitril e solvent mixtures showed that the polymerization rate of VP increases upon increasing the water content, whereas the polymerization rate of HEMA follows the opposite trend. These results are; interpreted in te rms of the strong dependence on the solvent properties of the photoche mical behavior of PyBu+ in the presence of the amine or monomers, Thus , the PyBu+ quenching by VP is almost negligible in both solvents (wa ter and acetonitrile). Whereas, the ''PyBu+ quenching rate constant by HEMA in water is 4 x 10(9) M-1 s(-1) and decreases four orders of mag nitude in acetonitrile. The quenching of PyBu+ by TEA in aqueous solu tions is controlled by hydrogen-bonding interactions between water mol ecules and the amine, Quantum yields of the pyrene radical anion (Phi( Py-)) also strongly depend on the water content, decreasing from 0.28 to 0.015 upon going from acetonitrile to water.