The free radical photopolymerization of N,N-dimethylacrylamide was investigated at 25 • C and at low conversion in several solvents ranging from weak polar solvents to water. The polymerization is strongly accelerated in the aqueous medium, with the polymerization rate increasing one order of magnitude when the solvent is changed from an organic one to aqueous medium. These results were analysed in terms of macroradical conformation, effect of medium viscosity, aggregate formation, hydrogen bond formation and effect of temperature. The results suggest that the main factor that controls the polymerization rate is a kinetic effect due to the hydrogen bonding between the amide carbonyl group and water molecules. Also, we found that polymer properties, such as the thermodynamic quality of the solvent for the polymer backbone and molecular weight control using transfer agents, are influenced by the intermolecular hydrogen bonding.

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The effect of solvent properties on the polymerization rate of 2-hydroxyethyl methacrylate (HEMA) was examined with the photoreaction of 4,4Ј-azobis(2amidinopropane) and photoinduced electron transfer of a thioxanthone derivative and triethanolamine as the radical source. The polymerization rate of HEMA was markedly affected by pH and the medium polarity. The rate increased over a pH range of 6 -8. The dependence of the polymerization rate on the amine concentration photoinitiated by the bimolecular system was different in water and acetonitrile as solvents. In aqueous medium, pH 9.5, the rate increased with the amine concentration reaching a constant value at 0.025 M amine; further amine addition inhibited the polymerization. In organic media the inhibition effect was not observed. Triethanolamine addition did not change the polymerization rate photoinitiated by the azo compound. Photochemical studies of the thioxanthone were carried out under the polymerization conditions. These studies allowed us to simulate the dependence of the polymerization rate on the amine concentration. The results are explained in terms of the interaction of the ketone excited states with the amine in the different media.

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