Dye-sensitized photopolymerization of methylmethacrylate in nonaqueous media

Abstract

The dye-sensitized photopolymerization of methylmethacrylate by visible light in nonaqueous media especially benzene has been investigated using long chain aliphatic amines as activators. For the typical system, eosin/cetyl dimethylamine/methylmethacrylate in benzene, the rate of polymerization has a square root dependence on light intensity and direct proportionality on monomer concentration, while with respect to eosin and cetyl dimethylamine, it passes through a maximum, indicating their dual role as both initiator and retarder. The molecular weight decreases with increase in light intensity and eosin concentration, and also with decrease in monomer concentration. However, the molecular weight passes through a maximum with cetyl dimethylamine concentration. Electrondonating groups attached to the benzene nucleus in the halogenated fluorescein dye stuffs accentuate the sensitizing action of dye stuffs, while electron-withdrawing groups deactivate it. The greater the chain length and the greater the amount of N-substitution in the long chain aliphatic amines, the greater is the activating influence. The effect of combination of dye stuffs as well as the effect of solvents on the rate of polymerization are also discussed. With increase in amine concentration, the average number of amino end groups per chain is reduced. The presence of hydroxyl end groups has also been demonstrated in systems containing alcohols. Presence of oxygen or air in the polymerization systems is always accompanied by an inhibition period and reduction in rate of polymerization. The overall activation energy has been found to be 20 kcal/mole. For the effect of different variables on the rate of polymerization and molecular weight tentative mechanisms following a free radical course have been suggested.