Comparative studies of the effects of dimethylaniline,methylaniline and aniline in the benzophenonesensitized photopolymerization of methyl methacrylate in bulk and in solution

Comparative studies of the photopolymerization of methyl methacrylate (MMA) at 35 using benzophenone (BP) as sensitizer in combination with dimethylaniline (DMA), methylaniline (MA) or aniline (A) are reported. In each case the initiator exponent is appreciably less than 0.5. Considering rates of polymerization, inhibition periods and apparent activation energy, the relative effectiveness of the amines in photopolymerization is DMA > MA > A. Solvent effects are also different in the 3 amine systems. In each case photoreduction of BP by the amine, through formation of the BP'-amine exciplex, leads to generation of an amine radical and the semipinacol radical, the former acting as an initiator and the latter as a terminator (primary radical termination). Kinetic analysis indicates that the rate constants of initiation, k_c for the amine radicals lie in the order DMA radical > MA radical > A radical.