Photopolymerization of methyl methacrylate using a morpholine-sulfur dioxide charge-transfer complex as the photoinitiator

Photopolymerization of the vinyl monomer (M) of methyl methacrylate (MMA) was kinetically studied by using near-UV/visible light at 40 degrees C and employing a morpholine (MOR) - sulfur dioxide (SO2) charge-transfer ( C-T) complex as the photoinitiator. The rate of polymerization (R-P) was found to be dependent on the morpholine: sulfur dioxide mole ratio; the 1 : 2 (MOR-SO2) complex acted as the latent initiator complex C which underwent further complexation with the monomer molecules to give the actual initiating complex I. Using the 1 : 2 (MOR-SO2) C-T complex as the latent initiator, the observed kinetics may be expressed as R-P proportional to [MOR-SO2](0.27)[M](1.10). Benzoquinone behaved as a strong inhibitor. Polymers obtained tested positive for the incorporation of a sulphonate-type end group. Polymerization followed a radical mechanism. Kinetic nonideality as revealed by a low initiator exponent and monomer exponent of greater than unity was explained on the basis of a prominent primary radical termination effect. (C) 1998 John Wiley & Sons, Inc.