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

Abstract

Photopolymerization of the vinyl monomer (M) of methyl methacrylate (MMA) was kinetically studied by using near-UV/visible light at 40°C and employing a morpholine (MOR)-sulfur dioxide (SO 2 ) 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-SO 2 ) 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-SO 2 ) C-T complex as the latent initiator, the observed kinetics may be expressed as R P [MOR-SO 2 ] 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.