The kinetic nonideality in the polymerization of methyl methacrylate was studied with the use of pyridine-sulfur dioxide charge transfer complex as the initiator under different conditions. The following systems were studied : (1) aqueous polymerization of methyl methacrylate (MMA) with the use of a pyridine-sulfur dioxide charge transfer complex as initiator, (2) photopolymerization of MMA initiated by the pyridine-sulfur dioxide complex in the presence of carbon tetrachloride, (3) photopolymerization of MMA in bulk and in a pyridine-diluted system with pyridine-sulfur dioxide alone and in combination with benzoyl peroxide as a photoinitiator. Polymerization in all these cases proceeded by radical mechanisms. The kinetic parameter k(p)(2)/k(t) for the aqueous system was 3.65 L mol(-1) s(-1), and for nonaqueous systems were 1.27 x 10(-2) to 1.40 x 10(-2) L mol(-1) s(-1). The monomer exponent and initiator exponent for ideal free radical polymerization systems are 1.0 and 0.5, respectively. In the system studied, the ideal kinetics were followed at specific concentration ranges of both monomer and initiator. At different concentration ranges, the systems behave nonideally. The kinetic nonidealities in monomer exponents, i.e., lower or higher than unity, were explained on the basis of (1) the rate-enhancing effect of different solvents, and (2) a radical generation step by in situ initiator monomer complexation reaction. The kinetic nonidealities in initiator exponent were analyzed and interpreted in terms of (1) primary radical termination, and (2) degradative initiator transfer with little reinitiator. Analysis of kinetic data shows that the degradative initiator transfer effect is more prominent in the present systems.