Remote methyl substituents were found to have a significant effect on the free radical ring-opening polymerization of cyclic allylic eight-membered disulfide monomers. High concentrations of initiator were required to achieve reasonable polymerization rates for the monomer with a greater number of methyl substituents, 2,2,4-trimethyl-7-methylene-1,5-dithiacyclooetane (1b). Monomer 1b polymerized significantly slower than the analogous monomer containing only one 2-methyl substituent, 2-methyl-7-methylene-1,5-dithiacyclooctane (1a). Values of k(p)/k(t)(0.5) (k(p) and k(t) are the rate coefficients for propagation and termination, respectively) for both monomers were obtained at 30-120 degrees C. Examination of the Arrhenius parameters for propagation revealed that the fragmentation step appeared to exert a greater influence on the overall propagation rate for la. Polymerization rates were influenced by depropagation at the relatively low temperatures of 50-60 degrees C (1a) and 70-85 degrees C (1b), and both monomers exhibited the same ceiling temperature of approximately 125 degrees C at [M](0) = 2 M in benzene.