Two cyclic allylic sulfide monomers, 6-methylene-2-methyl-1,4-dithiacycloheptane (MDTP) and 7-methylene-2-methyl-1,5-dithiacyclooctane (MDTO), were copolymerized with methyl methacrylate (MMA) using the pulsed laser polymerization technique. MDTO was also copolymerized with styrene (STY) under the same conditions. Reactivity ratios in bulk monomer at 25 °C, based on the terminal model, were determined from 1H NMR analyses of the copolymers as rMDTP = 0.85, rMMA = 11 (MDTP-MMA); rMDTO = 1.22, rMMA = 3.08 (MDTO-MMA); and rMDTO = 0.3, rSTY = 8.6 (MDTO-STY). The average propagation rate coefficients, 〈kp〉, were determined for the copolymerizations in the monomer composition ranges 0 ≤ fMDTP ≤ 0.6 (MDTP-MMA), 0 ≤ fMDTO ≤ 0.4 (MDTO-MMA) and 0 ≤ fMDTO ≤ 0.3 (MDTO-STY). It was not possible to obtain values for 〈kp〉 from mixtures containing higher mole fractions of MDTP or MDTO or for either homopolymer. The failure of pulsed laser polymerization in MDTP-and MDTO-rich solutions is presumably due to high rates of transfer to the cyclic allylic sulfide monomer. The MMA copolymerization data show clear deviation from the terminal model, similar to that observed by this group for 2-methylene-1,3-dioxepane. Significant solvent effects on the kp of MMA were observed in the presence of 1,5-dithiacyclooctane, used as a nonpolymerizing model compound for MDTP and MDTO.