Photopolymerization of methyl methacrylate in visible light was studied at 40°C using a pyridine-sulfur dioxide charge transfer complex as the initiator in the presence of carbon tetrachloride. In this study the [Py-SO2] used was high (0.5–3.2 mol/L), i.e., 6–40% (V/V), and the [CCL4] ranged between 0 and 1.4 mol/L, i.e., 0–10% (V/V). At a fixed [Py-SO2], Rpfollowed an increasing trend with increasing [CCL4] until the latter was about 2–3% of the total volume. The polymerization rates may be expressed as where Rpand Rp0are rates of photopolymerization in the presence and in the absence of CCL4, respectively. The overall rate, Rp, is proportional to [CCL4]0.5for [CCL4] & 0.2 mol/L.