The free-radical polymerization of maleimide photosensitized (λ= 4358 Å) by manganese carbonyl in the presence of carbon tetrachloride has been studied at 30°C. Kinetic observations have shown that the quantum efficiency of initiation is close to unity and that chain-termination is first-order in propagating radical concentration. Termination is strongly base-catalyzed and is subject to a deuterium isotope effect (kHt/kDt= 1.2). On the basis of these and other observations a detailed mechanism of termination is proposed involving formation of non-propagating succinimidyl radicals, which probably disproportionate with growing chains. We also report a (number-average molecular weight, intrinsic viscosity) relationship for polymaleimide in N,N-formdimethylamide at 30°C.