Network formation during copolymerization of styrene with a model bismaleimide, p-maleimidobenzoic anhydride, or with mixtures of p-maleimidobenzoic anhydride and methyl p-maleimidobenzoate was studied. The concentrations of pendent double bonds in copolymers, calculated from the consumption of monomers and copolymer composition, follow the general trend typical for vinyl-divinyl copolymerizations. A substantial fraction of pendent maleimide bonds remains in the system at the end of polymerization. The gel point conversions are much higher than for ring-free copolymerizations due to cyclization and steric hindrance of pendent double bonds. The gel point conversions increase with increasing content of the monomaleimide in the copolymerization mixture reaching 100% at 4 mol% of bismaleimide (12 wt% solution). The gel point conversions also increase with increasing dilution reaching 100% for the bismaleimide polymerization in 3 wt% solution. The steric hindrance effect on pendent double bond reactivity seems to be somewhat higher than for conventional vinyl-divinyl copolymerizations.