Radical and anionic homopolymerization of maleimide and N‐n‐butylmaleimide

The rate of homopolymerization of maleimide has been measured in dimethylformamide solution at 60°C. in the presence of azobisisobutyronitrile; it has been compared to that of N‐n‐butylmaleimide. The overall rates of polymerization are equal to Rp = k[M]1.1–1.2 [In]0.8 for maleimide, and Rp = k'[M] [In]0.5 for the N‐substituted imide. The difference of behavior has been interpreted on the basis of an intramolecular tautomery of the terminal group of the maleimide growing chain and the formation of a resonance‐stabilized succinimidyl radical. The relative ease of polymerization of these monomers and of maleic anhydride has been discussed. In the presence of sodium tert‐butoxide at 20°C. in dimethylformamide solutions, maleimide polymerizes with hydrogen isomerization. The percentage of N‐substituted isomerized units was evaluated at 70–75% by measurement of the rate of hydrolysis in 0.005N sodium hydroxide and comparison with succinimide and N‐butylsuccinimide. N‐n‐butylmaleimide undergoes ring opening together with anionic polymerization in the presence of sodium tert‐butoxide at 20°C. and butyllithium at ‐40°C. Unlike the radical‐initiated polymerization, it was impossible to obtain anionic copolymers of maleimide and N‐butylmaleimide with acrylonitrile and methyl methacrylate.