Precise Sequence Control and Thermal Characterization of N‑Substituted Maleimide Copolymers Containing Hydrazine Structure

N-Substituted maleimides are highly reactive and have been used for the synthesis of various thermoresistant polymer materials by radical copolymerization with vinyl monomers. In this study, we synthesized several maleimide monomers with N-amino substituents, i.e., N-(N',N'-dimethylamino)-maleimide, N-(N',N'-diphenylamino)-maleimide, and N-morpholinomaleimide, using N,N-disubstituted hydrazine compounds and maleic anhydride as the starting materials. We carried out radical copolymerization of the N-aminosubstituted maleimides with styrene, methyl acrylate, isobutyl vinyl ether, and limonene, and analyzed the composition and arrangement of the repeating monomer units in the produced copolymers in order to elucidate the detailed copolymerization mechanism, including propagation reactions controlled by terminal and penultimate unit models. In the copolymerization of the maleimides with styrene and methyl acrylate, alternating and random copolymers were formed, respectively, by the propagation processes according to the terminal model. In the copolymerization with isobutyl vinyl ether and limonene, copolymers containing predominant AAB repeating structures were formed under the penultimate unit control. It was also clarified that the introduction of compact and electron-donating N-substituents is promising for the induction of the penultimate unit effect. Then, the chemical and physical properties of the copolymers were characterized. The 10% weight-loss temperatures of the copolymers were in the range of 300-350°C in thermogravimetric analysis, indicating their excellent thermal stability. It was found that the copolymers containing a large number of maleimide units decomposed exothermically regardless of the atmosphere because the copolymers contained an N-N bond in their side chain, similarly to other nitrogen-rich polymer materials containing N-N bonds. The glass transition temperatures of the copolymers varied in the range of 40-220°C depending on the kind of vinyl monomers used and the composition of the copolymers, which agreed well with the values predicted from Fox's equation. We also attempted to synthesize N-(N'-phenylamino)-maleimide derived from a mono-substituted hydrazine compound and evaluated the role of the isolated 6-membered cyclic product on radical polymerization reactions.