N‐substituted maleimides polymerize in the presence of a radical initiator to give polymers with excellent thermal stabilities and transparency. In this study, we synthesized various maleimide copolymers with styrenes and acrylic monomers to control their thermal and mechanical properties by the introduction of bulky substituents and intermolecular hydrogen bonding. Three‐component copolymers of N‐(2‐ethylhexyl)maleimide in combination with styrene, α‐methylstyrene (MSt), or 1‐methylenebenzocyclopentane (BC5) as the styrene derivatives, and n‐butyl acrylate, 2‐hydroxyethyl acrylate, 4‐hydroxybutyl acrylate, or acrylic acid as the acrylic monomers were prepared by radical copolymerization. These copolymers were revealed to exhibit excellent heat resistance by thermogravimetric analysis. Glass transition temperatures increased by the introduction of bulky MSt and BC5 repeating units. The mechanical properties of the copolymer films were improved by the introduction of intermolecular hydrogen bonding. Optical properties, such as transmittance, refractive index, Abbe number, and birefringence, were determined for the copolymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1569–1579

UV absorption spectroscopic measurements and DFT calculations revealed that N-(alkyl-substituted phenyl)maleimides with substituents at the ortho position favored a twisted N-phenyl conformation, due to the steric hindrance between the maleimide ring and the substituted N-phenyl moiety. Highmolecular-weight copolymers were synthesized by radical copolymerization of the N-(alkyl-substituted phenyl)maleimides with n-butyl vinyl ether and n-butyl acrylate. The thermal properties of the copolymers were determined by thermogravimetric analysis and differential scanning calorimetry. The mechanical tensile tests under temperature control revealed the mechanical features of the copolymers depending on their repeating structure and composition. The significant temperature dependence of the modulus and strain of the copolymers was also clarified. Then, the transparency, refractive indices, and birefringence properties of the copolymer films were evaluated. It was confirmed that the maleimide copolymers had negative orientational birefringence with small absolute values and positive photoelastic birefringence. The effect of the conformational structure of the N-phenyl groups on the thermal, mechanical, and optical properties of the copolymers was discussed.[a] S. Nagase, Prof. A. Matsumoto