Thermal Properties of N-Phenylmaleimide-Isobutene Alternating Copolymers Containing Polar Groups to Form Intermolecular and Intramolecular Hydrogen Bonding

We have demonstrated that the alternating copolymers obtained from N -phenylmaleimides having hydroxy and carboxy substituents and isobutene show excellent thermal stabilities; namely, onset temperatures of decomposition higher than 350 °C and glass transition temperatures higher than 220 °C, depending on the structure and position of the polar groups in the N -phenyl group. The obtained copolymers were soluble in organic solvents, such as dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, and acetone, and transparent and brittle films were obtained by casting from their acetone solutions. The role of intermolecular hydrogen bonding for an increase in the glass transition temperature by the introduction of the polar groups was investigated by temperature-controlled IR spectroscopy. The formation of intramolecular hydrogen bonding for the N -2-hydroxyphenyl derivative was also revealed. The molecular conformations were discussed on the basis of the results of DFT calculations for the model compounds of the repeating unit in the copolymers.