Gas separation membranes made through thermal rearrangement of ortho-methoxypolyimides

Abstract

ortho-Methoxypolyimides were prepared from 3,3'-dimethoxybenzidine (DMAB) and hexafluoroiso-propylidene diphthalic anhydride (6FDA). High molecular weights of the resulting polymers were achieved, and the physical properties of the materials were investigated. The polyimides exhibited excellent thermal properties and film-forming capabilities. Polyimides were treated at high temperatures to promote thermal rearrangement (TR) processes. The final composition of the TR polymers seems not to correspond to TR-polybenzoxazoles, as was the case when analogous ortho-hydroxypolyimides were exposed to similar thermal treatments. A detailed study was carried out to elucidate the actual mechanism of the thermal rearrangement, comparing ortho-hydroxypolyimides, ortho-acetylpolyimides and ortho-methoxypolyimides. Results led to the conclusion that the chemical nature of the final TR polymers attained from ortho-methoxypolyimides is complex since imide, lactam and benzoxazole groups all seem to be present after thermal treatment. Gas permeation properties exhibited by thermally treated ortho-methoxypolyimides compared well with those of other TR-PBOs, showing CO2 permeability of 540 Barrers.