다양한 제조방법을 통한 기체분리용 열전환 폴리벤조옥사졸 분리막

Abstract

Conversion of hydroxyl-containing polyimides into polybenzoxazole can be achieved by thermal rearrangement of the aromatic polymer chain with decarboxylation at elevated temperature. Synthetic methods to prepare polyimide precursors are important for the resulting thermally rearranged (TR) polymer membranes. Here, we report on the effect of several imidization methods on the properties of TR-polymer membranes. Thermal and chemical imidizations are the most common routes to prepare polyimides, and solution thermal imidization using an azeotrope is also widely used, especially to obtain soluble polyimide-containing functional groups. We report here on the syntheses of ortho-functional polyimides from 4,4’-hexafluoroisopropylidene diphthalic anhydrides and 2,2’-bis(3-amino-4-hydroxyphenyl) hexafluoropropane by three different imidization methods. Acetate-containing polyimide by chemical imidization and further silylation treatment, as well as hydroxyl-containing polyimides by thermal and azeotropic imidization are compared with respect to various properties of both precursor polyimides and thermally rearranged polybenzoxazole (TR-PBO) membranes, by using thermogravimetric analysis, free volume measurement, positron annihilation lifetime spectroscopy, and gas permeation properties.