Synthesis and Properties of a High-Molecular-Weight Polyimide Based on 4, 4'-(hexafluoroisopropylidene) Diphthalic Anhydride

Abstract

A soluble polyimide with high molecular weight was synthesized from 4, 4'-(hexafluoroiso propylidene) diphthalic anhydride (6FDA) and 2, 2’-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (BAPAF) via two-step polycondesation procedure involving the preparation of poly(amic acid) (PAA) followed by chemical imidization. Effect of synthesis parameters on polyimide molecular weight involving material ratio, imidization temperature and imidization catalyst were studied. Synthesized PI was analyzed with respect to their molecular weights, chemical structures and solubility through GPC, FTIR, XRD and solubility tests respectively. The results showed that a high-molecular-weight PI was successfully synthesized from 4, 4'-(hexafluoroisopropylidene) diphthalic anhydride and 2, 2’-bis (3-amino-4-hydroxyphenyl) hexafluoropropane with imidization at 80°C for 3h, material ratio of n(BAPAF):n(6FDA) equal to 1:1 and catalyst of n(triethylamine):n (pyridine) less than1:3. The obtained PI showed excellent solubility in polar aprotic organic solvents such as NMP, DMAc, DMSO, THF and Acetone. Poly(6FDA-BAPAF) PI, with high molecular weight and excellent solubility, which was synthesized under lower imidization temperature that was equal to 80°C,could be easily obtained and convenient to process, thus it is a potential material for membrane separation.