Synthesis and Characterization of Highly Soluble and Oxygen Permeable New Polyimides Based on Twisted Biphenyl Dianhydride and Spirobifluorene Diamine

Abstract

The novel spirobifluorene diamine monomer, 2,7-bis-amino-2‘,7‘-di-tert-butyl-9,9‘-spirobifluorene, was obtained. The new organosoluble polyimides were prepared from spirobifluorene diamine containing bulky tert-butyl group and conventional dianhydrides as well as 2,2‘-bis(4‘ ‘-tert-butylphenyl)-4,4‘,5,5‘-biphenyltetracarboxylic dianhydride (BBBPAn) and 2,2‘-bis(4‘ ‘-trimethylsilylphenyl)-4,4‘,5,5‘-biphenyltetracarboxylic dianhydride (BTSBPAn), which are composed of a noncoplanar twisted biphenyl unit containing bulky p-tert-butylphenyl groups and/or p-trimethylsilylphenyl groups by high-temperature one step polymerization. The structures of polymers were confirmed by various spectroscopic techniques. The weight-average molecular weights and polydispersities of resulting polymers were in the ranges 48 300−183 900 and 2.10−3.26, respectively. The bulky and twisted noncoplanar structural feature confers an enhanced solubility of the polyimides because of a decrease in the degree of molecular packing and crystallinity while imparting a significant increase in both Tg and thermal stability by restricting segmental mobility. The new polyimides exhibit the high oxygen permeabilities (P(O2) = 18−121 barrer) and O2/N2 gas separation properties (P(O2)/P(N2) = 2.2−9).