Synthesis and characterization of highly soluble and oxygen permeable new polyimides based on twisted biphenyl dianhydride and spirobifluorene diamine

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 T-g and thermal stability by restricting segmental mobility. The new polyimides exhibit the high oxygen permeabilities (P(O-2) = 18-121 barrer) and O-2/N-2 gas separation properties (P(O-2)/P(N-2) = 2.2-9).