New polyimides for gas separation. 2. Polyimides derived from substituted catechol bis(etherphthalic anhydride)s

A new synthetic procedure was elaborated allowing for the preparation of aromatic dianhydrides. Methyl- and/or tert-butylcatechols were silylated at the OH groups and the resulting bistrimethylsilyl derivatives were used as nucleophilic reaction partners for 4-chloro- or 4-nitro-N-phenylphthalimides. The bis(o-etherphthalimides) were transformed into the corresponding bis(o-etherphthalic anhydrides) (six known ones, two new ones). For comparison, a trimethyl substituted bis(p-etherphthalic anhydride) was prepared using the same route. These dianhydrides were polycondensed with aromatic diamines such as 1,3-diamino-2,4,6-tetramethylbenzene, 1,4-diamino-2,3,5,6-tetramethylbenzene, 3,3'-dimethoxybenzidine, 3,3',5,5'-tetramethylbenzidine, or 2,2-bis(4-aminophenyl)hexafluoropropane. In total, 21 polyimides were isolated and characterized. The permeabilities and apparent diffusion coefficients of the pure gases He, H-2, N-2, O-2, CO2, and CH4 were measured for 12 selected polyimides in a time-lag apparatus at feed pressures below 1 bar. A correlation between the dianhydride monomer structure and gas permeability was found and discussed.