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 ar omatic dianhydrides. Methyl- and/or tert-butylcatechols were silylated at t he OH groups and the resulting bistrimethylsilyl derivatives were used as n ucleophilic 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 diamine s such as 1,3-diamino-2,4,6-tetramethylbenzene, 1,4-diamino-2,3,5,6-tetrame thylbenzene, 3,3'-dimethoxybenzidine, 3,3',5,5'-tetramethylbenzidine, or 2, 2-bis(4-aminophenyl)hexafluoropropane. In total, 21 polyimides were isolate d 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 sel ected polyimides in a time-lag apparatus at feed pressures below 1 bar. A c orrelation between the dianhydride monomer structure and gas permeability w as found and discussed.