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Twelve kinds of polyimide membranes have been prepared using three dianhydrides (including 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 3,3‘4,4‘-benzophenonetetracarboxylic dianhydride (BTDA), and 3,3‘4,4‘-biphenyltetracarboxylic dianhydride (ODPA)) and four diamines (including benzidine (BZD), bis(4-aminophenyl)phenyl phosphate (BAPP), 4,4‘-diaminodiphenylmethane (MDA), and 4,4‘-diaminodiphenyl ether (ODA)) via a two-step method. The polyimides were characterized by FT-IR, DSC, and wide-angle X-ray diffraction (WAXD). The permeation experiments of water + ethanol mixtures through 12 polyimide membranes were carried out at 333 K. The temperature dependence of pervaporation performances of ODA-based polyimide membranes is also investigated. The flux of ethanol + water mixtures through the polyimide membranes with the same dianhydrides increases following the order of BZD < ODA < MDA < BAPP. The permeation flux increases with increase in temperature and the relationships between the flux and temperature can be described by the Arrhenius equation. According to the Arrhenius equation, the active energies of water + ethanol mixtures in BTDA + ODA, BPADA + ODA, and ODPA + ODA membranes are (19.3, 26.0, and 30.6) kJ·mol-1, respectively. However, the relationship between the separation factor and the temperature is not so clear. In addition, the natural logarithm of flux J (ln J) increases linearly with the mean interchain distance.

The density and glass transition temperature (T g ) of 11 polyimides were investigated by experiments and predictions using the connectivity indices method to explore the structure-property relationships. The predicted results are in good agreement with the experimental data. The mean interchain spacings (d-spacings) of polyimides increase with the introduction of bridging groups, i.e., following the order: PDA < BZD < ODA < MDA < BDAF, while the densities increase in the order of MDA < BZD < PDA, and cohesive energy densities (CEDs) of polyimides change following the order of BDAF < MDA < ODA < BZD < PDA. In addition, the glass transition temperatures (T g 's) increase as the CEDs increase for the polyimides prepared from the same dianhydride and different diamines, whereas no certain correlation exists between T g 's and the values of the characteristic ratio (C 1 ). This indicates that the strength of interchain interaction influences the T g 's of polyimides much stronger than the chain flexibility.

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