Effect of structural isomerism on physical and gas transport properties of Troger's Base-based polyimides

The physical and gas transport properties of Troger's Base (TB)-based polyimides (PI-TBs) synthesized by isomeric monomers were rarely reported. Here, a series of PI-TBs was synthesized from two iso-ether dianhydrides [4,4'-oxydiphthalic anhydride (4,4'-ODPA)/3,4'-oxydiphthalic anhydride (3,4'-ODPA)] and two iso-biphenyl dianhydrides [3,3',4,4'-biphenyltetracarboxylic dianhydride (4,4'-BPDA)/3,4'-biphthalic anhydride (3,4'-BPDA)], with two diamines, 2,5-dimethyl-1,4-phenylenediamine (DPD) or 2,6-diaminotoluene (DAT). The solubility, microporosity, chain packing, mechanical performance and thermal stability, and gas transport properties were investigated for the PI-TBs derived from the isomeric dianhydrides. The polyimides derived from DPD and appropriate dianhydrides had better solubility and film-forming capability, mechanical properties, and higher gas permeability than those from DAT analogues. Furthermore, the polyimides based on different isomeric dianhydrides showed good solubility, mechanical properties, and high thermal stability and glass transition temperatures (T(g)s), up to 400 degrees C. The chemical structures of isomeric dianhydrides have a noticeable influence on the chain packing and gas separation performance of the PI-TBs. The PI-TBs with rigid 3,4'-/4,4'-BPDA residues showed microporosity and their BET values in the range of 235.2-324.9 m(2)/g. The PI-TB membranes from the 3,4'-BPDA showed both higher gas permeability and selectivity (H-2/CO2, H-2/CH4, CO2/CH4) compared to those from the 4,4'-BPDA. On the contrary, the PI-TB membranes from the 3,4'-ODPA had lower gas permeability with improved gas selectivity compared to those from the corresponding 4,4'-ODPA.

Automated summary

A series of Troger's Base (TB)-based polyimides (PI-TBs) with different physical and gas transport properties were synthesized by altering the isomeric monomers. The solubility, microporosity, chain packing, mechanical performance, thermal stability, and gas transport properties of the PI-TBs were investigated. The choice of different isomeric dianhydrides and diamines had a significant impact on the solubility, mechanical properties, and gas permeability of the resulting polyimides. The chemical structure of the isomeric dianhydrides also influenced the chain packing and gas separation performance of the PI-TBs.