• membranes;
  • separation techniques;
  • polycondensation;
  • thermal properties;
  • mechanical properties


In this article, three novel polymers based on poly(2,5-benzimidazole) (ABPBI) were synthesized by introducing propyl, isobutyl or n-butyl groups to its side chain through an alkyl substitution reaction. FTIR and 13C NMR were applied to confirm the formation of corresponding chemical groups. Their physical properties including crystallinity, thermal stability, mechanical strength, and micro-morphology were also characterized. Their solubility in common solvents were also tested to see if the modification will bring any improvement. Gas permeation properties of three derivative membranes prepared by a casting and solvent-evaporation method were tested with pure gases including H2, N2, O2, CH4, and CO2. It has been revealed that gas with a smaller molecular size owned a larger permeability. This means gas permeation in all prepared membranes should be diffusivity selective. Among all three modified ABPBI membranes, isobutyl substitution modified ABPBI (IBABPBI) showed the best selectivity of H2 over other gases such as N2 (∼185) and CO2 (∼6.3) with a comparable permeability (∼9.33 barrer) when tested at 35°C and 3.0 atm. Testing temperature increase facilitated gas permeation for all three membranes obviously; while in term of gas selectivity temperature increase showed diverse alteration because it brought variable impact on gas solubility of different gases. Even so, IBABPBI membrane still owned acceptable selectivity of H2 over N2 (∼118) and CO2 (∼6.3) with an almost doubled permeability (∼17.5 barrer) when tested at 75°C and 3.0 atm. Additional tests showed that running at high pressure did not bring any obvious deterioration to gas separation performance of IBABPBI membrane. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40440.