High performance carbon molecular sieve membranes derived from hyperbranched polyimide precursors for improved gas separation applications

A series of hyperbranched polyimides (HBPI) were selected as precursors for the production of carbon molecular sieve membranes (CMSMs) and the gas separation performance of the resultant CMSMs was explored. By varying the monomer compositions of HBPI precursor polymers, the influences of degree of branching on pore size and distribution of the CMSMs are investigated and examined. A CO2 permeability of 1085 Barrer with CO2/CH4 selectivity of 52 is attained. Thermal analyses reveal that the chain rigidity of the precursors increases with the degree of branching, while the density of the CMSMs shows an opposite trend. In view of the unique network structure offered by the HBPI precursors, it is speculated that the rigid network of the HBPI with the highest degree of branching has facilitated the formation of ultra-micropores, giving rise to the more constrained structure and improved diffusivity selectivity. The unique hyperbranched network structure found in HBPI possesses great potential to producing CMSMs with superior performance.