Simultaneously enhanced gas permeability and selectivity of polyimide membranes by the regulation of interchain microenvironment

A novel methodology was proposed to simultaneously enhance both permeability and selectivity of polyimide membranes through the synergistic regulation of interchain spacing, inter-chain interactions, and functional groups, collectively referred to as 'interchain microenvironment regulation'. Through reacting the -NH 2 group on the bulky diamines with the C-Br group on the polymer chains, we successfully linked the chains by bulky diamines. The results confirmed that the introduction of bulky groups inhibited chain stacking, increased d-spacing and free volume, resulting in enhanced permeability. Moreover, the CO 2 /CH 4 selectivity was significantly enhanced due to the synergistic effect between interchain interactions and the amino groups. In particular, the PI-Br-6%-NAPD membrane demonstrated a permeability coefficient 5 times greater than that of pure PI, reaching 311.71 Barrer. And its CO 2 /CH 4 selectivity was 3.87 times higher than pure PI, with a value of 74.88. It exceeded the 2008 Robeson upper bound for gas separation performance. In addition, enhanced interchain interactions endowed the membrane with good plasticization resistance, with a plasticization pressure of up to 450 psi. Membranes modified with other diamines also exhibited excellent gas separation performance. This study provided a feasible method for effectively regulating the interchain microenvironment to achieve high-performance gas separation.