Intrinsically microporous polyimides from p-phenylenediamine with fused cyclopentyl substituents for membrane-based gas separation

Abstract

In this study, a novel diamine, 1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene-9,10-diamine (DMNDA), was synthesized in six-steps using dicyclopentadiene and p-benzoquinone as the starting materials. Next, four polyimides of intrinsic microporosity (PIM-PIs) were prepared by the high-temperature polycondensation of DMNDA with four typical dianhydrides in m-cresol. The fractional free volumes (FFV) of these polymers were in the range of 0.193–0.216, decreasing in order of SBIDA > 6FDA > BTA > CpODA. Furthermore, the introduction of bulky fused cyclopentyl substituents resulted in free volume elements of ∼ 0.5 nm, evidenced by visible shoulders in the WAXD patterns. Consequently, the gas permeability and perm-selectivity of 6FDA-DMNDA were greater than those of the benchmark polymer, 6FDA-Durene. SBIDA-DMNDA and BTA-6FDA-DMNDA exhibited high H2 permeability, but modest H2/CH4 and H2/N2 selectivity, approaching the 2008 Robeson upper bounds. Furthermore, SBIDA-DMNDA showed a CO2 permeability of 1439 barrer and a CO2/CH4 selectivity of ∼ 14 at 10 bar, approaching the 2018 upper bound for CO2/CH4 mixed-gas separation.