Intrinsically microporous polyimides derived from norbornane-2-spiro-α-cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride

Abstract

Here, a series of intrinsically microporous polyimides (PIM-PIs) were prepared from norbornane-2-spiro-α-cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (CpODA) and archetypal contorted diamines, and their microstructures and gas transport properties were systematically investigated and compared with those of the counterparts derived from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). For certain diamines, the surface areas, interchain distances, and fractional free volumes (FFV) of the CpODA-derived PIM-PIs were considerably greater than those of the 6FDA-derived ones, and were in the range of 92–567 m2 g−1, 0.575–0.607 nm, and 0.194–0.246, respectively. Consequently, the CpODA-derived PIM-PIs overall displayed higher gas permeabilities and better gas separation performances compared to the 6FDA-derived ones. In particular, CpODA-TBDA2 and CpODA-DAT showed high H2 permeabilities (>600 Barrer) and moderate H2/N2 and H2/CH4 selectivities which approached or even surpassed the corresponding 2008 Robeson upper bounds. The excellent gas separation performance of these CpODA-derived PIM-PIs may be attributed to the contorted and bulky architecture of the CpODA residue, which led to reduced inter- and intra-molecular interactions and the formation of ultramicropores of <0.7 nm.