Intrinsically Microporous Polyimides Derived from 2,2′-Dibromo-4,4′,5,5′-bipohenyltetracarboxylic Dianhydride for Gas Separation Membranes

Abstract

This work aims to expand the structure–property relationships of bromo-containing polyimides and the influence of bromine atoms on the gas separation properties of such materials. A series of intrinsically microporous polyimides were synthesized from 2,2′-dibromo-4,4′,5,5′-bipohenyltetracarboxylic dianhydride (Br-BPDA) and five bulky diamines, (7,7′-(mesitylmethylene)bis(8-methyldibenzo[b,e][1,4]dioxin-2-amine) (MMBMA), 7,7′-(Mesitylmethylene)bis(1,8-dimethyldibenzo[b,e][1,4] dioxin-2-amine) (MMBDA), 4,10-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diamine (TBDA1), 4,10-dimethyl-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-3,9-diamine (TBDA2), and (9R,10R)-9,10-dihydro-9,10-[1,2]benzenoanthracene-2,6-diamine (DAT). The Br-BPDA-derived polyimides exhibited excellent solubility, high thermal stability, and good mechanical properties, with their tensile strength and modulus being 59.2–109.3 MPa and 1.8–2.2 GPa, respectively. The fractional free volumes (FFVs) and surface areas (SBET) of the Br-BPDA-derived polyimides were in the range of 0.169–0.216 and 211–342 m2 g−1, following the order of MMBDA > MMBMA > TBDA2 > DAT > TBDA1, wherein the Br-BPDA-MMBDA exhibited the highest SBET and FFV and thus highest CO2 permeability of 724.5 Barrer. Moreover, Br-BPDA-DAT displayed the best gas separation performance, with CO2, H2, O2, N2, and CH4 permeabilities of 349.8, 384.4, 69.8, 16.3, and 19.7 Barrer, and H2/N2 selectivity of 21.4. This can be ascribed to the ultra-micropores (<0.7 nm) caused by the high rigidity of Br-BPDA-DAT. In addition, all the bromo-containing polymers of intrinsic microporosity membranes exhibited excellent resistance to physical ageing.