Cardo polyimides/TiO2 mixed matrix membranes: Synthesis, characterization, and gas separation property improvement

Abstract

This paper reports the synthesis of a novel cardo type polyimide PI(BTDA–BAPF–DMMDA) based on 3,3′,4,4′-benzophenone-tetracarboxylic dianhydride (BTDA), 9,9′-bis (4-aminophenyl) fluorine (BAPF) and 4,4′-biamino-3,3′-dimethyldiphenyl-methane (DMMDA) using the low temperature solution copolymerization method, and cardo polyimide/TiO2 mixed matrix membranes (MMMs) were prepared by blending of TiO2 sol and the PI solution. The incorporation of the cardo groups was achieved through the reaction between the free –COOH of polyamide acid (PAA) and the –NH2 of the BAPF. The chemical structure and physical properties of membrane material were characterized using FTIR, 1H NMR, DSC and XRD. Results showed that the MMMs containing 24wt% of TiO2 sol were nano-composite membranes with strong interactions between inorganic TiO2 phase and organic PI phase. Compared with PI(BTDA–DMMDA) membrane, the addition of BAPF and TiO2 greatly improved the gas separation properties of cardo PI membranes and MMMs. The gas permeation (PO2) and ideal separation factor (aO2/N2) of the cardo polyimide PI/TiO2 membrane with a BAPF: BTDA molar ratio of 0.15:1 and TiO2 content of 24wt% were 4.5Barrer and 15.8 respectively, which were a respective 9.4 and 4.6 times higher than that of the PI(BTDA–DMMDA) membrane. The PO2 and aO2/N2 of the cardo polyimide/TiO2 MMMs prepared in this work were beyond Robeson’s trade-off upper bound, highly promising for future gas separation application.