Thermally rearranged polybenzoxazole copolymers incorporating Troger's base for high flux gas separation membranes

Abstract

A new class of thermally rearranged (TR) polymers was prepared via copolymerization of TR-able o-hydroxyl polyimide and non-TR-able polyimide incorporating highly rigid Tröger's Base (TB) units. The effect of TB content, type of TR-able diamine, and TR protocols on polymer properties and gas transport behaviors were thoroughly studied. TB moieties in the copolymers efficiently enhanced polymer rigidity and induced high Tg and TR temperature as confirmed by thermogravimetric analysis and dynamic mechanical analysis. Additionally, as the TB molar ratio increased, the interchain distances of precursor polyimides increased from 0.545 to 0.585 nm. The most important finding in this work was the synergistic effect between TR conversion and TB segments, which provide the optimum contents of TB in the copolymers. As a result, 6F6FTB-0.3-450 presented a maximum d-spacing value of 0.609 nm and excellent gas separation performance of 1567 Barrer for H2 and 1944 Barrer for CO2 along with a selectivity of 18.6 for H2/CH4 and 23.07 for CO2/CH4, surpassing the corresponding 2008 upper bounds. In addition, 6F6FTB-0.3 exhibited good plasticization resistance under CO2/CH4 mixed gas up to CO2 fugacity of ~15 bar.