Highly permeable polyimides incorporating Troger's base (TB) units for gas separation membranes

Abstract

Two novel polyimides incorporating Troger's Base (TB) units, Bio-PITB-1 and Bio-PITB-2, were facilely synthesized from lignin-based imide-containing diamines via TB polymerization. The polymers exhibited excellent thermal stability, finely tuned microporous structures with high BET surface areas (-569 m(2) g(-1)), high fractional free volumes (similar to 0.224), and appropriate inter-chain distances (similar to 0.68 and similar to 0.38 nm). Mechanically tough BioPITB membranes were successfully achieved due to their high molecular weights (-1.24 x 10(5) g mol(-1)) and good solubility in organic solvents. Bio-PITBs presented superior gas transport properties with improved gas permeability compared to the previously reported PI-TBs as well as Bio-TBPIs prepared from the same lignin based dianhydrides but different synthetic routes. As a result, Bio-PITBs located near the 2008 upper bounds in H-2/CH4, H-2/N-2, and CO2/CH4 gas pairs with H-2 and CO2 permeabilities over 1000 Barrer. Furthermore, the effects of membrane drying protocols and physical aging on gas transport behaviors of Bio-PITBs were investigated.