Decarboxylation Cross-Linking of Triptycene-Based Tröger’s Base Polymers for Gas Separation

Previous studies demonstrate that decarboxylation cross-linking improves both the plasticization resistance and gas separation properties of a polymer precursor. However, when the decarboxylation reactions were carried out at low temperatures (350–400 °C), gas permeability was low because of the intrinsically low gas permeability of the polymer precursor. In this work, we synthesized a series of highly permeable polymer precursors having a triptycene-based Tröger’s base (TB) backbone structure and different amounts of carboxylic acid side groups. The TB polymer precursors were heated in a temperature range of 275–400 °C to induce cross-linking. After cross-linking, a more open polymer structure was obtained, resulting in an increase in the free volume fraction and gas permeability. The lowest cross-linking temperature was 350 °C and the separation performances of the cross-linked polymers surpassed the “2008 Robeson Upper Bound” for the CO 2 /CH 4 and O 2 /N 2 gas pairs. Moreover, the cross-linked polymers were not plasticized by CO 2 at a pressure up to 30 bar.