Highly Thermally\nStable and Gas Selective Hexaphenylbenzene\nTroger’s Base Microporous Polymers

This study shows the multistep synthesis of a series\nof Tröger’s\nbase polymers of intrinsic microporosity (TB-PIMs) based on a hexaphenylbenzene\n(HPB) core, with a focus on evaluating their thermal stability, porosity,\nand CO<sub>2</sub> capture performance. Both ladder and linear structures\nwere prepared, designed to feature tunable nitrogen content and porosity.\nOur findings demonstrate that polymers with higher nitrogen content,\nsuch as tetra-TB-HPB, exhibit superior CO<sub>2</sub> affinity and\nselectivity, attributed to enhanced interactions with CO<sub>2</sub> and optimized micropore sizes. Linear TB-polymers 1 and 2 are also\nmade for comparison and show competitive performance in carbon capture,\nsuggesting that cost-effective, simpler-to-synthesize materials can\nachieve efficient gas separation. The study reveals that increased\nporosity significantly enhances CO<sub>2</sub> capacity and selectivity,\nparticularly in networked TB-HPB-PIMs with high surface areas and\nnarrow micropores, achieving values up to 544 m<sup>2</sup> g<sup>–1</sup>, CO<sub>2</sub> uptake of 2.00 mmol g<sup>–1</sup>, and CO<sub>2</sub>/N<sub>2</sub> selectivity of 45.6. The thermal\nproperties of these materials, assessed via thermogravimetric analysis\n(TGA), show that TB-HPB-PIMs maintain robust thermal stability in\nnitrogen atmosphere, with tetra- and hexa-TB-HPBs leading the series.\nHowever, in oxidative environments, denser polymers such as TB-HPB\nand linear TB-polymer 1 demonstrate higher performance, likely due\nto restricted air diffusion. Overall, our findings highlight the critical\nneed to balance porosity and thermal stability in TB-HPB-PIMs for\napplications in gas separation, carbon capture, and the potential\nfor these polymers as flame retardant materials. Tetra-TB-HPB stands\nout as the most promising material for CO<sub>2</sub> capture and\nthermal stability under inert conditions, while denser polymers like\nTB-HPB offer superior performance in oxidative environments.