A highly rigid and gas selective methanopentacene-based polymer of intrinsic microporosity derived from Tröger's base polymerization†
Polymers of intrinsic microporosity (PIMs) have been identified as potential next generation membrane materials for the separation of gas mixtures of industrial and environmental relevance. Based on the exceptionally rigid methanopentacene (MP) structural unit, a Polymer of Intrinsic Microporosity (PIM-MP-TB) was designed to demonstrate high selectivity for gas separations. PIM-MP-TB was prepared using a polymerisation reaction involving the formation of Tröger's base linking groups and demonstrated an apparent BET surface area of 743 m2 g−1 as a powder. The microporosity of PIM-MP-TB was also characterized by chain packing simulations. PIM-MP-TB proved soluble in chlorinated solvents and was cast as a robust, free-standing film suitable for gas permeation measurements. Despite lower gas permeability as compared to previously reported PIMs, high selectivities for industrially relevant gas pairs were obtained, surpassing the 2008 Robeson upper bound for H2/CH4 and O2/N2, (e.g., PO2 = 999 Barrer; αO2/N2 = 5.0) and demonstrating a clear link between polymer rigidity and selectivity. Upon aging, the permeability data move parallel to the Robeson upper bounds with a decrease of permeability, compensated by a related increase in selectivity. Mixed gas permeation measurement for CO2/CH4 and CO2/N2 mixtures confirmed the excellent selectivity of PIM-MP-TB for potentially relevant separations such as biogas upgrading and CO2 capture from flue gas. Importantly, unlike other high performing PIMs, PIM-MP-TB is prepared in four simple steps from a cheap starting material.
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