Synthesis and Characterization of New Polysulfones Containing Bulky Bridging Moieties for Gas Separation Membranes

Polysulfones are widely used polymer membranes for important commercial gas separations due to their excellent thermal and chemical resistance, mechanical stability and ease of synthesis. However, there is significant room for advancement of polysulfone membranes’ gas separation performance through innovative molecular design. Here, a series of new polysulfones have been synthesized from a standard diphenylene sulfone with either triptycene and/or phenolphthalein as the bulky bridging unit in the polymer backbone. The composition and chain architecture of this new series of polysulfones were systematically varied to investigate the influence of the rigid, bulky triptycene and phenolphthalein structures on fractional free volume, chain rigidity, and gas transport properties. Incorporation of the triptycene unit provided increased fractional free volume and higher chain rigidity, leading to excellent combinations of permeability and selectivity relative to the phenolphthalein-based polysulfone as well as relevant commercial membranes and previously reported polysulfones. In particular, the triptycene-based polysulfone showed significantly improved selectivities for all gas pairs tested, due to the intrinsic internal free volume of the triptycene unit. For example, the triptycene-based polysulfone displayed an ultrahigh H₂/CH₄ selectivity of 156 and an O₂/N₂ selectivity of 7.7, along with nearly doubled H₂ permeability and ∼21% higher O₂ permeability compared to commercial Bis-A polysulfone. Additionally, the triptycene-based polysulfone showed strong resistance to physical aging with little change in performance after 130 days.