(193ag) Gas Transport in Poly(arylene ether sulfones) with Finely Tuned Microstructure and Morphology

Polysulfones are widely used polymer materials for important industrial 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 macromolecular design and/or exquisite microstructure manipulation. Here, a series of new polysulfones have been synthesized from a standard diphenylene sulfone with select aromatic diols with bulky bridging unit such as 1,4-triptycene-1,4-diol (TRIP) and phenolphthalein (PHPHT) in systematically varied chemical composition and chain architecture for fundamental studies of structure-property relationship in polysulfones. Specifically, homopolymers (TRIP-PSF and PHPHT-PSF), random copolymers (TRIP-co-PHPHT PSF) and multiblock copolymers (TRIP-mb-PHPHT PSF) were prepared with well-controlled composition and chain architecture to investigate the influence of chemical structure and morphology on fractional free volume and gas transport properties of corresponding membranes.

Incorporation of the triptycene unit provided increased overall fractional free volume, higher chain rigidity as well as ultrafine microporosity, leading to excellent combinations of permeability and selectivity relative to the phenolphthalein-based polysulfone and previously reported polysulfones. For example, the triptycene-based polysulfone displayed an ultrahigh H₂/CH₄ selectivity of 159 and O₂/N₂ selectivity of 7.4, along with nearly doubled H₂ permeability and ~21% higher O₂ permeability compared to commercial Bis-A polysulfone. Variations in chain architecture (i.e., homopolymer vs. random vs. multiblock) have led to an unexpected yet exciting trend in gas separation performance. For example, a random copolymer (TRIP-co-PHPHT PSF) containing 1:1 molar ratio of TRIP and PHPHT showed significantly improved separation performance compared to its homopolymer components although its physical properties (e.g., T_g) lied expectedly in-between TRIP-PSF and PHPHT-PSF homopolymers. Specifically, random copolymerization has improved separation performance of TRIP-PSF homopolymer from just below the 1991 upper bound to above the 2008 upper bound for O₂/N₂ separation. Gas permeation test on multiblock copolymers are underway to further interrogate the effect of membrane morphology on gas transport properties, which is a largely unexplored structure parameter for glassy polymer membrane materials. In this paper, the synthesis, materials characterization, membrane properties and transport properties of this new series of polysulfones will be discussed, with a focus on elucidating underlying structure-property relationships for these new polysulfones.