(650f) Tailoring Free Volume Architecture in Polyimide Gas Separation Membranes Using Iptycene Structures
Development of robust polymeric membranes that can overcome the limits of permeability-selectivity tradeoff has been the main research focus in the field of membrane gas separation. Critical in the function of such polymeric membrane materials is the control of the free volume architecture defined by the chemistry and polymer chain dynamics to achieve excellent size sieving properties for gas separation. We have been working on using intriguing iptycene structure as the building block to construct hierarchically controlled “molecular cavity” architecture in polyimide membranes to simultaneously improve the permeability and selectivity. The rich structural hierarchy and versatile chemistry possibilities of iptycene structures offer unique opportunities for generating well-defined “molecular cavities” that are tunable to enable fast and selective molecular transport in these polyimide membranes. Our first generation of iptycene-polyimides prepared from triptycene-diamine and commercial 6FDA dianhydride showed very attractive gas separation performance because of the high fractional free volume introduced by the triptycene moieties. This talk will focus on two new generations of iptycene-containing polyimide membranes that were developed recently based on newly synthesized pentiptycene-diamine and triptycene-dianhydride, respectively. Specifically, replacing triptycene units with even bulkier pentiptycene moieties in the polyimide structure greatly improved the gas permeabilities with little loss in the selectivity due to larger and tunable internal free volume associated with pentiptycene units. To further manipulate the chain dynamics and free volume architecture, a triptycene-based dianhydride monomer was designed and synthesized to replace the commercial 6FDA dianhydride in the polyimide synthesis leading to highly rigid, fully iptycene-containing polyimides. These new series of iptycene-containing polyimide membranes will be discussed in depth regarding their synthesis, characterization, and gas transport properties. In particular, the fundamental correlations between the microscopic structures and macroscopic transport properties will be discussed for these new gas separation membranes.