Triptycene-Containing Polybenzoxazoles Membranes for Gas Separation

This paper reports on a new series of thermally rearranged polybenzoxazoles containing hierarchical triptycene unit for gas separation membranes that are ultra-selective and ultra-permeable with great potential for H₂ purification and CO₂ removal from natural gas. Triptycene moieties not only effectively disrupt chain packing allowing for microporous structure for fast mass transport, but also introduce ultra-fine microporosity via internal free volume enabling superior molecular sieving capability in the resulting PBO membranes. These triptycene-based polybenzoxazole (TPBO) membranes display among the highest gas selectivities for H₂ separations (i.e., α(H₂/N₂) = 96; α(H₂/CH₄) = 203) and natural gas purification (i.e., α(CO₂/CH₄) = 68) among existing glassy polymeric membranes, which has places TPBO membranes well above the 2008 upper bounds and even the most recent 2015 upper bounds. It is also demonstrated that microporosity and gas transport properties of TPBO films are highly tailorable by adjusting the copolymer composition and the ortho-functionality of the precursors. The highly diverse tunability, along with the excellent resistance towards membrane plasticization and physical aging, render the TPBO membranes with extremely versatile separation capability applicable for a wide range of important industrial separation processes. In this talk, synthesis and characterization of these new TPBO membranes will be presented. Disussions will focus on elucidating the fundamental relationship between microscopic structures with macroscopic transport properties for TPBO membranes. Mixed-gas permeation results and physical aging tests on these innovative membranes will be discussed as well.