2, University of California, Berkeley, Berkeley, California, United States
3, University of California, Berkeley, Berkeley, California, United States
4, Lawrence Berkeley National Laboratory, Berkeley, California, United States
5, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Polymer membranes are the material of choice for many gas separations owing to their high performance, scalable synthesis, and easy processing. However, they suffer from a fundamental permeability/selectivity tradeoff that defines the “upper bound” limitations of this technology.1 Membranes that perform at or above the upper-bound can be achieved through the thoughtful design of polymers containing significant microporosity and rigid backbone chemistries.2
Thermally rearranged polybenzoxazoles excel in this regard.3 Produced through high-temperature solid-state reactions that alter the chain packing of a precursor polyimide, these polymers display enhanced porosity and narrow pore size distributions, placing their performance at or above the upper bound for many relevant gas pairs.
Here, we demonstrate the synthesis and gas separation performance of a novel family of thermally rearranged polybenzoxazoles containing a backbone contortion of exceptional rigidity. The design of these polymers incorporates chemical functionalities featured in other state-of-the-art gas separation membranes into polyimides with ortho-functional groups (PIOFGs), which are subsequently thermally rearranged. Synthesis of the precursor polyimides and the pore network evolution during thermal rearrangement will be discussed. Additionally, we will examine gaseous analyte-polymer matrix interactions in the context of gas separation performance. These findings offer new insights into the design of gas separation membrane polymers and provide a path forward for further optimization of thermally rearranged polymers.
1) Robeson, L. M. J. Membr. Sci. 2008, 320, 390–400.
2) Freeman, B. D. Macromolecules 1999, 32, 375–380.
3) Robeson, L. M.; Dose, M. E.; Freeman, B. D.; Paul, D. R. J. Membr. Sci. 2017, 525, 18–24.