Remarkably Improved Gas Separation Performance of Polyimides by Forming "Bent and Battered" Main Chain Using Paracyclophane as Building Block.

The design and development of highly permeable, selective and stable polymer membranes are great challenges in the gas separation industry. Herein, we constructed two intrinsic microporous polyimides (6FPCA and 6FMCA) derived from two isometric diamines (PCA and MCA), which were synthesized by palladium catalyzed C—N coupling reaction. The PCA and MCA diamines contain a hollow beaded structure of 2,2′-paracyclophane as a building block with a specified window size of 3.09 Å. The chemical structures of monomers, polyimides were confirmed by NMR, FTIR, and elementary analysis. 6FPCA and 6FMCA exhibit good solubility, excellent thermal stability, and mechanical properties. 6FPCA exhibits much larger microporosity (434 versus 120 m2·g−1), FFV (0.22 versus 0.15), d-spacing (6.9 versus 5.9 Å), and over 10 times higher permeability with a very little decrease in selectivity than the corresponding polyimide (6FpA) with a plane structure, which remarkably increased their separation performance from far below the 2008 Robeson Upper bounds to reach these limitations for O2/N2 and CO2/CH4. Additionally, the 6FPCA also demonstrates good plasticization resistance, moderate aging properties, and high CO2/CH4 mixed-gas separation performance. These results indicate that paracyclophane subunit can be successfully incorporated into polymers to enhance their ultra-microporosity and separation properties, which open a new avenue for developing high performance gas separation membranes with topological ultra-micropores. [ABSTRACT FROM AUTHOR]