Title: New Meets Old: Accelerating Membrane-based CO2 Separation by Soluble Nanoporous Polymer Networks Produced Via Mechanochemical Oxidative Coupling

Achieving homogeneous dispersion of nanoporous fillers within membrane architectures remains a great challenge for mixed-matrix membrane (MMMs) technology. Imparting solution processability of nanoporous materials would help advance the development of MMMs for membrane-based gas separations. For the first time, we report a novel mechanochemical-assisted oxidative coupling polymerization strategy to create a new family of soluble nanoporous polymer networks. The solid-state ball-milling methodology affords inherent molecular weight control over polymer growth and therefore provides unexpected solubility for the resulting nanoporous frameworks. MMM-based CO2/CH4 separation performance was significantly accelerated by these new soluble fillers. We anticipate this facile protocol will facilitate new possibilities for the rational design and synthesis of soluble nanoporous polymer networks and promote their applications in membrane-based gas separations. The interest in curtailing greenhouse gas emissions through capture of CO2 from flue gas and removal of CO2 from synthesis gas (mainly CH4 and H2) has inspired an extensive search for novel methodologies capable of efficient separation of CO2. Membrane-based CO2 separation technology has gained significant attention as a promising solution, due to its lower energy costs and reduced environmental impact. Among the various types of CO2-selective membranes, polymeric membranes have been the most widely studied, whereas they suffer from a well-known compromise between the permeability and selectivity as shown in the upper bound Robeson curves. Coupling polymer matrices with nanoporous filler particles, for example nanoporous organic networks (NPNs), could lead to synergistic improvements in membrane-based CO2 separation performance, but difficulties are encountered in achieving homogeneous dispersion of these nanoporous fillers within MMMs. Although significant progresses have been made in the synthesis of NPNs by linking multidentate organic scaffolds towards a wide variety of potential applications, it remains a great challenge to fabricate soluble nanoporous organic networks (SNPNs) through a rapid and straightforward method, mainly because it is very difficult to control the growth of polymeric architectures. Ladder-like “polymers of intrinsic microporosities” (PIMs) with contorted sites have been reported as a family of soluble porous polymers and successfully utilized in membrane-based gas separations. Recently, Cooper el al. pioneered another successful synthesis of soluble porous polymer using a hyperbranching-based approach based on Suzuki-catalyzed aryl-aryl coupling copolymerization. The obvious downside is the use of the costly Pd-containing catalyst and necessity of complicated organic synthetic processes, significantly limiting the potential for practical implementation. In this regard, the search for novel techniques that are capable of efficient and facile synthesis of SNPNs is of great interest, importance, and urgency. Imparting solution processability would help advance development of NPNs and enable the combination of unique features such as intrinsically high porosity towards MMM-based CO2 separations. In this work, we report a novel strategy for the rationallydesigned synthesis of a novel family of SNPNs. The key to our approach lies in the use of a mechanochemical (MC)-assisted FeCl3-mediated oxidative coupling polymerization (OCP). MC synthesis strategy has been demonstrated as a versatile alternative technique that enables the preparation of nanoporous materials through sustainable solid-state assembly pathways. By using mechanochemisty to promote the oxidative polymerization, the molecular weight of the resulting materials can be controlled. Their homogeneous dispersion within membrane architectures were facilely realized, and MMM-based CO2/CH4 separation performance was significantly accelerated. A high CO2 permeability of 675 barrer together with a CO2/CH4 selectivity of [*] Dr. X. Zhu, Dr. C.C. Tian, T. Jin, Prof. S. Dai Department of chemistry, The University of Tennessee, Knoxville, Tennessee 37996-1600 Email: [email protected] Dr. C. W. Abney, Prof. S. Dai Chemical Sciences Division, Oak Ridge National Laboratory Oak Ridge, TN 37831, USA, Fax: (+1) 865-576-5235 Email: [email protected] Dr. X. Zhu, Dr. P. Zhang, Prof. H.-C. Zhou Department of chemistry, Texas A&M University, College Station, TX Dr. K.L. Browning, Dr. R. L. Sacci, Dr. G. M. Veith Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, United States Y.Y. Hua, Prof. G.P. Liu, Prof. W.Q. Jin State Key Laboratory of Materials-Oriented Chemical Engineering Jiangsu National Synergetic Innovation Center for Advanced materials Nanjing Tech University, Nanjing 210009, China. Email: [email protected]; [email protected] [**] Supporting information for this article is given via a link at the end of the document. Scheme 1. The synthesis route of soluble NPNs based on the oxidative coupling polymerization (OCP). 10.1002/anie.201710420 A cc ep te d M an us cr ip t Angewandte Chemie International Edition This article is protected by copyright. All rights reserved.