Polymer ultrapermeability from the inefficient packing of 2D chains


The promise of ultrapermeable polymers, such as poly(trimethylsilylpropyne) (PTMSP), for reducing the size and increasing the efficiency of membranes for gas separations remains unfulfilled due to their poor selectivity. We report an ultrapermeable polymer of intrinsic microporosity (PIM-TMN-Trip) that is substantially more selective than PTMSP. From molecular simulations and experimental measurement we find that the inefficient packing of the two-dimensional (2D) chains of PIM-TMN-Trip generates a high concentration of both small (<0.7 nm) and large (0.7–1.0 nm) micropores, the former enhancing selectivity and the latter permeability. Gas permeability data for PIM-TMN-Trip surpass the 2008 Robeson upper bounds for O2/N2, H2/N2, CO2/N2, H2/CH4 and CO2/CH4, with the potential for biogas purification and carbon capture demonstrated for relevant gas mixtures. Comparisons between PIM-TMN-Trip and structurally similar polymers with three-dimensional (3D) contorted chains confirm that its additional intrinsic microporosity is generated from the awkward packing of its 2D polymer chains in a 3D amorphous solid. This strategy of shape-directed packing of chains of microporous polymers may be applied to other rigid polymers for gas separations.

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Figure 1: A comparison of the macromolecular chain structures of PIM-TMN-Trip and PIM-TMN-SBI and their packing.
Figure 2: Data from the physical characterization of PIM-TMN-Trip (red) and PIM-TMN-SBI (blue).
Figure 3: High permeability regions of Robeson plots for important gas pairs.


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The research leading to these results has received funding from the Horizon 2020/FP7 Framework Program under grant agreement no. 608490, project M4CO2 and from the EPSRC (UK) grant numbers EP/M01486X/1 and EP/K008102/2. This work was also supported by the US National Science Foundation (DMR-1604376) and the Leverhulme Trust, UK (RPG-2014-308). High-performance computational resources were provided by the University of Florida Research Computing and the Research Computing and Cyberinfrastructure unit at Pennsylvania State University.

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I.R. prepared PIM-TMN-Trip. C.G.B. prepared PIM-TMN-SBI and performed the crystallographic study of the monomers. M.C. prepared the films for gas permeability and coordinated the experimental part of the project. B.C.G. verified the synthesis of PIM-TMN-Trip and performed the WAXS analysis. E.L. performed the high-temperature gas permeability measurements. M.C.F. performed the gas adsorption measurements and Horvath–Kawazoe analysis of pore-size distribution and designed the high-temperature gas permeability experiments. P.B. designed and performed the film conditioning protocol and carried out the elaboration of the single-gas permeability data to evaluate the transport parameters (Table 1: data series 1–5, 8–10). C.G. performed the single gas permeability measurements (Table 1: data series 1–5, 8–10), A.F. performed the single gas permeability measurements (Table 1: data series 6) and the elaboration of the data. J.C.J. performed the mixed gas experiments, the density and tensile strength analysis and supervised the gas permeability work and data elaboration. K.E.H. devised the methodology for simulation and analysis of the chain packing of PIMs related to PIM-TMN-SBI. T.P.L.A. performed the simulation and analysis of the chain packing of PIM-TMN-Trip. C.M.C. designed and supervised the chain-packing simulation work. N.B.M. designed the polymers and prepared the manuscript with input from all of the other authors.

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Correspondence to Neil B. McKeown.

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Rose, I., Bezzu, C., Carta, M. et al. Polymer ultrapermeability from the inefficient packing of 2D chains. Nature Mater 16, 932–937 (2017). https://doi.org/10.1038/nmat4939

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