GAS DIFFUSION IN POLYMERS OF INTRINSIC MICROPOROSITY VS GAS MOLECULAR PROPERTIES

Abstract: Polymers of intrinsic microporosity (PIMs) have a rigid and highly contorted polymer backbone, which prevents efficient packing1 and causes a high free volume. The latter confers to the PIMs a very high permeability, while the backbone rigidity is responsible for a high size selectivity2. The aim of this paper is the investigation of the role of the diffusion in the overall transport of gases in PIMs in comparison with traditional polymers used in gas separation membranes. Comparison of the diffusion coefficients in PIM-BTrip-TB with those in rubbery PEBAX®2533 and in glassy Teflon AF2400 demonstrates an exceptionally high molecular sieve-like size-selectivity for the larger gas molecules in the PIM due to its extremely stiff polymer structure (Fig.1). The size-sieving properties are related to the PIMs structure and to the molecular properties of the penetrant gas. The two distinct trends in the size dependence of the diffusion coefficients suggest different transport mechanisms for small and large molecules. The experimental transport parameters, determined by the so-called time lag method, will be supported by molecular modeling studies and explained in relationship with the effective size of the penetrant. Fig. 1 Diffusion coefficient in polymers as a function of the molecular diameter of the gas 4-6 Acknowledgements: This research received funding from the EU's Seventh Framework Program, GA 608490, project M4CO2. [1] Carta M et al.; Science 339, 303-307, 2013. [2] Rose I.et al. Nature Materials 16, 932-937, 2017. [3] Rose I.et al. ACS Macro Lett 4, 912-915, 2015. [4] Bernardo P et al.; Sep Purif Technol 97, 73-82, 2012. [5] Jansen JC, Friess K, Drioli E J Memb Sci 367, 141-151, 2011. [6] Teplyakov V, Meares P Gas Sep Purif 4, 66-74 1990.