Analysis of the Transport Properties of Thermally Rearranged (TR) Polymers and Polymers of Intrinsic Microporosity (PIM) Relative to Upper Bound Performance

The properties of polymers which lie along the upper bound are not necessarily determined purely by diffusion selectivity. For many materials, solubility selectivity helps push these limits, while diffusion selectivity is dominant for select gas pairs. A critical analysis of the comparison of diffusion selectivity, solubility selectivity, diffusivity, and solubility constants has been used to analyze the transport properties of thermally rearranged (TR) polymers and polymers of intrinsic microporosity (PIMs), two types of polymers which consistently preform at or beyond the polymer upper bound for select gas pairs (O₂/N₂ and CO₂/N₂). PIMs and TR polymers have higher diffusion coefficients than glassy polymers with similar size sieving abilities and have high O₂ and CO₂ solubility. Additionally, the previously determined diffusion gas kinetic diameters, d_g, provide the best correlation with diffusion coefficients of PIMs and TR polymers and serve to better analyze transport properties of upper bound materials.  Based on this analysis of diffusion and solubility data for PIMs and TR polymers, upper bound performance can be achieved when diffusion selectivity, diffusion coefficients, and gas solubility are all maximized.