Tuning microcavities in thermally rearranged polymer membranes for CO2 captureElectronic supplementary information (ESI) available: Detailed synthesis procedure and structural characterization of poly(o-hydroxylamide), WAXD analyses, modeling and PALS measurements. See DOI: 10.1039/c2cp23729f

Microporous materials have a great importance in catalysis, delivery, storage and separation in terms of their performance and efficiency. Most microporous materials are comprised of inorganic frameworks, while thermally rearranged (TR) polymers are a microporous organic polymer which is tuned to optimize the cavity sizes and distribution for difficult separation applications. The sub-nano sized microcavities are controlled by in situ thermal treatment conditions which have been investigated by positron annihilation lifetime spectroscopy (PALS). The size and relative number of cavities increased from room temperature to 230 C resulting in improvements in both permeabilities and selectivities for H 2 /CO 2 separation due to the significant increase of gas diffusion and decrease of CO 2 solubility. The highest performance of the well-tuned TR-polymer membrane was 206 Barrer for H 2 permeability and 6.2 of H 2 /CO 2 selectivity, exceeding the polymeric upper bound for gas separation membranes. Thermally rearranged polybenzoxazoles with tuned cavities for hydrogen purification and carbon dioxide separation even at high temperature were developed to apply for a syn gas separation.