Tuning microcavities in thermally rearranged polymer membranes for CO2 capture.

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.

Molecular structure-dynamics relationships in glassy poly(isophthalamide)s as revealed by wide angle x-ray scattering, dielectric loss spectroscopy, and molecular modelling.

The effect of molecular structure on the gamma relaxation dynamics has been studied in a set of aromatic poly(isophthalamide)s. This polymer family differ in the bridge group between phenylene rings [hexafluoroisopropylidene (C(CF(3))(2)) or ether] and also in the presence of t-butyl groups (C(CH(3))(3)) as pendant substituent on the five position of isophthalic ring. The results obtained from wide angle x-ray scattering in the glassy state indicated that both (C(CF(3))(2)) and (C(CH(3))(3)) groups favor the separation between chains, which is reflected on different interchain average distances. Dielectric experiments showed that both bulky groups favor the mobility in the glassy state. Molecular modelling methods were used to know the kind of molecular motions associated to the dielectric relaxation observed below the glass transition temperature.