Aromatic polysulfone copolymers for gas separation membrane applications

New polysulfone (PSF) copolymers from bis(4-fluorophenyl)sulfone and based on equimolar mixtures of the rigid/compact naphthalene moiety with bulky connectors from bisphenols: tetramethyl, hexafluoro, and tetramethyl hexafluoro, respectively, were synthesized to measure significant physical properties related to the gas separation field. The flexible and transparent polymer dense films TM-NPSF, HF-NPSF and TMHF-NPSF show high glass transition temperatures Tg ≅ 230 °C and high decomposition temperatures TD ≅ 400 °C (10 wt.% loss, in air). Free volume cavity sizes, as determined by PALS, are in the range of 94–139 Å3. Their gas permeability and selectivity combinations of properties, measured at 35 °C and 2 atm, are very attractive since their selectivity for the pair of gases H2/CH4, O2/N2, and CO2/CH4 are higher than those for commercial PSF membranes, having similar or superior permeability coefficients for the most permeable gases H2, O2, and CO2. Especially important is the tetramethyl naphthalene polysulfone TM-NPSF membrane which reports selectivities for H2/CH4, O2/N2 and CO2/CH4 of 122, 7.6 and 38 with corresponding permeability coefficients (in Barrers) of 17 for H2, 1.2 for O2, and 5.2 for CO2. These results are interpreted in terms of free volume size and glass transition temperature together with the respective contribution of gas solubility and diffusivity to the overall selectivity coefficients.