Gas Permeability and Selectivity in Thermally Modified Poly(oxyindole biphenylylene) Membranes Bearing a tert-Butyl Carbonate Group

The gas permeability and ideal selectivity in poly(oxyindole biphenylylene) polymers that bear a tert -butyl carbonate side group, PN-BOC, have been measured, at 35 °C and 2 bar. It is found that the thermal degradation of the thermo-labile side group, BOC, at moderate temperatures and times, is useful for designing membranes that overcome the typical trade-off between permeability and selectivity. TGA, FTIR-ATR, and DSC analysis reveal that thermal treatments of PN-BOC at 150 °C and short periods of time, 5–60 min, allow the design of membranes with better selectivity–permeability combinations than the pure PN-BOC precursor. For the gas pairs O 2 /N 2 and CO 2 /N 2, the PN-BOC 5 thermally treated membranes for 5 min show O 2 and CO 2 permeability coefficients higher by a factor of 2.3 with respect to that measured in PN-BOC, while retaining their selectivity. For the gas pairs H 2 /CH 4 and CO 2 /CH 4, the PN-BOC 60 thermally treated membranes for 60 min show a H 2 and CO 2 permeability coefficient higher by a factor of 1.7 and 1.4, respectively, while selectivity increases with respect to that of the PN-BOC precursor by 45% for H 2 /CH 4 and 24% for CO 2 /CH 4 .