Gas sorption and characterization of poly(ether-b-amide) segmented block copolymers

The solubilities of He, H-2, N-2, O-2, CO2, CH4, C2H6, C3H8, and n-C4H10 we re determined at 35 degrees C and pressures up to 27 atmospheres in a syste matic series of phase separated polyether-polyamide segmented block copolym ers containing either poly-(ethylene oxide) [PEO] or poly(tetramethylene ox ide) [PTMEO] as the rubbery polyether phase and nylon 6 [PA6] or nylon 12 [ PA12] as the hard polyamide phase. Sorption isotherms are linear for the le ast soluble gases (He, H-2, N-2, O-2, and CH4), convex to the pressure axis for more soluble penetrants (CO2, C3H8, and n-C4H10) and slightly concave to the pressure axis for ethane. These polymers exhibit high CO2/N-2 and CO 2/H-2 solubility selectivity. This property appears to derive mainly from h igh carbon dioxide solubility, which is ascribed to the strong affinity of the polar ether linkages for CO2. As the amount of the polyether phase in t he copolymers increases, gas solubility increases. The solubility of all ga ses is higher in polymers with less polar constituents, PTMEO and PA12, tha n in polymers with more polar PEO and PA6 units. CO2/N-2 and CO2/H-2 solubi lity selectivity, however, are higher in polymers with higher concentration s of polar repeat units. The sorption data are complemented with physical c haracterization (differential scanning calorimetry, elemental analysis, and wide angle X-ray diffraction) of the various block copolymers. (C) 1999 Jo hn Wiley & Sons, Inc.