Gas transport properties of poly(ether-b-amide) segmented block copolymers

The permeation properties of H-2, N-2, and CO2 were determined at 35 degree s C and pressures up to 15 atm in phase-separated polyether-b-polyamide seg mented block copolymers. These polymers contain poly(ethylene oxide) [PEO] or poly(tetramethylene oxide) [PTMEO] as the rubbery polyether phase and ny lon-6 [PA6] or nylon-12 [PA12] as the hard polyamide phase. Extremely high values of polar (or quadrupolar)/nonpolar gas selectivities, coupled with h igh CO2 permeability coefficients, were observed. CO2/H-2 selectivities as high as 9.8 and CO2/N-2 selectivities as high as 56 were obtained in polyme rs with CO2 permeability coefficients of approximately 220 x 10(-10) cm(3)( STP) cm/(cm(2) s cmHg). As the amount of polyether increases, permeability increases. Gas permeability is higher in polymers with less polar constitue nts, PTMEO and PA12, than in those containing the more polar PEO and PA6 un its. CO2/N-2 and CO2/H-2 selectivities are higher in polymers with higher c oncentrations of polar groups. These high selectivity values derive from la rge solubility selectivities in favor of CO2. Because CO2 is larger than H- 2 and has, therefore, a lower diffusion coefficient than H-2, the weak size -sieving ability of the rubbery polyether phase, which is the locus of most of the gas permeation, also contributes to high CO2/H-2 selectivity. (C) 2 000 John Wiley & Sons, Inc.