Characterization and transport properties of a novel aliphatic polyamide with an ethyl branch

The CO2 gas and water vapor transport properties of a novel aliphatic polyamide with an ethyl branch were investigated. The polymer was characterized with density measurements, differential scanning calorimetry, thermogravimetric analysis, and wide‐angle X‐ray diffraction analyses, and the amorphous and glassy nature of the polymer at the ambient temperature were confirmed. The CO2 sorption isotherm of the polymer appeared to obey the dual‐mode sorption isotherm, which was characteristic of the glassy state. The water vapor sorption below a relative humidity of 0.4 or 0.5 was explained in terms of the Brunauer–Emmett–Teller sorption mechanism, whereas that at a high relative humidity demonstrated a dissolution type of water vapor into the polyamide. The permeability coefficients of He, CO2, O2, and N2 gases through the membrane were as follows: P(He) > P(CO2) > P(O2) > P(N2). The novel polyamide membrane was more permeable to CO2, O2, and N2 gases than nylon 6 and nylon 66 membranes, containing a crystalline and hydrogen‐bonding nature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1955–1960, 2005