O2 and N2 gas permselectivity of alternating copoly(vinylidene cyanide–vinyl acetate)

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Abstract
The sorption and permeation of oxygen and nitrogen in and through alternating copoly(vinylidene cyanide–vinyl acetate) [copoly(VDCN–VAc)] (Tg = 176°C) membranes annealed for different periods just below Tg, 160°C, were investigated over the pressure range from 100 to 1000 cmHg. The dual‐mode sorption and mobility models were used to analyze the results. A sub‐Tg annealing of copoly(VDCN–VAc) caused a slight decrease in the amount of sorption in the membranes. This decrease in the amount of oxygen and nitrogen sorption can be attributed to a decrease in the Langmuir sorption capacity term, C′H, with increasing sub‐Tg annealing period. The densification of copoly(VDCN–VAc) membranes caused simultaneously by the annealing remarkably reduced diffusion coefficients for both gases. The reduction in diffusion coefficients of Langmuir mode, DH, for both gases was found to be larger than that of Henry's law mode, DD. Furthermore, permselectivity of oxygen to nitrogen, the ratio of permeability coefficient of oxygen to nitrogen (PO2/PN2), reached to 11.8 for the copoly(VDCN–VAc) annealed for 30 h. Evidently the reduction of DH and DD for nitrogen with increasing annealing period was much larger than that for oxygen.