AbstractA series of polymer/liquid crystal composite membranes, at several weight ratios, was prepared casting from a tetrahydrofuran solution of poly(vinyl chloride) (PVC) withN‐(4‐ethoxy‐benzylidene)‐4′‐butylaniline (EBBA). From the thermal analysis, microscopic observation, mechanical property, and gas permeation studies, the properties for a series of PVC/EBBA composite membranes were derived. DSC showed that PVC and EBBA were quite miscible and EBBA in composite membranes at below 30 wt was molecularly dispersed without forming crystal domains. Morphological observations exhibited that EBBA molecules interpenetrated in a continuous phase among the 3‐dimensional spongy networks of PVC matrix in the case of the 40/60 (PVC/EBBA, in wt ) composite membrane. Stable retention of EBBA in the composite membrane and its high mechanical durability might arise from such an aggregation structure. The permeability coefficients to oxygen gas,P02and nitrogen one,PN2through the 40/60 (PVC/EBBA) composite membrane showed a discontinuous jump with a several–tenfold increase in the vicinity of the crystal–nematic transition temperatureTKNof EBBA. The magnitudes ofP02and the separation factorsP02/PN2aboveTKNwere of the order of 10−9cm3(STP) cm−1s−1cm Hg−1and 2–3, respectively. The value ofP02/PN2reached a maximum just aboveTKN. TheP02−P02/PN2relationship aboveTKNexhibited an unusual behavior asP02/PN2inc
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