Per®aporation and sorption for the liquid mixture of benzene and cyclohexane by [ ( ) ] ( ) using poly bis phenoxy phosphazene PPOP membranes were characterized. Diffusi®ities, solubilities, interaction parameters, plasticization coefficients, and heats of sorption for benzene and cyclohexane in the membrane were determined from the ®apor sorption kinetics and isotherms, which were measured gra®imetrically by a continuous microbalance. Per®aporation operations offered a maximum selecti®ity of 3 at 35ЊC and the 35 ᎐ 50% feed concentration le®el of benzene. Normalized fluxes increased but the per-®aporation selecti®ity decreased slightly with temperature. The binary transport in the membrane was modeled by the solution᎐ diffusion model with an exponential form diffusi®ity to the concentration of each permeant. Coupling coefficients imbedded in the model were numerically determined by a proposed computation method. The model can illustrate not only concentration and diffusi®ity profiles for the permeants within the membrane, but their transport mechanism, which is consistent with the hypothesis of '' two layers'' in the membrane. The analysis of acti®ation energy for transport indicates that the permeation barrier for per®aporation is reduced much more than that of the single-®apor permeation through an unswollen membrane. 10 11 1 12 2 4 Ž . dC J l 2 2 sy , dz D exp A C q A C Ž .