Based on the expression of the index of coil interpenetration （i.e., the degree of coil overlap, ξb） of amorphous polymers in the bulk state proposed by Qian, the ξb was rewritten as ξb = ρb [η]θ/1.66 via Hory＇s intrinsic viscosity equation at them conditions. The ξb ofpoly （vinyl chloride） （PVC） dense membranes with different molecular weights and cellulose diacetate （CA） dense membranes prepared using different solvents were determined. The permeability, permeation coefficient （P） of nitrogen and permeation flux （J） of liquid through both membranes, respectively, was measured. P and J decreased exponentially with increasing ξb for PVC and CA membranes were revealed.
