Based on the mathematical model of Hadj-Romdhane and Danner describing the chromatographic process in a packed column

the infinite dilution diffusion coefficients of benzene

toluene and ethylbenzene in polyethylene membrane were measured in a temperature range of 341.2 - 363.2K by inverse gas chromatography.The correlation of the experimental data was preformed by using the modified Vrentas-Duda free-volume equation where the hole free volume was introduced to replace the whole free volume in the Vrentas- Duda initial equation.The correlated results show that the modified equation is a quite good description of the relationship between observed diffusion data and temperature.Based on the modified equation

a new generalized free-volume equation was established.The parameters a and b in the new equation are independent of the type of solvent and temperature of system but dependent on the structure of the polymer

so the new equation has the predictive capability.Once the values of the two parameters are determined from some solvent diffusion data of a certain solvent in a certain polymer

the diffusion data of another solvent in this polymer can be predicted by using the new equation.The solvent diffusion data of polystyrene/solvent and poly(methyl methacrylate)/solvent systems reported in literature and those of polyethylene/solvent system measured in this work were applied to verify the predictive capability of the new equation.Meanwhile the predicted results of the former two systems by using the new equation were compared with those calculated from the predictive version of Vrentas-Duda free-volume equation.These two equations have similar predictive accuracy.