A chromatographic technique for measuring activity coefficient of solvent at infinite dilution of solvent has been applied to polymer-solvent systems. The solid support is coated with polymer; a small amount of solvent is introduced into the carrier; its retention time is measured and used to calculate the activity coefficient. Basing on activity coefficients at different temperatures

the partial molal heat of mixing of the solvent in the stationary liquid has been calculated. Experimental results are given for benzene

toluene with polysty-rene at temperature range from 76℃ to 180℃.