The modified van der Waals' model suggested by our previous work is extended to the liquid polymers in this paper. A relation between the thermal pressure coefficient and the density of polymer, which can be used to calculate the thermal pressure coefficients of polymers accurately at the wide range of temperature, is established. where ν and M are the specific volume of polymer and the molar mass of a segment respectively, and A is the characteristic constant. It is found that the size of a segment is about equal to three structural units for five polymers examined.

Key words: HIGHPOLYMER, INTRINSIC PRESSURE