According to thermodynamic relation that the pressure of polymer liquids is the difference between thermal pressure and internal pressure

and the experimental isochors are good straight lines

an equation of state for polymer liquids is established. The thermal pressure is obtained by the principle of corresponding state and the internal pressure is derived from Lennard-Jones(6

12) potential. The equation of state contains three characteristic parameters which have clear physical significance and can be satisfactorily used to correlate pVT data of various polymer liquids. The correlation results with 18 homopolymers and 4 copolymers show that the total average absolute deviation of specific volume is 0.00042 cm38226;g-1 for the range of pressure from 0—50 MPa and 0.00063 cm38226;g-1 for full range of experimental pressure. This correlation results are better than those of the Simha-Somcynsky equation.