Cell theory and equation-of-state of chain molecular systems: Application to polymer solids

We use the Lennard-Jones and Devonshire cell theory without any ad hoc simp lification of the cell potential to obtain the equation-of-state (EOS) for chain molecular systems. The interactions of the central segment with secon d and third shells of neighbors are taken into account. Numerical values of the cell integrals are given in tabular form along with interpolation expr essions that cover the range of PVT variables appropriate to polymers. Resu lts of comparison with EOS based on square-well form are also discussed. Ap plication of the theory to polymer glasses of diverse structures is found t o be quite successful in explaining the PVT behavior over a wide range of t emperatures both at atmospheric and elevated pressures. Further, scaled vol ume at the glass-transition temperature is discovered to be a corresponding state property. Turning to crystals, the theory is generally in good accor dance with the PVT data of three well-studied polymers both at atmospheric and elevated pressures. For linear polyethylene the agreement is good up to 42 kbar for the room-temperature isotherm. On the other hand, at higher te mperatures where the data are limited to 5 kbar, the agreement is determine d to be satisfactory for the three polymers. (C) 2001 John Wiley & Sons, In c.