Study of binary interactions involving polyethylene and hydrocarbons by the melting point depression method

The thermodynamic interaction parameter, χφ, for a low-density polyethylene in p-xylene, ethylbenzene, and n-octane has been determined over a range of segment fraction, φ2, from 0.2 to 0.7 using the melting point depression method. Taking advantage of a unique feature of polyethylene, a new procedure has been proposed for evaluating the equilibrium melting points from data obtained by differential scanning calorimetry. The experimental χφ-φ2 relations conform well to the recent equation-of-state theory of polymer solutions. The exchange parameters of the model X12 and Q12 are accessible by a nonlinear least-squares algorithm. Apparently, the observed small values of χφ for the foregoing dispersion force interactions are originated from the negative contribution of the effective interaction energy as concluded by the present findings.