Chain dynamics of high molecular weight polyethylene as observed from heats of dissolution in slow calorimetry

The Setaram C80 calorimeter with large cells permits accurate measurements of heats in dilute solution. Slow calorimetry is well suited to follow slow phase changes unnoticeable by fast calorimetry. Heats of solution of nascent high molecular weight polyethylene (HMWPE) have been obtained in a slow T-ramp (v=1–12 K-h^–1) in a variety of solvents. A new contribution to the enthalpy of fusion of polyolefins has been found. The total heat of dissolution thus contains two contributions due (1) to the melting of orthorhombic crystals and (2) the disordering of a network of entangled chains. An investigation is made of the new contribution (2), which can evolve at low temperature since strain does not build up due to the solvent. Conditions to change the range of temperature at which the second contribution evolves (nature of the solvent, rate of heating, concentration, cycles of dissolution/crystallization) are investigated.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30-June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.