THERMOBAROMETRY AND DIFFERENTIAL ENTHALPIMETRY OF SOME POLYETHYLENEGLYCOLS THERMAL MEMORY EFFECTS OF POLYMERS

In order to study the thermodynamic behaviour of polymers in relation to temperature and pressure, we have performed measurements using two techniques: the differential temperature scanning calorimetry in the i sobaric mode and the temperature scanning thermobarometry in the isoch oric mode. Two kinds of information might be extracted from the experi mental data obtained on specially treated samples of polyoxyethylenegl ycols (PEG) of different molar masses: one concerns the ''classical'' thermodynamic properties and the other refers to the kinetic aspect of the crystallization process involving thermal ''memory'' effects. Fir stly, we have determined the variation of properties associated with t he solid-liquid phase changes such as: fusion temperatures (T(f)), ent halpies (DELTAH), and Clapeyron slope (DELTAH/T.DELTAV) and also, for each phase, we have estimated thermal pressure coefficients at constan t volume (gamma(V)). Then, we have studied the effect of various speci fic thermal treatments (isothermal growth) on the subsequent ''develop er'' thermograms or thermobarograms to evidence ''memory'' effects. Th is procedure allows to estimate the temperature (and the remaining tim e) of the isothermal growth. The experiments of the slow cooling cryta llization permit to differentiate the broadened peaks of freezing obta ined at high cooling rates into more refined crystallization events.