Enthalpy Relaxation of Polystyrene at Different Molecular Weight Using Fast Calorimetry

The enthalpy recovery of polystyrene materials with narrow molecular weight distribution is studied by means of fast calorimetry. Two different molecular weights, Mw, have been investigated, namely 2000K and 212k. Intrinsic isotherm experiments at aging temperatures ranging from above to below the nominal Tg have been reported. The effect of the cooling rate on the glass transition temperature is also exanimated and it is showed that the cooling rate-dependence of the Tg is Vogel-Fulcher and not Arrhenius. The main finding is that the enthalpy recovery kinetics is not affected by the molecular weight showing that the contribution to free volume related due to chain terminals is negligible in the molecular weight range (212k-2000k) analysed in this paper.