Polymer-polymer miscibility and enthalpy relaxations

Abstract

Annealing of polymers below the glass transition temperature results in a decrease in enthalpy that is recovered during heating. The enthalpy recovery is visible as an endothermic peak in a differential scanning calorimetry (DSC) scan. The position of this peak depends on the thermal treatment given and on the structure of the material itself. Because different polymers behave differently, the phenomenon can be utilized to investigate polymer-polymer miscibility of polymers with similar Tg values. Therefore, by annealing the blends at the temperature of interest and subsequent sub-Tg annealing, one can monitor phase behavior resulting from the initial treatment by inspection of the enthalpy recovery. Two systems were investigated to illustrate this: an immiscible blend of poly(vinyl chloride) and poly(isopropyl methacrylate) and a miscible blend of poly(vinyl chloride) and poly(methyl methacrylate).