Investigation on Anomalous Calorimetric Behaviors of Polystyrene and Triphenylmethyl Chloride Blends

Abstract

Polystyrene (PS), with three different molecular weights, and triphenylmethyl chloride blends were used to investigate their “cusp” in Tg-composition dependence by DSC. There exists a cusp in all three systems; with PS molecular weight increasing the critical concentration increases. The fitting results of three classical thermodynamics equations show the blends are not completely miscible. A free volume theory predicts the appearance of the cusp successfully. The dependence of PS content in amorphous phase of the mixtures on total PS concentration shows that when polymer concentration is low, the composition of the amorphous phase matrix is constant. For high polymer content blends, the relation indicates the polymer solution was completely amorphous and no crystalline phase appears, so it could be considered, approximately, as an “ideal solution.” The microphase separation, caused by molecular size asymmetry was proposed to explain the “cusp” in polymer–solvent systems. The investigation of heat capacity confirmed the theory proposed.