Thermodynamics of polymer blends based on poly(ε-caprolactone)/poly(vinyl methyl ether)

Abstract

The miscibility of the system poly(ϵ-caprolactone)/poly(vinyl methyl ether), PCL/PVME, was investigated using differential scanning calorimetry (DSC), solution calorimetry, optical microscopy (OM), Fourier transform infrared spectroscopy (FTIR), dilatometry, and internal pressure. The system is semicrystalline and the PCL crystallinity is sensitive to the composition of the blend and to the thermal treatment performed. The presence of a single glass transition temperature for all compositions is considered as an index of miscibility in the amorphous phase, but the evolution of crystallization and melting peaks shows that phase separation phenomena occur upon heating the system just above the PCL melting point, according to a `lower critical solution temperature' behaviour. The process of mixing is markedly endothermic and this means that the system is immiscible in the liquid phase, i. e. just above the PCL melting point. FTIR experiments demonstrate the absence of specific interactions between the two components. OM was used combined with DSC to investigate the occurrence of a melting point depression which can be used to evaluate the χ12 parameter. Finally, dilatometric and internal pressure techniques were used to obtain the required data for the evaluation of the interaction parameter, χ12, following the Patterson approach. The resulting value of the χ12 parameter is always positive and higher than the critical value in the considered temperature range. This behaviour indicates, too, that the system is not miscible when it is heated above the PCL melting point.