Melting behaviour and miscibility of poly(epsilon-caprolactone) plus poly(4-hydroxystyrene) blends

Differential scanning calorimetry has been used to study the melting behaviour, crystallinity and miscibility of poly(epsilon-caprolactone) (PCL) + poly(4-hydroxystyrene) (P4HS) blends. Three different heat treatments were selected. The development of PCL crystallinity was dependent on the blend composition. The increasing glass transition temperature (T-g) of blends, as they become richer in P4HS, was the cause of this dependence. The miscibility of the polymers was confirmed by detecting only a T-g in the blends, which could be closely described by the Fox rule. The thermograms exhibit double melting endotherms. The dependence of the melting temperature on the crystallization temperature shows that the lower endotherm corresponds to less stable crystals and the higher one to stable crystals. The lower endotherm was attributed to a secondary crystallization process. For the higher endotherm the thermodynamic melting temperatures of PCL in the pure state and in the blends were obtained using Hoffman-Weeks plots. The polymer-polymer interaction parameter was calculated from these data using the Nishi-Wang equation. The results are in good accordance with those obtained by inverse gas chromatography. Copyright (C) 1996 Elsevier Science Ltd.