Surface Studies of Polymer Blends. 3. An Esca, IR, and Dsc Study of Poly(ε-caprolactone)/Poly(vinyl Chloride) Homopolymer Blends

Angle-dependent electron spectroscopy for chemical analysis (ESCA or XPS), Fourier transform infrared spectroscopy with attentuated total reflectance (ATR-FTIR), and differential scanning calorimetry (DSC) results are presented for miscible and immiscible solvent-cast blends of poly(caprolactone) (PCL; MW = 33000) and poly(vinyl chloride) (PVC; MW = 190000). The DSC results showed that blends with less than 50 wt % PCL were miscible, with a single glass transition temperature. In addition, for blends with greater than or equal to 50 wt % PCL a melting temperature was detected and attributed to crystalline PCL. Since the blends in this composition range contained both crystalline and blended PCL, they were considered immiscible or incompatible. Analysis of the polymer/air interface by ESCA showed that the surface composition of the blends is equivalent to the bulk composition for blends with less than 50 wt % PCL. For blends with bulk composition between 50 and 90 wt % PCL, the surface composition analysis yielded a surface excess of PCL while the 90 wt % PCL blend exhibited an enrichment of blended PVC. The ATR-FTIR and transmission infrared results indicated that the PCL/PVC blends with less than 50 wt % PCL are homogeneous. ATR-FTIR results indicated that the relative amount of amorphous or blended PCL to semicrystalline PCL increases with greater sampling depths for blends containing 50–60 wt % PCL. From the infrared studies, shifts in the carbonyl stretch and C-0 bending bands indicate that the PCL becomes semicrystalline in blends with greater than or equal to 50 wt % PCL. The results taken together support a model of surface composition of homopolymer blends which directly relates to bulk miscibility.