Partial phase segregation in strongly hydrogen-bonded and miscible blends

The effect of intermolecular hydrogen bonding on the crystallization kinetics and the morphology of poly(c-caprolactone) (PCL)/4,4'-thiodiphenol (TDP) blends with TDP content 0-20 wt % has been investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray measurements, and in situ FT-IR. The equilibrium melting point (T-m(0)) of PCL in the PCL/TDP blends decreases with increasing the TDP content, suggesting the miscibility of the blends as expected when strong hydrogen bonding is involved. Following the depression of T-m(0). and the increase of glass transition (as reported in our previous works), the half-time of crystallization and the spherulite growth rate rapidly decrease with increasing TDP content. By small-angle X-ray scattering measurement, obvious extralamellar segregation of TDP was detected, the extent of which increased with increasing TDP content. The inter-spherulite segregation of TDP was also observed by a polarizing optical microscope and FT-IR microscope. For a given composition, the blends crystallized at 40 degreesC showed a higher extent of inter-spherulite segregation than that crystallized at 30 degreesC, which indicated that the crystal growth rate plays the dominant role in the morphological formation. With the progress of crystallization, the content of TDP in the inter-spherulite region increased, resulting in a continuous retardation of spherulite growth and a gradient distribution of TDP along the radius. Moreover, the crystallization of PCL component in the blends induced partial phase segregation in the final structure.