Morphological behavior of thermally treated polystyrene-b-polybutadiene-b-poly(ε-caprolactone) ABC triblock copolymers

The microphase morphology of a series of polystyrene-b-polybutadiene-b-poly(is an element of-caprolactone) ABC triblock copolymers (SBC) was studied by transmission electron microscopy (TEM) and synchrotron radiation small-angle X-ray scattering (SAXS) for selected samples. The studies were performed as a function of annealing time at high temperature (150 degreesC). Interestingly, even though crystallization took place under similar conditions (5 h at 40 degreesC), the annealing time at high temperature can influence the final morphology in such a way that within a copolymer (S51B09C40), a morphological transition from a lamellar-cylindrical (1c) to a cylindrical-ring (cr) morphology can occur. It was also observed that the copolymers reach varied levels of long-range order of the microdomains, depending on the composition. These results combined with the observation or not of well-defined spherulites in the bulk illustrate the strong "conflict" between microphase separation and crystallization, especially when the PCL content is relatively high. The morphological changes are directly related to the thermal behavior of the triblock copolymers, in particular, the melting temperature and Avrami parameter associated with the crystallization kinetics.