Polycaprolactone-based block copolymers. II. Morphology and crystallization of copolymers of styrene or butadiene and ε-caprolactone

Three series of amorphous semicrystalline poly(styrene-b-ε-caprolactone)s have been synthesized with polystyrene blocks of 6000 (series A), 40000 (series B), and 70000 (series C) molecular weight, respectively. In these materials, the polymer miscibility evolves from a situation where a diffuse interphase involves the major part of the volume of the copolymer (series A) to a sharp phase separation as observed for copolymers with the longest PS block (series C). The crystallization of PCL blocks is mainly governed by the phase morphology. In copolymers of series A, the crystallization rate of PCL blocks is slowed down the more as the miscibility with PS increases, and ultimately the degree of crystallinity X_c decreases significantly. When phase separation is sharp, X_c changes dramatically at the phase inversion and decreases when PS forms the continuous phase. At the inversion X_c depends on the mean size of the PCL microdomains as compared with the thickness of the crystalline lamellae. The periodicity of the phase morphology as observed by TEM is influenced by the solvent used in casting films, whereas monolamellar monocrystals can be obtained by a self-seeding technique.