CRYSTALLIZATION OF BLOCK COPOLYMERS .2. MORPHOLOGICAL-STUDY OF POLY(ETHYLENE GLYCOL) POLY EPSILON-CAPROLACTONE) BLOCK COPOLYMERS

Block copolymers consisting of poly(ethylene glycol) (PEG) and poly(epsilon-caprolactone) (PCL) were synthesized by adding epsilon-caprolactone to the PEG ends, and the morphology and melting behavior of these copolymers were investigated by small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). A binary blend of PEG and PCL oligomers was also prepared to compare the morphology with that of the copolymers. The long spacing L, an alternate period of the lamella and amorphous layer, evaluated from the angular position of the SAXS maximum dramatically decreased by adding a short PCL block to the PEG ends, and then increased linearly with connected PCL block length. The melting temperature T(m) showed maximum depression of ca. 20-degrees-C for the copolymer with an equal proportion of the PEG and PCL blocks. The WAXD results revealed that the crystals of the PEG and PCL blocks independently existed and there was no diffraction from an eutectic crystal composed of the two blocks. In the PEG/PCL blend, L and T(m) did not change with changing the PCL fraction and exactly corresponded to those of the constituent homopolymers. These facts suggest that the covalent bond between the PEG and PCL blocks restricts the formation of the favorable crystalline morphology which appears in the PEG/PCL blend, and eventually a characteristic morphology is formed in these copolymer systems.