Time-resolved small-angle X-ray scattering studies on the melting behavior of poly(ε-caprolactone)-block-polybutadiene copolymers

Heating measurements of crystallized poly(epsilon-caprolactone)-black-polybutadiene (PCL-b-PB) copolymers were performed using synchrotron small-angle X-ray scattering (SR-SAXS) to study the melting behavior of crystalline-amorphous diblock copolymers. The strong SAXS intensity peak, originating from the alternating structure of crystalline lamellae and amorphous layers (lamellar morphology), became broad in the course of melting and eventually a diffraction (or sharp intensity peak) arising from the microdomain structure emerged from this broad scattering peak, suggesting an interplay between the lamellar morphology and microdomain structure during melting. This is extremely different from the time-resolved SR-SAXS curve obtained during the crystallization of the microphase-separated PCL-b-PB, where the diffraction decayed steadily and the scattering peak (from the lamellar morphology) grew independently with increasing crystallization time. The melting behavior of PCL-b-PB evaluated from the SR-SAXS results was qualitatively compared with that of poly(epsilon-caprolactone) homopolymer (PCL). The long spacing of the lamellar morphology of PCL-b-PB, for example, decreased or remained constant during melting, whereas that of PCL increased slightly. The characteristics of the melting behavior of crystalline-amorphous diblock copolymers are discussed on the basis of the morphological reorganization from the lamellar morphology into the microdomain structure.