Crystallization of Block Copolymers IV. Molecular Weight Dependence of the Morphology Formed in ε-Caprolactone–Butadiene Diblock Copolymers

Abstract

The morphology formed in a series of ε-caprolactone–butadiene diblock copolymers (PCL-b-PB) has been quantitatively investigated by small-angle X-ray scattering (SAXS) and differential scanning calorimetry(DSC) as a function of total molecular weight (9400<Mw<39400) of the copolymers with a fixed composition (27 vol% PCL). A sharp X-ray diffraction in the melt was completely replaced with a strong scattering by the crystallization of PCL blocks, suggesting a morphological rearrangement from the microdomain structure into the lamellar morphology (alternating structure consisting of PCL lamellae and amorphous layers). This rearrangement was also confirmed by transmission electron microscopy and polarized microscopy. The spacings of the microdomain structure D and of the lamellar morphology L increased with increasing Mw, though the increasing rates were quite different between D and L. The lamellar thickness, evaluated from a combination of L and bulk crystallinity measured by DSC, was significantly reduced compared with the case of PCL homopolymers, indicating that the lamellar morphology is strongly affected by PB blocks. The scaling analysis of L showed an excellent agreement between the present system and other diblock copolymers with equilibrium morphologies.