Frank–Kasper σ phase in polybutadiene-poly( ε -caprolactone) diblock copolymer/polybutadiene blends

Microphase-separated structures in a polybutadiene-poly( ε -caprolactone) diblock copolymer (PB-PCL)/polybutadiene homopolymer (PB) blend were investigated by small-angle x-ray scattering (SAXS). Non-equilibrium spherical micelles were observed at temperatures ranging between 60 and 100 °C. An SAXS profile with  >60 scattering peaks was recorded at 140 °C. All the peak positions were in good agreement with theoretical Frank–Kasper σ phase peak positions. Thus, these results indicate the formation of a Frank–Kasper σ phase in the PB-PCL/PB blend at 140 °C. (paper)