Composition dependence of crystallized lamellar morphology formed in crystalline–crystalline diblock copolymers

Abstract

We have investigated the crystallized morphology formed at each temperature T c (20 °C ≤ T c ≤ 45 °C) in double crystalline poly(ɛ-caprolactone)- block-polyethylene (PCL- b-PE) copolymers as a function of composition (or volume fraction of PE blocks ϕ PE) by employing small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) techniques. When PCL- b-PE with ϕ PE ≤ 0.58 was quenched from a microphase-separated melt into T c, the crystallization of PE blocks occurred first to yield an alternating structure consisting of thin PE crystals and amorphous PE + PCL layers (PE lamellar morphology) followed by the crystallization of PCL blocks, where we can expect a competition between the stability of the PE lamellar morphology (depending on ϕ PE) and PCL crystallization (on T c). Two different morphologies were formed in the system judging from a long period. That is, the PCL block crystallized within the existing PE lamellar morphology at lower T c (<30 °C) to yield a double crystallized alternating structure while it crystallized by deforming or partially destroying the PE lamellar morphology at higher T c (>35 °C) to result in a significant increase of the long period. However, the temperature at which the morphology changed was almost independent of ϕ PE. For PCL- b-PE with ϕ PE ≥ 0.73, on the other hand, the morphology after the crystallization of PE blocks was preserved at every T c investigated.