Interplay between Crystallization and Phase Separation in PS‑<i>b</i>‑PMMA/PEO Blends: The Effect of Confinement

Abstract

Interplay between phase separation and crystallization under confinement for the blends of PEO homopolymers with different molecular weight and PS-<i>b</i>-PMMA block copolymer is studied. Phase structures of the blends are investigated by atomic force microscope (AFM) and theoretically simulated by the dissipative particle dynamics (DPD) method, and a phase diagram describing the phase structure is established. Low molecular weight PEO (PEO2) disperses uniformly in the PMMA block domain and causes a transition from cylinder phase to perforated lamellar phase, while high molecular weight PEO (PEO20) causes expansion of the cylinder domains and formation of disordered domains. Crystallization and melting behavior of the blends are detected by differential scanning calorimetry (DSC). The results show the liquid–liquid phase separation between PEO homopolymer and PMMA block under PS-<i>b</i>-PMMA microphase-separated structure is suppressed due to the hard confinement caused by glassy PS block. As a result, in the blends of PS-<i>b</i>-PMMA/PEO2, PEO2 is unable to crystallize, and in the blends of PS-<i>b</i>-PMMA/PEO20, PEO20 shows a more obvious melting point depression compared with the homopolymer blends of PMMA/PEO20