Temperature-induced and crystallization-driven self-assembly of polyethylene-b-poly(ethylene oxide) in solution

Abstract

In this paper, the well-defined diblock copolymers consisting a linear polyethylene (LPE) and a poly(ethylene oxide) (PEO), LPE-b-PEO, were synthesized by combining the ethylene living coordination polymerization with fluorinated bis(phenoxyimine) titanium catalyst and the living ring-opening polymerization of ethylene oxide initiated by hydroxyl-terminated polyethylene (LPE–OH) as a macromolecular initiator. We describe two methodologies for the self-assembly of LPE-b-PEO, namely temperature-induced self-assembly and crystallization-driven self-assembly. Transmission electron microscopy (TEM), atomic force microscopy (AFM) and dynamic light scattering (DLS) are employed to characterize the morphology, structure and hydrodynamic radius (Rh) of the self-assembled micelles. LPE-b-PEO is dissolved to form a molecular solution in trichlorobenzene (TCB) at 140 °C, while self-assembly could be driven when the crystallization of LPE blocks is induced by cooling to form diamond-shaped micelles with a mono-layer crystallized LPE lamella core. The resultant diblock copolymers can self-assemble into spherical micelles composed of a molten LPE core and a soluble PEO corona in DMF at 140 °C, that is above the melting temperature (Tm) of the LPE block. As the temperature decrease, the morphology changes from spherical to platelet-like micelle with a double-layer crystallized LPE lamella core sandwiched by solvent-swollen PEO corona. Furthermore, the confined crystallization of LPE block in nanosized self-assembled micelle core is investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXRD).