Spatial distribution of hydrophobic compounds in polymer micelles as explored by anomalous small-angle X-ray scattering near Br K-edge

Abstract

Spatial distributions of bromine-labeled hydrophobic molecules, 9-bromofluorene (BrFL) or ethyl 2-bromoisobutylate (BrEB), incorporated in micelles of amphiphilic block copolymers composed of hydrophilic poly(N,N-dimethylaminoethyl methacrylate) and hydrophobic poly(methyl methacrylate) (PDMAEMA-b-PMMA) were explored with anomalous small-angle X-ray scattering (ASAXS) near Br K-edge. ASAXS analyses clarified that BrFL was concentrated into small domain within hydrophobic PMMA core, whereas BrEB, which had similar molecular structure to the repeating unit of PMMA, was homogeneously dispersed in PMMA core. The concentration of BrFL into small domain within PMMA core was interpreted due to segregation of BrFL molecules from water penetrating into the PMMA core. On the other hand, the BrEB molecules were homogeneously dispersed in the PMMA cores because the molecular structure of BrEB was similar to the repeating unit of PMMA. The results in this work indicated that the differences of spatial distributions of hydrophobic compounds in polymer micelles were derived by the differences of intermolecular interactions between the hydrophobic molecules and the other components, such as a hydrophobic polymer and solvent, in hydrophobic cores of polymer micelles.