Morphology Evolution of Stimuli-Responsive Triblock Copolymer Modulated by Polyoxometalates.

Polyoxometalate (POM) H3PMo12O40 was coassembled with stimuli-responsive triblock copolymer poly(ethylene oxide)- block-polystyrene- block-poly(2-(dimethylamino)ethyl methacrylate) (PEO- b-PS- b-PDMAEMA) by electrostatic interactions. Depending on the POM contents, the hybrid complexes can self-assemble into a series of morphologies: micelles, rods, toroids, and vesicles. Unlike traditional morphology transition of amphiphilic block copolymer derived from a broad range of hydrophobic volume fractions, POM-induced morphology transitions just occurred in a narrow range of volume fractions. The length of rod micelles exponentially decreased with solvent compositions (tetrahydrofuran/H2O). The hybrid assemblies showed acid-base responsibility due to the PDMAEMA block. Rod micelles could further assemble and disassemble reversibly upon adding acid/base. Fluorescent polyoxometalate Na9EuW10O36 was also complexed with PEO- b-PS- b-PDMAEMA to prepare fluorescent vesicles. The vesicles showed off-on switchable fluorescence behavior accompanied with reversible vesicle-to-micelle transformation in response to pH stimuli.