Dual-Stimuli-Responsive Micelle of an ABC Triblock Copolymer Bearing a Redox-Cleavable Unit and a Photocleavable Unit at Two Block Junctions

Abstract

The design, synthesis, and study of a new dual-stimuli-responsible ABC-type triblock copolymer are reported. Using ATRP and click coupling reaction, the prepared copolymer is composed of poly(ethylene oxide) (PEO), polystyrene (PS), and poly[2-(dimethylamino)ethylmethacrylate] (PDMAEMA) and features a redox-cleavable disulfide junction between the PEO and PS blocks as well as a photocleavable o-nitrobenzyl linkage between the PS and PDMAEMA blocks. This design allows the triblock copolymer to respond to both a reducing agent like dithiothreitol (DTT) and UV light, while having the minimum number of stimuli-reactive moieties in the copolymer structure (two per chain). The disruption of the triblock copolymer micelles in aqueous solution was examined under the action of either UV light or DTT alone or combined use of the two stimuli. It was found that the removal of one type of hydrophilic polymer chains from the water-soluble corona of the micelles with a hydrophobic PS core, that is, either redox-cleaved PEO or photocleaved PDMAEMA, could only result in a limited destabilization effect on the dispersion of the micelles. Severe aggregation of the polymer was observed only by applying the two stimuli converting the triblock copolymer onto three homopolymers. By monitoring the quenching by aqueous medium of the fluorescence of a hydrophobic dye (Nile Red) loaded in the triblock copolymer micelles, the effect on the payload release was also investigated of the different ways in which the micelles can be disrupted by the stimuli.