Block Copolymer Micelles with a Dual-Stimuli-Responsive Core for Fast or Slow Degradation

We report the design and demonstration of a dual-stimuli-responsive block copolymer (BCP) micelle with increased complexity and control. We have synthesized and studied a new amphiphilic ABA-type triblock copolymer whose hydrophobic middle block contains two types of stimuli-sensitive functionalities regularly and repeatedly positioned in the main chain. Using a two-step click chemistry approach, disulfide and <i>o</i>-nitrobenzyle methyl ester groups are inserted into the main chain, which react to reducing agents and light, respectively. With the end blocks being poly­(ethylene oxide), micelles formed by this BCP possess a core that can be disintegrated either rapidly via photocleavage of <i>o</i>-nitrobenzyl methyl esters or slowly through cleavage of disulfide groups by a reducing agent in the micellar solution. This feature makes possible either burst release of an encapsulated hydrophobic species from disintegrated micelles by UV light, or slow release by the action of a reducing agent, or release with combined fast-slow rate profiles using the two stimuli

General Strategy for Making CO₂-Switchable Polymers

By discovering that poly­(<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate) (PDMAEMA) in water can react with carbon dioxide (CO₂) and have its lower critical solution temperature (LCST) reversibly tuned by passing CO₂ and argon (Ar) through the solution, we describe a general strategy for imparting a CO₂-switchable LCST or water solubility to polymers of broad interest like poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) and poly­[2-(2-methoxyethoxy)­ethyl methacrylate] (PMEO₂MA). We show that by easy copolymerization incorporating DMAEMA as a CO₂-responsive trigger into PNIPAM or PMEO₂MA, their LCST can effectively be switched by the gases. Two examples of applications were further demonstrated: upon CO₂ or Ar bubbling at a constant solution temperature, hydrogels could undergo a reversible volume transition and block copolymer micelles could be dissociated and reassembled. This study opens the door to a wide range of easily accessible CO₂-switchable polymers, enabling the use of CO₂ as an effective trigger for smart materials and devices

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

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 <i>o</i>-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

Two-Way CO₂‑Switchable Triblock Copolymer Hydrogels

CO₂-responsive ABA triblock copolymer hydrogels are described. Through rational block copolymer design, these hydrogels could undergo either CO₂-induced gel-to-sol or the reverse sol-to-gel transition. While the middle block B is water-soluble, the solubility of the two end blocks A can be switched by CO₂. For the gel-to-sol transition, the A block was made to have a lower critical solution temperature (LCST) that can increase upon CO₂ bubbling, while for the sol-to-gel transition, the A block was designed to have a LCST that decreases with CO₂. Repeated cycles of hydrogel formation and dissociation could be achieved by simply passing CO₂ and an inert gas alternately through the solution, at a constant temperature and without adding acids and bases for pH change. Moreover, CO₂-induced release of an encapsulated protein was demonstrated