Synthesis of pH/Redox-Double-Responsive Ferrocene-Containing Diblock Copolymers and Their Application in Controlled Release

A novel pH/redox-double-responsive ferrocene-containing diblock copolymer of poly(ethylene glycol)-block-poly[2-(2-((2-ferrocenyl ethyl ester) (methyl) amino) ethoxy) ethyl methacrylate] [mPEG113-b-P(Fe-N-EOMA)] was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. mPEG113-b-P(Fe-N-EOMA) is amphiphilic with PEG as hydrophilic block and the part containing ferrocene as hydrophobic block. For comparison, three other diblock copolymers were prepared by changing the molecular weight of the hydrophilic block and the microstructure of the hydrophobic block. The diblock copolymers have a critical pH in solution and increases with the increase of the hydrophilicity of the copolymers. The redox-response was confirmed by the shift of characteristic peak of ferrocene in the UV/vis absorption spectrum after adding of FeCl3/VC. The self-assembly behavior of these diblock copolymers in solution were then investigated. It shows that they have low critical micelle concentration (cmc), and the cmc decreases as the hydrophobicity of copolymers increases. Their morphology is varied, including sphere, lamella, aggregated sphere, and can be reversible changed by the stimulation of pH and redox. Finally, mPEG113-b-P(Fe-N-EOMA) was applied to the release of Nile Red (NR), which showed a good release efficiency. The prepared diblock copolymers have sensitive and reversible response properties, which provided ideas for the design of multistimuli-responsive polymers, and have good application prospects in drug-release.