Novel Temperature/pH/CO2/Redox-Quadruple-Responsive Ferrocene-Containing Homopolymers and Their Self-Assembly Behavior

A series of temperature/pH/CO2/redox-quadruple-responsive ferrocene-containing homopolymers were prepared for the first time. These homopolymers contain hydrophilic ethoxy group, amino group, and hydrophobic ferrocene (Fc) and were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. They showed four different stimuli responses. (1) They exhibit an upper critical solution temperature (UCST) in n-propyl alcohol and n-butanol, which can be adjusted by the molecular structure, molecular weight, and concentration. (2) They have a critical pH in aqueous solution and are affected by molecular structure, molecular weight, and concentration. (3) The CO2 response of the homopolymers was confirmed by cyclic bubbling CO2/N2 to the solution. (4) The redox response of homopolymers was demonstrated by adding a chemical oxidant (FeCl3)/reductant (VC) or electrical stimulation to the solution of homopolymers. In addition, these homopolymers are amphiphilic, and their self-assembly behavior in solution was investigated. It was found that they have different critical micelle concentrations (cmc) and can form lamella, sphere, and agglomerated sphere in solution, and the morphology can be reversibly changed by applying stimulation. Finally, the release behavior of micelles of the homopolymer was explored by wrapping Nile Red (NR), which proved that they had good release efficiency. These temperature/pH/CO2/redox-quadruple-responsive ferrocene-containing homopolymers expand the types of multistimuli-responsive homopolymers and have excellent application prospects in the fields of self-assembly, drug delivery, and electrode materials.