Triple-stimuli-responsive ferrocene-containing homopolymers by RAFT polymerization

Well-defined ferrocene-containing homopolymers were synthesized by RAFT homopolymerization of an acrylate monomer bearing a ferrocene (Fc) unit and an N,N-diethylamino ethyl (DEAE) group, i.e. 2-(3-(N-(2-(diethylamino)ethyl)-acrylamido)propanoyloxy)ethyl ferrocenecarboxylate (Fc-DEAE-AM). As an ideal redox-responsive group, hydrophobic Fc can be easily oxidized into hydrophilic Fc+ by certain oxidants, providing tremendous opportunities to produce various Fc-containing redox-responsive materials. On the other hand, the pH/CO2-responsive reversible nature of the DEAE group makes it possible to construct a smart system to adapt to the complex environment in practical application. The stimuli-responsive aggregation behavior of the well-defined poly(Fc-DEAE-AM) homopolymer is examined by the combination of a fluorescent probe, UV/vis transmittance, zeta potential, transmission electron microscopy (TEM), and dynamic light scattering (DLS). In fact, due to the redox and pH/CO2-responsive character provided by the Fc and DEAE groups, the poly(Fc-DEAE-AM) homopolymer exhibits distinct phase transition in aqueous solution. In addition, such a homopolymer could form typical spherical particles in acid aqueous solution, and the redox agent could lead to changes in the size and morphology of the aggregates. Thus, we provide a new and efficient way to prepare triple-stimuli-responsive Fc-containing homopolymers, which might be used as interesting building block for the fabrication of multiple stimuli-responsive functional materials.