Temperature/pH/redox-triple-responsive properties, self-assembly and controlled release behavior of novel diblock copolymers

Here, we prepared three types of temperature/pH/redox-responsive diblock copolymers with similar molecular weights, using poly(2-((acrylamidomethyl)(methyl)amino)ethyl ferrocene formate) (P(Fc-N-AM)) as the hydrophobic block and poly( N -isopropylacrylamide) (PNIPAM), poly(ethylene glycol) (PEG), poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) as the hydrophilic block, respectively. Subsequently, their triple-responsive properties were characterized. For temperature-response, they exhibited a lower critical solution temperature (LCST)-type cloud point (CP) in water, and an upper critical solution temperature (UCST)-type CP in ethanol and propanol, and the CP temperature was influenced by the molecular weight and type of the hydrophilic block. For pH-response, all copolymers showed a critical pH in water, and when the molecular weights were similar, their critical pH was also close. The redox-response was confirmed by the reversible change of the characteristic peak of ferrocene (Fc) upon the addition of redox reagents to the solution. Subsequently, these copolymers self-assembled in water to form spherical micelles with different sizes, which also possessed triple stimuli-responsive properties. Finally, by encapsulating Nile Red (NR), the release behavior of NR-loaded micelles under heating, the addition of acid and oxidant were tested. The above studies have enriched the types of temperature/pH/redox triple-responsive polymers, revealed the influence of hydrophilic blocks on the responsive properties and self-assembly behavior of copolymers, and indicated that these copolymers have promising applications in the fields of self-assembly and controlled release.