Responsive Polyphenol-Crosslinked Supramacromolecular Microgels with pH-Triggered Disassembly in Aqueous Solution

Abstract

This work focuses on the pH-triggered disassembly of supramacromolecular microgels, which are composed of the temperature-responsive poly(N-vinylcaprolactam) (PVCL) and the natural polyphenol tannic acid (TA). A systematic investigation of the microgel formation demonstrates that a retarded addition of tannic acid during semi-batch precipitation polymerization influences the yield, chemical composition, and properties of the microgels to a great extent. Microgel properties, such as size, deformability, and chemical stability, can be easily tuned by varying the ratio between both building blocks PVCL and TA. Finally, the pH-triggered disassembly of supramacromolecular microgels at different pH and temperatures demonstrates that their chemical structure can precisely control the degradation profile. Temperatures lower than the volume phase transition temperature (VPTT) of PVCL (T < 32 °C) and a pH > 10 result in a complete disassembly of the microgels into PVCL chains and TA due to the destruction of the hydrogen bonds responsible for the formation of a colloidal microgel. Interestingly, at temperatures above VPTT, the microgels keep their integrity due to enhanced hydrophobic interactions between the polymer chains of the microgel and are no longer affected by pH changes.