Hydrogen Bond-Directed Formation of Stiff Polymer Films Using Naturally Occurring Polyphenols

Although coatings cast from waterborne polymer dispersions are significantly more environmentally friendly than their solvent-based counterparts, their relatively poor mechanical properties limit their use. In this work, mechanically reinforced polymer films from waterborne dispersions are presented in which the stiffness is provided by the hydrogen bond-directed formation of a honeycomb microstructure. Blends of an acrylic copolymer latex containing a hydrogen bond accepting pyrrolidone group and tannic acid, a naturally occurring H-bond donating polyphenol, lead to a cellular structure with physically cross-linked tannic acid forming the cell walls and the acrylic polymer occupying the space inside the cell walls. It is demonstrated that the formation of the honeycomb microstructure was promoted by H-bond interactions and led to materials with greater mechanical performance. Furthermore, we show that the high strength of the phenol–amide interaction allows these mechanical properties to be retained even after extensive exposure to water. This approach opens the way to replacement of solventborne polymers in many applications that require hard polymer films.