Bottom-up design of model network elastomers and hydrogels from precise star polymers

Abstract

We introduce a platform for the simultaneous design of model network hydrogels and bulk elastomers based on well-defined water-soluble star polymers with a low glass transition temperature (T_g). This platform is enabled via the development of a synthetic route to a new family of 4-arm star polymers based on water-soluble poly(triethylene glycol methyl ether acrylate) (p(mTEGA)), which after quantitative introduction of functional end-groups can serve as suitable building blocks for model network formation. We first describe in detail the synthesis of highly defined star polymers using light and Cu-wire mediated Cu-based reversible deactivation radical polymerization. The resulting polymers exhibit narrow dispersities and controlled arm length at very high molecular weights, and feature a desirable low T_g of −55 °C. Subsequently, we elucidate the rational design of the stiffness and elasticity in covalent model network elastomers and hydrogels formed by fast photo-crosslinking for different arm lengths, and construct thermally reversible model network hydrogels based on dynamic supramolecular bonds. In addition, we describe preliminary 3D-printing applications. This work provides a key alternative to commonly used star-poly(ethylene glycol) (PEG) for model hydrogel networks, and demonstrates access to new main and side chain chemistries, thus chain stiffnesses and entanglement molecular weight, and, critically, enables the simultaneous study of the mechanical behavior of bulk network elastomers and swollen hydrogels with the same network topology. In a wider perspective, this work also highlights the need for advancing precision polymer chemistry to allow for an understanding of architectural control for the rational design of functional mechanical network materials.