(338y) Novel Synthetic Approach to Degradable Bottlebrush Polymers with Tailored Side-Chains

Bottlebrush polymers have a variety of potentially useful properties including a high entanglement molecular weight, low Young’s modulus, and rapid kinetics for self-assembly. However, the translation of these materials to real-world applications remains limited due to challenging synthetic pathways that rely on expensive reagents and complex, multi-step polymerizations. Additionally, most bottlebrushes are non-degradable. Herein, we present an inexpensive, versatile, and simple approach to synthesize degradable bottlebrush polymers under mild reaction conditions. Our approach relies on a-lipoic acid (LA), an inexpensive, naturally occurring, and biocompatible small molecule. We first tethered an initiator for atom transfer radical polymerization (ATRP) to LA and used this to synthesize polymer side-chains with various chemistries at room temperature and low catalyst loading. In contrast to prior studies where LA self-polymerizes above its melting temperature (approximately 60 °C), the LA-functionalized ATRP-initiator was stable at these temperatures. Next, under ultraviolet light (365 nm) without any catalyst and at ambient temperature, the LA-functionalized polymer side-chains undergo a “grafting-through” ring-opening polymerization (ROP) to produce bottlebrush polymers. We found that the backbone degree-of-polymerization (N_b) was sensitive to the solvent polarity but could also be tuned by the side-chain length (N_sc) and the concentration of polymer in solution. Additionally, the resulting bottlebrush polymers could be depolymerized to macromonomers, which could be recycled to produce new bottlebrush polymers. This work enables the inexpensive and large-scale preparation of degradable bottlebrush polymers with a variety of side-chain chemistries and will allow us and others to greatly advance the development of bottlebrush polymers for applications, including self-healing elastomers, drug delivery, and plastic recycling.