Versatile Light-Mediated Synthesis of Degradable Bottlebrush Polymers Using α-Lipoic Acid.

Bottlebrush polymers have a variety of useful properties including a high entanglement molecular weight, low Young's modulus, and rapid kinetics for self-assembly. However, the translation of bottlebrushes to real-world applications is limited by complex, multi-step synthetic pathways and polymerization reactions that rely on air-sensitive catalysts. Additionally, most bottlebrushes are non-degradable. Herein, we report an inexpensive, versatile, and simple approach to synthesize degradable bottlebrush polymers under mild reaction conditions. Our approach relies on the "grafting-through" polymerization of α-lipoic acid (LA)-functionalized macromonomers. These macromonomers can be polymerized under mild, catalyst-free conditions, and due to reversibility of the disulfide bond in LA, the resulting bottlebrush polymers can be depolymerized by cleaving disulfide backbone bonds. Bottlebrushes with various side-chain chemistries can be prepared through the atom transfer radical polymerization (ATRP) of LA-functionalized macromonomers, and the backbone length is governed by the macromonomer molecular weight and solvent polarity. We also demonstrate that LA-functionalized macromonomers can be copolymerized with acrylates to form degradable bottlebrush networks. This work demonstrates the preparation of degradable bottlebrush polymers with a variety of side-chain chemistries and provides insight into the light-mediated grafting-through polymerization of dithiolane-functionalized macromonomers.