In Search of a Weak Link: Toward Biodegradability and Circular Economies Using Cyclic Ketene Acetals

In 1982, William J. Bailey published the incorporation of cleavable ester bonds within the main chain of free radical (co)polymers. This was achieved via radical ring-opening polymerization (rROP) of cyclic ketene acetals (CKAs). This fascinating innovation resulted in degradable vinyl polymers, which otherwise would possess all-carbon backbones, thereby avoiding the sometimes undesirable chemical robustness typically observed in free radical (co)polymers. Naturally, this paved the way for a novel class of polymers and the resulting materials, which can be deployed in a wide range of applications. Since his initial work, many research groups have adopted the CKA methodology to impart degradability within free radical (co)polymers while maintaining desirable physical properties and the ease of synthesis associated with free radical polymerization. Despite this breakthrough being published over 40 years ago, several challenges remain, specifically for wholesale industrial implementation. Questions remain around biodegradability and subsequent toxicity, the application of optimal polymer reaction engineering to incorporate the cleavable bonds efficiently, large-scale CKA monomer synthesis, and their aqueous copolymerization under emulsion conditions. This Perspective highlights some of the overarching challenges in CKA polymer science and provides insights into future directions and challenges in rROP beyond conventional CKA monomers. A proof-of-concept for the chemical recycling of CKA-based vinyl polymers is also presented.