Sustainability and Polyesters: Beyond Metals and Monomers to Function and Fate

Conspectus Poor waste management and unchecked consumption underpin our current paradigm of plastics use, which is demonstrably unsustainable in the long term. Nonetheless, the utility and versatility of plastics suggest that the notion of a plastic-free society is also unsustainable. Responses to this conundrum are increasing, and among these are research efforts focused on the development of more sustainable plastics. This Account, written by trained chemists, reflects an academic research journey culminating in an appreciation of the importance of improving and enabling the overarching systems that plastics exist within. Our primary initial focus was on catalyst development because catalysts are key drivers of sustainability by improving the efficiency and ease of polymerization. Metal catalysts ranging in ligand structure and the incorporated metal(s) were developed for the preparation of traditional polyesters such as poly­(lactic acid) and polycaprolactone. The central themes in these works were stereocontrol (tacticity), efficiency (polymerization rate), and versatility (monomer scope). Alongside insights gained by systematically varying catalyst structure came impressive results gained through collaboration, including the remarkably high activity of novel heterometallic zinc catalysts toward various cyclic esters. This catalysis work was complemented by and slowly transitioned to a focus on polymer functionality and monomer design. Several fundamental studies focus on polymer topology, specifically star-shaped polyesters, tuned arm number, length, and tacticity. These reports feature emphases on the end of life (solvolysis) and physical properties of polymers, which were increasingly important themes as work shifted toward new methods of incorporating functionality in polymers produced by ring-opening polymerization. Three key highlights demonstrate this shift: the first two rely upon the exploitation of olefin metathesis (cross- and ring-closing) to functionalize polyesters or polyethers, and the third involves the manipulation of ring-opening polymerization equilibrium to enable selective monomer recovery from a polyester. Our foundational work on 1,3-dioxolan-4-one (DOX) monomers is then discussed because this emerging class of molecules offers a distinct synthetic pathway toward functional polyesters, both conventional and novel. With this DOX framework, polyesters that are usually challenging to synthesize (e.g., poly­(mandelic acid)) are acce