The production of conventional crosslinked polymer networks and their composites, i.e., thermosets and thermoset composites, occurs at a rate of many billions of kilograms of polymer annually. Unfortunately, thermosets cannot be melt-reprocessed into moderate- to high-value products because permanent crosslinks prevent melt flow. We have developed seven simple one-step or two-step chemistries to produce networks and their composites with dynamic covalent crosslinks that are robust at use conditions but allow for chemical recycling involving melt-state reprocessing. Unique to our research group, we have developed three approaches for melt-state processing or reprocessing of polymer networks and network composites made by free radical polymerization, including those synthesized directly from monomers containing carbon-carbon double bonds and those synthesized by radical-based reactive processing of thermoplastic polymer. These three approaches are the subject of my talk and involve the following: (a) alkoxyamine dynamic chemistry (like that involved in nitroxide-mediated polymerization), (b) dialkylamino disulfide dynamic chemistry, and (c) hindered urea bond dynamic chemistry.  These approaches allow for full crosslink density recovery after multiple reprocessing steps. An "Achilles' heel" has been identified regarding the application of dynamic covalent networks, i.e., such networks are subject to creep at elevated or sometimes even room temperature, which is often highly undesirable. We have successfully addressed this issue in several ways via these dynamic and other chemistries. Brief highlights of each of these accomplishments will be presented. Implications for making major gains in the sustainability of networks and network composites will be discussed as will the potential benefits of such chemistry for improving performance independent of sustainability concerns.

Transforming thermosets into thermoplastics: Three simple, radical-based dynamic covalent chemistries for sustainable chemical recycling of traditionally non-recyclable polymers

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.