In this talk, I discuss a general strategy to prepare degradable materials derived from the ring-opening metathesis polymerization of norbornenes. Polynorbornenes are found in many areas, ranging from probes for modulating living systems to industrially-relevant thermosets for structural applications. Due to the mechanism of olefin metathesis, these polymers feature backbones consisting of carbon-carbon bonds, which limits their ability to be broken down under mild conditions. This lack of degradability leads to their problematic persistence within living systems or within the environment. We address this limitation directly through the design of a new class of co-monomers, which introduce cleavable bonds throughout the polymer backbone. Through tailored monomer design, we tune the degradation rate of these materials under biologically relevant conditions by many orders of magnitude. This degradation was shown to be enabling in the context of new polymeric drug delivery systems, where we could promote the rate of clearance of polymeric drug carriers in vivo. We next applied our approach in the context of the industrially relevant thermoset poly-dicyclopentadiene (pDCPD), where we made the surprising discovery that only a small quantity of co-monomer was sufficient to allow these mechanically robust thermosets to be broken down into soluble fragments. At low co-monomer doping, we maintain the desirable mechanical properties of the parent material. These soluble fragments can be recycled back into the parent thermoset or further functionalized as a new class of nanoscale hydrocarbon fragments. Our results are uniquely enabled by how we introduce our cleavable bonds, and enabled us to develop a theoretical model that can be applied across all crosslinked polymer networks. Just as selective bond forming reactions have been instrumental in illuminating the dark matter of living systems, new chemical approaches to enable the selective degradation of materials can lead to unprecedented function. The lessons learned from our work can be generalized across all crosslinked polymeric materials, given suitable co-monomer design, and the resulting materials applied to areas such as biology and medicine. Towards this end, continued efforts at the interface of chemistry, biology, and materials science, akin to these approaches, will lay the groundwork for new strategies tackling longstanding challenges in fields ranging from biomaterials to sustainability.

Molecular approaches to engineer weak links into known materials

ACS Fall 2020 Virtual Meeting

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