Skeletal Editing of Polymer Backbones and Its Impact Across the Polymer Lifecycle.

ConspectusIn the last five years, interest in the precise modification of molecular cores─termed skeletal editing─has rapidly expanded in the Chemistry community. Beyond the intrinsic value of these transformations, skeletal editing also has value in the attention it brings to under-explored chemical challenges, whose solutions could transform the practice of Chemistry at large. In few contexts does this perspective ring as true as in the realm of polymers. Inspired by the revolutionary power of biologically derived machinery called CRISPR-Cas9 to edit nucleic acid polymers and, consequently, the genetic meaning encoded in them, we envisioned that skeletal editing of synthetic polymer backbones may also enable control over the structure and "meaning"─i.e., properties and function─of plastics. However, the idea of editing polymer backbones brings about numerous fundamental chemical questions that must be answered to make the vision a reality: for instance, how to constructively activate carbon-carbon and carbon-heteroatom bonds that make up typical polymer backbones and how to do so in a site-selective manner? While many fundamental questions have begun to be answered by the small molecule community, they are yet to be applied to the realm of polymers, and such adaptation often begets new scientific challenges. Moreover, as we begin to tackle these questions, we must always consider how advances in skeletal editing of polymer backbones impact the broader contexts of applications and sustainability of plastics.In this Account, we summarize our efforts to advance the skeletal editing of polymer backbones, focusing on how such methods can affect each stage of the polymer lifecycle: (1) provide an entry to previously challenging-to-access functional polymers or to existing ones but from new feedstocks, (2) evolve one type of polymer into another with associated changes in material properties, and (3) enable the breakdown of otherwise intractable polymer backbones. Along the way, we describe our rationale behind the selection and development of reactions utilized for skeletal editing. We explain how small molecule reactions often need to be adapted to suit polymeric substrates and the methodology optimizations we needed to do to accomplish our edits. We also discuss the considerations involved in the selection or design of polymeric substrates for editing with an eye toward what edits can add to polymer function and how to advance the field. We conclude with an outlook on outstanding challenges that we aim to address in future work establishing areas for future exploration within each of our topic areas.