Macromolecular Photoediting Using Single-Electron Logic.

Accessing the chemistry of reactive intermediates under mild conditions has significantly expanded the available chemical space for molecular transformations. Nowhere is this more apparent than in the context of photoredox catalysis. Despite abundant literature precedents for using this powerful methodology to build complex targets, there are comparatively few reports that leverage photoredox catalysis for macromolecular editing. Here, we report a mild photoredox approach that enables both the functionalization and degradation of polyalkenamers to valuable feedstocks. Irradiation with visible light (including natural sunlight) in the presence of a pyrillium photoredox catalyst promoted facile chain scission in a variety of substrates. This metal-free approach transformed high molar mass materials (>300 kDa) to low molar mass species (<15 kDa) within 10 min. Moreover, we could completely degrade macromolecules into a range of useful targets (C16-C29 species) within 96 h. Mechanistic and kinetic experiments were carried out to understand this reactivity, which could be coupled with hydrofunctionalizations to create tailored products.

Electroediting of Soft Polymer Backbones.

Synthetic methods that edit soft polymer backbones are critical technologies for tailoring the structures and properties of macromolecules. Developing strategies that leverage underexplored reaction manifolds are vital for accessing new chemical (and functional) space in soft materials. Here, we report a mild electrochemical approach that enables both degradation and functionalization of synthetic polymers. We found that bulk electrolysis (under either homogeneous or heterogeneous conditions) promoted facile, chemoselective chain scission in a variety of olefin-containing materials. Polymer degradation could also be coupled with functionalization (e.g., azidation) to afford new species that could serve as macromonomers.

General Access to Allene-Containing Polymers Using the Skattebøl Rearrangement.

Postsynthetic modification is a powerful strategy for tuning soft materials. While methods for side-chain functionalization abound, modifications of backbone structural elements can be difficult to achieve. This challenge arises, in part, from a lack of intrinsically reactive motifs that can be installed in the main chain of a polymer. Incorporating established synthetic handles into polymer architectures is paramount for overcoming this limitation. Allenes are salient examples of moieties that could be leveraged in a wide range of postsynthetic modifications; however, the synthesis of a polyallene has proven elusive. Using the metathesis polymer of norbornene as a model architecture, we have established the Skattebøl rearrangement as a facile route to polyallenes. Polymers with varying allene content (20-95%) were readily prepared in excellent yields (89-94%). These materials possess unique optical properties and can be engaged through further postsynthetic modifications. As such, polyallenes could serve as valuable platforms for developing functional soft materials.