Illuminating the Effects of Interchain Interactions on the Catalytic Amidation of C–H Bonds in Polyethylenes

Transformations of polyethylenes into more versatile materials could lead to new, more sustainable applications. Functionalization of C-H bonds in polyethylenes creates unique polymers with important properties, but the range of materials accessible by this approach is confined by the narrow scope of reactions that are amenable to these hydrocarbon polymers. Properties unique to macromolecules, such as chain-entanglements and high viscosities, could affect the relative rates and efficiencies of reactions. A deeper understanding of the origin of the differences in the catalytic transformations of polyethylenes from those of shorter alkanes would inform the design of new reactions tailored to these macromolecules and ultimately enable access to new materials. Here we show that noncovalent interactions of functionalized polymer chains affect the efficiency of the catalytic amidation of polyethylenes, limiting the maximum level of functionalization. We found that these noncovalent interactions increase with increasing levels of amide incorporation on the polymer and that these interactions alter the reaction media as the reaction progresses, ultimately suppressing catalytic amidation at later time points. We show that these effects can be mitigated by running reactions with cosolvents and that this approach allows for the highest levels of amide incorporation (up to 7 mol %, relative to monomer units). At this previously inaccessible level of functionalization, the resulting materials possess newfound properties, including dynamic cross-links that toughen the material. Ultimately, this work demonstrates that small-molecule models provide only a partial view into reactions of polyolefins and that factors unique to macromolecules must be considered to develop reactions with them.