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Amidyl radicals mediate a diverse array of intermolecular aliphatic C(sp3)–H and decarboxylative functionalizations. Interestingly, we have observed that decarboxylative processes proceed with excellent chemoselectivity even with substrates containing weak C(sp3)–H bonds. Herein, we report a mechanistic basis for understanding this high chemoselectivity of amidyl radicals through divergent reaction pathways. A computational assessment of the transition state SOMOs and intrinsic bonding orbitals for amidyl radical hydrogen atom transfer (HAT) and concerted proton-electron transfer (CPET) processes support a shift in mechanism between aliphatic C(sp3)–H or carboxylic acid O–H abstraction, which is supported by experimental studies. These findings provide a rationale for the chemoselectivity of decarboxylative reactions mediated by amidyl radicals. 

Upcycling plastic waste into reprocessable materials with performance-advantaged properties would contribute to the development of a circular plastics economy. Here, we modify branched polyolefins and postconsumer polyethylene through a versatile C−H functionalization approach using thiosulfonates as a privileged radical group transfer functionality. Cross-linking the functionalized polyolefins with polytopic amines provided dynamically cross-linked polyolefin networks enabled by associative bond exchange of diketoenamine functionality. A combination of resonant soft X-ray scattering and grazing incidence X-ray scattering revealed hierarchical phase morphology in which diketoenamine-rich microdomains phase-separate within amorphous regions between polyolefin crystallites. The combination of dynamic covalent cross-links and microphase separation results in useful and improved mechanical properties, including a ∼4.5-fold increase in toughness, a reduction in creep deformation at temperatures relevant to use, and high-temperature structural stability compared to the parent polyolefin. The dynamic nature of diketoenamine cross-links provides stress relaxation at elevated temperatures, which enabled iterative reprocessing of the dynamic covalent polymer network with little cycle-to-cycle property fade. The ability to convert polyolefin waste into a reprocessable thermoformable material with attractive thermomechanical properties provides additional optionality for upcycling to enable future circularity.