C–H Functionalization of Polyolefins to Access Reprocessable Polyolefin Thermosets

• Published in: Journal of the American Chemical Society Vol. 145; no. 50; pp. 27450 - 27458
• Main Authors: Neidhart, Eliza K., Hua, Mutian, Peng, Zhengxing, Kearney, Logan T., Bhat, Vittal, Vashahi, Foad, Alexanian, Erik J., Sheiko, Sergei S., Wang, Cheng, Helms, Brett A., Leibfarth, Frank A.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20-12-2023
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.3c08682

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.