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1. Ultrasmall amorphous zirconia nanoparticles catalyse polyolefin hydrogenolysis

   https://doi.org/10.1038/s41929-023-00910-x  

   Chen, Shaojiang; Tennakoon, Akalanka; You, Kyung-Eun; Paterson, Alexander L.; Yappert, Ryan; Alayoglu, Selim; Fang, Lingzhe; Wu, Xun; Zhao, Tommy Yunpu; Lapak, Michelle P.; et al (February 2023, Nature Catalysis)

   Abstract Carbon–carbon bond cleavage reactions, adapted to deconstruct aliphatic hydrocarbon polymers and recover the intrinsic energy and carbon value in plastic waste, have typically been catalysed by metal nanoparticles or air-sensitive organometallics. Metal oxides that serve as supports for these catalysts are typically considered to be inert. Here we show that Earth-abundant, non-reducible zirconia catalyses the hydrogenolysis of polyolefins with activity rivalling that of precious metal nanoparticles. To harness this unusual reactivity, our catalytic architecture localizes ultrasmall amorphous zirconia nanoparticles between two fused platelets of mesoporous silica. Macromolecules translocate from bulk through radial mesopores to the highly active zirconia particles, where the chains undergo selective hydrogenolytic cleavage into a narrow, C 18 -centred distribution. Calculations indicated that C–H bond heterolysis across a Zr–O bond of a Zr(O) 2 adatom model for unsaturated surface sites gives a zirconium hydrocarbyl, which cleaves a C–C bond via β-alkyl elimination. 

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2. Polyolefin Ionomer Synthesis Enabled by C–H Thioheteroarylation

   https://doi.org/10.1021/acs.macromol.3c01610  

   Tran, Quan H; Neidhart, Eliza K; Sheiko, Sergei S; Bras, Wim; Leibfarth, Frank A (November 2023, Macromolecules)

   Chemical upcycling of plastic waste into high-value materials has the potential to contribute to a more sustainable plastic economy. We report the synthesis of high-value ionomers directly from commodity polyolefins enabled by amidyl radical mediated C−H functionalization. The use of thiosulfonates as a linchpin functionality for the group transfer of a variety of heteroaryl groups provided tunable incorporation of ionizable functionality onto a variety of polyolefin substrates, including postconsumer polyethylene packaging waste. Synthetic, structural, and thermomechanical studies provided a comprehensive understanding of both structure−reactivity and structure−property relationships for polyolefin ionomers. X-ray scattering experiments conducted in the solid and melt states confirm the presence of ionic multiplets that serve as physical cross-links both below and above the melting temperature of polyolefin crystallites. The incorporation of ionic groups into the polyolefins yielded materials with significantly enhanced melt strength and tensile toughness. We anticipate that this approach to access performance-advantaged polyolefin ionomers from commodity substrates or plastic waste will enhance sustainability efforts and lead to new opportunities for this versatile class of thermoplastics. 

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3. Lightweight micro-cellular plastics from polylactide/polyolefin hybrids

   https://doi.org/10.1016/j.polymer.2016.08.102  

   Xu, Yuewen; Delgado, Paula; Todd, Alexander D.; Loi, Jesse; Saba, Stacey A.; McEneany, Ryan J.; Tower, Ted; Topolkaraev, Vasily; Macosko, Christopher W.; Hillmyer, Marc A. (October 2016, Polymer)
4. Tunable modalities in polyolefin synthesis via coordination insertion catalysis

   https://doi.org/10.1016/j.eurpolymj.2020.110100  

   Tran, Thi V.; Do, Loi H. (January 2021, European Polymer Journal)

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5. C–H Functionalization of Polyolefins to Access Reprocessable Polyolefin Thermosets

   https://doi.org/10.1021/jacs.3c08682  

   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; et al (December 2023, Journal of the American Chemical Society)

   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. 

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