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Branching number, pattern, and distribution of polyethylene (PE) significantly affect the crystalline structures at hierarchical length scales and thus dominate physical properties. Highly branched (HB) PE with over 100 branches per 1000 carbons (100b/1kC) can be synthesized from a sole ethylene feedstock using α-diimine nickel catalysts but results in complex 13C solution-state NMR spectra. In this study, we assign numerous 13C peaks that were unassigned in HBPEs synthesized via three nickel α-diimine catalysts. By application of an additive rule of 13C chemical shifts, several new microstructures are identified. The results successfully reveal new branching microstructures, including (i) the configuration of paired branches, (ii) continual paired branches, and (iii) methylated branch ends. Based on these new assignments, several insights into the chain-walking mechanisms of HBPEs are discussed. 

The catalytic conversion of carbon dioxide into polymers via high-energy comonomers offers a sustainable, low-cost, and low-emission approach for developing conveniently manufactured high-performance materials without competing for land-use or food resources. We present the synthesis of poly(amidoamine) polymers stoichiometrically derived from carbon dioxide, butadiene, and amines displaying useful mechanical properties (tensile strength 43 MPa, Young’s modulus 840 MPa, and flexural modulus 2.8 GPa). The low viscosity precursors are applicable to producing carbon fiber reinforced polymers with fiber wetting and rapid network formation (16 minutes at 150°C). This work reveals that internal hydrogen-bonding catalyzes the ring-opening polymerization, and the intramolecular alcohol moiety promotes chemical recyclability in acidic conditions, allowing fiber recovery with <1.0 wt % difference from virgin fiber and monomer in 72% yield. 

Highly branched polyethylene (PE) thermoplastic elastomer (TPE)s can be synthesized using Brookhart-type α-diimine nickel and palladium catalysts, which show a range of branching number and identity. In this work, we aim at elucidating the structure-property relationship of various PE-TPEs through solution-state and solid-state 13C NMR spectroscopy and mechanical tensile testing. By applying solid-state NMR spectroscopy, DSC, and XRD, it was revealed that small degrees of crystallinity (< 5%) yields polyethylenes that are sufficiently reinforced to exhibit TPE behavior. Across PE samples with similar branching numbers, we relate the effects of branch identity, crystallinity, and molecular weight on the tunable mechanical properties. The structure-property relationship of the PE-TPEs will be discussed.