Branching Pattern, Distribution, and Chain-Walking Mechanism of Highly Branched Polyethylenes Synthesized by α-Diimine Ni(II) Catalysts as Studied via 13C Solution-State NMR Spectroscopy

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.