,-Bis(2,4-Dibenzhydryl-6-cycloalkylphenyl)butane-2,3-diimine-Nickel Complexes as Tunable and Effective Catalysts for High-Molecular-Weight PE Elastomers.

Four examples of ,-bis(aryl)butane-2,3-diimine-nickel(II) bromide complexes, [ArN=C(Me)-C(Me)=NAr]NiBr (where Ar = 2-(CH)-4,6-(CHPh)CH (), Ar = 2-(CH)-4,6-(CHPh)CH (), 2-(CH)-4,6-(CHPh)CH () and 2-(CH)-4,6-(CHPh)CH ()), disparate in the ring size of the -cycloalkyl substituents, were prepared using a straightforward one-pot synthetic method. The molecular structures of and highlight the variation in the steric hindrance of the -cyclohexyl and -cyclododecyl rings exerted on the nickel center, respectively. By employing EtAlCl, EtAlCl or MAO as activators, - displayed moderate to high activity as catalysts for ethylene polymerization, with levels falling in the order (cyclohexyl) > (cyclopentyl) > (cyclododecyl) > (cyclooctyl). Notably, cyclohexyl-containing /MAO reached a peak level of 13.2 × 10 g(PE) of (mol of Ni) h at 40 °C, yielding high-molecular-weight (ca. 1 million g mol) and highly branched polyethylene elastomers with generally narrow dispersity. The analysis of polyethylenes with C NMR spectroscopy revealed branching density between 73 and 104 per 1000 carbon atoms, with the run temperature and the nature of the aluminum activator being influential; selectivity for short-chain methyl branches (81.8% (EtAlCl); 81.1% (EtAlCl); 82.9% (MAO)) was a notable feature. The mechanical properties of these polyethylene samples measured at either 30 °C or 60 °C were also evaluated and confirmed that crystallinity () and molecular weight () were the main factors affecting tensile strength and strain at break ( = 353-861%). In addition, the stress-strain recovery tests indicated that these polyethylenes possessed good elastic recovery (47.4-71.2%), properties that align with thermoplastic elastomers (TPEs).