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

Four examples of N,N-bis(aryl)butane-2,3-diimine-nickel(II) bromide complexes, [ArN=C(Me)-C(Me)=NAr]NiBr2 (where Ar = 2-(C5H9)-4,6-(CHPh2)(2)C6H2 (Ni1), Ar = 2-(C6H11)-4,6-(CHPh2)(2)C6H2 (Ni2), 2-(C8H15)-4,6-(CHPh2)(2)C6H2 (Ni3) and 2-(C12H23)-4,6-(CHPh2)(2)C6H2 (Ni4)), disparate in the ring size of the ortho-cycloalkyl substituents, were prepared using a straightforward one-pot synthetic method. The molecular structures of Ni2 and Ni4 highlight the variation in the steric hindrance of the ortho-cyclohexyl and -cyclododecyl rings exerted on the nickel center, respectively. By employing EtAlCl2, Et2AlCl or MAO as activators, Ni1-Ni4 displayed moderate to high activity as catalysts for ethylene polymerization, with levels falling in the order Ni2 (cyclohexyl) > Ni1 (cyclopentyl) > Ni4 (cyclododecyl) > Ni3 (cyclooctyl). Notably, cyclohexyl-containing Ni2/MAO reached a peak level of 13.2 x 10(6) g(PE) of (mol of Ni)(-1) h(-1) at 40 & DEG;C, yielding high-molecular-weight (ca. 1 million g mol(-1)) and highly branched polyethylene elastomers with generally narrow dispersity. The analysis of polyethylenes with C-13 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% (EtAlCl2); 81.1% (Et2AlCl); 82.9% (MAO)) was a notable feature. The mechanical properties of these polyethylene samples measured at either 30 & DEG;C or 60 & DEG;C were also evaluated and confirmed that crystallinity (X-c) and molecular weight (M-w) were the main factors affecting tensile strength and strain at break (& epsilon;(b) = 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).