N , N -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 N , N -bis(aryl)butane-2,3-diimine-nickel(II) bromide complexes, [ArN=C(Me)-C(Me)=NAr]NiBr 2 (where Ar = 2-(C 5 H 9 )-4,6-(CHPh 2 ) 2 C 6 H 2 ( Ni1 ), Ar = 2-(C 6 H 11 )-4,6-(CHPh 2 ) 2 C 6 H 2 ( Ni2 ), 2-(C 8 H 15 )-4,6-(CHPh 2 ) 2 C 6 H 2 ( Ni3 ) and 2-(C 12 H 23 )-4,6-(CHPh 2 ) 2 C 6 H 2 ( 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 EtAlCl 2 , Et 2 AlCl 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 × 10 6 g(PE) of (mol of Ni) -1 h -1 at 40 °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 13 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 2 ); 81.1% (Et 2 AlCl); 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 ( X c ) and molecular weight ( M w ) were the main factors affecting tensile strength and strain at break ( ε 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).