Bis(Tolyl)methyl‐ and Nitro‐Functionalized Unsymmetrical α‐Diimine Nickel Precatalysts for Polyethylene Elastomer: Enhanced Activity and Thermal Stability

ABSTRACT

Ethylene coordination‐insertion polymerization is strongly dictated by the steric and electronic modifications in the catalyst structure. Herein, the influence of bis(tolyl)methyl and nitro substituents—serving as steric and electronic modulators—on α‐diimine nickel bromide and chloride precatalysts is systematically investigated. Upon activation with either Me₂AlCl or MAO, both bromide and chloride complexes exhibited remarkable activities (as high as 1.8 × 10⁷ g_PE (mol_Ni)⁻¹ h⁻¹) and produced high‐molecular‐weight polyethylene elastomers (PEEs) with controlled dispersities across a broad temperature range (30°C–100°C); a notable activity of 1.8 × 10⁶ g_PE (mol_Ni)⁻¹ h⁻¹ with a molecular weight of 1.7 × 10⁵ g mol⁻¹ at 100°C reflects the excellent thermal robustness. Bromonickel precatalysts outperformed their chloro analogues in both activity and molecular weight, with less hindered variants favoring higher activity, while bulkier substituents promoted the formation of higher molecular weight polyethylene. High branching density, being dominated by methyl branches, corroborated the superior thermal (T_m > 100°C) and mechanical properties (σ_b up to 11 MPa), while elevated polymerization temperatures resulted in PEEs with high elasticity (SR = 74%). These findings elucidate the critical parameters of substituent variations and reaction conditions on directly polymerizing sole ethylene for PEE.