Ligand-Unsymmetrical Phenoxyiminato Dinickel Catalyst for High Molecular Weight Long-Chain Branched Polyethylenes

Abstract

An unsymmetrical bimetallic catalyst, (CF 3 / SO 2 )FI 2 -Ni 2 , having a CF 3 -functionalized phenoxyiminato Ni(II) center, which produces linear high-M w polyolefin (CF 3 /Ni) joined to an adjacent SO 2 -functionalized phenoxyiminato Ni(II) center, which produces highly branched low-M w polyolefin (SO 2 /Ni), was synthesized and fully characterized. In ethylene homopolymerizations, (CF 3 /SO 2 )FI 2 -Ni 2 affords monomodal (Đ = 1.7), highly, long-chain branched (69 branches/1000 C) polyethylenes with M w = 24 kg/mol. In contrast, bimetallic (CF 3 )FI 2 -Ni 2 and (SO 2 )FI 2 -Ni 2 produce high-M w (25 kg/mol) exclusively methyl-branched (40 branches/1000 C) and low-M w (4.5 kg/mol) highly branched (105 branches/1000 C) polyethylenes, respectively, while tandem monometallic (CF 3 )FI-Ni + (SO 2 )FI-Ni catalyst mixtures yield a bimodal polyolefin mixture (Đ = 6.4).

Recent Progress in Ethylene Polymerization Catalyzed by Ni and Pd Catalysts

“…A ligand‐asymmetric homobimetallic complex can offer the advantages of two active centers with different functions to synthesize PE with unique properties. Shu et al reported bimetallic complex 35 (Figure ), with unsymmetrical phenoxyiminato ligands inspired by a [Ti–Cr] heterobimetallic catalyst . However, the activity of complex 35 [20 kg PE (mol of Ni) –1 atm –1 h –1 ] is much lower than that of its mononuclear analogues [60, 335 kg PE (mol of Ni) –1 atm –1 h –1 ] under similar reaction conditions.…”

“…Structures of catalysts 35 , 36 , 37a – c , 38a – d , 39a , 39b , 40a – d , and 41a – f , ,. [27b], , , …”

“…Usually, PE with higher molecular weight can be generated by using bimetallic catalysts, due to the efficient blocking of the axial sites of the metal centers by the ligands, and to the metals suppressing β‐H elimination and/or chain transfer to some extent, whereas mononuclear catalysts experience only limited steric hindrance from ligands , ,. [27c], , , , For example, results (Table ) from Chen's group[27c] show that the molecular weight of the resulting polymer increase with increasing bulkiness at the ortho ‐aryl positions of catalysts and that higher molecular weight can be achieved by using bimetallic complexes 32a – e (Figure ) than with their mononuclear analogues 32f – h (Figure ).…”

“…Recent progress has revealed special applications of various new Ni and Pd catalysts. Unusual polymers such as ultra‐high‐molecular‐weight PE (UHMWPE), elastomeric polymers, and branched high‐molecular‐weight PE[4b], (BHMWPE) can be obtained through ethylene polymerization catalyzed by these catalysts. PE containing linear short branches, and hyperbranched–branched diblock polyolefins have been synthesized by a “tandem catalysis” one‐pot approach.…”

“…Gladysz et al designed a process termed “phase‐transfer catalyst activation” to eliminate the negative effects of pre‐coordinating bases and to avoid the use of cocatalyst . Shu et al used ligand‐asymmetric homobimetallic catalyst to imitate “tandem catalysis” and heterobimetallic catalysis …”