Efficient Slurry-Phase Homopolymerization of Ethylene to Branched Polyethylenes Using α-Diimine Nickel(II) Catalysts Covalently Linked to Silica Supports

Abstract

R-Diimine nickel(II) complexes covalently linked to a silica support were obtained by the reaction of an amino-or hydroxy-functionalized R-diimine nickel complex with silica particles treated with trimethyl aluminum. These silica-supported aryl R-diimine nickel(II) precatalysts linked via an amino (1a) or hydroxy functionality (1b-c) at the p-aryl position, and precatalysts linked via one (2a) or two (2b) hydroxy functionalities in the alkyl backbone were used in slurry polymerizations of ethylene to produce branched polyethylenes. Activation of precatalysts with ethylaluminum sesquichloride was effective even at very low Al/Ni ratios of 48. Initial polymerizations, performed at 60 °C and 150 psig ethylene, showed excellent productivities of up to 10.8 kg PE per gram of 1b (3.0 wt % nickel loading). Low productivities at temperatures above 60 °C can in part be overcome by increase in ethylene pressure. For example, a productivity of 6.0 kg PE per gram of 1b (3.0 wt % nickel loading) was obtained at 80 °C and 700 psig ethylene. The best polymerization productivities were obtained with trimethylaluminum as a traceless silica-linker, however, tetrachlorosilane and trichloroborane are attractive alternatives. Branching densities can be controlled by choice of ortho-aryl substituents. No reactor fouling occurs with these supported catalysts.

Synthesis of Supported Nickel Diimine Catalysts for Ethylene Slurry Polymerization

“…The nickel diimine complex, N2, is supposed to be covalently attached onto the TMA-treated silica. [16] Physiosorbed borates are assumed to activate the N2 complex, which was previously alkylated during treatment with TMA. Although the borate internal activator was physiosorbed onto the silica support, it is unlikely to be abstracted easily due to the poor solubility of borates in the hexane diluent, creating a very favorable supported catalyst for ethylene polymerization in slurry reactors.…”

“…Recently, Brookhart's group showed that covalent bonding between nickel diimine catalysts and functional groups on the support surface allows higher nickel loadings, leading to high activity as well as strong catalyst immobilization on the support surface. [15,16] Alkyl aluminum activators, such as methyl aluminoxane (MAO), are effective catalysts activators but require Al/transition metal ratios that may vary from hundreds to thousands. Alternatively, bulky anionic borates such as B(C 6 F 5 ) À 4 can be used as activators and provide a more precisely defined catalyst system due to their exactly characterized structures.…”

Recent progress in immobilization of late-transition-metal complexes with diimine ligands for olefin polymerization

“…Some studies suggested that covalent linking of soluble metal complexes to the support was the most effective way to reduce leaching [30,31], and the negative influence on the active sites was relatively small. Schrekker et al [32] synthesized α-diimine nickel precatalysts with an amino or hydroxyl functionality at the р-aryl position and precatalysts with one or two hydroxyl functionalities in the alkyl backbone ( Figure 2). …”

Preparation of Nanosilica/Polynorbornene Nanocomposite by Covalently Immobilized Silica‐Supported Acetylacetonate Palladium(II) Dichloride Catalyst

“…[ 25 , 26 ] Among them, nanoparticle supports may offer more advantages over bulk supports, such as increased surface area, mass transfer, and better heat and decreased internal surface area, [ 27 , 28 ] which made it in the use of slurry reactors. [ 29 ] Moreover, covalent linking of the soluble catalysts to the support is the most effective method to reduce the leaching phenomena. [ 19 ] In the case of olefin polymerization, steric crowding around the metal center and the growing polymer chain may lead to decreased activities, adverse mass transport effects, or both, [ 30 , 31 ] but the mechanism is still not clear, so there are a lot of works to do.…”