Synthesis of branched polyethylene by ethylene homopolymerization with a novel (α‐diimine)nickel complex in the presence of methylaluminoxane

Abstract

Branched polyethylene (PE) was prepared with a novel (␣-diimine)nickel(II) complex of 2,3-bis(2,6-dimethylphenyl)-butanediimine nickel dichloride {[2,6-(CH 3 ) 2 C 6 H 3 ONAC(CH 3 )C(CH 3 )ANO2,6-(CH 3 ) 2 C 6 H 3 ]NiCl 2 } activated by methylaluminoxane in the presence of a single ethylene monomer. The influences of various polymerization conditions, including the temperature, Al/Ni molar ratio, Ni catalyst concentration, and time, on the catalytic activity, molecular weight, degree of branching, and branch length of PE were investigated. According to gel permeation chromatography, the weight-average molecular weights of the polymers obtained ranged from 1.7 ϫ 10 5 to 6.0 ϫ 10 5 , with narrow molecular weight distributions of 2.0 -3.5. The degree of branching in the polymers rapidly increased with the polymerization temperature increasing; this led to highly crystalline to totally amorphous polymers, but it was independent of the Al/Ni molar ratio and catalyst concentration. At polymerization temperatures greater than 20°C, the resultant PE was confirmed by 13 C-NMR to contain significant amounts of not only methyl but also ethyl, propyl, butyl, amyl, and long branches (longer than six carbons). The formation of the branches could be illustrated by the chain walking mechanism, which controlled their specific spacing and conformational arrangements with one another.

Ethylene polymerization with imine and phosphine nickel complexes containing isothiocyanate

“…16 Nevertheless, the Materials, Nanoscience and Catalysis influence of the non-chelating ligand on the polymerization of olefins with nickel complexes has received less attention. 17,18 We have investigated the preparation of nickel diimine and iminophosphine complexes containing isothiocyanate (NCS) as a non-chelating ligand. In this paper we discuss the synthesis of those complexes, as well as their effect on the polymerization of ethylene with methylaluminoxane (MAO) as cocatalyst, comparing their performance with that of the analogous halides and with that of the diphosphine complexes containing chlorine or NCS groups.…”

Recent Research Progress of Branched and Functional Branched Polyethylene Prepared Using Ni- and Pd–Based Catalysts

“…Ethylene is a simplest monomer and recently, production of branched and functional branched polyethylene attracted significant attention in polymer chemistry [3,4] . On the one hand, the branched polyethylene with outstanding processability and film conveniently forming properties is prepared via microstructure control.…”

Unsymmetrical α‐diimine nickel (II) complex with rigid bicyclic ring ligand: Synthesis, characterization, and ethylene polymerization in the presence of AlEt2Cl

“…Recently, α‐diimine nickle (II) complexes have been disclosed owning great potential for the branching polymerization of ethylene through the modification of the ligands' steric and electronic properties 8–14. No matter how different the coordination environment of these reported α‐diimine nickle (II) complexes was, the degree of branching of the obtained polyethylenes below 0°C was trace 13, 14…”

“…It is reasonable to believe that the resultant ligand 1 and corresponding nickel (II) complex 1 exists as syn‐ and anti‐isomers. The effect of the interconversion of both isomers on ethylene polymerization was investigated, and the obtained polymer was characterized by GPC,13 C NMR, and DSC.…”