Preparation of linear low-density polyethylene from ethylene by tandem catalysis of titanium(IV) and nickel(II) non-metallocene catalysts

Abstract

Non-metallocene titanium(IV) complexes of 2-hydroxymethylphenol derivatives [O^O]TiCl2 2iPrOH (2–3), which can form a tandem catalytic system with a phenoxy-imine nickel complex (1), were firstly used as an in situ copolymerization catalyst to prepare linear low-density polyethylene (LLDPE) with ethylene as the sole monomer stock and Et2AlCl/Bu2Mg as the cocatalyst. During the reaction, 1/Et2AlCl oligomerized ethylene to linear α-olefins with high activity and selectivity, while 2–3/Et2AlCl+Bu2Mg copolymerized ethylene with the in situ generated α-olefins to LLDPE with high activity (up to 7.4×105g/molTihatm). The influence of the reaction conditions upon the catalytic activity and polymer structures and properties have been researched. The polymers were characterized by differential scanning calorimetry (DSC), high temperature gel permeation chromatography (GPC) and high temperature 13C NMR spectroscopy and they were proven to be LLDPE with ethyl and butyl branches. The compositions of comonomers were tuned efficiently from 2% to 6% by different reaction conditions such as reaction temperature, Ni/Ti molar ratio and Al/(Ni+Ti) molar ratio. The melting points, degree of crystallinity and molecular weights (2.7×105–1.5×106) also changed correspondingly with the reaction conditions.