Ethylene Polymerization using Combined Ni and Ti Catalysts Supported in situ on MAO‐Modified Silica

Abstract

Abstract Summary: Branched polyethylene/linear polyethylene blends (BPE/LPE) were prepared using the combined Ni( α ‐diimine)Cl 2 ( 1 ) ( α ‐diimine = 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediimine) and {Tp Ms* }TiCl 3 ( 2 ) (Tp Ms* = hydridobis(3‐mesitylpyrazol‐1‐yl)(5‐mesitylpyrazol‐1‐yl)) catalysts supported in situ on methylaluminoxane (MAO)‐modified silica (4.0 wt.‐% Al/SiO 2 ). The polymerization reactions were performed in toluene at two different polymerization temperatures (0 and 30 °C) and several nickel molar fractions ( x Ni ), using MAO as external cocatalyst. At all temperatures, the activities show an approximate linear correlation with x Ni , indicating a non‐synergistic effect between the nickel and the titanium species. Higher activities were found at 0 °C. The melting temperatures for the polyethylene blends produced at 0 °C decrease as x Ni increases in the medium, indicating good compatibility between the polyethylene phases made by both catalysts. The melting temperature ( T m ) of the polyethylene blends was shown to depend on the order in which the catalysts were immobilized on the MAO‐modified silica support. The initial immobilization of 1 on the support ( 2 / 1 /SMAO‐4) affords polymers with a lower T m than those produced with 1 / 2 /SMAO‐4. In addition, scanning electron microscopy (SEM) studies revealed that the spherical morphology of the supported catalyst is replicated in the polyethylene particles. Influence of polymerization temperature on the activity of 1 / 2 /SMAO‐4 with varying x Ni . magnified image Influence of polymerization temperature on the activity of 1 / 2 /SMAO‐4 with varying x Ni .