Ethylene polymerization using combined Ni and Ti catalysts supported in situ on MAO-modified silica

Branched polyethylene/linear polyethylene blends (BPE/LPE) were prepared using the combined Ni(alpha-diimine)Cl-2 (1) (alpha-diimine = 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine) and (Tp(Ms*))TiCl3 (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/SiO2). The polymerization reactions were performed in toluene at two different polymerization temperatures (0 and 30degreesC) 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 0degreesC. The melting temperatures for the polyethylene blends produced at 0degreesC 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).