Hybrid titanium catalyst supported on core-shell silica/poly(styrene-co- acrylic acid) carrier

摘要

Hybrid titanium catalysts supported on silica/poly(styrene-co-acrylic acid) (SiO_2/PSA) core-shell carrier were prepared and studied. The resulting catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, laser scattering particle analyzer and scanning electronic microscope (SEM). The hybrid catalyst (TiCl_3/MgCl_2/THF/ SiO_2TiCl_4/MgCl_2/PSA) showed coreshell structure and the thickness of the PSA layer in the two different hybrid catalysts was 2.0 μm and 5.0 μm, respectively. The activities of the hybrid catalysts were comparable to the conventional titanium-based Ziegler-Natta catalyst (TiCl_3/MgCl_2/THF/SiO_2). The hybrid catalysts showed lower initial polymerization rate and longer polymerization life time compared with TiCl_3/MgCl_2/THF/SiO_2. The activities of the hybrid catalysts were enhanced firstly and then decreased with increasing Ph_2/Pc_2h_4. Higher molecular weight and broader molecular weight distribution (MWD) of polyethylene produced by the core-shell hybrid catalysts were obtained. Particularly, the hybrid catalyst with a PSA layer of 5.0 μm obtained the longest polymerization life time with the highest activity (2071 kg PE mo1~(-1) Ti h~(-1)) and the resulting polyethylene had the broadest MWD (polydispersity index - 11.5) under our experimental conditions. The morphology of the polyethylene particles produced by the hybrid catalysts was spherical, but with irregular subparticles due to the influence of PSA layer.