Synthesis mechanisms of poly[styrene-co-(acrylic acid)]-supported TiCl _4 catalysts modified by magnesium compounds

摘要

Soluble poly[styrene-co-(acrylic acid)] (PSA) modified by magnesium compounds was used to support TiCl_4. For ethylene polymerization, four catalysts were synthesized, namely PSA/TiCl_4, PSA/MgCl _2/TiCl_4, PSA/(n-Bu)MgCl/TiCl_4, and PSA/(n-Bu)_2Mg/TiCl_4. The catalysts were characterized by a set of complementary techniques including X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and element analysis. Synthesis mechanisms of polymer-supported TiCl_4 catalysts were proposed according to their chemical environments and physical structures. The binding energy of Ti 2p in PSA/TiCl_4 was extremely low as TiCl_4 attracted excessive electrons from -COOH groups. Furthermore, the chain structure of PSA was destroyed because of intensive reactions taking place in PSA/TiCl_4. With addition of (n-Bu)MgCl or (n-Bu)_2Mg, -COOH became -COOMg- which then reacted with TiCl_4 in synthesis of PSA/(n-Bu)MgCl/TiCl_4 and PSA/(n-Bu)_2Mg/TiCl_4. Although MgCl_2 coordinated with -COOH first, TiCl_4 would substitute MgCl_2 to coordinate with -COOH in PSA/MgCl _2/TiCl_4. Due to the different synthesis mechanisms, the four polymer-supported catalysts correspondingly showed various particle morphologies. Furthermore, the polymer-supported catalyst activity was enhanced by magnesium compounds in the following order: MgCl_2 > (n-Bu)MgCl > (n-Bu)_2Mg > no modifier.