TiCl _4 immobilized on a composite support SiO _2/ MgCl _2·x(1,4-butanediol)/poly[styrene-co-(acrylic acid)] for ethylene polymerization: The barrier effect of poly[styrene-co-(acrylic acid)]

摘要

By immobilizing titanium-based Ziegler-Natta catalyst on composite support, SiO _2/MgCl _2·x(1,4-butanediol)/poly[styrene-co- (acrylic acid)] (SiO _2/MgCl _2·xBD/PSA) and SiO _2/MgCl _2·xBD/PSA/TiCl _4 (SMPT) were synthesized for ethylene polymerization. SiO _2/MgCl _2·xBD/TiCl _4 without PSA was also prepared for comparison. The results of energy-dispersive X-ray analysis, SEM, and thermogravimetric analysis demonstrated that SMPT had a unique core-mantle-shell structure. The PSA layer can be considered as a barrier for the mass-transfer of reactants based on the results of self-diffusion measurement by pulsed field gradient NMR and ethylene polymerization. The polyethylene produced by SMPT showed high molecular weight (MW) and broad molecular weight distribution (MWD). The influences of PSA content, hydrogen, and comonomer on the ethylene polymerization behavior were also investigated. The results further demonstrated that the PSA layer in the composite support had different diffusion capabilities to the reactants. The physical properties of the produced polyethylene implied the possibility to control the MW and MWD of polyethylene by the manipulation of PSA layer. The catalyst fragmentation during ethylene polymerization was also affected by the PSA shell due to its barrier effect.