By immobilizing titanium-based ZieglerNatta catalyst on composite support, SiO2/MgCl2 center dot x(1,4-butanediol)/poly[styrene-co-(acrylic acid)] (SiO2/MgCl2 center dot xBD/PSA) and SiO2/MgCl2 center dot xBD/PSA/TiCl4 (SMPT) were synthesized for ethylene polymerization. SiO2/MgCl2 center dot xBD/TiCl4 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. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012