Journal of Molecular Catalysis A: Chemical 236 (2005) 87–93 Synthesis of branched polyethylene from ethylene stock by an interference-free tandem catalysis of TiCl 4 /MgCl 2 and iron catalyst Zhicheng Zhang a,b , Zhanxia Lu a,b , Shangtao Chen a,b , Huayi Li a,b , Xiaofan Zhang a,b , Yingying Lu a , Youliang Hu a,∗ a Joint Laboratory of Polymer Science and Materials, Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China b Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China Received 12 December 2004; received in revised form 28 March 2005; accepted 29 March 2005 Available online 23 May 2005 Abstract An interference-free tandem catalysis based on iron catalyst and TiCl 4 /MgCl 2 , activated by MAO, was used to prepare branched polyethylene by polymerization of ethylene. No obvious deactivation due to the side reaction of catalysts and cocatalysts was detected during the reaction process, which commonly existed in tandem catalytic systems based on conventional Ziegler–Natta catalysts. A series of branched polyethylene with different properties have been prepared by adjusting of reaction temperature, Fe/Ti molar ratio and the amount of MAO used. The alteration of oligomers concentration in the reaction system, by changing of reaction conditions, led to the products with different branching degrees, thus the thermal properties and molecular weight. The products obtained in toluene at lower Fe/Ti ratios exhibited better morphology than those obtained at higher Fe/Ti ratios. © 2005 Elsevier B.V. All rights reserved. Keywords: Branched; Polyethylene (PE); Copolymerization; Catalyst 1. Introduction Polyethylene with short-chain branches, known as linear low-density polyethylene (LLDPE), is an important mem- ber of the family of polyethylenes and has become of in- terest to plastic industry in the recent past. Compared with high density polyethylene (HDPE), LLDPE exhibits a lower melting point, lower crystallinity, and lower density due to the presence of short-chain branches with controlled length and frequency on the polymer backbone, which effectively enhance the mechanical strengths of polyethylene products, such as the stiffness, stress-crack resistance, tensile strength, and most importantly, processability. ∗ Corresponding author. Tel.: +86 10 6256 2815; fax: +86 10 6255 4061. E-mail address: huyl@iccas.ac.cn (Y. Hu). Branched polyethylene is conventionally produced by ethylene copolymerization with -olefin comonomer, such as 1-butene, 1-hexene, and 1-octene with Ziegler–Natta cat- alysts or single-site catalysts. In the 1980s, Beach and Kissin [1] and Kissin and Beech [2] reported a one-step method for producing branched polyethylene from only ethylene using a dual function catalytic system, which is well known as tan- dem reaction or in situ copolymerization. In this procedure, a tandem reaction is carried out by two catalysts: 1-alkene is produced by one catalyst from ethylene oligomerization and is copolymerized by the other in situ with ethylene to produce LLDPE. The most interesting advantage over com- mon approaches is that only ethylene is used. The products with different properties could be obtained just by adjusting reaction conditions and the molar ratio of two catalysts. There were three kinds of tandem catalytic systems reported: Ziegler–Natta catalysts [1,2], single-site catalysts 1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molcata.2005.03.046