Preparation Of Reactor Blends Of Linear And Branched Polyethylene With Combined Cp₂TiCl₂/DMN Homogeneous And Supported Catalyst System

In this paper, a metallonce catalyst Cp₂TiCl₂ and a late metal catalyst DMN were used to form a combined catalysts system, and these two catalysts were supported in situ on the on mesoporous particles MCM-41. Ethylene was polymerized using the homogeneous and hetetogeneous combined catalysts system, activated with methylaluminoxane(MAO) in toluene. Differential scanning calorimetry(DSC), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to investigate the morphology and mixed condition of the polymer blends. The result showed that, the combined catalysts supported on MCM-41 could afford highly dispersed polymer blend of two incompatible polymers. The creative work can be summarized as following:(1) Ethylene was polymerized with Cp₂TiCl₂ and DMN combined catalyst, activated with methylaluminoxane(MAO). The reactor blends of branched and linear polyethylene were generated in situ in one reactor, using ethylene as the only monomer. The simplicity of this method allows the polymer properties to be tailored by simple adjustment of the catalyst ratio and polymerization conditions. The GPC analysis of all polyethylene samples showed monomodal molecular weight distributions with low polydispersities. DSC SEM and XRD analysis showed that, the branched and linear PE obtained at 0℃ showed good compatibility; while the PE obtained at 50℃ existed a certain level of phase segregation.The combined catalysts system of Cp₂TiCl₂ and DMN showed high activity. At 0 and 30℃, The overall catalyst activity increased linearly with catalyst Cp₂TiCl₂ molar fraction X_Ti , at 50℃, there was very little influence of Cp₂TiCl₂ molar fraction Xr, on the overall catalyst activity.(2) Combined Cp₂TiCl₂ catalysts were supported in situ on mesoporous particles for ethylene polymerization, using MAO as cocatalyst. Each catalyst polymerized ethylene independently during the polymerization reaction, generating linear/branched simultaneously and thus forming a reactor blend. The geometric constraints of MCM-41 significantly affected the polymer properties and morphology. The morphology and the thermal property of the polyethylene were characterized by DSC and SEM. The results showed that the combined catalysts supported on MCM-41could afford highly dispersed polymer blend of two incompatible polymers which couldn't be produced by using the common bimetallic complex catalysts. The even dispersion of polyethylene made from two type polyethylene chains resulted from the geometric constraints of mesopores materials MCM-41.