Supported Metallocene Complexes for Ethylene and Propylene Polymerizations:  Preparation and Activity

Abstract

Important research is currently underway to develop supported metallocene-based catalysts that could be widely used in the polyolefin industry. Recent developments concerning these systems are reviewed. The main preparation methods for metallocene immobilization on various supports are first systematized and described. Then, the nature and structure of active sites as well as their formation mechanism are analyzed. The performances for ethylene and propylene polymerizations of various supported metallocene systems are compared and discussed on the basis of the different catalyst preparations and of the operational polymerization conditions. Finally, the influence of metallocene heterogenization on the final polymer properties is examined.

Linear low-density polyethylene synthesis promoted by homogeneous and supported catalysts

“…According to Fig 1, the activity of (nBuCp) 2 ZrCl 2 /SiO 2 is almost four times lower when compared to the homogenous system. This has already been discussed in the literature 27 and can be explained taking into account that in the supported catalyst preparation, during the grafting reaction, different adsorptions might take place, leading to different sites on the surface, some of which are inactive for polymerization. Therefore not all the Zr present in the catalyst is necessarily an active species.…”

XPS investigation of the electronic environment in selected heterogenized zirconocene catalysts

“…18,19 When it is treated subsequently with MAO, the following occurs: MAO, being a Lewis acid, methylates Et(Ind) 2 ZrCl 2 ; consequently, a bridged zirconocenium methyl species (Cation 2), presumed to be trapped and stabilized in multi-coordinate crown alumoxane complex(es), is produced: 20,21 these zirconocenium cations provide the polymerization catalytic sites and are postulated to differ in the electronic and steric effects with respect to the silica surface. 3,18,19 In Method 2, MAO first reacts with the silica surface OH groups to form stable Si-O-Al bonds. The surface-anchored MAO plays the following roles: methylation, Cl ion abstraction and crown alumoxane complex(es) formation (Cation 2).…”

“…A solvent-free process is economical but the resin morphology influences the packing density, particulate flow behaviour and polymer processability. 1 The literature reveals 2,3 several outstanding problems in heterogeneous metallocene catalysis and the associated slurry olefin polymerization. Heterogenized metallocenes show a drastic decrease in catalytic activity and the catalyst precursors leach off the support.…”

Control of molecular weight and polydispersity in polyethylene/needle-like shaped clay nanocomposites obtained by in situ polymerization with metallocene catalysts

“…Unlike the Ziegler-Natta catalyst, the use of metallocene catalysts in in situ polymerization can be very sensitive to the filler surface. This sensitivity is due to the immobilization process included the co-catalyst instead of a single catalyst molecule as in most in situ polymerization processes [35,36]. Moreover, immobilizing the co-catalyst onto the clay was carried out without previous clay calcination.…”