Timo Leinonen

Mn doping of the Ziegler-Natta PP catalyst support material

Preliminary tests have shown that if MnCl2 is used as a support material a polypropylene with a low molecular weight is produced. The activity of these catalysts is low. A low molecular fraction increases, however, the gloss of moulded products. As a molecular fraction with short chain length also acts as a lubricant in the polymer this short chain material would be an advantage if it is produced simultaneously with the normal high molecular weight polypropylene. This ability to influence the molecular weight distribution of the product was the reason why MnCl2 was chosen as a doping salt in the MgCl2 support material. The effect of Mn doping on the MgCl2 support material has been investigated. The following conclusions have been drawn from this investigation: (i) Very good morphology is achieved if the MnCl2 concentration is below 30%. At higher doping concentrations the result is poor morphology. (ii) Large catalyst particles were produced. The particles were of great mechanical strength, leading to the formation of large polymer particles with a very narrow PSD. No fines were produced partly due to agglomerization. This advantage was achieved only if the MnCl2 concentration was below 30%. (iii) Optimum Mn doping concentration was 10 mol%. Using this doping concentration activity increased 25% (100% if kg PP/g Ti units are used). No loss in isotacticity. At higher Mn concentrations activity decreased linearly. The molecular weight distribution was effected. A broader MWD was achieved. The greatest effect was achieved with a Mn concentration of 10 mol%. The polydispercity increased from the standard value of 3 to 7. At higher Mn concentrations the MWD decreased steadily. Low molecular weight polypropene can be produced by using pure MnCl2 as support material. (iv) The pore size distribution is effected by the Mn doping. A large portion of pores between 1 and 3 microns are produced. In standard polypropylene the largest fraction is to be found between 10 and 100 microns.

Solid state 13C NMR characterisation study on fourth generation Ziegler–Natta catalysts

In this study, solid state (13)C NMR spectroscopy was utilised to characterize and identify the metal-ester coordination in active fourth generation (phthalate) Ziegler-Natta catalysts. It is known that different donors affect the active species in ZN catalysts. However, there is still limited data available of detailed molecular information how the donors and the active species are interplaying. One of the main goals of this work was to get better insight into the interactions of donor and active species. Based on the anisotropy tensor values (δ(11), δ(22), δ(33)) from low magic-angle spinning (MAS) (13)C NMR spectra in combination with chemical shift anisotropy (CSA) calculations (δ(aniso) and η), both the coordinative metal (Mg/Ti) and the symmetry of this interaction between metal and the internal donor in the active catalyst (MgCl(2)/TiCl(4)/electron donor) system could be identified.

A Study of Ziegler–Natta Propylene Polymerization Catalysts by Spectroscopic Methods

Ziegler–Natta polymerization catalysts were characterized by a complex of surface- and bulk-sensitive methods (DRIFTS, XPS, ESR, and XAS = XANES + EXAFS). A diffuse-reflectance Fourier-transform IR spectroscopy (DRIFTS) study showed the presence of strong Lewis acid sites in different concentrations and absence of strong basic sites in the polymerization catalysts. X-ray photoelectron spectroscopy (XPS), electron-spin resonance (ESR), and (X-ray absorption near-edge structure (XANES) analysis revealed the presence of Ti4+, Ti3+, Ti2+, and Ti1+ species in the surface layers and in the bulk of catalysts. The samples under study differ drastically in terms of the number of ESR-visible paramagnetic sites. The EXAFS study shows the presence of a Cl atom as a nearest neighbor of the absorbing Ti atom.