Some peculiar aspects of a new catalyst for propene polymerization

Abstract

An investigation was carried out on the preparation of highly disordered samples of MgCl (in delta -form), starting from different Mg-alkyls and chlorinating agents. Successively we studied which kind of silica carrier had to be preferred and which treatment was strictly'necessary to achieve a qualified catalyst precursor showing outstanding performance.Different routes were investigated to support the active, disordered MgCl on the silica carrier and then some following ways to complete the catalyst. The final result of this investigation was the synthesis of a catalyst showing the best performance with reference to the parameters of use in every polymerization process.It has to be e.g. mentioned: 2 2 high yield, referred to the residual content of Mg, Ti and Cl; no activity decrease when operating at a very high hydorgen concentration; possibility to polymerize also at elevated temperatures; very high isotactic index and stereoregular structure, as measured by the NMR technique; possibily to reach high MFR (Melt Flow Rate) (up to 400 g IPP/lO min at 23OoC, 2,16 kg, ASTM D 1238L); outstanding morphology and flowability.

Theoretical investigation of (MgCl2)xpolynuclear species formed during preparation of MgCl2-supported Ziegler–Natta catalysts from solid solvates

“…The X-ray powder diffraction profiles of the so-obtained active form of MgCl 2 show a broad asymmetric halo in the 2 range 30-35 , a broad peak centred at 2 ' 50.1 (as in curves a of Fig. 2), whereas the diffraction maximum at 2 ' 15 may be totally absent, or substituted with a broad halo (Di Di Noto & Bresadola, 1996;Luciani et al, 1995;Marigo et al, 2000). In some cases, the absence of any diffraction peak at 2 ' 15 indicates that the active form of MgCl 2 consists of single Cl-Mg-Cl structural layers (monolayers) (Zannetti et al, 1988;Auriemma et al, 2000).…”

Silyl diol ester as a new selectivity control agent in MgCl2-supported Ziegler–Natta systems for propylene polymerization: catalyst structure and polymer properties

“…[2][3][4] Consequently, the catalyst activity, microstructure of the resulting poly(a-olen) including stereoregularity, molecular weight (M w ), and polydispersity index (PDI), and the hydrogen response in the polymerization process will be affected by SCAs. [5][6][7][8][9][10][11][12] Therefore, the evolution of a new generation of polypropylene catalysts is strongly related to the introduction of new structures and functions that have the potential to act as IDs and EDs. 13 In particular, the fourth generation of catalysts incorporating phthalate as the most common commercial ID and alkoxy silane as an ED has been successful in producing highly isotactic polypropylene, but phthalate is frequently criticised for its environmental and health risks.…”

Thermodynamics of Formation of Uncovered and Dimethyl Ether-Covered MgCl2 Crystallites. Consequences in the Structure of Ziegler–Natta Heterogeneous Catalysts

“…The resulting active system is of extreme chemical complexity, and the polypropylene obtained presents very different properties. The nature of the added Lewis bases is fundamental in terms of performance, because it can significantly impact (i) the tacticity of the obtained polypropylene from a large fraction of almost atactic polymer (as in the absence of any Lewis base) to almost exclusively highly isotactic polymers, (ii) the molecular mass distribution, that can be rather narrow or rather broad, and (iii) the response to molecular hydrogen, which clearly allows one to control the molecular masses of the produced polymers. − However, the Lewis bases clearly have a significant impact upon the morphology of the final catalyst, because they can stabilize small primary crystallites of MgCl 2 and/or influence the amount and distribution of TiCl 4 in the final catalyst.…”