By P. C. Barbe
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Additional info for Catalytical and Radical Polymerization
A p p l y i n g this technique to TiC1JMgC12 catalysts activated with T E A o r D E A C at temperatures between - - 5 0 °C and 20 °C and at A1/Ti ratios between 1 and 20, Z a k h a r o v so) was able to detect the presence o f the four principal Table 4. EPR data o n T i 3+ ions formed in titanium-magnesium catalysts of various composition ~0) By permission of Hiithig & Wepf Verlag Signal Value of g-factor Coordination Proposed composition and localization site of Ti3+ compounds A gi = 1,940 gt~ = 1,89-1,90 Distorted Octahedron Solid solution of TiCla in MgCI2 B g± = 1,915-1,925 Distorted Octahedron Ti3÷ ions in chlorine environment, exchanged-bonded with one another or with TiCI3 associates C g = 1,970 Tetrahedron TiC13 molecules stabilized in the MgCI2 surface G g= D g = 1,96 TiCIa - 3 Py complex E g = 1,90 Compound CI~Ti3+OH F g = 1,89 1,99 Ti3+ compounds with titanium-alkyl or titanium-hydride bonds The Catalytic System Ti-Complex/MgCl2 25 signals (A, B, C, G) reported in Table 4 corresponding to Ti a+ ions with different symmetry and coordination states, which he attributed, respectively, to: a solid solution of TiCI3 in MgC12 (A); Ti 3÷ ions in a pure chlorine environment exchangebonded with one another or with TiC13 associates (B); TiC13 molecules stabilized on the MgCI2 surface (C); Ti 3÷ ions with alkyl or hydride ligands ((3).
This may further explain the conflicting data of Soga and Guastalla and Giarmini. In fact, in the first case the polymerization was carried out at atmospheric pressure while the second was at relatively high pressures (3-4 kg/cm2). The influence of hydrogen on the MWD of popypropylene obtained with TIC14] EB/MgC12--A1Et3/EB was recently studied by Keii 119~ bS,lw//~n was found almost independent of the hydrogen pressure, indicating that the theory based on non-uniformity of surface sites is the most plausible cause for MWD broadening.
Petkov 123)also found some activating effect of hydrogen during the polymerization of ethylene with TIC14 + Mg(C6Hs)z--AIEtzC1 at high temperatures. Besides the facilitation of polymeric chain desorption from the catalytic surface, an easier realkylation of the T i - - H bond at high temperatures was also hypothesized. Such a bond would, on the other hand, be considered a termination step at normal polymerization temperatures. The influence of hydrogen on the molecular weight of the polypropylene obtained at 40 °C with the TiCI4/EB/MgCIa--AIEt3/EB catalyst system has recently been studied by Soga and Siono 124).