PROPYLENE POLYMERIZATION WITH CATALYSTS CONTAINING DIVALENT TITANIUM

The behavior in propylene polymerization of divalent titanium compound s of type [eta(6)-areneTiAl(2)Cl(8)], both as such and supported on ac tivated MgCl2, has been studied and compared to that of the simple cat alyst MgCl2/TiCl4. Triethylaluminium was used as cocatalyst. The Ti-ar ene complexes were active both in the presence and in the absence of h ydrogen, in contrast to earlier reports that divalent titanium species are active for ethylene but not for propylene polymerization. C-13-NM R analysis of low molecular weight polymer fractions indicated that th e hydrogen activation effect observed for the MgCl2-supported catalyst s should be ascribed to reactivation of 2,1-inserted (''dormant'') sit es via chain transfer, rather than to (re)generation of active trivale nt Ti via oxidative addition of hydrogen to divalent species. Decay in activity during polymerization was observed with both catalysts, indi cating that for MgCl2/TiCl4 catalysts decay is not necessarily due to overreduction of Ti to the divalent state during polymerization. In et hylene polymerization both catalysts exhibited an acceleration rather than a decay profile. It is suggested that the observed decay in activ ity during propylene polymerization may be due to the formation of clu stered species that are too hindered for propylene but that allow ethy lene polymerization. (C) 1997 John Wiley & Sons, Inc.