ABSTRACT
The act ive forms of t i tanium trichloride most commonly used in Ziegler-Natta polymerizations are the violet �-, Y-, or <5-phases [4] , the latter form being achieved by mechanical alteration of the �- and i'-forms. The precursor � - and ')I-phases are most easily prepared by the chemical reduction of t itanium tetrachloride, under controlled condi t ions. The choice of reducing agents varies, based on the desired s tructural and morphological form of TiCl 3 and the range of react ion condit ions available. Along with other group 2, 1 2, and 1 3 metal alkyls, Grignard reagents are very effective in this context [5] . Since the reactions involve alkylation of the TiCl4 and homolysis of the consequently formed Ti-R bond, the nature of the R group and the choice of X for the Grignard reagents are not crucial [6] . Most Grignards demonstrate sufficient alkylating power for reactions
EI,O TiCl4 + EtMgCl -----+TiCI 3 • MgCl 2 • nEt20
C,H " TiCl4 + BuMgCl · nBu20 -----+TiCI 3(s) + MgClz{s)
101 TiCl4 + C 1 2 H 2 3 MgCl -----+TiCI 3(s)
Ti(OEt)4 + BuMgCI -----+Ti(II I)(OEr)xCly ' 3TH F(s)
carried out in hydrocarbon or ether solvents at ambient or elevated temperatures. The choice of condit ions is dictated by the solubil ity and alkylating potential of the mixture [7-9] . Obviously, the presence of some ether enhances the rate of the reaction, although long-chain alkyl groups, such as dodecyl moieties, allow the use of an ether-free toluene medium with appropriate results. In addit ion, by varying reactions condi tions, solvents, and reagent ratios, the physical and structural characteristics of the catalyst precursors can be controlled. The use of Grignard reagents has also been extended to the reduction of titanium alkoxides, with the concomitant formation of mixed Ti l l l haloalkoxides, which are sui table as Ziegler-Natta catalyst precursors.
