ADDITIVE EFFECTS OF LEWIS-BASES ON PROPENE POLYMERIZATION OVER MGCL2-SUPPORTED TICL4 CATALYSTS COMBINED WITH CP(2)TIME(2)

Propene polymerization was conducted with TiCl4/(Lewis base)/MgCl2-Cp( 2)TiMe(2) catalysts in the presence of ethyl benzoate (EB) and/or 2,2- diisobutyl-1,3-dimethoxypropane (DBDMP). The addition of small amounts of these Lewis bases to MgCl2 before supporting TiCl4 decreased the a mount of Ti in the catalyst and improved catalyst isospecificity. The results suggested that the Lewis base is selectively coordinated on th e MgCl2 surface where aspecific sites had been formed. The addition of the Lewis bases during the polymerization increased polymerization ra te followed by rapid deactivation. Deactivation was second order on th e polymerization rate and the deactivation rate constant depended on b oth structure and amount of the Lewis base. GPC analysis of the produc ed polymers indicated that the addition of the Lewis bases increased t he molecular weight of isotactic polypropene (IPP). Polydispersity dep ended on the Lewis base: it became narrower by EB and broader by DBDMP . The C-13 NMR spectra of IPPs revealed that EB improved the microtact icity of IPP more effectively than DBDMP. ESR spectra of the catalysts indicated that the amount of isolated Ti3+ species increased in the p resence of EB.