Polymerization of Propylene by Using Mg(OEt)_2-DNBP-TiCl_4 Catalyst with Alkoxy Disislanes as External Donor

摘要

The effect of different external silane donors on the activity and isotacticity of polypropylene prepared by using Mg(OEt)_2-phthalate ester-TiCl_4-AlEt_3-alkoxy disi-lane catalyst systems has been investigated.In the case of catalyst systems containing (trimethylsilyl)methylalkyldimethoxysilanes [Me_3SiCH_2Si(OMe)_2R] as external do-nors,the bulky Me_3SiCH_2-group was effective in converting aspecific sites into isospe-cific ones,followed by the increase of activity and isospecificity of the obtained polymer.Catalyst activity and isotacticity of the polymer increased with the decrease of the number of alkoxy groups in the substituted alkoxy disilanes.The effect of alkoxy groups between alkoxy disilanes and alkylaluminum as cocatalyst on the active sites of the catalyst and the influence of the size of alkoxy groups in disilane compounds were examined,respectively.Some correlation between molecular weight,molecular weight distribution,and isospecificity was also observed.