Polypropylene Chain Structure Regulation by Alkoxysilane and Ether Type External Donors in TiCl4/DIBP/MgCl2-AlEt3 Ziegler-Natta Catalyst

Two different monoethers, CH3CH2CH2CH2OCH3 (NBME) and (CH3)2CHCH2-OCH3 (IBME), and Ph2Si(OCH3)2 were used as external donors in propylenepolymerization using MgCl2/TiCl4/DIBP catalyst (DIBP: diisobutyl phthalate)activated by triethylaluminium (TEA). The monoethers alone showed no improvementin the isotacticity index of polypropylene (PP). When one of the ethers andPh2Si(OCH3)2 were added together in the polymerization system as compositeexternal donors, the propylene polymerization activity and isotacticity index wereincreased as compared to those of the systems with only silane as external donor,though the melting temperature and melting enthalpy of PP decreased. The effects ofthe external donors on the active center distribution of the catalyst system aredemonstrated by deconvolution analysis of the PP molecular weight distribution intomultiple Flory components, and the mechanism of external donor regulation effects isdiscussed. All the results show that adding monoether in MgCl2/TiCl4/DIBP-TEA/silanecatalyst system can reduce the stereoregularity of the isotactic chains of the polymerwhile, it maintains the atactic PP fractions at a very low level.