THE ROLES OF GRIGNARD-REAGENT IN THE ZIEGLER-NATTA CATALYST FOR PROPYLENE POLYMERIZATION

Grignard reagent PhMgCl was added during the preparation of the cataly st system MgCl2/di-n-butyl phthalate (DNBP)/TiCl4-AlEt3/diphenyl dimet hoxyl silane (DPDMS) to improve its performance. It was found that PhM gCl could enhance both the activity of the catalyst and the isotactici ty of the products, but decreased the Ti content of the catalysts unde r the same preparation conditions. The polymerization kinetics showed that PhMgCl accelerates the decay in the same time that it increased t he initial and final polymerization rates. By means of UV-vis spectros copy, electron spin resonance (ESR) spectroscopy, and the Ti content d etermination of the catalysts, the multiple roles of PhMgCl were discl osed: reduction of Ti4+ to Ti3+, association with MgCl2 to replace par t of TiCl4 in aspecific active sites, and complexing with the original active sites to form new active sites. (C) 1997 John Wiley & Sons, In c.