External Donor Induced Direct Contact Effects on Mg(OC₂H₅)₂‐Based Ziegler‐Natta Catalysts for Propylene Polymerization

Abstract

Summary: Effects of external donor induced direct contact without alkylaluminum were studied for Ziegler-Natta catalysts containing monoester and diester as internal donors on the catalytic performances such as activity and stereoselectivity. Traditional slurry polymerizations were carried out for rather short period after direct contact for a variety of time. GC analysis was also performed to observe replacement phenomena of donors during direct contact. It was postulated that the different performances of the catalysts were greatly affected by the pair of internal and external donors.

Kinetics of the propylene polymerization with prepolymerization at high temperature using Ziegler‐Natta catalyst

“…When the catalyst solid was not precontacted with a mixed solution of TEAl, D‐donor and hexane before being injected into the reactor, the cocatalyst TEAl had to diffuse to the temporarily poisoned sites to form active centers in the bulk propylene during the polymerization period. However, the concentration of TEAl was diluted by a mass of liquid propylene, so that the significant portions of the active centers were not activated, which resulted in lower polymerization rates …”

Basicity of Stereoregulating Electron-Donor Compounds in Ziegler–Natta Catalysts: A Study by Infrared Spectroscopy and Chemical Exchange Reactions

“…It has been observed before that external donors of the silyl ether or diether type, such as phenyltriethoxysilane (PTES), 9 cyclohexylmethyldimethoxysilane (CHMDMS) 10 and 2,2-diisopropyl-1,3-dimethoxypropane (DIPDMP) 11 displace EB and dibutyl phthalate (DBP) from a MgCl 2 support even in the absence of an alkylaluminum cocatalyst (Scheme 1). 9−11 Our studies on the consecutive exposure of MgCl 2 to donors with different basicities, such as EB, DBP, VP and PTMS, show that the extent to which a weaker donor is displaced by a stronger one is accurately explained by the Δν OH -derived basicities of the electron donors used, if differences between monodentate and bidentate donor binding modes are taken into account.…”

The effect of mixed and individual silane external donors on the stereo-defect distribution, active sites and properties of polypropylene synthesized with fourth generation Ziegler—Natta catalyst

“…Participation of each active center in poly merization, determines the microstructure and final properties of products [6]. In general, during the pro pylene polymerization with fourth generation Zie gler-Natta catalysts, the most part of internal donor is extracted from the surface of MgCl 2 support by alkyl aluminium cocatalyst [7][8][9]. Then the presence of external electron donor in the polymerization system for protecting the stereo-regularity of active sites is required.…”