Effects of molecular dispersion state of surface Ti species on ethylene-propylene copolymerization with TiCl3-based Ziegler-Natta model catalyst

Abstract

The dispersion state of surface Ti species is one of the most important factors affecting the polymerization properties of MgCl 2 -supported heterogeneous Ziegler-Natta catalysts. In this paper, ethylene-propylene copolymerization was carried out using a novel Ziegler-Natta model catalyst with "isolated" and "clustered" TiCl 3 molecules on MgCl 2 . At a lower ethylene/propylene feed ratio, the dispersion state of the Ti species strongly affected both the composition and sequence distribution of the copolymers. The "isolated" Ti species gave a relatively random copolymer, and clustering of Ti species enhanced the bulkiness. The addition of an external donor basically deteriorated the random copolymerization character of the "isolated Ti species but the degree of deterioration depended on the type of donors. On the other hand, the balance between the monomer feed and consumption dominated the copolymerization performance at a higher ethylene/propylene feed ratio to obscure the effects of the dispersion state.

Precise Active Site Analysis for TiCl3/MgCl2 Ziegler-Natta Model Catalyst Based on Fractionation and Statistical Methods

“…TiCl 3 /MgCl 2 model catalysts with a variety of Ti contents ranging from 0.011 to 1.3 wt% were prepared according to the previously reported procedure [5][6][7]. In brief, a specified amount of TiCl 3 ·3Py and milled MgCl 2 (donated by Toho Titanium Co., Ltd., a specific surface area of 65.1 m in n-heptane at r.t. for 3 h under N 2 , followed by repetitive washing with n-heptane.…”

“…Recently, we have reported the influences of the Ti dispersion state on propylene polymerization performances using TiCl 3 /MgCl 2 model catalysts with controlled Ti dispersion states [5][6][7]. In brief, the model catalysts were prepared by treating TiCl 3 ·3pyridine with diethylaluminum chloride (DEAC) in the presence of milled MgCl 2 .…”

Kinetic elucidation of comonomer‐induced chemical and physical activation in heterogeneous ziegler‐natta propylene polymerization

“…In Ziegler‐Natta olefin polymerization, the enhancement of polymerization rate ( R p ) by the addition of comonomer is well known as the comonomer effect 1. The effect has been widely observed in copolymerization of ethylene with α‐olefins and of propylene with ethylene or the other α‐olefins 7, 11, 24–33. A great deal of effort has been devoted to providing several mechanistic explanations of the comonomer effect.…”

Origin of Chemical Composition of Ethylene/Propylene Copolymer Produced with Ziegler–Natta Catalyst

“…The TiCl 3 /MgCl 2 model catalysts were prepared according to a previously reported procedure, where a specified amount of TiCl 3 ·3Py was reacted with MgCl 2 in the presence of DEAC (Al/Ti = 78) in n ‐heptane for 3 h under N 2 , followed by repetitive washing. The usage of the TiCl 3 ·3Py molecular precursor enables high dispersion of TiCl 3 on MgCl 2 , while originally solid TiCl 3 does not migrate easily on MgCl 2 surfaces compared with TiCl 4 .…”