Hitoshi Matsuoka

Stopped-Flow Techniques in Ziegler Catalysis

The stopped-flow method, by which a quasi-living polymerization process can be realized within an extremely short period (ca. 0.2 s), has been proven to be one of the most powerful techniques for studies on the nature of the active sites and elucidation of the olefin polymerization mechanism based on the information from the polymers obtained in the initial stage of polymerization. It has been demonstrated that a better and deeper understanding of many controversial problems in Ziegler catalysis has been achieved, such as arguments concerning the non-uniformity of the active sites, the intrinsic kinetic parameters, the effects of catalyst preparation conditions, the role of cocatalysts, hydrogen and electron donor, etc. The successive modifications to the basic stopped-flow system have led to extensive applications in investigating the catalyst pretreatment effects induced by various reagents, as well as developing a series of novel block copolymers.

Variation in the Isospecific Active Sites of Internal Donor-Free MgCl2-Supported Ziegler Catalysts: Effect of External Electron Donors

The stopped-flow polymerization of propylene was carried out using an internal donor-free MgCl 2 -supported Ziegler catalyst in the absence or presence of external electron donors. The variation in the isospecific active sites was investigated based on the isotacticity distribution of the poly(propylene) analyzed by the TREF method. Highly isospecific active sites derived from the highest isotactic fraction (elution temperature by TREF: >112 °C) exist in the electron donor-free catalyst system. The addition of external electron donors converted parts of the aspecific into isospecific active sites, but showed no effects on the highests isospecific active sites. The external electron donor sterically affects a coordination vacancy of each aspecific titanium species and, consequently, transfers if into an isospecific active site of high, but not highest isospecificity.

Kinetic investigation of propene polymerization with stopped‐flow method

The stopped-flow technique, by which a quasi-living polymerization process can be performed within an extremely short period (ca. 0.2s), is a powerful method for kinetic investigation in Ziegler catalysis. Significant understanding of many controversial problems was achieved, such as arguments concerning the nonuniformity of the active sites, the accurate kinetic parameters, the active sites formed in the different stages, the role of cocatalyst, the effects of hydrogen and electron donors, etc..

Recent Developments in Toransition Metal-Catalyzed Polymerization. II. Investigation of the Distribution of Isospecificity of Active Sites on the MgCl2-Supported Ziegler Catalyst by Temperature Rising Elution Fractionation Analysis.

本研究では, 昇温溶離分別法 (TREF) を用いて分析したポリプロピレン (PP) の立体規則性 (イソタクチック) 分布を基に, MgCl2担持型Ziegler触媒が有するイソ特異的活性点の特性分布と内部および外部ドナーがその分布に及ぼす効果を調べた. 内部および外部ドナーを含まないMgCl2担持型Ziegler触媒系を用いた, ストップフロー法によるプロピレン重合で得られたポリマーのTREF噺から, Ti, Mg, Clのみからなる触媒からも, 高イソタクチックPPをはじめ, 異なる立体規則性をもつポリマーが得られ, 本触媒においても活性点の立体特異性に分布のあることがわかった. ドナーの添加効果に関する検討では, 内部ドナーは非立体特異的活性点の生成を抑制する効果があるのみならず, もっとも立体特異性の高い活性点の創製に重要な役割を果たしており, 一方, 外部ドナーは非立体特異的活性点をイソ特異的活性点へ変換させることはできるものの, その効果は低く, しかももっとも立体特異性の高い活性点への変換には効果をもたないことがわかった.

Basic Approaches for the Design of Active Sites on the Traditional Ziegler Catalysts

In this paper, three basic approaches for the design of active sites on the traditional Ziegler catalysts are discussed for the future breakthrough of this type of catalysts. Firestly, the Variation of isospecific active sites formed on a MgCl2-supported TiCl4 catalyst in the absence or presence of external electron donor was specified by the stopped-flow method based on the isotacticity distribution of the polypropene. Besides the depression of the formation of some aspecific active sites, the effect of addition of external electron donor is to transfer some of the aspecific titanium species into isospecific active site. Secondly, hydrogen dissociation sites were found to be derived from the over-reduced Ti species due to deactivation during propene polymerization. Finally, the enantioselectivity and diastereoselectivity of the active sites for copolymerization of propene and 1, 5- hexadiene were studied. It was made clear that the steric hindrance in the vicinity of active sites increases with the isospecificity of the active sites.