Living Copolymerization of Ethylene with Norbornene Catalyzed by Bis(Pyrrolide-Imine) Titanium Complexes with MAO

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• 作者：Yasunori Yoshida ; Jun-ichi Mohri ; Sei-ichi Ishii ; Makoto Mitani ; Junji Saito ; Shigekazu Matsui ; Haruyuki Makio ; Takashi Nakano ; Hidetsugu Tanaka ; Mitsuhiko Onda ; Yukari Yamamoto ; Akira Mizuno ; and Ter
• 刊名：Journal of the American Chemical Society
• 出版年：2004
• 出版时间：September 29, 2004
• 年：2004
• 卷：126
• 期：38
• 页码：12023 - 12032
• 全文大小：247K
• 年卷期：v.126,no.38(September 29, 2004)
• ISSN：1520-5126

文摘

Bis(pyrrolide-imine) Ti complexes in conjunction with methylalumoxane (MAO) were found towork as efficient catalysts for the copolymerization of ethylene and norbornene to afford unique copolymersvia an addition-type polymerization mechanism. The catalysts exhibited very high norbornene incorporation,superior to that obtained with Me₂Si(Me₄Cp)(N-tert-Bu)TiCl₂ (CGC). The sterically open and highlyelectrophilic nature of the catalysts is probably responsible for the excellent norbornene incorporation. Thecatalysts displayed a marked tendency to produce alternating copolymers, which have stereoirregularstructures despite the C₂ symmetric nature of the catalysts. The norbornene/ethylene molar ratio in thepolymerization medium had a profound influence on the molecular weight distribution of the resultingcopolymer. At norbornene/ethylene ratios larger than ca. 1, the catalysts mediated room-temperature livingcopolymerization of ethylene and norbornene to form high molecular weight monodisperse copolymers(M_n > 500 000, M_w/M_n < 1.20). ¹³C NMR spectroscopic analysis of a copolymer, produced under conditionsthat gave low molecular weight, demonstrated that the copolymerization is initiated by norbornene insertionand that the catalyst mostly exists as a norbornene-last-inserted species under living conditions.Polymerization behavior coupled with DFT calculations suggested that the highly controlled livingpolymerization stems from the fact that the catalysts possess high affinity and high incorporation ability fornorbornene as well as the characteristics of a living ethylene polymerization though under limited conditions(M_n 225 000, M_w/M_n 1.15, 10-s polymerization, 25 C). With the catalyst, unique block copolymers [i.e.,poly(ethylene-co-norbornene)₁-b-poly(ethylene-co-norbornene)₂, PE-b-poly(ethylene-co-norbornene)] weresuccessfully synthesized from ethylene and norbornene. Transmission electron microscopy (TEM) indicatedthat the PE-b-poly(ethylene-co-norbornene) possesses high potential as a new material consisting ofcrystalline and amorphous segments which are chemically linked.