Ring-expansion metathesis polymerization: Catalyst-dependent polymerization profiles

被引：0

作者：

Xia, Yan ^{[1
]}

Boydston, Andrew J. ^{[1
]}

Yao, Yefeng ^{[2
,3
]}

Kornfield, Julia A. ^{[1
]}

Gorodetskaya, Irina A. ^{[1
]}

Spiess, Hans W. ^{[2
]}

Grubbs, Robert H. ^{[1
]}

机构：

[1] Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, United States

[2] Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

[3] Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, East China Normal University, North Zhongshan Road 3663, 200062 Shanghai, China

来源：

Journal of the American Chemical Society | 2009年 / 131卷 / 07期

关键词：

Ring-expansion metathesis polymerization (REMP) mediated by recently developed cyclic Ru catalysts has been studied in detail with a focus on the polymer products obtained under varied reaction conditions and catalyst architectures. Depending upon the nature of the catalyst structure; two distinct molecular weight evolutions were observed. Polymerization conducted with catalysts bearing six-carbon tethers displayed rapid polymer molecular weight growth which reached a maximum value at ca. 70% monomer conversion; resembling a chain-growth polymerization mechanism. In contrast; five-carbon tethered catalysts led to molecular weight growth that resembled a step-growth mechanism with a steep increase occurring only after 95% monomer conversion. The underlying reason for these mechanistic differences appeared to be ready release of five-carbon-tethered catalysts from growing polymer rings; which competed significantly with propagation. Owing to reversible chain transfer and the lack of end groups in REMP; the final molecular weights of cyclic polymers was controlled by thermodynamic equilibria. Large ring sizes in the range of 60-120 kDa were observed at equilibrium for polycyclooctene and polycyclododecatriene; which were found to be independent of catalyst structure and initial monomer/catalyst ratio. While six-carbon-tethered catalysts were slowly incorporated into the formed cyclic polymer; the incorporation of five-carbon-tethered catalysts was minimal; as revealed by ICP-MS. Further polymer analysis was conducted using melt-state magic-angle spinning 13C NMR spectroscopy of both linear and cyclic polymers; which revealed little or no chain ends for the latter topology. © 2009 American Chemical Society;

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摘要：

Journal article (JA)

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页码：2670 / 2677