Xia, Yan and Boydston, Andrew J. and Yao, Yefeng and Kornfield, Julia A. and Gorodetskaya, Irina A. and Spiess, Hans W. and Grubbs, Robert H. (2009) Ring-Expansion Metathesis Polymerization: Catalyst-Dependent Polymerization Profiles. Journal of the American Chemical Society, 131 (7). pp. 2670-2677. ISSN 0002-7863 http://resolver.caltech.edu/CaltechAUTHORS:20090902-085242708
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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 ^(13)C NMR spectroscopy of both linear and cyclic polymers, which revealed little or no chain ends for the latter topology.
|Additional Information:||© 2009 American Chemical Society. Received October 25, 2008. Publication Date (Web): January 29, 2009. Supporting Information Available: Kinetic plot of catalyst initiation studies, Mw versus time for REMP of COE, GPC traces of REMP of COE and COE macrocycles, and 1H NMR spectrum of COE macrocycles. This material is available free of charge via the Internet at http://pubs.acs.org. This work was supported by the Department of Energy (DE-FG02-05ER46218). We gratefully acknowledge Materia, Inc. for the generous gift of catalyst 1. A.J.B. thanks the NIH/NCI for a postdoctoral fellowship. We thank Professor Manfred Wilhelm and Dr. Robert Graf for help with the melt-state 13C NMR spectroscopy, Professor Gregory B. McKenna for helpful discussions, Matthew M. Van Wingerden and Dr. Nathan F. Dalleska for help with ICP-MS, and John B. Matson and Ron Walker for maintaining the GPC.|
|Official Citation:||Ring-Expansion Metathesis Polymerization: Catalyst-Dependent Polymerization Profiles Yan Xia, Andrew J. Boydston, Yefeng Yao, Julia A. Kornfield, Irina A. Gorodetskaya, Hans W. Spiess, Robert H. Grubbs Journal of the American Chemical Society 2009 131 (7), 2670-2677.|
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|Deposited By:||Tony Diaz|
|Deposited On:||09 Sep 2009 23:00|
|Last Modified:||26 Dec 2012 11:18|
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