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Robert H Grubbs - One of the best experts on this subject based on the ideXlab platform.
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ru catalyzed cis selective living ring opening Metathesis Polymerization of various monomers including a dendronized macromonomer and implications to enhanced shear stability
Journal of the American Chemical Society, 2020Co-Authors: Jungah Song, Robert H Grubbs, Gregory I Peterson, Kitaek Bang, Tonia S Ahmed, Jongchan Sung, Taelim ChoiAbstract:An unsaturated polymer’s cis/trans-olefin content has a significant influence on its properties. For polymers obtained by Ring-Opening Metathesis Polymerization (ROMP), the cis/trans-olefin content...
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examining the effects of monomer and catalyst structure on the mechanism of ruthenium catalyzed ring opening Metathesis Polymerization
Journal of the American Chemical Society, 2019Co-Authors: William J Wolf, Robert H GrubbsAbstract:The mechanism of Ru-catalyzed Ring-Opening Metathesis Polymerization (ROMP) is studied in detail using a pair of third generation ruthenium catalysts with varying sterics of the N-heterocyclic carbene (NHC) ligand. Experimental evidence for polymer chelation to the Ru center is presented in support of a monomer-dependent mechanism for Polymerization of norbornene monomers using these fast-initiating catalysts. A series of kinetic experiments, including rate measurements for ROMP, rate measurements for initiation, monomer-dependent kinetic isotope effects, and activation parameters were useful for distinguishing chelating and nonchelating monomers and determining the effect of chelation on the Polymerization mechanism. The formation of a chelated metallacycle is enforced by both the steric bulk of the NHC and by the geometry of the monomer, leading to a ground-state stabilization that slows the rate of Polymerization and also alters the reactivity of the propagating Ru center toward different monomers in c...
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Synthesis of Highly Cis, Syndiotactic Polymers via Ring-Opening Metathesis Polymerization Using Ruthenium Metathesis Catalysts
Journal of the American Chemical Society, 2013Co-Authors: Lauren E. Rosebrugh, Benjamin K Keitz, Vanessa M. Marx, Robert H GrubbsAbstract:The first example of ruthenium-mediated Ring-Opening Metathesis Polymerization generating highly cis, highly tactic polymers is reported. While the cis content varied from 62 to >95% depending on the monomer structure, many of the polymers synthesized displayed high tacticity (>95%). Polymerization of an enantiomerically pure 2,3-dicarboalkoxynorbornadiene revealed a syndiotactic microstructure.
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ruthenium catalyzed equilibrium ring opening Metathesis Polymerization of cyclopentene
Polymer Chemistry, 2013Co-Authors: Robert Tuba, Robert H GrubbsAbstract:Polypentenamer was synthetized by equilibrium Ring-Opening Metathesis Polymerization (ROMP) using well-defined ruthenium catalyst systems. It was found that the equilibrium time is influenced by the catalyst loading or the catalyst activity, however as expected, the overall cyclopentene conversion is determined only by the applied reaction temperature. Equilibrium of the growing chain and monomer was observed and the activation enthalpy and entropy were determined as: ΔH = −5.6 kcal mol−1; ΔS = −18.5 cal mol−1 K−1. So far these values are the lowest which are reported for cyclopentene Polymerization catalyst systems. This unique feature of the equilibrium Polymerization opens a way for the synthesis of durable, environmentally friendly elastomers where tires can be not only synthetized but also readily recycled by the same transition metal catalyst system.
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cis selective ring opening Metathesis Polymerization with ruthenium catalysts
Journal of the American Chemical Society, 2012Co-Authors: Benjamin K Keitz, Alexey Fedorov, Robert H GrubbsAbstract:Cis-selective Ring-Opening Metathesis Polymerization of several monocyclic alkenes as well as norbornene and oxanorbornene-type monomers using a C–H activated, ruthenium-based Metathesis catalyst is reported. The cis content of the isolated polymers depended heavily on the monomer structure and temperature. A cis content as high as 96% could be obtained by lowering the temperature of the Polymerization.
Christopher W. Bielawski - One of the best experts on this subject based on the ideXlab platform.
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A Ring-Opening Metathesis Polymerization Catalyst That Exhibits Redox-Switchable Monomer Selectivities
WILEY-V C H VERLAG GMBH, 2018Co-Authors: Dominika N. Lastovickova, Huiling Shao, Peng Liu, Christopher W. BielawskiAbstract:A Ring-Opening Metathesis Polymerization catalyst supported by a redox-active N-heterocyclic carbene was synthesized and found to undergo reversible reduction. In its neutral form, the catalyst polymerized 1,5-cis,cis-cyclooctadiene at a higher rate than that of a norbornene derivative; however, upon reduction, the selectivity was found to reverse. Utilizing this oxidation state dependent selectivity, a series of copolymers with controlled compositions, microstructures, and physical properties were prepared by redox-switching the catalyst over the course of a series of Polymerization reactions. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim8
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A Ring-Opening Metathesis Polymerization Catalyst That Exhibits Redox-Switchable Monomer Selectivities
Chemistry: A European Journal, 2017Co-Authors: Dominika N. Lastovickova, Huiling Shao, Gang Lu, Christopher W. BielawskiAbstract:A Ring-Opening Metathesis Polymerization catalyst supported by a redox-active N-heterocyclic carbene was synthesized and found to undergo reversible reduction. In its neutral form, the catalyst polymerized 1,5-cis,cis-cyclooctadiene at a higher rate than that of a norbornene derivative; however, upon reduction, the selectivity was found to reverse. Utilizing this oxidation state dependent selectivity, a series of copolymers with controlled compositions, microstructures, and physical properties were prepared by redox-switching the catalyst over the course of a series of Polymerization reactions.
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living ring opening Metathesis Polymerization
Progress in Polymer Science, 2007Co-Authors: Christopher W. Bielawski, Robert H GrubbsAbstract:Abstract Since the discovery of olefin Metathesis in the mid-1950s, there has been great interest in using this versatile reaction to synthesize macromolecular materials. More recently, living Ring-Opening Metathesis Polymerization (ROMP), a variation of the olefin Metathesis reaction, has emerged as a particularly powerful method for synthesizing polymers with tunable sizes, shapes, and functions. The technique has found tremendous utility in preparing materials with interesting biological, electronic, and mechanical properties. This review covers the fundamental aspects of living ROMP and briefly traces its historical development from a catalyst-design perspective. Highlights from the recent literature are used to illustrate the utility of living ROMP in the preparation of macromolecular materials with advanced structures and functions. A discussion on the current status of state-of-the-art catalysts for use in living ROMP reactions as well as opportunities for the future concludes this review.
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synthesis of cyclic polybutadiene via ring opening Metathesis Polymerization the importance of removing trace linear contaminants
Journal of the American Chemical Society, 2003Co-Authors: Christopher W. Bielawski, Diego Benitez, Robert H GrubbsAbstract:The synthesis of cyclic polybutadienes using Ring-Opening Metathesis Polymerization (ROMP) was accomplished. A cyclic Ru alkylidene catalyst, where a terminal ligand was covalently linked to the Ru alkylidene, was used to polymerize either 1,5-cyclooctadiene (COD) or 1,5,9-trans-cis-trans-cyclododecatriene (CDT). Trace amounts of an acyclic impurity, 4-vinylcyclohexene, found in the COD led to samples which were contaminated with linear polymer. In contrast, CDT, which was free of the impurity, afforded pure cyclic polymer. These results provide a convenient method for discerning samples of pure cyclic polymer from those which contain trace to large amounts of linear polymer. Furthermore, they emphasize the need to use monomers that are free of acyclic impurities when preparing cyclic polymers using ROMP.
Andrew J Boydston - One of the best experts on this subject based on the ideXlab platform.
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integration of metal free ring opening Metathesis Polymerization and organocatalyzed ring opening Polymerization through a bifunctional initiator
Polymer Chemistry, 2019Co-Authors: Andrew J BoydstonAbstract:We have investigated the use of metal-free Ring-Opening Metathesis Polymerization (MF-ROMP) in combination with organocatalyzed Ring-Opening Polymerization (o-ROP) to produce diblock copolymers with highly disparate block compositions via exclusively metal-free methods. Use of a bifunctional initiator bearing a vinyl ether as organic initiator for MF-ROMP and an alcohol for initiation of o-ROP allowed for investigation of three synthetic approaches: (1) sequential Polymerization with isolation of the intermediate macroinitiators, (2) simultaneous bidirectional Polymerizations, and (3) “one-pot” sequential monomer addition. Macroinitiators formed by first conducting o-ROP were successfully used in subsequent MF-ROMP to prepare diblock copolymers. Simultaneous MF-ROMP and o-ROP was thwarted by incompatible cross-combinations of catalysts and monomers. Finally, a straightforward “one-pot” synthesis of block copolymers, using o-ROP followed by MF-ROMP, was realized by sequential addition of each monomer-catalyst combination.
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comparison of pyrylium and thiopyrylium photooxidants in metal free ring opening Metathesis Polymerization
Synlett, 2016Co-Authors: Laura M M Pascual, Damian G Dunford, Adam E Goetz, Kelli A Ogawa, Andrew J BoydstonAbstract:Systematically varied pyrylium and thiopyrylium photo-oxidants have been evaluated in the metal-free Ring-Opening-Metathesis Polymerization (MF-ROMP) of norbornene. Across the series, we observed higher conversion into polynorbornene from thiopyrylium species in comparison with pyrylium salts that were otherwise similarly functionalized. Additionally, more electron-rich photo-oxidants (i.e., weaker oxidants) correlated with higher conversions.
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developments in externally regulated ring opening Metathesis Polymerization
Synlett, 2015Co-Authors: Kelli A Ogawa, Adam E Goetz, Andrew J BoydstonAbstract:This account details externally regulated Ring-Opening Metathesis Polymerization (ROMP) methods. Various external stimuli are discussed which collectively span chemical, thermal, photochemical, electrochemical, and mechanical modes of catalyst activation. Specific attention is also given to the recent development of a metal-free approach to ROMP that includes electro-organic and photoredox-mediated systems. 1 Introduction 2 Externally Regulated Ring-Opening Metathesis Polymerization 2.1 Acid-Activated Ring-Opening Metathesis Polymerization Catalysts 2.2 Thermally Activated Ring-Opening Metathesis Polymerization Catalysts 2.3 Mechanically Activated Ring-Opening Metathesis Polymerization Catalysts 2.4 Photochemically Activated Ring-Opening Metathesis Polymerization Catalysts 2.5 Redox-Activated Ring-Opening Metathesis Polymerization Catalysts 3 Metal-Free Ring-Opening Metathesis Polymerization 3.1 Electro-organic Ring-Opening Metathesis Polymerization 3.2 Photoredox-Mediated Ring-Opening Metathesis Polymerization 4 Conclusions and Outlook
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metal free ring opening Metathesis Polymerization
Journal of the American Chemical Society, 2015Co-Authors: Kelli A Ogawa, Adam E Goetz, Andrew J BoydstonAbstract:We have developed a method to achieve Ring-Opening Metathesis Polymerization (ROMP) mediated by oxidation of organic initiators in the absence of any transition metals. Radical cations, generated via one-electron oxidation of vinyl ethers, were found to react with norbornene to give polymeric species with microstructures essentially identical to those traditionally obtained via metal-mediated ROMP. We found that vinyl ether oxidation could be accomplished under mild conditions using an organic photoredox mediator. This led to high yields of polymer and generally good correlation between Mn values and initial monomer to catalyst loadings. Moreover, temporal control over reinitiation of polymer growth was achieved during on/off cycles of light exposure. This method demonstrates the first metal-free method for controlled ROMP.
Yan Xia - One of the best experts on this subject based on the ideXlab platform.
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tuning the reactivity of cyclopropenes from living ring opening Metathesis Polymerization romp to single addition and alternating romp
Angewandte Chemie, 2019Co-Authors: Zexin Jin, Peng Liu, Rui Zhang, Yan XiaAbstract:Ring-Opening Metathesis Polymerization (ROMP) has become one of the most important living Polymerizations. Cyclopropenes (CPEs) remain underexplored for ROMP. Described here is that the simple swap of 1-methyl to 1-phenyl on 1-(benzoyloxymethyl)CPEs elicited strikingly different modes of reactivity, switching from living Polymerization to either selective single-addition or living alternating ROMP. The distinct reactivity stems from differences in steric repulsions at the Ru alkylidene after CPE ring opening. Possible olefin or oxygen chelation from ring-opened CPE substituents was also observed to significantly affect the rate of propagation. These results demonstrate the versatility of CPEs as a new class of monomers for ROMP, provide mechanistic insights for designing new monomers with rare single-addition reactivity, and generate a new functionalizable alternating copolymer scaffold with controlled molecular weight and low dispersity.
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precise placement of single monomer units in living ring opening Metathesis Polymerization
Chem, 2019Co-Authors: Benjamin R Elling, John D Feist, Yan XiaAbstract:Summary Precise control of the location and sequence of monomers in a narrow-disperse polymer chain remains a significant challenge. Our strategy uses selective and quantitative single additions of cyclopropene (CPE) derivatives to precisely place functional moieties at desired locations along a polymer chain during the living Ring-Opening Metathesis Polymerization (ROMP) of norbornenes (NBEs). In order to completely reinitiate the chain end after single addition of a CPE, we lowered the reaction temperature and added a labile ligand. Under our optimized conditions, we demonstrated the exclusive placement of single moieties at pre-determined locations along a polynorbornene (PNBE) homo or block co-polymer while maintaining narrow MW distributions and controlled MWs. Some polymers were used to synthesize precisely controlled branched architectures. The ability to control the location and number of individual functional groups in a polymer chain opens exciting opportunities for the precise synthesis and manipulation of polymer structures, architectures, assemblies, and properties.
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ring opening Metathesis Polymerization of 1 2 disubstituted cyclopropenes
Chemical Communications, 2016Co-Authors: Benjamin R Elling, Yan XiaAbstract:The Ring-Opening Metathesis Polymerization (ROMP) of 1,2-disubstituted cyclopropenes (CPs) has been explored for the first time using Grubbs 3rd generation catalyst. A range of 1,2-CPs yielded polymers with controllable MWs and low dispersitities, and allowed the synthesis of block copolymers, absent from secondary Metathesis. However, there existed a competing intramolecular termination pathway for these monomers, limiting the timescale for their ROMP to stay living.
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importance of macromonomer quality in the ring opening Metathesis Polymerization of macromonomers
Macromolecules, 2015Co-Authors: Yew Chin Teo, Yan XiaAbstract:Various macromonomers (MMs) were synthesized using controlled radical Polymerization (CRP) by either directly growing from a norbornene-functionalized initiator or chain transfer agent (“direct-growth” or DG method) or coupling a norbornenyl group to preformed polymers (“growth-then-coupling” or GC method). The degree of control for the Ring-Opening Metathesis Polymerization (ROMP) of these MMs was found to be dependent on which synthetic method was used for the MMs. Narrowly dispersed brush polymers were consistently obtained from the GC-MMs. In contrast, the DG-MMs resulted in brush polymers with a small high-molecular weight (MW) shoulder or broader molecular weight distribution (MWD). Matrix-assisted laser desorption ionization time-of-flight mass spectrometry of DG-MMs showed the presence of a small amount of α,ω-dinorbornenyl telechelic species resulting from the biradical combination during Polymerization. A control study further revealed that even the presence of 1 mol % α,ω-norbornenyl telechelic...
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living alternating ring opening Metathesis Polymerization based on single monomer additions
Journal of the American Chemical Society, 2015Co-Authors: Benjamin R Elling, Yan XiaAbstract:By judiciously modulating the ring strain and sterics, we developed a class of disubstituted cyclopropenes that selectively underwent single monomer addition in Ring-Opening Metathesis but readily underwent alternating Ring-Opening Metathesis Polymerization with low-strain cyclic olefins in a living fashion. The substituents on cyclopropenes effectively inhibited homoaddition and prevented secondary Metathesis on the polymer backbone. The resulting polymers had controllable molecular weights and end groups, very low dispersities, and high regularity in microstructure under optimized conditions. 1H and 13C NMR spectroscopy and MALDI-TOF MS showed a rigorously alternating sequence. Interestingly, disubstituted cyclopropenes were found to present zero-order kinetics, indicating their rapid single addition and the rate-determining ring opening of the low-strain olefin.
Taelim Choi - One of the best experts on this subject based on the ideXlab platform.
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ru catalyzed cis selective living ring opening Metathesis Polymerization of various monomers including a dendronized macromonomer and implications to enhanced shear stability
Journal of the American Chemical Society, 2020Co-Authors: Jungah Song, Robert H Grubbs, Gregory I Peterson, Kitaek Bang, Tonia S Ahmed, Jongchan Sung, Taelim ChoiAbstract:An unsaturated polymer’s cis/trans-olefin content has a significant influence on its properties. For polymers obtained by Ring-Opening Metathesis Polymerization (ROMP), the cis/trans-olefin content...
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one pot in situ fabrication of stable nanocaterpillars directly from polyacetylene diblock copolymers synthesized by mild ring opening Metathesis Polymerization
Journal of the American Chemical Society, 2012Co-Authors: Kiyoung Yoon, Jihoon Jang, Taelim ChoiAbstract:We report a direct one-pot route for the preparation of supramolecules from simple polyacetylene diblock copolymers synthesized by mild Ring-Opening Metathesis Polymerization of cyclooctatetraene. This in situ nanoparticlization of conjugated polymer (INCP) approach is advantageous over conventional self-assembly processes because this method does not require any tedious postsynthetic treatments. Also, this direct approach provides intriguing supramolecules with a unique nanostructure resembling a caterpillar. Furthermore, the new supramolecules are highly stable adducts because the polyacetylene core block provides an exceptionally strong driving force for the self-assembly. Even though pristine polyacetylene is unstable in air, the polyacetylene segment in the nanocaterpillar is very stable because it is protected within the shell of the supramolecule.
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accelerated ring opening Metathesis Polymerization of a secondary amide of 1 cyclobutene by hydrogen bonding interaction
Organic Letters, 2011Co-Authors: Kil Sun Lee, Taelim ChoiAbstract:A hydrogen-bond-assisted model is proposed for Ring-Opening Metathesis Polymerization (ROMP) of a secondary amide of 1-cyclobutene, resulting in the fastest reaction rate in a nonpolar solvent, toluene. This new model was supported by the investigation on how the solvent effect affected the NMR spectra, ROMP kinetic studies, and the coPolymerization of monomers 1 and 2.
