Synthesis of Copolymers by Alternating ROMP (AROMP)

Song, Airong; Parker, Kathlyn A.; Sampson, Nicole S.

doi:10.1021/ja809661k

Cited by 110 publications

(123 citation statements)

References 25 publications

(17 reference statements)

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“…The sterically demanding propagating carbene that results from an alkyne prevents the reversibility of the chain-transfer process. Sampson and co-workers used cyclohexene in combination with strained substituted cyclobutenes to synthesize alternating ROMP polymers 62,63 . The substituted cyclobutenes do not propagate with ruthenium metathesis catalysts, and hence cyclohexene was used as a CTA to synthesize alternating polymers, incorporating the cyclohexene unit in the polymer backbone.…”

Section: Resultsmentioning

confidence: 99%

Catalytic living ring-opening metathesis polymerization

Nagarkar

Kilbinger

2015

Nature Chem

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In living ring-opening metathesis polymerization (ROMP), a transition-metal-carbene complex polymerizes ring-strained olefins with very good control of the molecular weight of the resulting polymers. Because one molecule of the initiator is required for each polymer chain, however, this type of polymerization is expensive for widespread use. We have now designed a chain-transfer agent (CTA) capable of reducing the required amount of metal complex while still maintaining full control over the living polymerization process. This new method introduces a degenerative transfer process to ROMP. We demonstrate that substituted cyclohexene rings are good CTAs, and thereby preserve the 'living' character of the polymerization using catalytic quantities of the metal complex. The resulting polymers show characteristics of a living polymerization, namely narrow molecular-weight distribution, controlled molecular weights and block copolymer formation. This new technique provides access to well-defined polymers for industrial, biomedical and academic use at a fraction of the current costs and significantly reduced levels of residual ruthenium catalyst. In olefin metathesis reactions, olefinic bonds are rearranged with the help of a transition-metal catalyst 1,2 . In the early days following the discovery of this reaction, ill-defined catalysts 3 were used to carry out this transformation. After Herisson and Chauvin 4 had proposed a reaction mechanism, the olefin metathesis reaction was better understood and soon gained much popularity. Typical catalysts used for olefin metathesis reactions include those based on ruthenium (developed mainly by the Grubbs group 5 ), tungsten and molybdenum (developed mainly by the Schrock group 6 ). Owing to the low oxophilicity of ruthenium compared to those of molybdenum and tungsten, the ruthenium metathesis catalysts (commonly known as Grubbs' catalysts) are more tolerant towards many polar functional groups and residual impurities, as well as to water 7 . Therefore, these catalysts are the catalysts of choice in highly functional organic chemistry transformations as well as for the majority of metathesis polymerizations carried out today. Catalysts G1 (first generation) and G3 (third generation) are the most widely used ruthenium initiators for ring-opening metathesis polymerization (ROMP). In comparison to the G1 initiator, the third-generation catalyst G3 exhibits very fast initiation and propagation rates, and thereby gives polymers with very narrow dispersities and an excellent control over their molecular weights. Owing to its superior stability as well as the favourable polymerization kinetics, the third-generation Grubbs' catalyst G3 was used for this work. ROMP is a polymerization technique that uses the metathesis of cyclic olefins to synthesize linear polymers. Depending on the structure of the monomer, such polymerizations can be controlled perfectly to give polymers with a narrow molecular weight distribution and a controlled average molecular weight. Ring-strained monomers, li...

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Section: Resultsmentioning

confidence: 99%

Catalytic living ring-opening metathesis polymerization

Nagarkar

Kilbinger

2015

Nature Chem

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“…The presumed C=C bond coupling reaction does not occur, but both species nicely collapse through cyclopropanation and subsequent ring enlargement to produce cyclobutenes, a class of interesting compounds whose synthesis currently represents a challenging task. [10,11] The procedure depicted herein provides different substituted cyclobutenes yet in moderate yield in a straightforward, atom-economic, and simple manner. It is also proved that this concept can be integrated into more complex synthetic sequences that involve metal carbene species, a fact that demonstrates the great capability of copper(I) to sequentially catalyze various reactions of different nature.…”

Section: Methodsmentioning

confidence: 99%

Discrimination of Diazo Compounds Toward Carbenoids: Copper(I)‐Catalyzed Synthesis of Substituted Cyclobutenes

et al. 2009

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In the last few years the role of diazo compounds in organic synthesis, particularly in cyclization reactions via metal carbenoids (metal: ruthenium, copper, rhodium, etc.) has been prominent. [1] By taking advantage of the ease with which these metal carbenes collapse into the corresponding symmetrical alkenes (homocoupling), we and others have been able to access nonsymmetrical alkenes by the selective heterocoupling of diazoacetate esters with copper(I) [2] and ruthenium(II) [3] carbene complexes [Eq. (1)]. Interestingly, the metal-catalyzed selective cross-coupling reaction between two different diazo substrates has been reported recently [Eq. (2)]. [4] At this point, we became intrigued as to whether discrimination between appropriately selected diazo compounds, for instance simple diazo and vinyldiazo systems, could be attained. Firstly, we found that [Cu(MeCN) 4 ]BF 4 catalyzes the reaction between ethyl vinyldiazoacetate and ethyl diazoacetate at room temperature. Surprisingly, the expected cross-coupling conjugated diene was not formed, but diethyl 2-methylcyclobutene-1,3-dicarboxylate was obtained in moderate yield as the sole heterocoupling product [Eq. (3)].This initial result seems to encompass, among others, two relevant features: 1) it represents a novel [3+1] coupling between diazo compounds, wherein two CÀC bonds rather than one C=C bond are formed, and 2) it might provide direct access to a relevant, uncommon structure. Therefore, herein we report our preliminary studies on the synthesis of cyclobutene structures by copper(I)-catalyzed cyclization of vinyldiazoacetate esters and diazo compounds (Table 1).First, [Cu(MeCN) 4 ]BF 4 (5 mol %) was added to a solution of ethyl 2-diazo-3-methylbut-3-enoate 1 a (R 1 = Me) and ethyl diazoacetate 2 a (R 2 = CO 2 Et, R 3 = H) in CH 2 Cl 2 at room temperature. After stirring the reaction mixture for two hours the solvent was removed and the resulting mixture was subjected to column chromatography, affording the cyclobutene 3 aa in 33 % yield along with ethyl maleate and ethyl fumarate (entry 1). The yield could be increased to 45 % using tert-butyl diazoacetate 2 b (entry 2). The cyclization of 1 a with

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“…86 This success derives from the combination of two monomers, neither of which forms a homopolymer under ROMP conditions. A unique alternating ROMP is achieved using a combination of norbornene monomer 37 having carboxy groups and monomer 38 having amino groups (Scheme 25).…”

Section: Recent Advances In Rompmentioning

confidence: 99%

Recent advances in ring-opening metathesis polymerization, and application to synthesis of functional materials

Sutthasupa

Shiotsuki

Sanda

2010

Polym J

329

273

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This article reviews the development of catalysts for ring-opening metathesis polymerization (ROMP), synthesis of polymers bearing amino acids and peptides by ROMP of functionalized norbornenes, formation of aggregates and micelles, and applications of the polymers to medical materials. It also describes the control of monomer unit sequences, that is, living polymerization to synthesize block copolymers, and alternating copolymerization that is achieved on the basis of acid-base interactions. Polymer Journal (2010) 42, 905-915; doi:10.1038/pj.2010.94; published online 13 October 2010Keywords: alternating copolymerization; amino acid; block copolymerization; living polymerization; metathesis catalyst; peptide; ROMP INTRODUCTIONOlefin metathesis reactions are metal-mediated carbon-carbon (C-C) double bond exchange processes, 1,2 which were discovered in the mid 1950s. Chauvin proposed the commonly accepted mechanism for metathesis involving a metallacyclobutane, as illustrated in Scheme 1. 3 Initially, olefin metathesis was regarded as an odd reaction, but now it has undoubtedly established the position as one of the most important C-C bond formation reactions applicable to synthesis of a wide variety of useful products. In the early stages, transition metal chlorides were used as catalysts for the reaction, but the transition metal carbene complex catalysts designed by Schrock and Grubbs have remarkably advanced mechanistic analysis and control of catalytic activity by the choice of ligands. In 2005, Chauvin, Grubbs and Schrock were awarded the Nobel Prize in chemistry for development of the metathesis method in organic synthesis.Olefin metathesis polymerization is an application of metathesis reactions to polymer synthesis and includes ring-opening metathesis polymerization (ROMP) and acyclic diene metathesis (ADMET) polycondensation (Scheme 2). ADMET has been extensively developed by Wagener since 1987 4 for the synthesis of polyolefins having regularly spaced functional group branches and high thermal stability and crystallinity. 5,6 ADMET is also useful for synthesizing polymeric materials containing in-chain functionality. Although the general structures of the polymers obtained by ROMP and ADMET are illustratable in the same fashion as shown in Scheme 2, a completely different treatment is necessary from the viewpoint of polymerization kinetics. The former involves chain polymerization, whereas the latter is a step-growth polymerization process.

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Synthesis of Copolymers by Alternating ROMP (AROMP)

Cited by 110 publications

References 25 publications

Catalytic living ring-opening metathesis polymerization

Catalytic living ring-opening metathesis polymerization

Discrimination of Diazo Compounds Toward Carbenoids: Copper(I)‐Catalyzed Synthesis of Substituted Cyclobutenes

Recent advances in ring-opening metathesis polymerization, and application to synthesis of functional materials

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