Competition between Diels-Alder cycloaddition and spontaneous copolymerization of 1-methoxy-1,3-butadiene with electrophilic olefins

Mikhael, Michael G.; Padías, Anne Buyle; Hall, H. K.

doi:10.1021/ma00068a005

Cited by 18 publications

(20 citation statements)

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“…Both reactions proceed via second-order kinetics. Similar results were obtained from the investigations of the spontaneous reactions of 2-methyl-2,4-pentadiene (1,1-dimethylbuta-1,3diene) and of 1-methoxybuta-1,3-diene with electrophilic olefins, respectively [16] [17].…”

Section: Scheme 1 Tetramethylene Intermediates Initiating Spontaneousupporting

confidence: 84%

The Relationship of Cycloaddition Reactions to Spontaneous Vinyl Polymerizations

Hall

Padías

2005

Helvetica Chimica Acta

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To Professor Rolf Huisgen with grateful appreciation for his contributions to organic polymer chemistry! The zwitterionic ± biradical tetramethylene proposed by Huisgen as the key intermediate in stepwise [2 2] cycloaddition reactions has been shown to be the crucial intermediate in spontaneous vinyl polymerizations as well. Predominantly biradical tetramethylenes initiate free-radical copolymerizations, while predominantly zwitterionic tetramethylenes initiate cationic or anionic homopolymerizations. Stepwise cycloaddition is viewed as a spontaneous polymerization lacking a propagation step. These tendencies could be correlated in the form of an organic chemists Periodic Table, which has recently been put on a quantitative basis.Huisgen also showed experimentally that [4 2] Woodward ± Hoffman-allowed cycloadditions are completely concerted. Spontaneous copolymerizations accompanying these cycloadditions, therefore, were ascribed to the s-trans diene form. This concept was given support by kinetics studies, as well as by exclusive cycloaddition from s-cis cyclopentadiene, and exclusive copolymerization from s-trans verbenene.Introduction. ± The great poet builds larger than he knows. This familiar saying also applies to great scientists. When Rolf Huisgen was studying the role of the tetramethylene intermediate in [2 2] cycloaddition reactions, surely the idea that this intermediate might play an important role in polymer chemistry never crossed his mind. Yet this has proven to be the case.During the 1960s and 1970s, polymer chemists encountered various unexpected and perplexing observations in vinyl polymerizations. A tendency of the monomer units to alternate in the copolymer chain was observed. This was the case when electron-rich monomers, such as styrene or vinyl ethers, were copolymerized with electron-poor monomers, such as methyl acrylate or acrylonitrile. As the donor and acceptor character of the co-monomers increased, the alternation tendency grew stronger and stronger. Eventually, a new phenomenon set in, namely spontaneous polymerization. At first, spontaneous copolymerization occurred by a radical mechanism to form strictly alternating copolymers. With still stronger donor-substituted monomers, homopolymers of the donor monomer were found, which could only be formed by a spontaneous cationic homopolymerization.Attempts by polymer chemists to understand these phenomena centered on the visible charge-transfer (CT) complexes formed by the two monomers. It was attractive to suppose that free-radical homopolymerization of this CT complex would lead to the observed strictly alternating copolymers. But how this explained the cationic homopolymers or the CT complex initiated polymerizations, was not made clear.

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Section: Scheme 1 Tetramethylene Intermediates Initiating Spontaneousupporting

confidence: 84%

The Relationship of Cycloaddition Reactions to Spontaneous Vinyl Polymerizations

Hall

Padías

2005

Helvetica Chimica Acta

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“…1 3-Methoxy-cis-1,2,3,6-tetrahydrophthalic Anhydride (10c). 12 The title compound was prepared by dissolving equimolar amounts of trans-1-methoxy-1,3-butadiene (8c, Aldrich, 5.0 g, 59 mmol) and maleic anhydride (5.8 g, 59 mmol) in acetonitrile (100 mL). The reaction mixture was stirred at room temperature for 24 h under nitrogen.…”

Section: Methodsmentioning

confidence: 99%

Reevaluation of Tetrahydrophthalic Anhydride as an End Cap for Improved Oxidation Resistance in Addition Polyimides

2004

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Several substituted 1,2,3,6-tetrahydrophthalic anhydride end caps, including the 3-phenyl, 3-methoxy, 3-trimethylsilyloxy, and 3,6-diphenyl analogues, were synthesized via the Diels−Alder condensation of the corresponding butadienes and maleic anhydride. These anhydrides, as well as the commercially available 3-hydro and 4-methyl analogues, were each ground up together with methylenedianiline in a 2:1 ratio and heated gradually from 204 to 371 °C, with the thermolysis followed by NMR. Generally speaking, a transformation via monoimide to bisimide was observed in the lower temperature range, followed by competition between cross-linking and aromatization. We believe that this competition produces a substantial percentage of aromatic product, with the concomitant lowering of the relative amount of cross-linking and is responsible for both improved thermooxidative stability of tetrahydrophthalic end-capped polyimides and their substantial frangibility. The thermolysis of the tetrahydrophthalimides under an inert atmosphere dramatically lowers the amount of aromatization; hence, the mechanism for aromatization is an oxidative one.

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“…This might be due to the larger electron disparity in the case of DMB/MA-ZnC12, which favors the cycloaddition reaction [6,7]. No cycloaddition was observed for MPD because of steric hindrance at its terminal carbon atom.…”

Section: Discussionmentioning

confidence: 99%

“…l-methoxy-1,3-butadiene: fumaronitrile system [l, 61. If the electronic disparity is large, cycloaddition is favored over copolymerization, as observed in the case of the spontaneous reaction of l-methoxy-1,3-butadiene with methyl P,P-dicyanoacrylate [6]. On the other hand, weak acceptor olefins, such as acrylonitrile AN, require heating to undergo spontaneous copolymerization with or cycloaddition to 2,3-dimethyl-1,3-butadiene DMB [5].…”

Section: Introductionmentioning

confidence: 99%

Effect of ZnCl₂ on the spontaneous copolymerization of methyl acrylate with substituted 1,3‐dienes

1996

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The reactions of the mildly electron-poor olefin methyl acrylate (MA) with three electron-rich substituted hydrocarbon 1,3-dienes, namely 2,3-dimethyl-1,3-butadiene (DMB), 4-methyl-1,3-pentadiene (MPD) and isoprene (IP) were investigated in 1,2-dichloroethane in the presence of various amounts of zinc chloride at different temperatures. ZnC1, complexes with the ester group of MA and increases the MA's electron-poor character and therefore its tendency towards reactions with electron-rich dienes. In the absence of ZnCl,, no reaction occurs between the investigated dienes and MA under the used reaction conditions. Both alternating copolymers and [4+2] cycloadducts formed spontaneously in the presence of ZnC1, even at room temperature.The structure ofthe diene and its nucleophilicity control the product distribution.For the DMB and IP systems, raising the reaction temperature and increasing the ZnC1, concentration enhance the overall reaction rate and in most cases also favor the cycloaddition over the copolymerization. IP is less reactive than DMB. With MPD only copolymer is formed because the two terminal methyl groups retard the concerted [4+2] cycloaddition.These results are in agreement with a postulated mechanism involving competition between the formation of a n-allyl2-hexene-1,6-diradical, capable of initiating free radical copolymerization, and concerted [4+2] Diels-Alder cycloaddition.

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Competition between Diels-Alder cycloaddition and spontaneous copolymerization of 1-methoxy-1,3-butadiene with electrophilic olefins

Cited by 18 publications

References 1 publication

The Relationship of Cycloaddition Reactions to Spontaneous Vinyl Polymerizations

The Relationship of Cycloaddition Reactions to Spontaneous Vinyl Polymerizations

Reevaluation of Tetrahydrophthalic Anhydride as an End Cap for Improved Oxidation Resistance in Addition Polyimides

Effect of ZnCl₂ on the spontaneous copolymerization of methyl acrylate with substituted 1,3‐dienes

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Competition between Diels-Alder cycloaddition and spontaneous copolymerization of 1-methoxy-1,3-butadiene with electrophilic olefins

Cited by 18 publications

References 1 publication

The Relationship of Cycloaddition Reactions to Spontaneous Vinyl Polymerizations

The Relationship of Cycloaddition Reactions to Spontaneous Vinyl Polymerizations

Reevaluation of Tetrahydrophthalic Anhydride as an End Cap for Improved Oxidation Resistance in Addition Polyimides

Effect of ZnCl2 on the spontaneous copolymerization of methyl acrylate with substituted 1,3‐dienes

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Effect of ZnCl₂ on the spontaneous copolymerization of methyl acrylate with substituted 1,3‐dienes