[2.2]Paracyclophane mit definiertem Substitutionsmuster – Schlüsselverbindungen zum mechanistischen Verständnis der Gilch‐Reaktion zu Poly(<i>p</i>‐phenylenvinylenen)

Wiesecke, Jens; Rehahn, Matthias

doi:10.1002/ange.200390131

Cited by 4 publications

(18 citation statements)

References 23 publications

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“…Unfortunately, in all our earlier experiments, 8,12,13 the monomer activation process 1a f 2a stopped after approximately 40-70% conversion when temperatures where adhered to where autoinitiation of chain growth is reliably suppressed (<-50°C). This fact might be due to either insufficient reactivity of 1a or limited solubility of KO t Bu.…”

Section: Introductionmentioning

confidence: 66%

“…Recently, we could show that R-chloro-pquinodimethanes 2a represent the real active monomers. 8 They are formed from starting materials 1a via dehydrochlorination. Moreover, there is strong evidence that the subsequent chain growth is initiated by diradicals 3a which form via spontaneous dimerization of a small number of monomer molecules 2a (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

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Toward Controlled Gilch Synthesis of Poly(p-phenylenevinylenes): Synthesis and Thermally Induced Polymerization of α-Bromo-p-quinodimethanes

Schwalm

Rehahn

2007

Macromolecules

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It is general consensus that in Gilch polymerizations the 1,4-bis(halomethylene)benzene starting material first changes into an R-halo-p-quinodimethane intermediate which then acts as the real active monomer in the subsequent chain growth process. Recently, we could verify the formation of R-chloro-p-quinodimethane directly via in-situ NMR spectroscopy at low temperatures. However, quantitative formation of this pquinodimethane was not possible there. Now, we show that even such quantitative conversion into the active monomer is possible if bromomethylene-functionalized starting materials are used instead of their chloromethylene counterparts. Moreover, it is even possible to induce chain growth leading to PPV in a very controlled way by carefully warming the obtained solution of p-quinodimethane. In this manner, the temperature can be determined where chain growth startssand hence thermal energy is sufficient for the initiating process. Finally, we could reconfirm that the chain growth is a radical polymerization here as well, initiated by diradicals formed via spontaneous dimerization of a low number of R-bromo-p-quinodimethane monomers. This proof could be provided by quantitatively analyzing the effect of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO): depending on the molar ratio of monomer and scavenger, the chain growth is either retarded or completely prevented.

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Section: Introductionmentioning

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Toward Controlled Gilch Synthesis of Poly(p-phenylenevinylenes): Synthesis and Thermally Induced Polymerization of α-Bromo-p-quinodimethanes

Schwalm

Rehahn

2007

Macromolecules

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“…5-Methoxy-2-(bethylhexyloxy)-1,4-bis(chloromethylene)benzene 1 was prepared according to the literature. [7] THF was dried over sodium/ benzophenone and distilled under nitrogen prior to use.…”

Section: Methodsmentioning

confidence: 99%

“…Based on the results obtained, and backed by information available from other groups, we proposed a more detailed mechanistic picture (Scheme 1). [7] In the first step, potassium tert-butanolate (KOtBu) converts the starting material, 1,4-bis(chloromethylene)-benzene 1, into p-quinodimethane 2, which represents the active monomer. A minor fraction of the p-quinodimethane…”

Section: Introductionmentioning

confidence: 99%

The Effect of Persistent TEMPO Radicals on the Gilch Polymerization

Wiesecke¹,

Rehahn²

2007

Macromol. Rapid Commun.

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The mechanism of the Gilch polymerization leading to poly(p‐phenylene vinylenes) is still a matter of controversial discussion. Similar to some other research groups, we strongly favor a basically radical process. Moreover, we believe it is initiated by spontaneously formed diradicals. Here, we describe further experimental evidence which clearly supports the assumed initiation step: it is shown how the polymerization process is affected quantitatively when different amounts of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) are added as a scavenger. In full agreement with our expectations, the chain growth is either retarded or completely prevented, depending on the respective molar ratio of monomer and scavenger.magnified image

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“…On the contrary, some aspects are still under controversial discussion, such as the question as to whether the chain growth is anionic or/and radical. [8,21] Based on careful analysis of what is published, and on our own experimental findings, we postulate an exclusively radical chain growth mechanism. More precisely, we assume an ongoing sequence of chemical conversions during the Gilch reaction as is roughly sketched in Scheme 1.…”

Section: Introductionmentioning

confidence: 90%

Direct Observation of α‐Chloro‐p‐quinodimethane as the Real Monomer in the Gilch Polymerization Leading to Poly(p‐phenylene vinylene)s

Wiesecke¹,

Rehahn²

2007

Macromol. Rapid Commun.

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It is the general consensus that in Gilch polymerizations the 1,4‐bis(chloromethylene)benzene starting material first changes into p‐quinodimethane intermediates which then act as the real monomers. However, direct observation of these intermediates has not been possible so far. This is because usually the p‐quinodimethane auto‐initiates its rapid radical polymerization instantaneously, keeping its concentration extremely low throughout the whole process. Here it is shown that, when the reaction is carried out at very low temperatures, the formation of p‐quinodimethane still proceeds but chain growth is suppressed. Hence, the concentration of the active monomer reaches a level sufficient for NMR analysis.

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[2.2]Paracyclophane mit definiertem Substitutionsmuster – Schlüsselverbindungen zum mechanistischen Verständnis der Gilch‐Reaktion zu Poly(p‐phenylenvinylenen)

Cited by 4 publications

References 23 publications

Toward Controlled Gilch Synthesis of Poly(p-phenylenevinylenes): Synthesis and Thermally Induced Polymerization of α-Bromo-p-quinodimethanes

Toward Controlled Gilch Synthesis of Poly(p-phenylenevinylenes): Synthesis and Thermally Induced Polymerization of α-Bromo-p-quinodimethanes

The Effect of Persistent TEMPO Radicals on the Gilch Polymerization

Direct Observation of α‐Chloro‐p‐quinodimethane as the Real Monomer in the Gilch Polymerization Leading to Poly(p‐phenylene vinylene)s

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