Superelectrophiles in Aromatic Polymer Chemistry

Colquhoun, Howard M.; Zolotukhin, Mikhail G.; Халилов, Л. М.; Джемилев, У. М.

doi:10.1021/ma001579o

Cited by 42 publications

(56 citation statements)

References 11 publications

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“…[6] The thermal stability was very good; no decomposition could be observed by heating at 420 8C under a nitrogen atmosphere (heating rate in both cases ¼ 10 K min À1 ).…”

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confidence: 95%

“…The linear analogues have been shown to display a high glass-transition temperature (T g ) and excellent thermal stability. [6] The use of para-phenoxybenzophenones as the aromatic reaction partner results exclusively in para-substitution and hence in structural homogeneity of the polymer. [6] Therefore, the AB 2 monomer 1 was designed and synthesized by Stille coupling of the tin derivative 3 and 5-bromo-1-methylisatin (4) [7] (Scheme 1).…”

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confidence: 99%

“…[6] The use of para-phenoxybenzophenones as the aromatic reaction partner results exclusively in para-substitution and hence in structural homogeneity of the polymer. [6] Therefore, the AB 2 monomer 1 was designed and synthesized by Stille coupling of the tin derivative 3 and 5-bromo-1-methylisatin (4) [7] (Scheme 1). The methyl group was introduced to enhance the solubility of both the monomer and the polymers and to facilitate the characterization of the latter by NMR spectroscopy.…”

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confidence: 99%

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Synthesis, Characterization, and Modification of Hyperbranched Poly(arylene oxindoles) with a Degree of Branching of 100 %

Smet

Schacht

Dehaen

2002

Angew. Chem. Int. Ed.

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Hyperbranched polymers are of high importance as readily available substitutes for dendrimers. Whereas the preparation of the latter requires a multistep synthesis, hyperbranched polymers can be obtained in a single step. [1] However, a degree of branching of 100 %, which is a characteristic property of dendrimers, can be achieved only by postsynthetic modification [2] or when certain requirements for the monomer are met. [3] To date, the only example of a hyperbranched polymer (which necessarily consists exclusively of dendritic and terminal units) was based on an AB 2 monomer possessing an azine and a maleimide functional group, which react in a ™criss-cross∫ cycloaddition. [4] However, to improve features such as accessibility, convenience of functionalization, and attractive physical properties, it is highly desirable to devise new strategies towards hyperbranched polymers with a degree of branching of 100 %.We applied the acid-catalyzed condensation of isatins [5] with aromatic compounds for the synthesis of hyperbranched poly(arylene oxindoles). The linear analogues have been shown to display a high glass-transition temperature (T g ) and excellent thermal stability. [6] The use of para-phenoxybenzophenones as the aromatic reaction partner results exclusively in para-substitution and hence in structural homogeneity of the polymer. [6] Therefore, the AB 2 monomer 1 was designed and synthesized by Stille coupling of the tin derivative 3 and 5-bromo-1-methylisatin (4) [7] (Scheme 1). The methyl group was introduced to enhance the solubility of both the monomer and the polymers and to facilitate the characterization of the latter by NMR spectroscopy. As it is known that this type of condensation of isatin and aromatic compounds exclusively yields 3,3-diaryl oxindoles, [5] we can exclude the possibility of the presence of linear units in the hyperbranched polymers obtained from 1. The tin derivative 3 was obtained by palladium-catalyzed transmetalation of the bromide 2 and hexakis-n-butylditin. The bromide 2 was formed by Friedel± Crafts acylation of diphenyl ether (five-fold excess) with 4-bromobenzoyl chloride.Monomer 1 was polymerized over 24 h using trifluoromethanesulfonic acid, to yield the polymers 5 a±d, which possess 3,3-diaryl oxindole groups as dendritic units and isatin residues at the periphery. These polymers were soluble in chloroform, dichloromethane, and toluene. They were poorly soluble in THF and insoluble in acetone. These solubility properties are in sharp contrast to the linear analogues which were only soluble in highly polar solvents such as N,Ndimethylacetamide and N-methylpyrrolidinone, or in the presence of strong acids. [6] As can be seen from Table 1, the obtained molecular weights are strongly dependent upon the reaction temperature and the concentration. At room temperature, only oligomers were obtained although, according to the literature, [6] the linear polymerization occurred readily at 25 8C. Higher temperatures and higher concentrations favor the formation of higher molecul...

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“…[6] The thermal stability was very good; no decomposition could be observed by heating at 420 8C under a nitrogen atmosphere (heating rate in both cases ¼ 10 K min À1 ).…”

mentioning

confidence: 95%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Synthesis, Characterization, and Modification of Hyperbranched Poly(arylene oxindoles) with a Degree of Branching of 100 %

Smet

Schacht

Dehaen

2002

Angew. Chem. Int. Ed.

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“…In its original definition [26], superelectrophilicity referred to the increased reactivity of electrophiles in the presence of a superacid [27,28], which, in the case of keto groups, is believed to doubly protonate the carbonyl O, rendering the carbonyl C highly susceptible to nucleophilic attack [29][30][31][32]. The original definition was extended [25] to include the coordination of Lewis acids to the lone pair on a positively charged heteroatom, an example being the reaction between chloromethyl methyl sulfide and chlorobenzene (to give methylthiomethylation products) that occurs in the presence of a 2:1 molar excess of AlCl 3 [33].…”

Section: Introductionmentioning

confidence: 99%

A DFT study of the formation of xanthydrol motifs during electrophilic poly(aryl ether ketone) synthesis

et al. 2015

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The reaction pathway of the cyclization of 2-phenoxybenzophenone into 9-phenyl-9H-xanthen-9-ol in the presence of acid and an excess of AlCl33 was studied using density functional theory. This type of reaction is known to occur during the Friedel-Crafts polycondensation of poly(aryl ether ketones) following the undesired benzoylation of nucleophilic positions ortho- to the growing polymer's ether groups. The formed defect acts as an undesired terminator of the polymer chain, causing severe problems in the polymer's melt state. A branched, multistep mechanism reminiscent of the Friedel-Crafts acylation reaction is discovered; the reaction starts with the protonation of the carbonyl oxygen, followed by intramolecular electrophilic attack on the carbonyl carbon that determines the turnover frequency of the catalytic cycle and ends by deprotonation of the Wheland intermediate.

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“…5 In the following Communication, we describe superacid-promoted hydroxyalkylation reactions of 1,2-indandione and substituted derivatives. The conversions lead to 2,2-diaryl-1-indanone products and a mechanism is proposed involving a deprotonated superelectrophilic intermediate.…”

Section: Introductionmentioning

confidence: 99%