The polymerization of pyromellitic dianhydride with diphenylmethane diisocyanate

A novel polyimide forming reaction is reported. Pyromellitic dianhydride undergoes a condensation polymerization with diphenylmethane diisocyanate in solution or under melt-fusion conditions to give polydiphenylmethanepyromellitimide (II) and carbon dioxide. Polymer II was characterized by inherent viscosity, infrared spectrum, and thermogravimetric analysis. An intermediate Polymer I was isolated which appeared to contain seven-membered rings in the backbone. It is postulated that these rings eliminate carbon dioxide to form polyimide II.     

Synthesis of benzophenone tetracarboxylic dianhydride and pyromellitic dianhydride incorporated biscitraconimides and their thermal polymerization

Biscitraconimides incorporated with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) were synthesised. Their curing behavior as well as thermal stabilities were investigated. The intermediate amic acids were prepared by the reaction of 4-amino 4′-citraconamic acid diphenyl sulphone, 4-amino 4′-citraconamic acid diphenyl ether, and 12-amino 1-citraconamic acid dodecane with BTDA and PMDA, respectively. Six amic acids formed were then imidized by cyclocondensation with acetic anhydride. The imide monomers were obtained and these were cured at 225–240°C. The thermal stabilities of the polymers so formed were investigated and compared. © 1996 John Wiley & Sons, Inc.     

Acylation of acetylcellulose with pyromellitic dianhydride

The cross-linking reactions of acetylcelluloses having different levels of acetyl groups with pyromellitic dianhydride in homogeneous media have been investigated. A relationship has been established between the static exchange capacity (SEC) and the content of hydroxy groups in the acetylcellulose and the exterification conditions (homogeneous or heterogeneous-solid phase). It has been shown that on the interaction of acetylcellulose with pyromellitic dianhydride under homogenous conditions there is a uniform distribution of cross-linkages over the whole length of the acetylcellulose macromolecule, which enables products with high SEC values to be obtained.Tashkent Institute of Chemical Technology. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 515–520, July–August, 1999.     

Polymerization of pyromellitic dianhydride with 3,3′-diaminobenzidine in aprotic solvents I. Reaction variables

The solution polymerization of pyromellitic dianhydride with 3,3′-diaminobenzidine to form poly(amide acid amine) was investigated under a variety of reaction conditions. Polymer viscosity and gel formation were highly affected by changes in the order of monomer addition, the type of process (powder or solution), monomer concentration, monomer stoichiometry, and type of solvent. Minor effects were noted with changes in polymerization temperature and the presence of small amounts of water. A limiting intrinsic viscosity of 1.2–1.5 dl/g was observed, regardless of polymerization conditions. The polymerization had a strong tendency to gel at high concentrations and when monomer molar ratios approached 1:1. The conditions which retarded or promoted the formation of macrogel were well-defined, and macrogel but not microgel could be prevented. The polymerization was conducted successfully only in aprotic solvents. No imidazopyrrol-one units were detected in polymer made in polyphosphoric acid at elevated temperatures.     

Polymerization of pyromellitic dianhydride with 3,3′-diaminobenzidine in aprotic solvents II. Dilute solution studies

Solution properties were determined for the poly(amide acid amine) obtained from the room-temperature polymerization of pyromellitic dianhydride with 3,3,-diaminobenzidine in aprotic solvents. Membrane osmometry data, viscosity studies, solution aging studies, and pH–viscosity relationships were given. Anomalous upswings in viscosity–concentration plots were attributed to absorption or capillary wall effects and not to polyelectrolyte effects, such as were induced by addition of strong bases. Similar absorption effects were found with polyamic acid solutions, in contrast to earlier reports that these polyimide precursors were polyelectrolytes. Unfavorable storage characteristics of the polymer solutions were explained by aging studies which showed that at 25°C dilute solutions exhibited a rapid drop in viscosity; in concentrated solution a slow increase to gelation was observed.     

Synthesis of polypyromellitimidoamides from dihydrazides of aromatic and aliphatic acids and pyromellitic dianhydride

Polyamido acids have been synthesized from pyromellitic dianhydride and dihydrazides of terephthalic, isophthalic, sebacic, and adipic acids. The polyamido acids obtained have been cyclized at 220° C, and it has been shown by IR spectroscopy that the polymers contain five-membered imide rings.     

Quantum chemical study of aromatic diamine and dianhydride reactivities in acylation reactions

Semi-empirical calculations of isolated diamines and model anhydrides and of their interaction energy, ΔE, have been made. Reactivity indices of diamines and dianhydrides (atom charges, characteristics of frontier orbitals) have been found. Analysis of the ΔE components has shown that chemical structure of diamines affects mainly electrostatic and charge transfer contributions to ΔE. Chemical structure of diahnydrides influences most significantly charge transfer component. Results of the ΔE calculation have substantiated the choice of reactivity indices.     

Electrode reduction mechanism of aromatic nitriles in aprotic solvents: Benzonitrile

The electrode reaction mechanism of benzonitrile in anhydrous DMF has been studied by polarography, potential sweep voltammetry, macroscale electrolysis, e.p.r. spectrometry and kinetic analysis. The relatively stable radical anion formed by one-electron addition decays according to a first order kinetic law, with formation of benzene and CN^? as final products together with substantial amounts of the alkene and alkylamine corresponding to the tetraalkylammonium salt used as background electrolyte. The results are interpreted in terms of a mechanism involving protonation of the anion radical by the solvent and the back-ground electrolyte, followed by dismutation of the resulting neutral radical with the anion radical and elimination of CN^? ions from the anionic species thus formed. By phenol addition CN^? elimination is prevented and the reduction proceeds to 1-cyclohexene-1-nitrile or to cyclohexane-nitrile, depending on the reduction potential.     

A re-investigation of the reactions of pyromellitic acid and its dianhydride with sulphur tetrafluoride

The fluorination of pyromellitic acid (1) with sulphur tetrafluoride or pyromelliticdianhydride (2) by means of an SF₄---HF mixture gave, besides the expected 1,2,4,5-tetrakis(trifluoromethyl)benzene (3), considerable amounts of 5,6-bis(trifluoromethyl)-1,1,3,3-tetrafluoro-1,3-dihydroisobenzofuran (4) and detectable quantities of1,1,3,3,5,5,7,7-octafluoro-1,3,5, 7-tetrahydrobenzo[1,2-c:4,5-c′]difuran (5). Acidic hydrolysisof 4 gave 4,5-bis(trifluoromethyl)phthalic acid (6) which on treatment with SF₄ andHF yielded compounds 3 and 4.     

Natural phenolic compounds in the reaction with a nitrogen-centered radical in an aprotic solvent

Kinetics and mechanism of the reaction of vegetable phenols (PhOH) with 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH?) in a polar aprotic solvent, dimethyl sulfoxide, were studied. The reaction of natural phenols with DPPH? in dimethyl sulfoxide occurs in two stages. In the first stage, a proton-coupled electron transfer (PCET) occurs from a PhOH molecule to DPPH? to give primary transformation products, phenoxyl radicals (PhO?) and diphenyl hydrazine (DPPH–H), and in the second, the hydrazyl radical is consumed in the reaction with PhO? transformation products, enolized dimers, which is confirmed by NMR spectroscopy. A relationship was revealed between the antiradical activity of phenols in the reaction with DPPH? (ln k) and the ionization potential of the phenolates being formed.     

Condensation reaction with methylketones and aromatic compounds containing electron-repelling groups

Aryl tellurium trichlorides and tribromides undergo condensation reactions with acetone, acetophenone, N-dimethylaniline and resorcinol, giving rise to aryl tellurium dihalides. Aryl tellurium triiodides are not reactive. The dihalides derived from N-dimethylaniline and resorcinol undergo ionic interchange reactions with halide ions. When treated with reducing agents the dihalides derived from N-dimethylaniline are reduced to the corresponding tellurides, while the other dihalides are cleaved to the diaryl-ditellurides.     

Structure of the dibenzoylphthalic acids obtained by condensation of pyromellitic dianhydride with benzene

Conclusions A method has been developed for the isolation of 2,4-dibenzoylisophthalic and 2,5-dibenzoylterephthalic acids from the mixtures formed during the Friedel-Crafts condensation of pyromellitic dianhydride with benzene. The structure of the acids obtained has been investigated by PMR and DR speetroscopy. The ability of 2,5-dibenzoylterephthalic acid to undergo tautomeric interconversions (normal or cyclic forms) has been discovered.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 368–372, February, 1976.     

Oxidative polymerization of aromatic hydrocarbons: A study of kinetics and mechanism

Aromatic hydrocarbons were homopolymerized by means of an oxidative polymerization reaction with the use of the catalyst system anhydrous aluminum chloride–cupric chloride. The kinetics of the benzene homopolymerization carried out under different experimental conditions was followed by the determination of the amounts of cuprous ion and polymeric product formed in the reaction. Cuprous ion was spectrophotometrically titrated in the form of its complex with 2,2′-biquinolyl (cuproine). The experimental results do not agree with cationic mechanism for this reaction previously proposed in the literature. Ethylbenzene was kinetically studied under the same experimental conditions. In view of the experimental evidences obtained in this work and on some literature data, a mechanism based on formation of cation-radicals is proposed for the oxidative polymerization reaction when carried out under the studied conditions.     

Photoinduced ionic polymerization. III. Cationic polymerization and copolymerization of cyclohexene oxide and α-methylstyrene in the presence of pyromellitic dianhydride

The photoinduced ionic polymerization of cyclohexene oxide was studied in the presence of pyromellitic dianhydride. The polymerization is initiated by the excited chargetransfer complex between cyclohexene oxide and the electron-acceptor and proceeds by a cationic mechanism. Photoinduced cationic polymerization of α-methylstyrene was also observed in the presence of pyromellitic dianhydride. The initiation mechanism of the polymerization was elucidated by means of electron spin resonance measurements. The concentration of pyromellitic dianhydride anion-radicals measured in this way was found to be proportional to the rate of polymerization. This result shows clearly that the photopolymerization is initiated by cation-radicals formed from photoexcited donoracceptor complexes. The attempted photocopolymerization of cyclohexene oxide and α-methylstyrene gave a mixture of homopolymers. The composition of the product depends on the wavelength of the light used.     

Catalytic effects of hydrogen-bond acceptor solvent on nucleophilic aromatic substitution reactions in non-polar aprotic solvent: reactions of phenyl 2,4,6-trinitrophenyl ether with amines in benzene-acetonitrile mixtures

The effect of addition of small amounts of hydrogen-bond acceptor solvent, acetonitrile, to the benzene medium of the reactions of phenyl 2,4,6-trinitrophenyl ether with aniline and cyclohexylamine, respectively have been investigated. The addition produced similar effects in the two reactions—continuous rate increase with increasing amounts of acetonitrile. The results are interpreted in terms of the effect of amine-solvent interaction on the nucleophilicity of the amines and are in accord with our expectations based on the effects observed for hydrogen-bond donor solvent, methanol on the same reactions. It is also established from the results that the role of hydrogen-bond acceptor co-solvent could be played by an added more basic non-nucleophilic amine.     

A DFT study on secondary reaction pathways in the acid-catalysed Beckmann rearrangement of cyclohexanone oxime in aprotic solvent

In recent studies regarding acid-catalysed Beckmann rearrangement of cyclohexanone oxime in aprotic solvents it has been observed that a quite surprising hydrolysis of the starting material, i.e., cyclohexanone oxime, occurs even if the experimental conditions and the water concentration in the reaction mixture can not justify such a side-reaction. Being this apparent hydrolysis critical for catalyst selectivity and poisoning, a computational DFT study on a possible secondary reaction pathway, involving a bi-molecular reaction between two cyclohexanone oxime molecules in acid media as the primary step, is here reported to explain the experimental results.