Dilute solution studies of nitrogen-substituted polyurethanes

A high molecular weight linear polyurethane was prepared by the polyaddition of equimolar amounts of ethylene glycol and methylene bis(4-phenyl isocyanate). Varying amounts of the labile carbamate protons of the polyurethane backbone were substituted by a number of groups of varying length and composition. The resultant grafted or nitrogen-substituted polyurethanes were then studied viscometrically in both polymer solvent and in a polymer solvent—nonsolvent mixture. The configuration of the nitrogen-substituted polyurethane was found to be dependent upon the number and length of pendent branches.     

Dilute solution properties of a polyurethane. I. Linear polymers

A linear polyurethane of high molecular weight was prepared in solution by the polyaddition of equimolar amounts of ethylene glycol and methylene bis(4-phenyl isocyanate). The polymer was fractionated by using a direct sequential extraction procedure, with a solvent–nonsolvent system consisting of N,N′-dimethylformamide (DMF) and acetone (A). The resulting fractions were characterized by viscosity and lightscattering measurements. The relationship between the intrinsic viscosity and molecular weight was found in DMF at 25°C. to be [η] = 3.64 × 10^?4M^0.71. The unperturbed polymer chain dimensions were determined from intrinsic viscosity measurements carried out under experimentally determined theta conditions.     

Une méthode simple de calcul des structures électroniques (σ + π) des borazines et des boroxines substitués de symétrie D3h: une estimation théorique de l'aromaticité comparée de ces molécules

Résumé Une utilisation conjointe des méthodes L.C.A.O.-C.U.V. et d'itération tournante permet d'atteindre des structures électroniques ( + ) cohérentes avec l'U.V.(et donc le gradient de population électronique de liaison qui conditionne l'aromaticité) de huit borazines et boroxines, substitués ou non, de symètrie D _3h . L'échelle d'aromaticité obtenue permet de rendre compte des propriétés magnétiques (RMN, RQ, effet Faraday, diamagnétisme) de ce type de molécules. On parvient en particulier aux deux conclusions essentielles suivantes: les borazines sont nettement plus aromatiques que les boroxines isologues et la greffe de groupements méthyles ou d'atomes de chlore, qu'elle se fasse sur le bore ou sur l'azote, confère toujours au dérivé substitué une aromaticité au moins égale à celle du borazine lui-même.

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A simple method to calculate the - and -electron structure of borazines and of substituted boroxines of symmetry D_3h: A theoretical estimation of the relative aromaticity of those molecules

( + ) electronic structures calculations are performed for eight D _3h borazines and boroxines, using in concert previously published U.V.-consistent H.M.O.-L.C.A.O. and bond by bond iteration methods. An estimation of bond electronic populations gradients is so obtained, allowing to set up a new aromaticity scale for such molecules. The main results are the following: Borazines are much more aromatic than isologous boroxines and B-or N-graft of alkyl groups or chlorine atoms never decreases (and generally increases) aromaticity.

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Zusammenfassung Es wird für acht Borazol- und Boroxolverbindungen mit D _3h -Symmetrie unter Verwendung einer am UV-Spektrum geeichten iterativen HMO-LCAO-Theorie die - und -Elektronenstruktur bestimmt. Hiermit kann eine Abschätzung des Gradienten der Bindungselektronendichten gewonnen werden, aus der eine Einteilung der Moleküle nach ihrem aromatischen Charakter hervorgeht. Es ergibt sich, daß die Borazole aromatischer sind als die isoelektronischen Boroxole und daß eine Substitution der H-Atome am Bor oder Stickstoff durch Chlor oder Methylgruppen die Aromatizität fast immer erhöht, jedenfalls aber nie erniedrigt.

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Recherche effectuée dans le cadre de la R.C.P. n du C.N.R.S.     

Le spectre d'absorption infrarouge de l'acétate de méthyle perdeutéré

Résumé Les spectres d'absorption infrarouge de l'acétate de méthyle et de l'acétate de méthyle perdeutéré ont été étudiés de 300 à 4000 cm^–1. La comparaison des spectres a permis l'attribution certaine des bandes de l'acétate de méthyle, en particulier de la bande observée vers 1245 cm^–1 qui correspond à une vibration concernant la liaison C-O.

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Summary The infrared absorption spectra of methyl acetate and the perdeuterated methyl acetate have been studied from 300 to 4000 cm^–1. The comparison of the spectra has made it possible to attribute certain of the bands of methyl acetate, in particular the band observed around 1245 cm^–1, which corresponds to a vibration involving the C-O bond.

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Zusammenfassung Die Absorptionsspektren von Methylacetat der Zusammensetzung CH₃COOCH₃ und CD₃COOCD₃ im Infrarot wurden zwischen 300 und 4000 cm^–1 untersucht. Der Vergleich dieser Spektren führte zur sicheren Zuordnung der Banden des Methylacetats, insbesondere der bei 1245 cm^–1 gelegenen Bande, die der C-O-Bindung zugehört.

     

Cyclocopolymerization of dicyclic dienes and maleic anhydride to fused ring systems

The cyclocopolymerization of maleic anhydride and four 1,5- and 1,6-dienes (bicyclopentene, bicyclohexene, dicyclopentenyl ether, and dicyclohexenyl ether) and one tetraene (quartercyclopentene) is described. Soluble, low molecular weight copolymers were obtained from all five compounds. Their compositions approach 2:1 copolymer ratios. Fused ring structures are proposed as the main repeating units. Among the compounds listed, bicyclopentene copolymerized most easily and gave good conversions for monomer ratios of 2:1. Quartercyclopentene and dicyclopentyl ether, the other five-membered ring compounds, also polymerized to good-to-fair yields. However, a monomer ratio of about 4:1 was required to obtain conversions comparable to a 2:1 maleic anhydride—bicyclopentene polymerization. The six-membered systems, bicyclopentene and dicyclopentenyl ether, gave consistently low conversions, even with a 4:1 monomer ratio. The influence of the initiator system, initiator concentration, and reaction medium was studied on copolymerizations of bicyclopentene. Best results were obtained in acetic anhydride with azobisisobutyronitrile as the initiator.     

Normal mode analysis of oligomeric proteins: Reduction of the memory requirement by consideration of rigid geometry and molecular symmetry

A method is presented to reduce the memory requirement of normal mode analysis applied to systems containing two or more large proteins when these systems exhibit symmetry properties. We use a rigid geometry model (i.e., only the dihedral angles of the polypeptide chain are considered as variables). This model allows a reduction by a factor of 8 on average of the number of variables with a concomitant freezing of the high-frequency modes. The symmetry properties of the system are used to reduce further the number of variables that must be considered in the computation. Application of group theory leads to a factorization of the matrices of interest (the coefficient and the Hessian matrices) into independent blocks along the diagonal. The initial, reducible representation is thus transformed into a number of irreducible representations of smaller dimensions. In the case of the C₂ symmetry group, the method leads to a reduction of the size of the matrices that must be manipulated during the computation (coefficient matrix, Hessian matrix, and eigenvectors matrix) by a factor of 256 compared with the usual normal mode analysis in Cartesian coordinate space. The method is particularly well adapted to the study of the dynamics of oligomeric proteins because these proteins often display symmetry properties (e.g., virus coat proteins, immunoglobulins, hemoglobin, etc.). In favorable cases, in conjunction with X-ray diffuse scattering data, the study of systems showing allosteric properties might be considered. © 1994 by John Wiley & Sons, Inc.     

Recent developments in the synthesis and functionalization of conducting poly(thiophenes)

The mechanism of the electropolymerization of thiophene derivatives has been investigated by varying the electrosynthesis conditions and the monomer structure. The results of these analyses led to the definition of optimized electrosynthesis conditions allowing the control of the electrical and electrochemical properties of poly(thiophenes). On the basis of these results, the properties of these polymers have been modified by means of a new one-step electrosynthesis of conducting composite materials and by the direct electropolymerization of tailor-made functionalized monomers. For this purpose, the steric conditions associated to the various possibilities of covalent derivatization have been analyzed, leading to the definition of a “functionalization space”, compatible with the preservation of high conductivity and electrochemical reversibility in the resulting polymers. This concept has been applied to the synthesis of highly conducting chiral poly(thiophenes) on which an effect of enantioselective molecular recognition has been demonstrated for the first time.     

Practical aspects of suppressed ion chromatography for cations in human serum

In spite of the good accuracy and precision of ion chromatographic methods for the determination of mono- and divalent cations in human serum, the major drawback with these methods were problems with the membrane suppressor's performance. Here, we described experiments undertaken to solve these problems. We address in particular the use of histidine-sulfuric acid eluents, sample purification with OnGuard-A cartridges and chromatographic “front-cut” for divalent cations. The latter two adaptations, resulting in removal of the anionic species from the sample, were successful in solving the observed suppressor problems. The eluent substitution, moreover, allowed us to switch from the chemical to the electric suppression mode. We believe that these adaptations will allow secure and robust determination of cations in human serum samples with ion chromatography.     

Thermodynamics of complexation of monovalent metal cations by the ionophore monensin free acid in acetonitrile

The standard Gibbs functions, enthalpies, and entropies for the formation of the complexes of monensin acid with monovalent metal cations in acetonitrile were obtained using various methods (conductometry, potentiometry, and calorimetry). Complexation is appreciable (from 2.0 to 4.5 in terms of association constant logarithm) and controlled mainly by the enthalpic effect. Comparison with formation of the corresponding neutral complexes permits a comparison to the process of monensin mediated transport of cation in membranes. A two-step process involving first the formation of the acidic complex is suggested.     

Investigation of the formation of poly(ethylene terephthalate) with model molecules. IV. Catalysis of the esterification of ethylene glycol with benzoic acid and of the condensation of ethylene glycol monobenzoate

The esterfication of ethylene glycol (EG) with benzoic acid (BA) is an acid-catalyzed reaction which leads, as a first intermediate, to ethylene glycol monobenzoate (EGMB). This compound has an ? OH group which is more active towards carboxylic groups than the first ? OH group of EG. Moreover, it is a key intermediate in the formation of sideproducts containing diethylene glycol (DEG) moieties. The condensation reaction of EGMB was particularly studied in the presence of carboxylic acids or metal derivatives as catalysts. Titanium is the most active. Sb, which is widely used in the industrial synthesis of PET, needs to be present at a high level of concentration to show an activity. The presence of carboxylic groups in the reaction medium does not affect its activity, but it is necessary to remove the ethylene glycol as soon as it is formed in order to keep it active during the condensation reaction.