bluuebunny/crossref_metadata_2025_split huggingface dataset:
Etude de radicaux libres forméas par irradiation ultraviolette de l'amidon: Application aux réctions de photodégradation et de photogreffage
Authors: Merlin André , Fouassier Jean‐Pierre 
Published: April 2003

AbstractGeneral investigations of radical processes in starch were carried out. ESR experiments showed that UV irradiation of starch, both in photosensitized and unphotosensitized experiments, results in chain scission and radical generation on the glucosidic ring. It was shown that benzophenone, deoxybenzoin and derivatives (2a–d) are efficient sensitizers. The ESR spectra were interpreted by assuming superposition of three signals; they were ascribed to radicals formed by chain scission and hydrogen abstraction. In addition photodegradation processes of starch in the presence and absence of photosensitizers were investigated. The amount of chain scissions was followed under various experimental conditions and appeared as a function of the initiator. Moreover, oxygen was shown to enhance the yield of chain scissions: this was explained through the formation of peroxide functions at C1‐position. UV light induced grafting of a vinyl monomer onto starch was also investigated. It appeared that chemical grafting can easily be achieved through a radical reaction. Moreover, the percentages of grafting and degradation were strongly dependent on the photoinitiator. The whole results gave the possibility to select an efficient initiator of the grafting reaction. In the case of methyl methacrylate, α,α‐dimethoxydeoxybenzoin (2a) appears to be the most efficient initiator. However, previous works as well as the present work suggest that the grafting efficiency is strongly dependent on the three components: substrate, monomer, and initiator.
Internal mobility of PMMA in concentrated CDCl3 solutions, 1. 1H NMR spectra
Authors: Zajíaček Jaroslav , Pivcová Hana , Schneider Bohdan 
Published: April 2003

AbstractMeasurements of the second moment and analysis of the derivative shape of 1H NMR spectra of PMMA have shown that in CDCl3 solutions containing 60% (w/w) or more of polymer, the internal mobility of PMMA is similar to the mobility of the pure polymer. The main chain is rigid on the NMR scale, and only CH3 groups are mobile. The motion of CH2 groups, representing the segmental mobility of the backbone chain, becomes appreciable on the NMR scale at concentreations of 60–50%, depending on the temperature. Measurements of 1H MAR‐NMR spectra of solutions containing 30% or more of polymer indicate spatial anisotropy of internal motions of PMMA. This spatial anisotropy is probably due to intermolecular interactions of ester groups, similarly as in the gels of the PMMA stereocomplex.
Die molekulargewichtsverteilung bei der kontinuierlichen anionischen polymerisation
Authors: Panke Dietrich 
Published: April 2003

AbstractEquations are given for the continuous anionic polymerization in a tubular reactor which describe the resulting molecular weight distribution as a function of the size of the mixing zone and of the concentration of chain terminating impurities in the solution of the monomer. Polymerization of styrene and of butyl methacrylate was conducted with different initiator concentrations, and the size of that part of the reactor where backmixing occurs was estimated from the molecular non‐uniformity of the polymers, whereas the degree of polymerization allows the determination of the concentration of the impurity. This latter quantity apparently increases with initiator concentration in the case of methacrylate polymerization and therefore suggests a reaction of the initiator with the ester group to occur. The shape of the molecular weight distribution indicates termination of the growing methacrylate chains, possibly by reaction of living chain ends with ester groups.
Decay studies of poly(vinyl chloride) electrets
Authors: Talwar Inder Mohan , Behari Shyam 
Published: April 2003

AbstractThermoelectrets of poly(vinyl chloride) were prepared at 4, 14, 20 kV/cm and 105, 115, 125 and 135°C. The final charge is always homocharge, though the initial one depends upon the polarizing parameters. With 4 and 14 kV/cm, up to 125°C, the initial charge is homo, increasing with the polarizing temperature Tp. At 135°C, it is heterocharge tending to increase with the polarizing field Ep. From the thermally stimulated depolarization glow curves, the number of dipoles per monomeric unit of the material is calculated; it is seen that this number cannot account for the heterocharge. A mica spacer placed between the dielectric and one electrode suppresses the peak current. A model is proposed to explain the electret behaviour.
Synthesen und charakterisierung polymerer cyaninfarbstoffe
Authors: Koßmehl Gerhard , Bocionek Peter 
Published: April 2003

AbstractFrom 2,3,5,6‐tetramethylthiazolo[4,5‐f]benzothiazoldiium diperchlorate (9) and the ortho esters 2a–d or 1,1,3,3‐tetramethoxypropane (4) polymeric cyanines with trimethine (10a), substituted trimethine (10b–d), respectively pentamethine units (11) were synthesized. Model compounds (3a–e, 5, 7a–d, 8) were prepared from 1a, 1b and 6, analogously. The structures were confirmed by elemental analyses, IR, and electronic spectra. In addition, the model compounds were characterized by their 1H NMR and mass spectra.
Oxydation photothermique et photocatalysée des polyundécanamides
Authors: Tang Ly , Lemaire Jacques , Sallet D. , Mery J.‐M. 
Published: April 2003

AbstractPhotothermal and TiO2‐ or ZnO‐photocatalyzed oxidations of type B‐ and type K‐polyundecanamides (RILSAN) were studied analytically and kinetically. IR spectrophotometry and chemical titration showed that hydroperoxy groups in the polymer reach a fairly high photostationary concentration. Then the primary photoproducts A decompose into products with imido groups (C), the concentration of which are increasing until a photostationary value. Under irradiation, the imides C are converted into acids and amides; in thermooxidation acids are the main products. The intermediate products in photocatalysed oxidation were found to be the same as in photochemical oxidation; a photochemical protection of hydroperoxides and imides was observed, due to the inner filter effect of the absorbing pigments. It could be shown that in polychromatic light the photocatalytic activity of TiO2 (rutile) is more important than its inner filter effect; this antagonism does not depend on the concentration of the photoactive pigment.
Conformational analysis of poly(oxymethylene)
Authors: Miyasaka Taira , Kinai Yoshiyuki , Imamura Yoshio 
Published: April 2003

AbstractThe conformational energies of the lower members of poly(oxymethylene), 2,4‐dioxapentane and 2,4,6‐trioxaheptane were estimated by the empirical force field method. The gauche states of the internal rotation around the skeletal CO bonds were successfully predicted to be of lower energies in both molecules. In order to calculate the unperturbed dimension and dipole moment of poly(oxymethylene), rotational isomeric state approximations were made by using the results obtained from the force field calculations on 2,4,6‐trioxaheptane. The first‐order interaction energy was estimated to be a large negative value, and the second‐order interaction energies for g±g± had non‐zero values. Although these parameters were significantly different from those estimated earlier, they reproduced the observed results fairly well. Thus the “gauche effect” of poly(oxymethylene) was explained by taking account of the effects contributed by the lone pairs of electrons on the oxygen atoms. As adopted in this study, the procedure joining the empirical force field method to the statistical mechanical one was shown to be effective for the investigation of many sorts of configuration‐dependent properties of chain molecules.
Mechanical shear degradation of polymers in solution by turbulent flow, 3. The influence of chemical constitution and thermodynamic quality of the solvent on shear degradation
Authors: Müller Hans Georg , Klein Joachim 
Published: April 2003

AbstractMechanical shear degradation of polyisobutylene, polystyrene, poly(vinyl chloride), poly(methyl methacrylate), poly(decyl methacrylate), poly(methyl acrylate), and 1,4‐polybutadiene in dilute solutions of tetrahydrofuran (THF) are studied under turbulent flow conditions through a capillary, in order to study the effect of the chemical constitution on shear degradation. In addition the influence of solvent quality on shear degradation is investigated. The changes of the molecular weight distribution curves were followed by gel permeation chromatography (GPC), in order to determine the degradation constants ki for the corresponding molecular weight distribution fractions M̄i. GPC calibration via the concept of universal calibration, Mark‐Houwink relations for polyisobutylene, poly(methyl methacrylate), poly(methyl acrylate), 1,4‐polybutadiene, and poly(dimethylsiloxane) in THF as solvent had to be established for this purpose. Substantial differences in the rate constants ki were observed as a function of M̄i, whereas a master curve resulted for all polymers except 1,4‐polybutadiene when ki was plotted against the number of main chain carbon atoms n̄i for each molecular weight M̄i. From this the shear degradation of CC single bond polymers can be represented by ki = C · n̄, C being independent of the chemical nature of the CC single bond polymer, and a varying from 1,7 to 2,6. This means that in addition to the shape of the deformed macromolecule to be degraded not only its hydrodynamic volume (in rest) but also its chain length plays an important role. As to the influence of solvent quality, the degradation constants were found to increase with decreasing solvating power of the solvent. Mechanical shear degradation of the type discussed here takes place in drag reduction by polymers.
Polymer conformation and NMR chemical shifts, 51H and 13C NMR spectra of poly(methyl methacrylate)
Authors: Koinuma Hideomi , Sato Kota , Hirai Hidefumi 
Published: April 2003

AbstractTacticity‐dependent splittings observed in 1H and 13C NMR spectra of poly(methyl methacrylate) are elucidated by a theoretical procedure which consists of conformational analysis of the polymer chain and shielding calculation. The conformation is analyzed by the statistical mechanical method combined with the force field energy calculation on the dyad sequence models. As significant shielding factors, diamagnetic, anisotropic, and electrostatic terms are taken into account for the chemical shifts of 1H NMR, while paramagnetic, diamagnetic, and anistropic terms are considered for 13C NMR. The calculation is used to assing the α‐methyl proton, methoxyl proton, methylene proton, quaternary carbon, methylene carbon, α‐methyl carbon, carbonyl carbon, and methoxyl carbon peaks split due to dyad and triad cotacticities. The results are generally consistent with the observed spectra. Especially, the calculated splitting widths are in quantitative agreement with the observed splittings of the methoxyl and α‐methyl protons resonances as well as of the carbonyl and α‐methyl carbons resonances. Effects of temperature and stereoregularity on the spectra are also discussed.
Kinetic dialysis as a method for determining mixed micelle composition
Authors: Lake Mathew 
Published: April 2003

AbstractA new method for the determination of the cmc using a dialysis technique which allows monomeric species to diffuse through but not micelles has been applied for determining the mixed micelle composition. The method is based on determining the amount of surfactant that diffuses through at two different times which allows for the calculation of the cmc by use of the appropriate equation. This method requires the preparation of only one concentration of solution and lends itself particularly well to the determination of the composition of mixed micelles.
Novel chain polymers by condensation of metal(II) coordinated salicylaldehyde with diamines
Authors: Maurya Pyare L. , Agarwala Badri V. , Dey Arun K. 
Published: April 2003

AbstractCoordination polymers, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \rlap{--} (MtL\rlap{--} )}_{\rm n} $\end{document} were synthesized by condensation of bis(salicylaldehydo)‐metal(II) (metal = Co, Ni, and Cu) with diamines (1, 4‐diaminobenzene and 4,4′‐diaminobiphenyl). Their composition, structure, thermal stability, and physical properties were investigated by analytical, magnetic, spectral (IR and DRS), the thermogravimetric studies. It was found that in the bis(salicylaldehydo)metal(II)‐chelates, two salicylaldehyde molecules are linked to each metal ion through the oxygen atoms of the phenolic and aldehydic groups and in the polymeric complexes the nitrogen atoms of the amino groups replace the aldehyde oxygens. The diamine molecule is thus acting as a bridging unit between two salicylaldehydometal(II) units, forming structures 1 and 2. The polymers obtained from 4,4′‐diaminobiphenyl (2a−c) are thermally more stable than those from 1, 4‐diaminobenzene (1a−c), the order of thermal stability in both cases being Ni(II) > Cu(II) > Co(II). Co(II) and Cu(II)‐complexes are paramagnetic, whereas Ni(II)‐complexes are diamagnetic. The reflectance spectra along with the magnetic data suggest a square planar structure for Cu(II) and Ni(II)‐complexes, and a tetrahedral one for the Co(II)‐complexes.
Viscosity/temperature relationships for dilute solutions of poly(2,4,5‐trichlorophenyl methacrylate)
Authors: Hadjichristidis Nikos , Touloupis Costas , Karvounis Sotiris 
Published: April 2003

AbstractThe actual viscosity η of six fractions of poly(2,4,5‐trichlorophenyl methacrylate) (PTCPh) with weight‐average molecular weight M̄w, ranging from 9,11 · 104 to 94,8 · 104, was determined in benzene at a number of temperatures from 22 to 60°C. The variation of the pre‐exponential term A and the apparent activation energy of viscous flow Q, with molecular weight and concentration was studied. Moore's equations are valid for PTCPh. The temperature coefficient of the unperturbed dimensions dln 〈r20〉/dT estimated from the intrinsic viscosity data by using the Burchard‐Stockmayer‐Fixman relation, is −3 . 10‐3 (from 22 to 40°C) and −0,87 . 10‐3 (from 40 to 60°C). These negative values indicate that extended configurations of PTCPh in benzene must be associated with lower energies.
Complexation between polyions and hydrous inorganic oxides and adsorption properties of complex
Authors: Kurokawa Yōichi , Sasaki Mitsuru 
Published: April 2003

AbstractComplexation between polyelectrolytes and hydrous inorganic oxides was investigated by turbidity and conductance measurements. Vapor (water and organic) adsorption isotherms on the complex were determined as a function of relative humidity with a gravimetric method. The adsorptivity increases in the order benzene < acetone < methanol < water, which corresponded to the order of polarity of the adsorbate. This result may be primarily attributed to the ion site of the complex, because each complex has relative low specific area (1–30 m2/g). However, it has higher surface area compared to the polyelectrolyte complex (<1 m2/g) reported in a previous paper. Adsorption of heavy metals and amino acids on the complex was also examined.
Radiation induced molecular size changes in native and denatured deoxyribonucleic acid under anoxic conditions. A pulse radiolysis study
Authors: Washino Komei , Schnabel Wolfram 
Published: April 2003

AbstractNative DNA (M̄w: 5 · 106 and 2 · 107) was irradiated at a concentration of 0,l g/l in Ar‐ or N2O‐saturated solutions. Emphasis was given to reactions induced by OH radicals. The solutions were irradiated with single 16MeV electron pulses (100 ns pulse length) in conjunction with time‐resolved Rayleigh light scattering measurements. It turned out that crosslinking and double strand breakage (dsb) can be clearly separated, the former proceeding faster than the latter. The extent to which the two processes—which counteract with respect to changes of the light scattering intensity (LSI)—occur, depends strongly on the ionic strength of the solution. At [NaClO4] > 10−1 mol/l crosslinking is the predominant process, which is assumed to be caused by the fact that hcrit, the critical length for the accomplishment of dsb, is strongly reduced. Thus, up to several hundred single strand breaks (ssb) per chain can remian ineffective with respect to the generation of dsb at high ionic strength. Crosslinking can occur both as an inter‐ and an intramolecular process. As inferred from light scattering measurements singlestranded DNA did not crosslink at a concentration of 0,l g/l and at low ionic strength, but underwent main‐chain rupture. The rate of LSI decrease is correlated to the rate of fragment diffusion. The half‐life time of the LSI decrease depends on M̄w as τ½ ∝︁ M̄. It was concluded that the lifetime of the species responsible for ssb is shorter than a few ms.
Small‐angle X‐ray scattering studies of L‐leucine dehydrogenase
Authors: Hiragi Yuzuru , Soda Kenji , Ohshima Toshihisa 
Published: April 2003

AbstractThe small‐angle X‐ray scattering of L‐leucine dehydrogenase (EC 1.4.1.9) from Bacillus sphaericus in 0,2 M sodium phosphate buffer (pH 7,28) was investigated. The following molecular parameters were determined: radius of gyration, as 50,8 Å from the Guinier plot and 48,5 Å from the distance distribution function; molecular weight, as 267 000; volume, as 623 000 Å3; and degree of hydration, as 0,95 g H2O/g of enzyme. By comparing the observed scattering curve with those calculated with a number of models, a hollow cylinder with 47,0 Å of outer radius, 10,3 Å of inner radius and 119,0 Å of length was proposed as a most plausible model for the enzyme.
Polyelectrolyte complexes, 3. The interaction between heparin and protamine
Authors: Cundall Robert B. , Jones Gareth R. , Murray David 
Published: April 2003

AbstractThe interaction of heparin with salmine protamine was investigated using the electrostatically bound fluorescent probes acridine orange and eosin Y and the 1‐(dimethylamino)‐5‐naphthalene sulfonyl group which is covalently bound to the protamine molecule. Dye displacement experiments indicate a 1 : 1 pairing of anionic heparin sites with cationic protamine sites. Further binding of heparin occurs, after all the cationic sites of protamine are bound up with heparin. This is thought to occur as a result of the different affinities of the sulfate and carboxyl groups of heparin for guanidino groups; the sulfate groups binding preferentially to the complex releasing some of the bound carboxyl groups. Fluorescence polarisation measurements suggest a heparin‐protamine complex greater in volume than would be expected from a simple pairing of heparin and protamine molecules, indicating some degree of cross‐linking. The limiting salt concentrations for the heparin‐protamine complex were determined in the prescence of a number of Group IA and IIA metal chlorides.
Effect of cooling rate on the structural relaxation of poly(oxy‐2,6‐dimethoxy‐1,4‐phenylene) and poly(oxy‐2,6‐dimethyl‐1,4‐phenylene)
Authors: Jauhiainen Tuure‐Pekka 
Published: April 2003

AbstractThe activation enthalpies for the structural relaxation of poly(oxy‐2,6‐dimethoxy‐1,4‐phenylene) and poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) were determined by studying the dependence of the limiting fictive temperature on the cooling rate, using a differential scanning calorimeter (DSC) interfaced to a computer. The molar mass dependence of the activation enthalpies complied with the empirical equation, ΔH˙ = ΔH − A/M, where ΔH is the activation enthalpy of an infinite chain length polymer, Mv is the viscosity‐average molar mass, a = 0,64, and A is a constant that depends on the free volume of the chain ends of the polymers. The values of ΔH are 433 kJ/mol for poly(oxy‐2,6‐dimethoxy‐1,4‐phenylene) and 449 kJ/mol for poly(oxy‐2,6‐dimethyl‐1,4‐phenylene).
Allowance for polymolecularity in polymer structure‐property relationships
Authors: Bareiss Rolf E. , Chiantore Oscar , Guaita Marino 
Published: April 2003

AbstractRelations between molar mass M and molar mass dependent properties E of polymers are mostly strictly valid only for monomolecular samples i:

For polymolecular polymer samples the corresponding averages Mav and Eav must be applied:

Provided the kind of average (number‐, weight‐ or any general average) of e.g. Mav is known, the corresponding average Eav is given by. Eqs. (1a, b). This is demonstrated for the relationships of van't Hoff and Mark‐Houwink, frequently used for the determination of molar masses of polymers. It is also shown that the four different relations for the expansion factor α by Flory‐Stockmayer, Fixman, Ptitsyn, and by Yamakawa‐Tanaka can be applied to polymolecular polymer samples (i.e. without fractionation), provided the corresponding averages[η]av and Mav from the Mark‐Houwink relationship are taken for the evaluation of the parameters KΘ and B′.
Induced circular dichroism in cholesteric and twisted smectic mesophases
Authors: Sato Yukio , Hatano Masahiro 
Published: April 2003

AbstractA new twisted smectic mesophase formed in Tween 80 (1) (monooleate of the ether of sorbitan with 4 mol of polyethyleneglycol)‐water system was found. The induced circular dichroism (CD) spectra of achiral molecules dissolved in this twisted smectic mesophase are compared with those in the thermotropic cholesteric mesophase. Pyrene and fluorene and their derivatives, acridine, phenazine, and phenothiazine were used as achiral molecules (solute molecules). It was found that the signs and shape of the induced CD bands observed in the twisted smectic mesophase were dependent on the solute concentration. The magnitude of the induced CD bands was dependent on the symmetry of the solute molecules and the value of the geometrical ratio of short‐axis to long‐axis of the solute molecules. Furthermore, it was demonstrated that the relative polarization directions of the solute molecules could be determined by means of the induced CD in the Tween 80‐water system using a simple modified C2‐symmetry rule.
Induced circular dichroism of biphenyl and its derivatives in mesophase
Authors: Sato Yukio , Tajiri Akio , Hatano Masahiro 
Published: April 2003

AbstractThe mesophase induced circular dichroism (CD) of biphenyl and its derivatives was investigated using the Tween 80 (monooleate of the ether of sorbitan with 4 mol of polyethyleneglycol)‐water system, which can form a twisted smectic mesophase. The sign of CD bands in this mesophase is explained by a modified C2‐symmetry rule, since it can be considered that alignment of the solute molecules in this mesophase can be elucidated in terms of a pseudo‐C2 symmetry, when the concentration of the solute is comparatively high. The assignments of the electronic transitions of the solute molecules show a good accordance with results of magnetic circular dichroism study.
Statistics of random macromolecular networks, 1. Stepwise polymerization of polyfunctional monomers bearing identical reactive groups
Authors: Durand Dominique , Bruneau Claude‐Marcel 
Published: April 2003

AbstractThe molecular parameters of macromolecular networks made by stepwise polymerization of polyfunctional monomers bearing identical reactive groups are established from the calculation of the probability that a functional group leads to a finite chain. The determination of this finite chain probability as a function of reaction extent and characteristics of the system is computed directly from very simple implicit equations. Thus, sol fraction, cross‐link density, effective network chains numbers, dangling trees numbers, and cycle rank are derived easily in very general systems.