bluuebunny/crossref_metadata_2025_split huggingface dataset:
Expansion coefficients of hydrolysed polyacrylamides from intrinisc viscosities
Authors: Kulkarni Rajendra A. , Gundiah Subbaraya 
Published: April 2003

AbstractPartially hydrolysed polyacrylamide samples were used as model polyelectrolytes and the variations of the intrinsic viscosities with the extent of hydrolysis and molecular weight were used to determine the relative applicability of the various macroion expansion theories. Expanison coefficients solely attributable to the presence of electrostatic charges were calculated with reference to the intrinisic viscosities of the parent polyacrylamides, assuming that the polyacrylamide corresponds to the discharged state of the macroion from hydrolysed polyacrylamides. Similarly, total expansions and expansions attributable to long‐range interactions were evaluated using the estimated intrinsic viscosities at the theta temperature of the parent polyacrylamide and the hydrolysed sample, respectively. The electrostatic expansion coefficients are independent of molecular weight and the long‐range expansion coefficients are almost independent of the extent of hydrolysis at high charge densities. In the absence of closed expressions predicting the variation of the expansion coefficients with the concentration of ionizable groups, equivalent expressions based on different theories were deduced assuming that i2/Cs is proportional to the concentration of ionizable groups where i is the extent of ionization of the polyelectrolyte and Cs is the concentration of the added salt. The variation of the electrostatic expansion coefficient with the charge density could not be represented according to any of the theories on macroion expansion. However, attributing the total expansion to the presence of electrostatic charges alone, the Fixman and Chien‐Ishihara theories allow a good representation of the data. At very low charge densities, the expansions due to long‐range interference effects also can be accounted for by the Fixman and Chien‐Ishihara theories.
Charakterisierung von disperisionen durch gekopplete H2O/D2O‐ultrazentrifugenmessungen
Authors: Mächtle Walter 
Published: April 2003

AbstractThe particle size distribution is one of the most important characteristics of aqueous polymer dispersions (diameter range 20 < D < 2000 nm). In addtion, the knowledge of the average particle density ρPM, the density distribution, and the particle refractive index nPM gives information about the chemical composition of dispersions. We report of an ultracentrifuge method which allows to determine all these values simultaneously in one single run. For that purpose the dispersion is measured simultaneously in 3 media of different density, i.e., in H2O, H2O/D2O (1:1, by wt.), and D2O. We use a preparative ultracentrifuge with an analystical rotor with trubidity optics, but instead of an 1‐cell‐rotor an 8‐cells‐rotor and a multiplexer are used. In order to measure very small and very large particles simultaneously in one single run we do not work at the usual constant number of rotor revolutions, but at a rate of revolutions increasing from 0 to 40000 min−1. The ultracentrifuge is connected with a computer on‐line. The calculations are based on Stokes' law and Mie's light scattering theory for homogeneous isotropic spherical particles.
Syntheses and properties of tertiary peptide bond containing‐polypeptides, 3. Syntheses of monodisperse‐sequential polypeptides having the sequence of L‐leucyl‐L‐leucyl‐L‐leucyl‐L‐prolyl‐L‐prolylglycine
Authors: Narita Mitsuaki , Nagasawa Satoshi , Chen Junn‐Yann , Sato Hisaya , Tanaka Yasuyuki 
Published: April 2003

AbstractIn order to demonstrate the usefulness of the “peptide segment separation method” for syntheses of large peptides and proteins, a model series of sequential polypeptides, Boc‐[(Leu)3‐(Pro)2‐Gly]n‐OBzl (n = 4, 6, 8, 10, and 12), were prepared by the reaction of Boc‐[(Leu)3‐(Pro)2‐Gly]2‐OH with H‐[(Leu)3‐(Pro)2‐Gly]n‐OBzl (n = 2, 4, 6, 8, and 10) using dicyclohexylcarbodimide and 1‐hydroxy‐1 H‐benzotriazole as coupling reagents. The resulting peptides are assembled by the sequence of Gly‐(Leu)3 separated by the (Pro)2 sequence. Regardless of the increase in peptide chain length of the amino component, the coupling reactions with 1‐methyl‐2‐pyriolidone were achieved in high yields. Throughout the investigation, excellent solubility in usual polar solvents used for peptide syntheses is preserved. The purification of the peptide series by recrystallization could be completely achieved and HPLC on a gel filtration (styrenedivinylbenzene copolymer) column showed all the peptides to be monodisperse.
Micellization of a radial copolymer with four polystyrene‐block‐polybutadiene branches
Authors: Procházka Karel , Glöckner Gottfried , Hoff Miloš , Tuzar Zdeněk 
Published: April 2003

AbstractSimilarly to the three‐block copolymer poly(styrene‐b‐butadiene‐b‐styrene), a radial block copolymer with four brances consisting of inner polybutadiene and outer polystyrene blocks forms, in a mixed solvent tetrahydrofuran/ethanol, spherical micelles with a polybutadiene core and polystyrene shell. The equilibrium between these micelles and the molecularly dissolved copolymer was studied as a function of the solvent composition by means of light scattering, sedimentation velocity, and GPC. The sedimentation diagrams were interpreted taking into account the Gilbert theory of mobile equilibrium in systems of associating macromolecules.
Novel syntheses of alternating copolymers with amide and thioether linkages by polyaddition reactions of bifunctional cyclic iminoethers with dithiols
Authors: Nishikubo Tadatomi , Iizawa Takashi , Tokairin Atsushi 
Published: April 2003

AbstractAlternating copolymers with amide and thioether linkages were synthesized by addition reactions of bisoxazolines 1a – 1f and bisoxazines 2a and 2b with dithiols 3a – c in aprotic polar solvents. The reactions of the aromatic bifunctional cyclic iminoethers such as 1a, 1c, 2a, and 2b with the dithiols 3a and 3c in N‐methyl‐2‐pyrrolidone gave polymers with high molecular weight. However, the reactions of the aliphatic derivatives such as 1e and 1f with dithiols as well as the reactions of the bifunctional cyclic iminoethers with 3b led to polymers of low molecular weights. The reactions of methyl substituted bisoxazolines 1b and 1d with dithiols gave also polymers of low molecular weight.
Electro‐optical effects of azo dye containing liquid crystalline copolymers
Authors: Ringsdorf Helmut , Schmidt Hans‐Werner 
Published: April 2003

AbstractThe synthesis and phase behaviour of azo dye containing liquid crystalline side group copolymers are described. These Copolymers show the same electro‐optical effects as low molar mass guest‐host systems. Their macroscopic oriented nematic structure can be frozen in below the glass transition temperature resulting in a polymer film with dichroic properties. The behaviour of the copolymers (phase behaviour, surface and electric field orientation) can be improved via mixtures with low molar mass liquid crystals.
Segmented block copolymers of uniform chain length and defined structure, 2. Investigation of some physical properties
Authors: Krüger J. K. , Marx A. , Roberts R. , Unruh H.‐G. , Bitar M. B. , Nguyen‐Trong Hao , Seliger H. 
Published: April 2003

AbstractSome physical investigations of segmented block copolymers of uniform chain length and defined structure and their constituents are described. Special attention was payed to the thermal behaviour of these new substances with respect 1. to the phase transformations in the solid and liquid state and 2. to the thermal stability of the materials. Several of these oligomers show phase transitions in the solid state. In some instances, the morphology of the solid material depends strongly on the sample history. The influence of the crystallization conditions is discussed. For the special case of esters of 4,4′‐isopropylidenediphenol (bisphenol A) with isophthalic acid detailed investigations by dielectric and Brillouin spectroscopy of the glass‐forming process are presented.
Propene polymerization with a magnesium chloride‐supported Ziegler catalyst, 2. Molecular weight distribution
Authors: Keii Tominaga , Doi Yoshiharu , Suzuki Eiichi , Tamura Masanori , Murata Masahide , Soga Kazuo 
Published: April 2003

AbstractThe kinetic features of the molecular weight distributions (MWDs) of polypropylene produced with TiCl4/MgCl4/C6H5COOC2H5/Al(C2H5)3as catalyst are investigated as functions of the polymerization time and the concentrations of Al(C2H5)3, C6H5COOC2H5and hydrogen. The MWDs are dependent upon the concentrations of Al(C2H5)3and C6H5COOC2H5, and are correlated with a change of the isotactic index of the produced polymers. In contrast, both MWD and the number‐average molecular weight M̄nremain unchanged during the polymerization from 5 s to 3 h. When hydrogen is added as a chain transfer reagent, M̄ndecreases as anticipated but the polydispersity index (M̄w/M̄n) is independent of the hydrogen concentration. The MWDs obtained with this supported catalyst are rather narrow (3≤ M̄w/M̄n≤8)and are represented by a log‐normal form or Wesslau equation, which is different from the MWDs (6≤ M̄w/M̄n≤20) obtained with the traditional TiCl3catalysts, which are represented by the Tung equation. Broadening of the MWD obtained with heterogeneous catalysts is also discussed. The constancy of M̄w/M̄n, independent of the hydrogen concentration leads to the important conclusion that non‐uniform surface sites on heterogeneous catalysts are responsible for the broadening of the MWD. A surface heterogeneity of the propagation rate constant,kp, is demonstrated on the basis of the kinetic data, concerning the effect of CO‐inhibition on the polymerization rate. A surface distribution function ofkp, capable of accounting for the broad MWDs, is presented and discussed in terms of a distribution of the activation energy for the propagation step.
Télomérisation du chlorure de vinylidène, 1. Réaction avec le tétrachlorure de carbone par catalyse rédox
Authors: Belbachir Mohamed , Boutevin Bernard , Piétrasanta Yves , Rigal Gérard 
Published: April 2003

AbstractThe redox telomerization of vinylidene chloride with carbon tetrachloride catalyzed by iron or copper salts was thoroughly studied. The DP of the telomers obtained vary from 1 to 100, roughly. The concentration of the reactants and the nature of the solvents exert some effect on the molecular weight distribution. The first adducts 1a – 1d (n = 1 to 4) were isolated and identified by NMR spectroscopy and viscosimetry.
Etude des propriétés électro‐optiques de i' adn par biréfringence électrique a faible champ, 2. Mécanismes d'orientation et de relaxation
Authors: Marion Christian , Perrot Brigitte , Roux Bernard , Bernengo Jean‐Claude 
Published: April 2003

AbstractThe electric birefringence of calf thymus DNA is measured at different low electric field strengths with rectangular and bipolar pulses as a function of concentration, ionic strength and molecular weight, and these results are interpreted in terms of orientation and relaxation mechanisms. The orientation of DNA is mainly due to an induced dipole, but the results reveal a slow induced moment, which is saturated, when low field strengths are applied. A well‐defined slow relaxation mechanism is demonstrated, which is attributed to the orientation of DNA as a whole. The long relaxation time decreases when high electric fields or high DNA concentrations are used, and the fact that the decay of the birefringence also contains short relaxation times does not reflect the polydispersity of the samples. The comparison between the molecular lengths determined from long relaxation times and the theoretical lengths of rigid cylinders shows an important coiling of DNA, when the fragments are longer than 110 – 120 nm.
Secondary structure of peptides, 14. FT‐IR and 13C NMR CP/MAS investigation of the helix stability of solid poly(L‐proline)s
Authors: Müller Detlef , Stulz Josef , Kricheldorf Hans R. 
Published: April 2003

AbstractPrimary amine and pyridine‐initiated polymerizations of L‐proline‐N‐carboxyanhydride (Pro‐NCA) at 20 or 100°C yield exclusively or predominantly 103‐helices. Only primary amine‐initiated polymerizations in 1,4‐dioxane at 100°C result in partial formation of 31‐helices. The stability of both 103‐ and 31‐helices against conformational transitions was investigated in various organic non solvents or salt solutions at 100 or 150°C. A 103 → 31 transition was only observed in protic non solvents such as formamide, water, or propionic acid, but not in alcohols. A 31 → 101 helix transition was observed in alcohols and most aprotic solvents but not in formamide, water, or propionic acid. Hence, it is concluded that the formation of 31 helices by primary amine‐initiated polymerizations in 1,4‐dioxane at 100°C is a kinetically controlled consequence of the reaction mechanism. The usefullness of 13C NMR CP/MAS spectra and Fourier‐Transform IR spectra for the quantitative analysis of composed secondary structures is compared and discussed.
Study of the state of titanium ions and the composition of the active component in titanium‐magnesium catalysts for ethylene polymerization
Authors: Zakharov Vladimir A. , Makhtarulin Sergei I. , Poluboyarov Vladimir A. , Anufrienko Vladimir F. 
Published: April 2003

AbstractThe state of Ti3+ ions formed at various steps of preparation and activation of highly active titanium‐magnesium catalysts of various composition (dry milling of TiCl3 with MgCl2; reduction of TiCl4 by nonsolvated magnesium dialkyl; interaction of the TiCl4/MgCl2 system with an organoaluminium compound) was studied by the ESR method. It was found that in all systems studied the same three types of Ti3+ ions in the chlorine environment are formed, differing in coordination and localization sites in MgCl2. The content of these ions depends on the composition and preparation conditions of the catalysts, and does not exceed 20% of the total content of titanium. Most of the Ti3+ ions formed in all systems enter the composition of particles or surface aggregates of TiCl3 and appear in the ESR spectra only after dissolution of the sample in pyridine. The active centers of titanium‐magnesium catalysts are supposed to be constituents of these particles or of surface aggregates.
Reaction of tert‐butoxyl radicals with electron‐rich α‐methylvinyl monomers
Authors: Grant Richard D. , Rizzardo Ezio , Solomon David H. 
Published: April 2003

AbstractThe reactions of tert‐butoxyl radicals with α‐methylstyrene and with isopropenyl acetate were examined. Allylic hydrogen abstraction was shown to compete with addition to the double bond at the CH2 group. The proportion of abstraction relative to addition increases with increasing solvent polarity, however, this effect is more pronounced in the reactions of isopropenyl acetate than in those of α‐methylstyrene.
Stereochemistry in “living” coordination polymerization of propene initiated by vanadium‐based catalytic systems
Authors: Doi Yoshiharu , Koyama Tetsuya , Soga Kazuo , Asakura Tetsuo 
Published: April 2003

AbstractSoluble catalysts of V(acac)3 and AIR2X (R = C2H5, n‐C3H7, i‐C4H9; X = Cl, Br) initiate a living polymerization of propene at −78°C to afford monodisperse polymers of syndiotactic structure. The stereochemistry of the living polymerization was investigated by examining the structures of monomdisperse polypropylenes and of propylene‐ethylene block copolymers by means of 13C NMR spectroscopy. It was found that syndiotactic‐ and regio‐specificities of the soluble vanadium‐based catalysts are not influenced by the sequence length of the living polymer chain.
Vinyl polymerization, 425. Radical polymerizations of vinyl monomers initiated with diphenyl disulfied and urea
Authors: Ouchi Tatsuro , Beika Nobuaki , Imoto Minoru 
Published: April 2003

AbstractPolymerizations of vinyl monomers initiated with diphenyl disulfide (1) and urea were carried out in 1,4‐dioxane/water (vol. ratio 7:3). Methyl methacrylate (MMA) and methacrylic acid were found to be easily polymerized with this system, whereas the polymerization of styrene and acrylonitrile is not initiated. The polymerization was found to proceed by a radical mechanism. The polymerization of MMA was kinetically investigated.
Influence of annealing on the formation of long polyenes during PVC degradation
Authors: Gerrard Donald L. , Maddams William F. , Shapiro Jacob S. 
Published: April 2003

AbstractMass polymerised poly(vinyl chloride) (PVC), subjected to annealing treatment between 85–140°C under air, nitrogen, vacuum, and hydrogen chloride environment, was found to undergo very slight decomposition in which long polyenes (with more than ten conjugated carbon‐carbon double bonds) were produced. Despite the presence of these polyenes the thermal stability of the resin at 190°C remained unaltered. Resin stability was also unaffected by the atmosphere in which the resin was annealed. By contrast, urea clathrate PVC, known to be highly crystalline, decomposed 300% faster than mass PVC and generated very long polyene sequences (n ≥ 42) at 190°C. The results are discussed in terms of two possible morphological populations of polymer.
Darstellung und polymerisation von diestern aus 2,2′‐methylendiphenolen und acryl‐, methacryl‐ bzw. Crotonsäure
Authors: Böhmer Volker , Funk Rüdiger , Kiełkiewicz Jedrzęj , Vogt Walter 
Published: April 2003

AbstractSeveral mono‐ and diesters of four selected 2,2′‐methylenediphenols with acrylic, methacrylic, and crotonic acid were synthesized for the first time. Special emphasis was paid to the preparation of diesters with two different acyl groups which could be obtained via the corresponding monoesters. The radical polymerization of these esters with AIBN (mainly in benzene) gave insoluble (crosslinked) products from dimethacrylates and soluble (linear) polymers from mixed diesters with methacrylic and crotonic acid, while the dicrotonates are not reactive.
Random coil configurations of poly(diethylene glycol isophthalate). Capability of model network formation
Authors: Riande Evaristo , Guzmán Julio , de Abajo Javier 
Published: April 2003

AbstractValues of the mean‐square dipole moment 〈μ2〉 of poly(diethylene glycol isophthalate) were determined as a function of temperature by means of dielectric experiments carried out on solutions of the polymer in benzene. The value of the dipole moment ratio 〈μ2〉/(nm2), where nm2 is the mean‐square dipole moment of the chains in the idealization that all of the skeletal bonds are freely jointed, is 0,697 at 30°C. Trifunctional model networks were prepared by endlinking hydroxyl‐terminated chains with an aromatic triisocyanate. From thermoleastic experiments performed on the networks over the temperature range 20–80°C, it was found that the value of the temperature coefficient of the unperturbed dimensions 103 d In 〈r2〉0/dT amounts to 1,05 ± 0,17 K−1. The dipole moments and the temperature coefficients of both the dipole moments and the unperturbed dimensions were critically interpreted in terms of the Ratational Isomeric State (RIS) model. Stress‐strain experiments were also performed at 70°C on swollen and unswollen networks. The analysis of the isotherms suggests that the chemical crosslinks are not sufficient to account for the high modulus exhibited by the networks.
Untersuchungen zu Modifikationen von Polyamid‐6 und Polyamid‐4 mit eingelagerten Alkalihalogeniden
Authors: Votteler Christine , Hoffmann Volker , Trafara Gundolf 
Published: April 2003

AbstractPolyamide‐6 (PA‐6) and polyamide‐4 (PA‐4) doped with alkali halides were investigated by X‐ray diffraction, thermal analysis, infrared and far infrared spectroscopy at various temperatures (10 K – 300 K). The solubility of the alkali halides in PA‐4 is better than in PA‐6. Small ions are molecularly dispersed in PA‐6 and PA‐4. Alkali ions are coordinated to the oxygen, halide ions to the nitrogen of the amide group. The degree of crystallinity of the polyamides depends on the concentration of the alkali halides and the ion radii. Alkali halides stabilize modifications of the polyamides with not fully extended chains. In polyamides crystallized from the melt some alkali halides stabilized the γ‐modification or similar structures. The modification is nearly independent of the alkali halide concentration and will not be destroyed by washing out the alkali halides. If the polyamides are crystallized from formic acid, alkali halides promote a pleated sheet structure with antiparallel chains. The factor group of the layer is D2, indicated by a low temperature splitting of the B2 vibration modes.
The phase behaviour of a poly(ether sulfone) with poly(ethylene oxide)
Authors: Walsh David J. , Singh Vir Bhanu 
Published: April 2003

AbstractBlends of poly(ethylene oxide) with a poly(ether sulfone) were prepared by casting from a common solvent and were found to be miscible and show a single, composition dependent, glass transition temperature. Mixtures in both cyclohexanone and N,N‐dimethylformamide phase, separated on heating and thus conditions need to be carefully chosen to obtain homogeneous blends. At higher PEO contents, PEO crystallised from the blends at lower temperatures. The melting point depression, as determined by trubidity measurements, was used to calculate an interaction parameter which was negative, as expected for miscible polymers. The blends also phase separated on heating, and the cloud point curve could be measured by turbidity measurements and confirmed by both visible and electron microscopy. The cloud point curve was very skew with a minimum at around 10 wt.‐% PES content. This was not a strong function of the molecular weight and the skew nature was thus presumably due to differences in the state parameters of the pure components. The blends showed a very high mobility with sharp and reproducible could points which might make them ideal for future miscibility studies.
Crystal and molecular structure of S,S‐[sulfonylbis(1,4‐phenylene)] di(thiobenzoate) as a model compound for the respective polymers
Authors: Garbarczyk Józef 
Published: April 2003

AbstractThe molecular and crystal structure of S,S‐[sulfonylbis(1,4‐phenylene)] di(thiobenzoate) (1) was determined from X‐ray diffractometer data. The crystals are monoclinic, P21/a, with Z = 4 in the unit cell of the dimensions: a = 14,050 Å, b = 10,404 Å, c = 16,734 Å and β = 110,57°. The structure was resolved by direct methods and refined by least‐squares techniques up to R = 0,049 for 2466 independent reflections. The molecules of 1 are asymmetric: the thiobenzoate substituents are syn and anti with relation to the central sulfonyl groups and the thiocarbonyl groups do not lie in the planes of the phenylene rings. Three aromatic rings are nearly perpendicular. From energetic calculations the possibility for a rotation around the S1 – C8 bond was evidenced. The results allow to explain the low crystallinity of the polymer consisting of 1 segments.
Asymmetric induction copolymerization of isobutyl vinyl ether with indene by (−)‐menthoxyaluminium dichloride and (−)‐menthoxytitanium trichloride
Authors: Yamaguchi Hidemasa , Doiuchi Tohru , Kawamoto Kohzoh , Yasuzawa Takashi 
Published: April 2003

AbstractThe copolymerization of isobutyl vinyl ether with indene was carried out with (−)‐menthoxyaluminium dichloride (1) and (−)‐menthoxytitanium trichloride (2) as initiators. Although optically active copolymers were obtained in the copolymerization in non‐polar solvents, the copolymers prepared in a polar solvent was optically inactive. From the linear relationship between the optical rotation and the diad probability P2 (m1 m2) of the copolymers, it was found that asymmetric carbon atoms were introduced in vinyl ether monomeric units but not in indene ones.