bluuebunny/crossref_metadata_2025_split huggingface dataset:
NMR contact shifts and local conformation in poly(4‐vinylpyridine N‐oxide)‐Ni(II) complexes
Authors: Ghesquière Denis , Chachaty Claude 
Published: April 2003

AbstractThe 1H and 13C NMR contact shifts induced by Ni2+ ions in aqueous solutions were used to elucidate the conformation of poly[1‐(1‐oxo‐4‐pyridyl)ethylene] (1) and of the model compound 1,3‐bis(1‐oxo‐4‐pyridyl)propane (2). The equilibrium position of the pyridine N‐oxide ring relative to the adjacent methine or methylene group was deduced from the angular dependence of the hyperfine coupling of β‐protons and ‐carbons, assuming a twofold potential energy for the rotation about the C4N axis. In the case of 1 it could be shown that the dihedral angle between the plane HβCαC4 and the plane of the ring is 15±5°.
The formation of cyclic oligomers by cationic degradation of poly(phenylthiirane)
Authors: Vancraeynest Wilfried M. , Goethals Eric J. 
Published: April 2003

AbstractPoly(phenylthiirane)s obtained by polymerization with different initiators were degraded to isomeric cyclic dimers 1, 2, 3, and 4 by treatment with cationic initiators. Analysis of the mixture of the four different isomers gives evidence of a fast transalkylation reaction when a cationic initiator is present in the polymer solution.
Depolarization thermocurrent of polyethylene containing additives
Authors: Lacabanne Colette , Chatain Daniel 
Published: April 2003

AbstractThe influence of antioxidants and ionic agents on Depolarization Thermocurrents (DTC) of low density polyethylene has been studied. Ionic agents increase the height of the potential barrier which + involved in the relaxation observed at highest temperature/lowest frequency at a given frequency/temperature (χ). The relaxations observed at lower temperature/higher frequency (β and γ) are not modified by ionic agents but by antioxidants: the activation energy of the relaxation time increases and the preexponential factor decreases for both β and γ modes. Some of the processes constituting the β and γ modes are non‐ohmic. They may be attributed to charge motions.
A study of methods for measuring the tacticity of poly(vinyl chloride) by proton magnetic resonance spectroscopy
Authors: Robinson Melvin E. R. , Bower David I. , Maddams William F. , Pyszora Henryk 
Published: April 2003

Abstract60 MHz undecoupled α‐, 90 MHz undecoupled β‐, and 90 MHz decoupled α‐ and β‐proton spectra were measured for seven poly(vinyl chloride) samples, four of these being commercial type polymers, the others were prepared at +75°C, +5°C and −30°C. The results were used to assess the preferred approach to the determination of tacticity. The reproducibility of the values from different solutions of a given polymer is significantly worse than that between a series of runs on a particular solution, showing that sampling errors are larger than those from instrumental sources. Although the 60 MHz spectra were found to be unsatisfactory when interpreted on a first order basis, curve fitting methods, which were similar to those used for the other types of spectra and involved the use of reasonable assumptions for chemical shifts and coupling constants, gave results of comparable precision to those from the two types of decoupled spectra and superior to those from the undecoupled 90 MHz spectra. The preferred approach is to combine the results from α‐ and β‐proton spectra and to examine more than one solution of a given material. The applicability of Bernoullian propagation statistics was assumed in the majority of the curve fitting calculations; in the cases where this was not so the results were used to test this assumption and it has proved to be valid.
Polymerization of vinyl monomers photoinitiated by benzoylated polystyrene
Authors: Bartoň Jaroslav , Capek Ignác , Šušoliak Ondrej , Juraničová Viera 
Published: April 2003

AbstractThe rate of the polymerization of vinyl monomers photoinitiated (at λ = 365 nm) by benzoylated polystyrene in N,N‐dimethylformamide (DMF) decreases in the sequence vinyl acetate>acrylonitrile>methyl methacrylate ≫ styrene ≈ 0 and is related to the rate constant of propagation of the mentioned monomers. In addition to DMF, aromatic hydrocarbons (benzene, toluene, p‐xylene), cyclohexane and tetrahydrofuran were employed as hydrogen donors. The maximum polymerization rate was achieved in the system containing p‐xylene; the system with benzene turned out inefficient for the initiation of acrylonitrile polymerization. Turbidimetric titration of a soluble fraction of the acrylonitrile polymerization in DMF in presence of benzoylated polystyrene showed that the soluble fraction does not contain graft copolymers of benzoylated polystyrene with acrylonitrile. It is assumed, however, that the polyacrylonitrile in the insoluble fraction is bound to benzoylated polystyrene in the form of graft copolymers.
Synthesis of a cationic polyelectrolyte by successive quaternization of 1,4‐bis(2‐diethylaminoethyl)benzene
Authors: Kataoka Kazunori , Ohki Nobutaka , Tsuruta Teiji , Donkai Nobuo , Inagaki Hiroshi 
Published: April 2003

Abstract1,4‐Bis(2‐diethylaminoethyl)benzene (4), synthesized from 1,4‐divinylbenzene (1) and diethylamine (2) with lithium diethylamide as catalyst, was successively quaternized with 1,4‐dibromobutane (5) to prepare a cationic polyelectrolyte 6 of the ionene type. Apparent molecular weights of the ionene samples were estimated by the sedimentation equilibrium method, and the result is discussed in connection with the true molecular weight. The rate constants for quaternization of first and second nitrogen atom of 4 (k1 and k2) were determined by the use of 13C NMR. It was found that the ratio of the rate constants, (k2/(k1/2)), markedly decreased in the 4/5 system, though it remained unity in the 4 ethyl bromide system.
Homopolymerisation von styrol mit titan(III)‐chlorid/alkylhalogenid‐initiatoren
Authors: Moszner Norbert , Hartmann Manfred 
Published: April 2003

AbstractThe polymerization of styrene initiated by titanium(III) chloride/alkyl halide redox systems was studied. Among the alkyl halides examined, the highest rate of polymerization was found in the system titanium(III) chloride/carbon tetrachloride. The polymerization rate can be described by the equation Rp=k·[Ti(III)]0,5·[CCl4]0,5·[St]1,0. The polymerization proceeded via a radical mechanism. The overall activation energy was estimated as 57,3 kJ/mol. It was found that titanium(III) chloride/chloroacetic acid systems, too, could initiate the polymerization of styrene.
Bestimmung von sequenzlängenverteilungen hydrierter polyalkenylene durch metathese‐abbau, 1. Homogen hydriertes polybutadien
Authors: Ast Wolfgang , Zott Christian , Kerber Robert 
Published: April 2003

AbstractPartially hydrogenated 1,4‐polybutadiene is degraded into GC‐detectable reaction products after olefin‐metathesis with 4‐octene in the presence of WCI6/(CH3)4Sn. 1,4‐polybutadiene is homogeneously hydrogenated with p‐toluenesulfonohydrazide and serves as copolymer with non‐hydrogenated and hydrogenated repeating units. Hydrogenated sequences up to an undecade are detectable. The experimental monomer sequence length distribution agrees satisfactorily with the theoretical one calculated under the assumption of an ideal statistical copolymer.
Syntheses of polyamides containing theophylline and thymine
Authors: Hattori Masahira , Kinoshita Masayoshi 
Published: April 2003

Abstract2‐(1,3‐Dimethyl‐2,6‐dioxo‐2,6‐dihydropurin‐7‐yl)methylsuccinic acid (2a) and 2‐(5‐methyl‐2,4‐dioxo‐1,2,3,4‐tetrahydropyrimidin‐1‐yl)methylsuccinic acid (2b) were synthesized via the addition reaction of theophylline and thymine, respectively, to dimethyl methylenesuccinate, followed by hydrolysis of the resulting ester. The dicarboxylic acid derivatives 2a and 2b were further converted to their di‐p‐nitrophenyl esters 3a and 3b, which were allowed to polycondense with diamines such as 1,6‐diaminohexane, 1,2‐diaminoethane, 3‐aminomethylbenzylamine, and piperazine in solutions. The resulting polyamides are white powders with molecular weights in the range of about 2000–6000. The DP of the polyamides varies with the kind of diamines and solvent used. All polyamides are soluble in DMSO and formic acid, the polyamides deriving from esters 3a and 3b and 1,2‐diaminoethane and piperazine are also soluble in water.
Epoxydation de copolymères triséquencés styrène‐isoprene‐styrène par l'acide monoperoxyphtalique
Authors: Pinazzi Christian , Guillaume Pierre , Reyx Danièle 
Published: April 2003

AbstractStyrene isoprene styrene copolymers (SIS) modified by epoxidizing were investigated in order to obtain adhesive materials. Influences of experimental parameters (concentrations, solvents, compositions of SIS) are shown for epoxidation with monoperoxyphtalic acid at a yield of modification lower than 50%.
Synthesis and exchange reactions of biodegradable drug‐binding matrices
Authors: Ferruti Paolo , Tanzi Maria Cristina , Vaccaroni Francesco 
Published: April 2003

AbstractSuccinic esters of starch and dextrane (STS and DTS) have been prepared and transformed into the corresponding imidazolides. These are difficult to isolate in a pure state. Without previous isolation, however, they react smoothly with alcohols or amines giving the corresponding polymeric esters or amides. STS benzotriazolide has also been prepared, and isolated in a pure state. It has been found to have the same reactivity towards alcohols and amines than other previously described polymeric benzotriazolides. These results demonstrate that STS or DTS activated amides offer new opportunities to prepare polymer drug adducts with a main backbone degradable to safe metabolites in the body fluids.
Effects of mechanical stress on the reactivity of polymers: Shear degradation of polyacrylamide and dextran
Authors: Basedow Arno Max , Ebert Klaus Heinrich , Hunger Hartmut 
Published: April 2003

AbstractThe mechanical degradation of polyacrylamide and dextran and the acid hydrolysis of dextran at different pH values is investigated in concentrated solutions in high shear laminar flow fields. The kinetics of degradation of polyacrylamide show that the reaction is first order, the rate constants of degradation are proportional to the molecular weight, and the polymer molecules are broken preferentially near the center of the chain. It is found that shear stress is the controlling factor of the degradation process, the rate constants increasing in poor solvents and with decreasing temperatures. The limiting molecular weight is a direct function of the shear stress. For dextran a transition range exists in which shear degradation is favored by hydrogen ions at pH values at which no hydrolysis occurs in the absence of a shearing field.
Solution properties and flexibility of poly(2‐biphenylyl methacrylate)
Authors: Alexopoulos John , Hadjichristidis Nikos 
Published: April 2003

AbstractDilute solution properties of poly(2‐biphenylyl methacrylate), (poly[1‐(2‐biphenylyloxycarbonyl)‐1‐methylethylene], POB) were studied by viscosity, sedimentation, light scattering and osmotic pressure in different solvents. The solvent dependence of intrinsic viscosity, [η], Huggins constant, KH, Mark‐Houwink exponent, a, and expansion factor, αη, is very weak, although the chemical nature of the solvents is quite different (CHCl3, tetrahydrofuran, benzene, 1,4‐dioxane). For poly(4‐biphenylyl methacrylate) (poly[1‐(4‐biphenylyloxycarbonyl)‐1‐methylethylene], PPB) and other aromatic polymethacrylates the changes of [η], KH, a and aη are very high. The unperturbed dimensions calculated from viscometric and light scattering data by different methods, are in excellent agreement with one another and good agreement with those obtained from sedimentation data. POB has a higher flexibility factor (σ = 2,8) than PPB (σ = 2,7). In our opinion this is due to the fact that the 2‐biphenylyl group is closer to the main chain than the 4‐biphenylyl group. The very high value of σ explains the weak solvent dependence of [η], KH, a and αη in the case of poly(2‐biphenylyl methacrylate).
Potentiometric and viscometric study of the conformational transitions of 2‐hydroxyethyl methacrylate‐methacrylic acid copolymers
Authors: Prokopová Eva , Štol Miroslav , Knižáková Eva , Bohdanecký Miloslav 
Published: April 2003

AbstractThe dependence of the apparent dissociation constant and of intrinsic viscosity on the degree of dissociation of 2‐hydroxyethyl methacrylate‐methacrylic acid copolymers was investigated. It was found that the conformational transition indicated in the potentiometric titration was distinct only with copolymers containing at least ca. 48 mole% of methacrylic acid. The transition is probably related with the local configurational and conformational structure while being uncorrelated with the transition of the coiled form of the macromolecule into the expanded one.
Functional monomers and polymers, 56. Effects of ionic strength on the structure of Cu(II)· poly(vinylimidazole) and Cu(II)· imidazole complexes in aqueous solution
Authors: Sato M. , Kondo K. , Takemoto K. 
Published: April 2003

AbstractThe effect of ionic strength on the structure of Cu(II) complexes of imidazole and poly(4(5)‐vinylimidazole) in aqueous solution was studied by viscometric, spectrophotometric, and electron spin resonance (ESR) techniques. Frequency of the center of the absorption band in visible region (λmax) and ESR spectra of the polymeric Cu(II) complex were different from those of the low‐molecular‐weight Cu(II) complex. The spectra of polymeric Cu(II) complex were different in the presence of sodium perchlorate, but it was not the case for the low‐molecular‐weight Cu(II) complex. The reduced viscosity of the polymeric Cu(II) complex and the polymeric ligand decreased with a rise of the concentration of sodium perchlorate. It was proposed that the conformational change in the polymeric ligand resulted in a structural change of the Cu(II). poly(4(5)‐vinylimidazole) complex.
Solubility and polymer‐solvent interaction parameters of 1,2‐polybutadiene
Authors: Yamashita Shinzo , Minoura Yuji , Maekawa Etsuji 
Published: April 2003

AbstractThe dilute solution behavior of 1,2‐polybutadiene newly developed was not anomalous within the range of crystallinity up to 25%. Therefore, the solubility and polymer‐solvent interaction parameters could be determined by means of usual measurements of dilute polymer solutions. The former has been estimated from viscosity measurement proposed by Mangaraj. The latter was determined using the second virial coefficient obtained from osmotic pressure and light‐scattering measurements.
Absorption of low molecular weight compounds in aqueous dispersions of polymer‐oligomer particles, 2. A two step swelling process of polymer particles giving an enormous increase in absorption capacity
Authors: Ugelstad John , Kaggerud Kari Herder , Hansen Finn Knut , Berge Arvid 
Published: April 2003

AbstractA novel method for preparation of stable emulsions of slightly water soluble compounds is described. The method implies that the slightly water soluble compound diffuses through water and becomes absorbed into polymer particles which in a previous step have been brought to absorb a water insoluble, relatively low molecular weight compound. By this two step swelling process the polymer particles can be brought to absorb more than 100 times their own volume of the low molecular weight compounds to form stable o/w emulsions of the latter, with high oil content, and with a droplet size and size distribution which is completely determined by the size of the polymer particles in the latex applied initially. Monodisperse emulsions with large droplet size could easily be prepared. When the slightly water soluble compound added in the second step is a vinyl monomer which may subsequently be polymerized, the method represents a seed technique which is especially favourable for preparation of latexes with large particles size, including monodisperse latexes, with high solid content.
Poly(allylbenzene). Dielectric properties
Authors: Boiteux Gisèle , Seytre Gérard , Berticat Philippe , Merle Gérard , Dubois Jean‐Claude 
Published: April 2003

AbstractPoly(allylbenzene) or poly(3‐phenyl‐1‐propene) belongs to the family of poly‐α‐olefin polymers of known mechanical properties. After synthesis and characterization, the dielectric behaviour of this polymer was determined over a wide temperature range (−32°C to 107°C) at frequencies from 20Hz to 10kHz. The results contribute to the study of the relaxation spectroscopy of poly‐α‐olefins.
La fusion et la cristallisation de la poly(α,α‐diéthyl‐β‐propiolactone): Comparaison avec d'autres polylactones
Authors: Normand Yves , Aubin Madeleine , Prud'homme Robert E. 
Published: April 2003

AbstractMeasurements of crystallization kinetics were made for a sample of poly(α,α‐diethyl‐β‐propiolactone) (DEPL) (syst. name: poly(oxy‐2,2‐diethyl‐1‐oxotrimethylene)). An Avrami exponent of 2 was found indicating a two‐dimensional growth rate of the crystal, following a pre‐determined and heterogeneous nucleation mode. Two melting peaks were found for most samples. The second melting peak (at high temperatures) is probably due to the re‐crystallization of part of the sample initially present under the first melting peak. A value of 21kJ.mol−1 was also determined for the heat of fusion of DEPL by the diluent method. This value leads to a degree of crystallinity of 17% which is about four times smaller than that found for poly(pivalolactone) (syst. name: poly(oxy‐2,2‐dimethyl‐1‐oxotrimethylene)). We have also determined an equilibrium melting temperature of 531 K for this polymer and an entropy of fusion of 40J.mol−1. K−1. Finally, the surface free energies σ and σe for the lamellar crystals were found to be 12.10−7J.cm−2 and 72.10−7J.cm−2, respectively.
Synthesis of 1,3,6,8‐tetraphenyloctane as a tetramer model for polystyrene
Authors: Clouet Gilbert , Brossas Jean 
Published: April 2003

AbstractThe styrene tetramer, 1,3,6,8‐tetraphenyloctane (5), was prepared by addition of styrene and phenethyl bromide (4) in a 1:1 mole ratio to a stirred suspension of lithium in tetrahydrofuran. The reaction was found to proceed via 1,4‐diphenyl‐1,4‐butanediyldilithium (3), which reacts “in situ” with the alkyl halide 4 to give the tetramer 5. Mass and NMR spectra were found to be in agreement with the proposed structures.
Solution properties of poly(N‐isopropylacrylamide)
Authors: Chiantore Oscar , Guaita Marino , Trossarelli Luigi 
Published: April 2003

AbstractThe results obtained by light scattering and viscosity measurements on unfractionated samples of poly(N‐isopropylacrylamide) dissolved in methanol and in water seem to show that the chain molecules assume different conformations in the two solvents. In methanol solutions at 25°C, poly(N‐isopropylacrylamide) (poly[1‐(N‐isopropylaminocarbonyl)ethylene]) molecules apparently behave as normal flexible chains, whereas in aqueous solutions at the same temperature the interactions between polymer molecules and the solvent seem to produce chain uncoiling toward more extended structures which become unstable at higher temperatures.
On the copolymerization of acrylonitrile with styrene in the presence of Lewis acid, 1. Effect of zinc chloride concentration
Authors: Bartoň Jaroslav , Werner Peter 
Published: April 2003

AbstractThe copolymerization of acrylonitrile (AN) with styrene (St) is studied in the presence of Lewis acid (LA) (zinc chloride and zinc nitrate) in homogeneous reaction system. It is revealed that the rate of copolymerization (Rp) only slightly increases with the concentration of Lewis acid in the range of ratios [LA]/[AN]≦0,01 at constant concentrations of comonomers and source of radicals, i. e. 2,2′‐azoisobutyronitrile (AIBN). An increase in Rp appears when the ratio [LA]/[AN]≧0,05 is reached. The dependence of log Rp on log [AIBN] is not linear in the systems containing Lewis acid, but is a function of both the total concentration of Lewis acid and AIBN in the reaction system. For the system St‐AN‐Zn(NO3)2 the dependence of the reciprocal value of molecular weight of copolymer on the rate of copolymerization is linear and does not exhibit the minimum found for the system St‐AN‐ZnCl2. The results of kinetic investigations are interpreted from the view‐point of the present ideas on the mechanism of copolymerization in the presence of Lewis acid.
Polyoxirannes et polythiirannes comportant un centre chiral dans la chaine latérale, 2. Polymérisation de (2RS,3S)‐ et (2S,3S)‐époxy‐1,2 méthyl‐3 pentanes
Authors: Goguelin Michel , Sepulchre Maurice 
Published: April 2003

Abstract1,2‐Epoxy‐3‐methylpentanes (1) of different diastereoisomeric compositions were polymerized using anionic (tert‐BuOK, KOH), stereospecific (ZnEt2/H2O, ZnEt2/MeOH), or stereoelective (ZnEt2/R(−) 3,3‐dimethyl‐1,2‐butanediol (R( − ) DMBD)) catalysts. In all the cases a preferential incorporation of the (2R,3S) diastereoisomer in the polymer chain was observed. With anionic and coordinated anionic achiral catalysts the election was low but significant, whereas with the chiral ZnEt2/R( − ) DMBD system, in the case of the polymerization of the (2RS,3S) monomer, the election was high and corresponded to a stereoelectivity ratio of r = 4, the highest one obtained up to now for oxiranes. The observed effects are due to the presence of a chiral centre in the side chain of the monomer.
Linear oligopeptides, 55. Infrared conformational analysis of polyethyleneglycol‐bound alanine and valine homo‐L‐oligopeptides in the solid state and in solution
Authors: Bonora Gian Maria , Palumbo Manlio , Toniolo Claudio , Mutter Manfred 
Published: April 2003

AbstractThe IR absorption properties of three series of monodisperse, chemically and optically pure, PEG‐bound linear homo‐oligopeptides having the general formula t‐Boc‐(L‐Ala‐)1–8Gly‐OPEG, t‐Boc‐(L‐Val‐)1–7Gly‐OPEG and t‐Boc‐(L‐Val‐)2–8Gly‐OPEG‐M were investigated in the solid state and in solution. In the latter case the study was extended to solvents of largely different polarity and different concentrations. In the solid state the Ala and Val peptides from n = 5 to n = 8 assume essentially a β‐structure. The occurrence of the unusual parallel‐chain β‐conformation was suggested for the N‐deblocked Val highest peptides. The conformational analysis in deuterochloroform at high dilution showed that a much higher content of intramolecularly H‐bonded forms exist in Ala4 than in the Val4 peptides. At higher concentrations chain length, solvent, and side chain effects are all operative in determining the extent of peptide association. The influence of the bi‐ and monofunctional polymeric supports on the conformational properties of the Ala and Val homo‐oligopeptide series is also discussed. Finally, preliminary results on the relationship between reactivity of the polymer‐bound growing peptide chain during the step‐by‐step synthesis and peptide conformation are reported.
Über die kinetik der vorkondensation von ethylenglykol mit linearen α,ω‐dicarbonsäuren in der schmelze
Authors: Ueberreiter Kurt , Hager Wilhelm 
Published: April 2003

AbstractThe kinetics of precondensation of ethylene glycol with the dicarboxylic acids: oxalic, malonic, succinic, glutaric, adipic, and pimelic acid was investigated.The course of the reaction was followed by weighing the reaction water. The final rate equation was found to be of 6th order. This is explained by assuming that only free–OH and COOH groups are capable of the condensation reaction, their number being given by an association equilibrium. These effects are reflected by alternating numerical values of reaction enthalpies and entropies. The idea of an association is stressed by IR‐spectroscopic measurements.