bluuebunny/crossref_metadata_2025_split huggingface dataset:
Empirical molecular weight distribution functions as determined from gel permeation chromatography data
Authors: Jakeš Jaromír , Saudek Vladimír 
Published: April 2003

AbstractTwo‐ and three‐parameter functions commonly used for the description of the molecular weight distribution of polymers were determined from gel permeation chromatography data for 80 water‐soluble samples of polymers derived from glutamic acid. Two methods were applied: the moment method in which two or three different molecular weight averages are used, and a least squares adjustment method using the whole chromatogram. Convergence difficulties observed in the past were overcome, and a fully automated computer procedure was developed. The moment method, although virtually the only one still in use, often gives inexact results: sometimes the type of two‐parameter distribution is wrongly assigned, or the description of experimental data cannot be improved by adding yet another parameter. On the other hand, in all cases under study the least squares method gave a function which describes the real distribution within the limits of experimental error. Although the majority of samples could be described by employing one of the common two‐parameter functions, the more general three‐parameter function, encompassing all two‐parameter ones as special cases, has the advantage of wider applicability. It is shown that the standard gel permeation chromatography data often cannot provide reliable values of higher molecular weight moment averages, including M̄z. Hence, it may be inferred that in the description of the experimental molecular weight distribution curves the least squares method should be preferred over the moment method.
Molecular characterization of soluble poly(1,4‐divinylbenzene) obtained by anionic polymerization of 1,4‐divinylbenzene with lithium alkylamide as initiator
Authors: Kajiwara Kanji , Suzuki Hidematsu , Inagaki Hiroshi , Maeda Mizuo , Tsuruta Teiji 
Published: April 2003

AbstractA series of soluble poly(1,4‐divinylbenzene) (PDVB) samples was prepared by anionic polymerization of 1,4‐divinylbenzene (DVB) in tetrahydrofuran with a varying amount of diisopropylamine. The dilute solution properties of the PDVB samples were examined with conventional methods including viscosimetry, sedimentation equilibrium, and light scattering measurements. The results suggest a considerable amount of long branches in soluble PDVB though not all of the pendant vinyl groups are consumed to form branches. A tree‐like model was proposed for the present system. The data were analysed quantitatively according to this model which yielded a consistent pair of values of the z‐average mean‐square radius of gyration 〈S2〉 and the intrinsic viscosity [η].
Synthesis of a rhodium‐poly(4‐vinylpyridine) complex: Electrochemical behaviour of a modified platinum electrode
Authors: Cancela Juan J. , Fernández‐Otero Toribio 
Published: April 2003

AbstractComplexes of Rh(I) with 4‐vinylpyridine and poly(4‐vinylpyridine) were isolated and studied by infrared and electronic spectra and elemental analysis. The electrochemical behaviour of a platinum electrode coated with metal‐polymer complex was studied by consecutive potential sweeps. The complex was oxidized at potentials higher than 600 mV (S.C.E.) in 0,5 M H2SO4 and reduced at lower potentials. Consecutive sweeps produce a reticulation of the complex and therefore lead to electrode stabilization. The influence of the anodic and cathodic limits of the potential sweeps and of the metal to polymer ratio was also studied. The cathodic photoresponse of this electrode and its conductivity in a Fe2+ /Fe3+ solution is also reported.
Theta‐behaviour of poly(p‐tert‐butylstyrene)‐block‐poly(dimethylsiloxane)‐block‐poly(p‐tert‐butylstyrene)
Authors: Küçükyavuz Zühal , Küçükyavuz Savaş 
Published: April 2003

AbstractThe theta‐behaviour of poly(p‐tert‐butylstyrene)‐block‐poly(dimethylsiloxane)‐block‐poly(p‐tert‐butylstyrene) ABA type triblock copolymers containing ca. 28% by weight tert‐butylstyrene was studied in the selective solvents 1‐nitropropane and 2‐butanone using the phase separation method. The theta‐temperatures in these solvents were found to be 157°C and 31°C, respectively. The intrinsic viscosities of the copolymers in 2‐butanone (MEK) were obtained at different temperatures. The Mark‐Houwink‐Sakurada exponent α in MEK at 31°C is greater than 0,5, suggesting that the theta‐behaviour of block copolymers is different from that of the homopolymers due to the presence of repulsive interactions between incompatible blocks.
Molecular weights and molecular dimensions of perfluoropolyether fluids
Authors: Cantow Manfred J. R. , Larrabee Richard B. , Barrall Edward M. , Butner Richard S. , Cotts Patricia , Levy Frank , Ting Thomas Y. 
Published: April 2003

AbstractThe weight‐average molecular weights of a series of fractions from two structurally different types of perfluoropolyether fluids were determined by low‐angle laser light scattering. The limiting viscosity numbers of both sets of fractions were measured in Freon TF® and related to molecular weights. By using established polymer solution theory, the coil dimensions of the molecules were calculated. Samples from both sets of fractions were subjected to analysis by gel permeation chromatography and the coil dimensions were derived by using the principle of universal calibration. Results from both methods agree well. Bulk viscosities and molecular weights were correlated.
Addition polymerization of 1,4‐diethynylbenzene with 1,4‐benzenedithiol and properties of the resulting copolymer
Authors: Kobayashi Eiichi , Ohashi Toyoshi , Furukawa Junji 
Published: April 2003

AbstractA novel addition polymerization of 1,4‐diethynylbenzene (1) with 1,4‐benzenedithiol (2) was studied under UV‐irradiation in toluene solution at −20°C. The addition polymerization was found to proceed rapidly and a pale‐yellowish polymer precipitated with the progress of the reaction (M̄n = 7500). A soluble polymer was recovered from the toluene solution by evaporation. Its M̄n value was estimated to be 3000. When an excess amount of 2 was used (mole ratio 1:2 = 2:3), the yield of the insoluble polymer increased. TG of the polymer indicated its decomposition point to be ≈500°C in air. The electroconductivity of the insoluble and soluble polymers was found to be 10−2 S · cm−1 and 10−5 S · cm−1 when doped with I2 at room temperature, respectively, and the conductivity was reversibly increased with increasing temperature up to 90°C. At T > 90°C the iodine was released and the conductivity decreased.
Interactions of human hemoglobin with high‐molecular‐weight dextran sulfate and diethylaminoethyl dextran
Authors: Nguyen Trong Q. 
Published: April 2003

AbstractThe binding of hemoglobin with high molecular weight dextran sulfate and diethylaminoethyl (DEAE) dextran was studied by turbidimetry, viscosimetry, ultrafiltration and oxygen affinity measurements. The results indicate that a complex is formed between hemoglobin and the charged dextrans through salt bridges. This complexation can lead to precipitation if the ionization degree of hemoglobin is high enough to develop an extensive neutralization of the charges of polyionic dextrans. At the pH value near to the isoelectric point, complexation still occurs, probably through salt bridges between the polyelectrolytes and the ionized sites of opposite charge on the hemoglobin molecule, but the complexes remain soluble in solution. Binding appears to be stronger for the hemoglobin‐dextran sulfate compounds than for the hemoglobin‐DEAE dextran compounds. The oxygen affinity of hemoglobin is greatly decreased in the presence of dextran sulfate, indicating a stabilization of the deoxyhemoglobin with respect to the oxyhemoglobin.
Anionic ring‐opening polymerization of 2,2‐dimethyltrimethylene carbonate
Authors: Keul Helmut , Bächer Reinhard , Höcker Hartwig 
Published: April 2003

AbstractThe anionic ring‐opening polymerization of 2,2‐dimethyltrimethylene carbonate in solution with sec‐butyllithium as initiator was found to result under suitable conditions in a bimodal molecular weight distribution, vic. cyclic oligomers and a high‐molecular‐weight polymer. The concentration of cyclic oligomers approaches that of a ring chain equilibrium. In the kinetically controlled regime high polymer yields were obtained. Optimum reaction conditions for a polymer yield of 85 – 95% are a temperature of −10°C, an initial monomer concentration of 10 weight‐% and toluene as solvent. In THF the ring chain equilibrium is achieved readily. The ceiling temperature was determined to be ≈ 30°C. The homopolymer was characterized by spectroscopic, thermoanalytical and viscosity measurements. A high degree of crystallinity was observed.
Effect of the number of crystallizable blocks on the lamellar crystalline structure of block copolymers from poly(4‐tert‐butylstyrene) and poly(ethylene oxide)
Authors: Gervais Monique , Gallot Bernard , Jérome Robert , Teyssié Philippe 
Published: April 2003

AbstractLinear block copolymers tBSEO with an amorphous block of poly(4‐tert‐butylstyrene) (PtBS) and a crystallizable block of poly(ethylene oxide) (PEO) as well as branched block copolymers tBS(EO)2 with two PEO chains linked at the same end of a PtBS block exhibit a lamellar liquid‐crystalline structure in the dry state as well as in the presence of a preferential solvent of the PtBS block. In this structure the crystallized chains are folded in two superposed layers. To investigate the effect of the number of the PEO blocks, a linear and a branched copolymer with identical relative molecular masses and copositions were studied by X‐ray diffraction and differential scanning calorimetry. It was shown that the melting temperature, the degree of crystallinity, and the number of folds of the PEO chains are higher for the linear copolymer than for the branched one.
Deuteron NMR study of molecular order and motion of the mesogenic side groups in liquid‐crystalline polymers
Authors: Pschorn Uwe , Spiess Hans Wolfgang , Hisgen Bernd , Ringsdorf Helmut 
Published: April 2003

AbstractThe molecular order and mobility of two liquid‐crystalline polyacrylates with phenyl benzoate moieties as mesogenic side groups and (CH2)m spacers (m = 2 and m = 6) were investigated by pulsed 2H NMR. The mesogenic side groups were isotopically labelled at the terminal phenylene ring. In the glassy state the orientational distribution function was characterized from the angular dependence of the 2H NMR line shape of samples macroscopically ordered in their nematic phase by the 8,4 T magnetic field of an NMR spectrometer. It was found to be Gaussian with widths of ± 18,5° and ± 10,5° for the m = 2 frozen nematic and m = 6 frozen smectic system, respectively. The phenylene rings undergo 180° jumps about their local C2‐axes in the glassy state. The time‐scale of this process, however, was found not to be uniform. Instead, the analysis of 2H NMR line shapes and their intensities as a function of temperature yielded a log‐Gaussian distribution with correlation times characteristic of amorphous solids, 2,2 versus 2,5 decades in width and mean activation energy ĒA = 42 versus 47 kJ/mol for the m = 2 and m = 6 system, respectively. The correlation times for the centre of the distribution agree with those obtained by dielectric relaxation measurements of the same systems, suggesting that reorientation of the whole mesogenic group is detected via the phenylene rings.
Phase‐transfer catalytic activity of phosphonium salts bound to microporous polystyrene resins by long spacer chains
Authors: Tomoi Masao , Kori Nobuo , Kakiuchi Hiroshi 
Published: April 2003

AbstractSupports of polystyrene with long spacers were prepared by bromoalkylation of microporous, crosslinked polystyrene resins with ω‐bromoalkenes using CF3SO3H as catalyst. The dependence of the phase‐transfer catalytic activity of phosphonium salts bound to the polystyrene resins by long spacer chains, derived from the bromoalkylated polystyrene resins, on the percentage of ring substitution, on the degree of crosslinking, and on spacer‐chain length was studied. The high activity of the catalyst with long spacer chains was explained by the increased reactivity of the active site, induced by the increased lipophilicity of the catalyst, and by the facilitated ion exchange which was brought about by an increased distance between the active site and the polymer backbone.
Chemical modification of polydienes, 3. Copolymers with polytetrahydrofuran by grafting‐from butadiene polymers
Authors: Cameron G. Gordon , Qureshi M. Younus , Rudin Alfred 
Published: April 2003

AbstractPolybutadienes of various microstructures and some butadiene copolymers were epoxidised to low levels (<1 mol‐%) with m‐chloroperbenzoic acid. The epoxide groups functioned as initiation sites for a “grafting‐from polymerization” of tetrahydrofuran (THF) catalysed by BF3. By conducting the reaction in dilute THF solution ([Monomeric unit] < 0,3 mol · 1−1) with a large excess of BF3 over epoxide groups, gel formation was avoided. The conversion of THF was less than 2% and the copolymers contained from 10 to 50% polytetrahydrofuran (PTHF) comprising graft chains of molar mass up to 43000 g · mol−1. The relative rate of grafting tended to decrease as the content of trans‐1,4 units in the backbone polymer increased, and, unusually, there was a small increase in volume during the graft copolymerization. The graft copolymers had a two‐phase morphology consisting of amorphous rubber and crystallites of PTHF. The latter function as physical crosslinks which break down above the melting point of PTHF, so that the materials behave as thermoplastic elastomers.
Paramagnetic amphiphiles
Authors: Dulog Lothar , Ritter Ralf , Hauser Manfred , Brosig Stefan 
Published: April 2003

AbstractSurface active N‐oxyl radicals containing aliphatic chains were prepared from palmitinic, stearic and oleic acid chlorides by reaction with 4‐hydroxy‐(or‐4‐amino‐) 2,2,6,6‐tetramethyl‐piperidine or its N‐oxyl. In the former case the resulting esters or amides were subsequently oxidized. A dioleyl ester (3b) was prepared analogously from 2,2,6,6‐tetramethyl‐4‐bis(2‐hydroxyethyl)aminopiperidine. Surface tension data of aqueous solutions were determined and micelle formation was confirmed by light transmission measurements. The size of the water droplets in hexane solution of the dioleoyl derivative was estimated by the fluorescence spectroscopic method to 4,62 nm.
Block polymers obtained by means of anionic polymerization. Polystyrene‐block‐poly(ε‐caprolactone) and polystyrene‐block‐poly(2,3‐dimethyltrimethylene carbonate)
Authors: Keul Helmut , Höcker Hartwig 
Published: April 2003

AbstractThe anionic ring‐opening polymerization of ε‐caprolactone and 2,2‐dimethyltrimethylene carbonate in toluene as solvent with polystyryllithium or lithium polystyrylethoxide resp. lithium polystyrylmethoxide as initiators, results in the formation of the corresponding block polymers as major products, beside small amounts of homopolymer. The block copolymers were isolated chromatographically from the mixture and analyzed spectroscopically.
Thermo‐rétraction et orientation moléculaire du poly(téréphtalate d'éthylène) soumis a une déformation uniaxiale homogène et plastique
Authors: Rietsch François 
Published: April 2003

AbstractA study of molecular orientation in drawn and shrunk poly(ethylene terephthalate) was undertaken at 80°C and 120°C for samples drawn at (i) 80°C (homogeneous deformation) and (ii) two‐stage drawing: a homogeneous pre‐orientation at 80°C, followed by cold drawing at 20°C. The results (birefringence, residual shrinkage ratio, crystallinity) are discussed in terms of molecular disorientation in the noncrystalline region which occurs upon the shrinkage process.
The role of polymer chain tacticity of cyclolinear polydecaorganocyclohexasiloxanes in the formation of a mesomorphic state
Authors: Makarova Natalia N. , Godovsky Yuli K. , Kuzmin Nikolai N. 
Published: April 2003

AbstractNew trans‐ and cis‐polydecaorganocyclohexasiloxanes of intermediate tacticity between transtactic and cistactic and atactic were prepared by heterofunctional polycondensation of the trans‐ and cis‐isomers of 2,8‐dichlorodecaorganocyclohexasiloxanes with the corresponding dihydroxydecaorganocyclohexasiloxanes. Composition and molecular structure of polymers obtained were determined by means of elemental analysis, IR and 29Si NMR spectroscopy, intrinsic viscosity, and molecular weight analysis. Using DSC, X‐ray and optical analysis the influence of chain tacticity on the formation of a mesophase and on the crystalline state was determined. All the polymers studied exhibit a mesophase state the temperature interval of which is dependent on chain tacticity.
Etude par diffusion de la lumière du système ternaire solvant/polydiméthylsiloxane/poly(méthacrylate de méthyle)
Authors: Anasagasti Marisol , Katime Issa , Strazielle Claude 
Published: April 2003

AbstractThe ternary system solvent (1)/polydimethylsiloxane (2)/poly(methyl methacrylate) (3) was investigated by light scattering. First the measurements were realized on mixtures containing low‐molecular‐weight polydimethylsiloxane: M2 ≪ M3. In a second step, high and comparable molecular weights of both polymers were chosen for the measurements. The thermodynamic interaction parameter χ23 was determined from light scattering data (spinodal) and demixtion curves as a function of concentration and molecular weight of the polymers. Also the variation of the angular repartition of the scattered light was studied and the results were compared with calculated values.
A composite model for the thermal conductivity of semicrystalline polymers
Authors: Biswas Prabir K. , Sengupta Shyamal , Basu Asok N. 
Published: April 2003

AbstractA phenomenological model is proposed which considers the polymer as an aggregate of units. The units are composed of two distinct phases — amorphous and crystalline. The thermal conductivity of a unit is calculated in terms of those of its constituents. In the undrawn state these units are distributed randomly, and the isotropic thermal conductivity of the bulk results. The development of strong anisotropy in thermal conductivity is explained in terms of the preferred orientation of these units. The structural features of this model are similar to those employed for the interpretation of the mechanical properties. The change in orientation of the units was deduced from the experimental data of birefringence. Finally, the results obtained from the composite model for several semicrystalline polymers are compared with the experimental data and other existing calculations. The model is found to give a fair overall description of the thermal conductivity in the cases of polypropylene, polyoxymethylene, low and high density polyethylene, and polychlorotrifluoroethylene.
Bis(2‐chloroethyl)amine bound to copolymers of N‐(2‐hydroxypropyl)methacrylamide and methacryloylated oligopeptides via biodegradable bonds
Authors: Ringsdorf Helmut , Schmidt Brigitta , Ulbrich Karel 
Published: April 2003

AbstractDrug carriers were prepared by combining oligopeptidic sequences with synthetic polymeric chains. Soluble copolymers of N‐(2‐hydroxypropyl)methacrylamide (HPMA) were synthesized containing oligopeptidic side chains terminating in a drug model (p‐nitroaniline). The susceptibility of these oligopeptidic sequences to degradation on incubation with lysosomal enzymes and human serum was evaluated by monitoring the p‐nitroaniline liberation. It was shown that the drug model can be attached to the polymer carrier by means of an oligopeptidic spacer stable in blood serum and degradable after the polymer has been in contact with intracellular lysosomal enzymes. The studied polymer carriers were used for binding an anticancer drug, bis(2‐chloroethyl)amine.
Anionic polymerization of fluorine‐containing vinyl monomers, 6. Polymerizations of fluoroalkyl acrylates and methacrylates initiated by organoaluminium compounds
Authors: Narita Tadashi , Hagiwara Tokio , Hamana Hiroshi , Miyasaka Takehiko , Wakayama Akira , Hotta Tetsuo 
Published: April 2003

AbstractThe anionic polymerizations of 2,2,2‐trifluoroethyl acrylate (1a), 2,2,2‐trifluoroethyl methacrylate (1b), 2,2,2‐trifluoro‐1‐trifluoromethylethyl acrylate (2a), and 2,2,2‐trifluoro‐1‐trifluoromethylethyl methacrylate (2b) were examined with triethylaluminium and diethylaluminium active methylene chelate compounds as initiators. 2b was polymerized with triethylaluminium. Diethyl(ethyl cyanoacetato)aluminium was found to produce polymers of 1a and 1b. Diethyl(acetylacetonato)aluminium and diethyl (dimethyl malonato)aluminium, however, show low reactivity towards these four monomers. The resulting polymers show unimodal molecular weight distribution with number‐average molecular weights of 104−105, measured by GPC. The initiation reaction and the copolymerization reactivity with styrene support the anionic polymerization mechanism.
Polymeric insecticides, 2. Synthesis and bioevaluation of polymeric controlled release systems with covalently bound N2‐(4‐chloro‐2‐methylphenyl)‐N1,N1‐dimethylformamidine (chlordimeform) analogues
Authors: Lohmann Dieter , d'Hondt Christian 
Published: April 2003

AbstractPolymerizable N2‐(4‐chloro‐2‐methylphenyl)‐N1‐methylformamidine derivatives of (N‐demethyl‐chlordimeform) (2) were prepared, bearing either 4‐vinylbenzyloxy‐ or 2‐methacryloyloxyethoxycarbamoyl groups (5 and 7), and in addition, a triazatriphosphorine derivartive of 2 (8). The carbamoyl groups and the P‐N linkages in the monomers, respectively, were specifically designed to release the insecticide 2 under the particular microenvironmental conditions on cotton leaves by hydrolytic cleaveage, triggered by the pH 8–10 of the leaf surface. Biossaying experiments using larvae of the Egyptian Cotton Leafworm (Spodoptera littoralis) on cotton plants confirmed methacrylate 7 as the only compound with sufficient bioactivity. Corresponding homo‐ and copolymers of 7, containing covalently bound pendent moieties of 2, showed advantageous physiochemical properties with regard to improved efficiency and reduced environmental and handling risks in conventional foliar applications. The biological data suggest that the release rates of the active agent from the polymers vary significantly, depending on the hydrophilicity of the comonomers and the type of formulation used.
Kinetics of the amine salt initiated polymerization of ε‐caprolactam with regard to tetrahedral intermediates
Authors: Bertalan György , Nagy Tibor T. , Rusznák István , Tőke László , Anna Péter , Marosi György , Domján Pál 
Published: April 2003

AbstractA computer simulation of the kinetics of the amine salt initiated lactam polymerization was carried out using an extended kinetic model. In the reaction scheme the formation and relatively fast two‐way reaction of a tetrahedral intermediate, as well as the role of the acid in its formation were incorporated. On the basis of the extended kinetic model the calculated lactam conversion and the concentration of N‐terminal groups, respectively, have been found to be in good agreement with the experimental values for both the amine salt initiated and the hydrolytic lactam polymerization. The numerical values of rate and equilibrium constants are given.