bluuebunny/crossref_metadata_2025_split huggingface dataset:
Critical opalescence of polymer solutions at high pressures
Authors: Kiepen Friedheinz , Borchard Werner 
Published: April 2003

AbstractWith a new type of high‐pressure cell the angular dependence of light scattering intensities at scattering angles θ between 30° and 150° can be measured as a function of pressure P. The linear extrapolation of (Iθcorr)−1 as a function of sin2 (θ/2) to θ = 0 does not show an angular dependence of the scattering intensities. For this result the term including sin2 (θ/2) in Debye's equation for the critical opalescence vanishes. The reason for this is probably due to the low molar mass of the polystyrene (number‐average molar mass M̄n = 1 000 g/mol). This means that the range of molecular forces of a polymer/solvent system is too small to be detected by light scattering. A second linear extrapolation of (Iθcorr)−1 to θ = 0 as a function of P yields the spinodal points of the system polystyrene/pentane in the temperature‐pressure‐concentration diagram.
Polymers with carbazolyl groups, 3 Fluorescence properties of some polysiloxanes with pendant carbazolyl groups
Authors: Hennecke Manfred , Strohriegl Peter 
Published: April 2003

AbstractThe polarized fluorescence spectra and the time‐resolved fluorescence decay of some novel carbazole‐containing polysiloxanes were measured in solution and in the solid state. The fluorescence data show that these polymers, due to the conformational freedom of the carbazole group, are free of excimer‐forming sites. As indicated by the extensive fluorescence depolarization in solid solution, the migration of excitation energy along the chain is fast with respect to the fluorescence lifetime, and the number of migrational steps comes up to the number of chromophores per chain. If the polymers were prepared starting from commercial carbazole (which contained small amounts of aromatic impurities), the occurrence of sensibilized benzocarbazole‐like fluorescence in the solid state and in concentrated solution demonstrates the high efficiency of transferring the excitation energy to a suitable acceptor.
Effect of cationic surfactants on the permeability across a membrane of poly[butyl methacrylate‐co‐N‐methyl‐N‐(4‐vinylphenethyl)ethylenediamine]‐graft‐poly(L‐glutamic acid)
Authors: Chung Dae‐won , Kurosawa Koichi , Maeda Mizuo , Inoue Shohei 
Published: April 2003

AbstractThe effects of three cationic surfactants, dodecylammonium chloride (C12N+), dodecyldimethylammonium chloride (C12N+ 2C1), and dodecyltrimethylammonium chloride (C12N+ 3C1), on the permeability of 1‐phenyl‐1,2‐ethanediol were investigated for the membrane of poly[butyl methacrylate‐co‐N‐methyl‐N‐(4‐vinylphenethyl)ethylenediamine]‐graft‐poly(L‐glutamic acid) (PLGA) (1b), the permeating pathway being composed of the polypeptide domain. The membrane treated with a surfactant shows a decrease in permeability due to the coil‐to‐helix transition of PLGA induced by the surfactant. The effects of the three surfactants on the permeability was found to be of the order: C12N+ > C12N+2C1 > C12N+3C1.
Photoinitiators and photoinitiation, 8 The photoinduced α‐cleavage of acylphosphine oxides. Identification of the initiating radicals using a model substrate
Authors: Baxter Jane E. , Davidson R. Stephen , Hageman Hendrik J. , Overeem Ton 
Published: April 2003

AbstractThe photodecomposition of diphenyl‐2,4,6‐trimethylbenzoylphosphine oxide (1) was studied both in solution at 40°C and in thin films in the presence of 1,1‐di‐p‐tolylethylene as a model substrate for vinyl monomers. Both primary radicals resulting from α‐cleavage of 1 were found to add to the olefinic double bond of the model substrate (initiation). The diphenylphosphinoyl radical (3) proved to be twice as effective as the 2,4,6‐trimethylbenzoyl radical (2) under all conditions. Oxygen (air) considerably reduced the initiating efficiencies fp, in particular fp(2) (of radical 2). The addition of triethylamine partially restored the overall initiating efficiency in all likelihood by oxygen scavenging. A direct contribution of triethylamine‐derived radicals to the initiation was not observed.
Crystallinity and thermal behaviour of trans‐poly(1‐octenylene)
Authors: Schneider Wolfgang A. , Müller Michael F. 
Published: April 2003

AbstractThe commercially available poly(1‐octenylene) Vestenamer® formed by the metathetic polymerization of cyclooctene with a tungsten catalyst, is highly crystalline at room temperature; it shows specific properties as a blend component, thus favourably influencing the processing characteristics and the final product quality. Differential scanning calorimetry, infrared and torsion pendulum experiments indicate that the melting temperature and the degree of crystallinity depend on the concentration of trans double bonds, on their distribution along the polymer chain as well as on the sample history. The formation of crosslinks induced by very intensive UV irradiation of 100 μm thin films leads to a reduction of the melting temperature and the crystallinity. A correlation between stiffness (shear modulus G′) and crystallinity was found for samples with varying amounts of trans double bonds.
Polymerization of macromonomers, 3. Monomer reactivity ratios in radical copolymerization of poly(tetrahydrofuran) macromonomers with 2‐vinylnaphthalene
Authors: Asami Ryuzo , Takaki Mikio , Matsuse Takashi 
Published: April 2003

AbstractMethacrylate‐terminated poly(tetrahydrofuran) (MA‐PTHF) and acrylate‐terminated poly‐(tetrahydrofuran) (A‐PTHF) macromonomers (M2) were radically copolymerized with 2‐vinylnaphthalene (2‐VN, M1). The composition of copolymers was determined by UV spectroscopy taking advantage of the very high absorption coefficient (UV) of the monomeric units of 2‐VN in copolymer. The monomer reactivity ratios r1 and r2 evaluated are as follows. MA‐PTHF: r1 =1,3 ± 0,21, ± 0,05; A‐PTHF: r1 = 2,5 ± 0,35, r2 = 0,10 ± 0,05. These reactivity ratios were compared with those in the copolymerizations of 2‐VN with the corresponding small monomers and were discussed in terms of polymer (hindering) effect and the concept of equal reactivity of growing chain.
Optically controlled ligand delivery, 1. Synthesis of water‐soluble copolymers containing photocleavable bonds
Authors: Yen Hung‐Ren , Kopeček Jindřich , Andrade Joseph D. 
Published: April 2003

AbstractTo verify the possibility of developing a ligand delivery system which is controlled by light pulses, we synthesized copolymers of N‐(2‐hydroxypropyl)methacrylamide (1) containing sidechains terminated in ligands (Boc‐Gly, fluorescein, tetramethylrhodamine) bound via photocleavable 2‐nitrobenzyl groups. Copolymers in solution were exposed to light of wavelength ≈︁ 360 nm which resulted in release of the bound ligands. Depending on the experimental conditions (type of solvent, presence of oxygen) changes in the structure of released fluorochromes were observed (photofading effect). These effects were quantified by determining the binding constants of released modified fluorochromes with monoclonal antifluorescyl anti‐bodies.
Electron transfer from carbanionic salts to linear sequences of conjugated double bonds, 2. Reaction with trans‐β‐carotene
Authors: Rudatsikira Alphonse , François Bernard , Mathis Claude 
Published: April 2003

AbstractThe reactions of a set of organoalkaline compounds with trans‐β‐carotene (Car) were studied in solution (using UV/Vis, ESR, and mass spectroscopy) and compared with the reactions of the same set with insoluble polyacetylene. It was shown that the naphthalene radical ion and the dicarbanionic dimer of 1,1‐diphenylethylene, 1,1,4,4‐tetraphenyl‐1,4‐butanediide, react with Car by a simple electron transfer leading to Car radical ion and dianion. This dianion is protonated by methanol mainly at carbon 7 or 7′. On the contrary of diphenylalkyllithium compounds add to Car double bonds. This addition of 1 mol of diphenylalkyllithium per Car takes place mainly at the central double bond. sec‐Butyllithium (sec‐BuLi) reacts also by addition to Car. The addition products are in some cases instable and decompose to radical ions through a non‐elucidated mechanism. These transfer or addition reactions with Car, as well as the exclusive electron transfer observed with polyacetylene, are rationalized on the basis of the relative redox potentials of reactants.
Sulfopropylated hemicellulose: Synthesis and NMR characterization
Authors: Focher Bonaventura , Marzetti Annamaria , Naggi Annamaria , Torri Giangiacomo 
Published: April 2003

AbstractSulfopropylation of hemicelluloses was achieved in dimethyl sulfoxide solution. The progress of sulfopropylation reaction was studied as a function of the dimsyl/hemicellulose ratio, reaction time with dimsyl (dimethylsulfinyl carbanion), propanesultone/hemicellulose ratio, and reaction time with propanesultone. The degree of substitution of sulfopropylhemicelluloses ranged between 0,5 and 1,1 as a function of experimental conditions. Intrinsic viscosity (0,1—0,3 dl/g) and molecular weight measurements (15000 g.mol—1) showed a controllable degradation of hemicellulose chains during the reaction. The NMR characterization of enzymatically degradated sulfopropylhemicelluloses indicated a homogeneous substitution along the polysaccharide chains. A significant regioselectivity for the OH‐2 hydroxyl groups was observed only for DS ≤ 0,5.
Blends of poly(tetramethylene terephthalate) with a liquid‐crystalline polyester, poly(decamethylene 4,4′‐terephthaloyldioxydibenzoate), 2. Crystallization kinetics and melting behaviour
Authors: Pracella Mariano , Chiellini Emo , Dainelli Dario 
Published: April 2003

AbstractThe isothermal crystallization kinetics, the morphology and melting behaviour of blends of poly(tetramethylene terephthalate) {poly(butylene terephthalate), (PBT)} with a thermotropic liquid‐crystalline polyester, poly(decamethylene 4,4′‐terephthaloyldioxydibenzoate) (HTH10), were studied in the composition range 0—50 wt.‐% of HTH10 by optical microscopy and differential scanning calorimetry. The spherulite growth rate and the overall crystallization rate of PBT from melt blends are markedly depressed by the presence of the mesomorphic component. Changes of superstructure and of primary nucleation density of PBT spherulites in the blends were observed. The analysis of the melting behaviour of these samples indicates that the stability of PBT crystals and their reorganization processes on heating are dependent on the blend composition. A decrease of the equilibrium melting temperature of PBT is found with increasing the amount of HTH10. According to previously reported investigations on the same system, the results are discussed in respect of the onset of interactions between the two polymers in the liquid state.
On the reaction of catenapoly(diphenoxy‐λ5‐phosphazene) with sulfur trioxide
Authors: Montoneri Enzo , Gleria Mario , Ricca Giuliana , Pappalardo Giuseppe C. 
Published: April 2003

AbstractThe reaction of catenapoly(diphenoxy‐λ5‐phosphazene) (1) with SO3 in 1,2‐dichloroethane at 15°C, applying a mole ratio m = [SO3]/[‐–P(OC6H5)2N—] ≤ 1,0 and subsequent quenching with water, leads to catenapoly(diphenoxy‐λ5‐phosphazene‐co‐diphenoxy‐λ5‐phosphazenium hydrogen sulfate) (2) containing up to 57% protonated nitrogen. At m > 1,0 C‐sulfonation occurs, resulting in the formation of water‐soluble catenapoly[diphenoxy‐λ5‐phosphazene‐co‐diphenoxy‐λ5‐phosphazenium hydrogen sulfate‐co‐bis(sulfophenoxy)‐λ5‐phosphazenium hydrogen sulfate] (3). The latter can be converted into catenapoly[diphenoxy‐λ5‐phosphazene‐co‐bis(sulfophenoxy)‐λ5‐phosphazene] (4b) by treatment with alkali and subsequent percolating through a cation exchange resin. Analytical results show that C‐sulfonation is preceded by the formation of a polymer‐SO3 donor‐acceptor complex.
Synthesis of polysulfone‐block‐polysiloxane copolymers, 4. A model study of the limitation of hydrosilylation coupling
Authors: Torrès Ghislaine , Madec Pierre‐Jean , Maréchal Ernest 
Published: April 2003

AbstractHydrosilylation reactions of 1‐allyloxy‐3‐phenoxy‐2‐propanol (3) as model compound were carried out with α‐dimethylsilyl‐ω‐hydrooligosiloxane (7; M̄n = 1200) in the presence of hexachloroplatinic acid. It was found that under stoichiometric conditions only 75‐–80% of the allyl groups were hydrosilylated, due to some isomerization of the allyl groups into vinyl groups, which do not undergo hydrosilylation. This isomerization could be shown to be sensitive to the type of the allyloxy structure. Thus, for example, allyloxybenzene does not undergo isomerization.
Stereospecific functionalization of poly(vinyl chloride)
Authors: Millán José‐Luis , Martínez Gerardo , Mijangos Carmen , Gómez‐Daza Mariano 
Published: April 2003

AbstractThe substitution reaction of PVC with sodium dimethyldithiocarbamate (NaDC) and sodium azide (NaN3) was performed in cyclohexanone and dimethylformamide at various temperatures. The degree of compositional heterogeneity was estimated and found to be important up to conversions of about 0,5%, but to vanish afterwards. The evolution of unreacted iso, hetero and syndiotactic triads was measured by 13C NMR spectroscopy. For conversions of at least up to 12%, the content of both the isotactic and heterotactic triads was found to decrease, relative to the syndiotactic ones, but at different relative rates depending on the nucleophile. From these results, together with the kinetic ones, it is concluded that the reaction proceeds by a stereoselective mechanism. The results are discussed on the basis of a hypothesis concerning the role of the local triad conformations in PVC that contain the TT isotactic diad conformation. The results enable the selective substitution of PVC with NaDC and NaN3, which may be used as a useful tool to prepare specific graft copolymers based on PVC.
Condensation polymerization of 2,2′‐diiodobiphenyl‐4,4′‐dicarbonyl dichloride with some mono‐ and dihydroxy aromatic compounds
Authors: Banihashemi Ahmad , Ameri Farahnaz 
Published: April 2003

AbstractSeveral potentially thermostable polyesters 3a–1 were prepared by Schotten‐Baumann condensation of 2,2′‐diiodo‐4,4′‐biphenyldicarbonyl dichloride (1) with several aromatic hydroxy compounds 2a–1. The reactivity of 1 towards various phenols was tested and the spectra of the resulting model compounds 4a–d were compared with those of the polymers. With some exceptions (3h and 3c) the polyesters were found to be soluble in organic solvents. Their inherent viscosities vary between 0,1 and 0,45 dl · g−1 (in CHCl3 at 25°C). The values of the inherent viscosity were in the range of 0,06–0,45 dl/g (c = 0,2 g/dl in CHCl3 at 25°C). The melting points of the polymers were found to be higher than 300°C.
Polymerization of 1‐alkynes initiated by transition metal carbene complexes, 2. Kinetics and mechanism of the initiation reaction
Authors: Lucas Christine , Soum Alain , Fontanille Michel 
Published: April 2003

AbstractA kinetic study of the initiation reaction of alkyne polymerization by a transition metal intramolecular coordinated carbene complex, was carried out. It showed that there is a slow disappearance of the initial carbene and simultaneously appearance of both active species and organic side‐products. Their structures were determined by GC‐MS. The apparent rate constants of both initiation and side‐reactions were measured and the corresponding thermodynamic parameters established. According to the experimental results, a mechanism of the initiation reaction is proposed. In the first step a replacement of the intramolecular double bond of the initiator by the triple bond of a monomer molecule takes place and in the second step the insertion of the monomer. The resulting carbenic active species may lead either to organic products via cyclopropanation reaction or to a high‐molecular‐weight polymer.
Synthesis and electrical conductivity of poly(1,4‐phenylenevinylene‐co‐2,5‐thienylenevinylene)
Authors: Shim Hong‐Ku , Lenz Robert W. , Jin Jung‐Il 
Published: April 2003

AbstractCopolymers containing either 1,4‐phenylenevinylene or 2,5‐dimethoxy‐1,4‐phenylenevinylene units combined with 2,5‐thienylenevinylene units were prepared in film form from precursor polymer films of the respective sulfonium salt polymers, which, in turn, were synthesized by the copolymerization of the respective bis(sulfonium salt) monomers. All of the copolymers could be “doped” with iodine to obtain films with high electrical conductivities and good air stability.
Electrochemical polymerization of some dihydrobenzodipyrroles
Authors: Zotti Gianni , Schiavon Gilberto , Berlin Anna , Ferraccioli Raffaella , Pagani Giorgio , Sannicolo Franco 
Published: April 2003

AbstractAnodic coupling of the dihydrobenzodipyrrole isomers 1H,8H‐pyrrolo[3,2‐g]indole (1), 1H,7H‐pyrrolo[3,2‐f]indole (2), and 1H,5H‐pyrrolo[2,3‐f]indole (3) in 0,1 M tetraethylammonium perchlorate in acetonitrile produces polymeric films which are reversibly oxidized around 0,3 V vs. Ag/Ag+ with 0,5 electrons per monomeric unit. IR reflectance, UV‐vis and cyclic voltammetry show that the oxidized polymers undergo easy overoxidation at the benzene ring without affecting the charge storage ability. Conductivities (0,2–5 Ω−1 · cm−1) are higher than those presented by chemically prepared samples (10−4 – 10−1 Ω−1 · cm−1) and are attributed to more ordered structures of the polymers.
Inertie photochimique du poly(fluorure de vinylidène) à courte et à grandes longueurs d'onde
Authors: Philippart Jean‐Louis , Siampiringue Narcisse , Strassel Albert , Lemaire Jacques 
Published: April 2003

AbstractThe photooxidizability of poly(vinylidene fluoride) films has been examined at the short wavelength (λ = 254 nm) at 30°C and at long wavelengths (λ > 300 nm) at 60°C. No oxidized groups can be observed in the infrared and ultraviolet spectra of films exposed for long periods of time. Variations of mechanical properties and of permeabilities for CO2 or O2 can only be observed after very long exposures. Introduction of photoactive pigments such as ZnO or TiO2 does not induce any photocatalyzed oxidation in prolonged exposures.
Thermodynamic stability of mixtures containing statistical copolymers, 1. Phantom‐lattice treatment of chemically modified polymers
Authors: Koningsveld Ronald , Macknight William J. 
Published: April 2003

AbstractFor two statistical copolymers containing the same repeating units to be miscible their chemical compositions should not differ by more than a maximum tolerable composition difference. Measurements of the miscibility behaviour of mixtures of brominated polystyrenes by Kambour et al. can be interpreted if the small changes in molecular volume caused by bromination are taken into account with a simple extension of Scott's model. The feature is in accordance with the well‐known sensitivity of polymer blend miscibility to small changes in chain length. The relatively small extension of the model already changes the value of the pairinteraction parameter (χ) drastically, which exemplifies the necessity to let χ values in literature be accompanied by precise information about the model used in the evaluation.
Thermal degradation of anionically prepared poly(methyl methacrylate)s
Authors: Chiantore Oscar , Guaita Marino , Rendina Gabriele 
Published: April 2003

AbstractThermal degradations of samples of poly(methyl methacrylate), prepared with different anionic initiators, were compared. It could be shown that the polymers prepared with 1,1‐diphenylhexyllithium and with the tetramer of α‐methylstyrene degrade in one step at temperatures higher than 300°C, whereas those prepared with cumylcesium exhibit two degradation steps, one at temperatures lower and one at temperatures higher than 300°C. By means of end group analysis and molecular weight determinations it could be concluded that the low temperature degradation step of poly(methyl methacrylate), prepared with cumylcesium, involves initiation at the polymer chain ends.
Azo polymers — syntheses and reactions, 2. Selfcrosslinking, swelling and DSC experiments
Authors: Nuyken Oskar , Weidner Richard , Schuster Robert H. 
Published: April 2003

AbstractPolymers containing azo groups and CC‐double bonds were crosslinked by heating to the temperature at which cleavage of the azo functions covalently linked to the polymer backbone takes place. The crosslinking process was characterized by swelling experiments and by DSC. From the reaction enthalpy the number of polymer chains initiated by one radical was estimated. Swelling experiments and DSC showed that the crosslinking efficiency of the radicals increases with the temperature at which the azo groups are split off and with the instability of the radicals. Polymers containing also functions with different thermostability were used for selective stepwise network formation.
Copolymerization of cycloalkenes with ethylene in presence of chiral zirconocene catalysts
Authors: Kaminsky Walter , Spiehl Regina 
Published: April 2003

AbstractThe chiral catalyst ethylene(bisindenyl)zirconiumdichloride/methylaluminoxane, which is soluble in hydrocarbons, allows the polymerization of cyclic alkenes, e. g. cyclopentene, to form isotactic polymers. No ring opening reaction occurs. To reduce the high melting point of the polycyclopentene, copolymers with ethylene were synthesized. The copolymerization of cyclopentene with ethylene shows similar reaction rates as found for the homopolymerization of ethylene. From 13C NMR spectroscopically calculated rates of incorporation of cyclopentene or cycloheptene in the polymers the copolymerization parameters can be deduced. With increasing polymerization temperature from −10 to 20°C the r1 values rise significantly from 80 to 300. Up to 10 mol‐percnt; of cyclopentene monomeric units in the polymer the comonomer is incorporated statistically, whereas a higher content of comonomer leads to two‐block formation.
Analysis of mutual exclusions in multichain athermal systems
Authors: Cifra Peter , Romanov Andrej 
Published: April 2003

AbstractThe concentration‐dependent decrease of the entropy of polymer chains in polymer solutions is treated by Monte Carlo simulation technique and by blob analysis. The results suggest the existence of a universal relation for this dependence over a broad concentration range. Differences between the observed combinatorial entropy of the multichain system and the behaviour proposed by mean‐field treatments as well as implications for treatments of the melting entropy of a polymer are pointed out.
Interpretation of the effects of segmental friction on the diffusion coefficients of polymer chains
Authors: Stepto Robert F. T. 
Published: April 2003

AbstractPreviously established variations with chain length and solvent of the segmental friction coefficient (ζ) of poly(methylene) chains in dilute solution are rediscussed and reanalysed as effects due to chain dynamics. The assumption of a solvent continuum, common to all theories of the diffusion coefficient (D), is seen to be a gross but presently unavoidable oversimplification. Given this situation, Kirkwood‐Riseman (K‐R) (rigid‐body) hydrodynamics are shown to provide a satisfactory basis for correlating changes in ζ. (The use of full Oseen hydrodynamics brings only a minor improvement). Basically, because the differences between segmental and centre‐of‐mass velocities increase with chain length then ζ also increases, bringing relative reductions in values of D compared with those calculated on the basis of constant ζ. In addition, values of ζ are smaller in solvents of larger molar volume and/or viscosity, consistent with more slippage between segment and solvent. In the limit of infinite chain length, the ratio, ψ(∞), of equilibrium radius and Stokes‐Einstein diffusion radius, rD, is shown to be reduced significantly below the value of 1,505 predicted by K‐R hydrodynamics for the freely‐jointed chain in a continuum. The reduction in ψ(∞), essentially an increase in rD, is due to less penetration of the molecular domain by the solvent in real systems. Larger values of rD, because of less penetration, appear to occur with solvents of higher molar volume and/or viscosity (e.g. quinoline, cf. benzene), although the values of ζ in such solvents are smaller.