bluuebunny/crossref_metadata_2025_split huggingface dataset:
OH‐radical‐induced crosslinking and strand breakage of poly(vinyl alcohol) in aqueous solution in the absence and presence of oxygen. A pulse radiolysis and product study
Authors: Ulanski Piotr , Bothe Eberhard , Rosiak Janusz M. , von Sonntag Clemens 
Published: April 2003

AbstractHydroxyl radicals were generated radiolytically in N2O‐ or N2O/O2(4:1)‐saturated aqueous solutions of poly(vinyl alcohol) (PVAL) or its low‐molecular‐weight model compound pentane‐2,4‐diol (PD). Using the pulse radiolysis technique, the rate constant of OH with PD and PVAL has been determined to be 2,3 · 109 dm3 · mol−1 · s−1 and 1,5 · 108 dm3 · mol−1 · s−1, respectively. Upon OH attack two kinds of radicals are generated: (i) tertiary α‐hydroxyalkyl radicals and (ii) alkyl radicals. The former rapidly reduce tetranitromethane yielding the stable nitroform anion, and from its yield it is calculated that 70–75% of the radicals are α‐hydroxyalkyl radicals in both systems. In the presence of oxygen, the carbon‐centered radicals are converted into the corresponding peroxyl radicals. The α‐hydroxyalkylperoxyl radicals eliminate HO2˙/O2˙ in spontaneous and base‐catalyzed reactions (rate constants ≈700 s−1 and ≈2,3 · 109 dm3 · mol−1 · s−1, respectively). There are marked differences in the rates of the bimolecular radical decay reactions. The carbon‐centered radicals of PD decay with a rate constant of 5 · 108 dm3 · mol−1 · s−1, whereas those of PVAL decay, under pulse‐radiolytic conditions, mainly intramolecularly (loop formation), with rate constants which reach, at high radical numbers per macromolecule, values as high as 1010 dm3 · mol−1 · s−1. With PD it was shown by product studies that the radicals mainly (90%) disproportionate and dimerize only to 10%, thus limiting the yield of crosslinks in PVAL to the latter value. The bimolecular decay rates of the organic peroxyl radicals in O2˙ containing solutions are more difficult to investigate because of the effective unimolecular HO2˙‐elimination reaction. However, it is estimated that the peroxyl radicals of both compounds decay (under otherwise equal conditions) more than one order of magnitude slower than the carbon‐centered radicals. The measured yields of strand breaks in oxygenated solutions as well as the yields of intermolecular crosslinks under anoxia, determined with PVAL by low‐angle laser light‐scattering at different dose‐rates and pH values, support these conclusions.
Phase‐restricted radiation crosslinking in semicrystalline polyolefins investigated by two‐dimensional solid‐state nuclear magnetic resonance
Authors: Beckham Haskell W. , Spiess Hans Wolfgang 
Published: April 2003

AbstractThe utility of two‐dimensional wideline separation (2D WISE) NMR in following the phase dependence of the radiation‐induced crosslinking of multiphase materials has been demonstrated. Crosslink production in semicrystalline polyolefins by high‐energy electron irradiation in air was monitored via the experimentally resolved 1H lineshapes of the respective amorphous and crystalline regions. It was shown that radiation‐induced crosslinks can be primarily restricted to one phase or the other by proper functionalization, or nonfunctionalization, of the host polymer. Poly(1,23‐tetracosadiyne), a diacetylene‐functionalized polyethylene, was synthesized and shown to predominantly undergo crystalline‐phase crosslinking for dosages of 100 kGy and less. Thus, chain mobility within amorphous regions may be maintained upon radiation‐induced crosslinking. In comparison, linear polyethylene exhibited amorphous‐phase crosslinking for electron beam radiation dosages of at least 400 kGy; application of 2D WISE NMR represents a direct method for following this well‐known process.
Dimerizations of acrylate monomers with sodium hydroxymethanesulfinate and characterization of the products
Authors: Wang Cheng‐Chien , Kuo Jen‐Feng , Chen Chuh‐Yung 
Published: April 2003

AbstractThe reactions of sodium hydroxymethanesulfinate (sodium formaldehyde sulfoxylate, SFS) with various monomers, including acrylates, methacrylates, styrene and vinyl acetate, were studied. The reaction products formed depended on the molecular structure of the monomers and acidity of the reaction solution. Among the monomers studied, acrylates with resonance stability values Q between 0,38 and 0,45 produced diacrylate sulfones in neutral conditions. The other monomers or reaction conditions did not result in a dimer. The obtained diacrylate sulfones were characterized by elemental analysis, mass spectrometry, IR spectra, normal 1H and 13C NMR, CHn (n = 1, 2 and 3) subspectra by Distortionless Enchancement by Polarization Transfer at θ = 3π/4, as well as by 1H‐ 13C 2D‐NMR spectra using Correlated Spectroscopy and Heteronuclear Multiple Bonding Correlation methods. A possible reaction mechanism for the formation of dimers is suggested. The morphology and thermal properties of these diacrylate sulfones were determined.
Anionic polymerisation of propylene oxide. Investigation of double‐bond and head‐to‐head content by NMR spectroscopy
Authors: Yu Ga‐Er , Masters Andrew J. , Heatley Frank , Booth Colin , Blease Trevor G. 
Published: April 2003

AbstractPropylene oxide was anionically polymerised in bulk at 80°C under a range of initial conditions, from zero hydroxyl content to a mole ratio of hydroxyl to potassium catalyst of 10. The double bond content of the polymers was measured by 1H NMR spectroscopy over a wide range of conversions, and values of the transfer constant were determined. The results were fitted to a reaction mechanism involving suppression of the transfer reaction by hydrogen bonding of hydroxyl groups to active ion pairs. The head‐to‐head content of the polymers was measured by 13C NMR spectroscopy. The overall proportion (approximately 4%) of ‘head‐to‐head’ reactions relative to head‐to‐tail addition was not greatly affected by suppression of the transfer reaction, since an increase in the number of head‐to‐head additions compensated the decrease in proton abstraction from methyl groups via the transfer reaction.
Immobilization of enzymes by multilayer microcapsules
Authors: Pommersheim Rainer , Schrezenmeir Jürgen , Vogt Walter 
Published: April 2003

AbstractA method is described to obtain a new type of microcapsules for immobilization of enzymes or living cells. The wall of these capsules consists of several layers of poly(ethyleneimine) and poly(acrylic acid). The idea is that diverging properties of the whole assembly can be better controlled when the membrane is built up by several consecutive steps, each being optimized with respect to a special property, for example, permeability or mechanical strength. The encapsulation of acidic phosphatase and the cleavage of p‐nitrophenyl phosphate was used as a model system. The charged capsules were characterized by their enzymatic activity, as a function of membrane composition (number and sequence of layers) and storing time. The permeability for the substrate and the retaining ability for the enzyme were also measured.
Ferroelectric liquid crystalline polysiloxanes designed for high second‐order nonlinear susceptibilities
Authors: Wischerhoff Erik , Zentel Rudolf , Redmond Maura , Mondain‐Monval Olivier , Coles Harry 
Published: April 2003

AbstractFerroelectric liquid crystalline (FLC) copolysiloxanes containing suitable comonomers (“NLO‐chromophores”) for second harmonic generation (SHG) have been prepared. Their important feature is a donor‐acceptor π‐system sited perpendicular to the long axis of the side‐group moieties in order to adopt the polar ordering of the ferroelectric LC phase. The influences of the mesogen structure and of the content of NLO‐chromophores on the liquid crystalline and ferroelectric properties are studied. The desired chiral smectic C* phase is retained up to 30 mol‐% of chromophore. Also, first measurements of second harmonic generation have been performed.
Bacterial production of polyesters bearing phenoxy groups in the side chains, 1. Poly(3‐hydroxy‐5‐phenoxypentanoate‐co‐3‐hydroxy‐9‐phenoxynonanoate) from Pseudomonas oleovorans
Authors: Ritter Helmut , von Spee Astrid Gräfin 
Published: April 2003

AbstractThe production of phenoxy‐substituted poly(3‐hydroxyalkanoates) (PHA) by Pseudomonas oleovorans was investigated. 11‐Phenoxyundecanoic acid was used as a single carbon source for the bacterial culture. At the maximum growth rate of the culture, the cells were isolated by centrifugation. The cells were lyophylized and then extracted with trichloromethane, yielding a comb‐like copolyester. Methanolysis of this polyester was performed to characterize the incorporated hydroxyacids. This proved the polyester to be a copolymer: poly(3‐hydroxy‐5‐phenoxypentanoate‐co‐3‐hydroxy‐9‐phenoxynonanoate) (5; 6:1 mole ratio). GPC measurements with polystyrene as standard indicated Mn values of approximately 76 000 and a molecular weight distribution index of Mw/Mn = 2,3. The copolyester showed a glass transition at 14°C.
In situ X‐ray absorption spectroscopy at the K‐edge of red phosphorus in polyamide 6,6 during a thermo‐oxidative degradation
Authors: Küper Gerhild , Hormes Josef , Sommer Klaus 
Published: April 2003

AbstractWe present a new method for studying the influence of flame retardants as a function of time and temperature by measuring the X‐ray absorption spectra of the corresponding additive. Here, red phosphorus in polyamide 6,6 was investigated at the phosphorus K‐edge using synchrotron radiation. The thermo‐oxidative degradation of the polymer was simulated by heating the sample up to 300°C. XANESXANES, EXAFS: X‐ray absorption spectroscopy investigating the near edge structure or the fine structure of the extended region, respectively.
spectra were monitored during the degradation process at different temperatures and at a constant reaction temperature as a function of time. The degradation reaction was analyzed by comparing the XANES spectra of red phosphorus and orthophosphoric acid, and the reaction was identified as an oxidation of red phosphorus to H3PO4. The results so obtained are confirmed by the EXAFS spectra of the additive in the polymer sample recorded before and after the thermo‐oxidative degradation process, and by the EXAFS spectra of suitable reference compounds.
Novel regular‐network polyurethane films from polyols and diisocyanates
Authors: Kiyotsukuri Tsuyoshi , Nagata Minoru , Okada Hiroyuki , Miura Daisuke , Tsutsumi Naoto 
Published: April 2003

AbstractNovel regular‐network polyurethane films were prepared from polyols of phloroglucinol (1), 2,4,2′,4′‐tetrahydroxybenzophenone (2) or glycerol (3), and diisocyanates of hexamethylene diisocyanate (6), 4,4′‐diphenylmethane diisocyanate (4,4′‐methylenebis(1,4‐phenylene) diisocyante (5)) or p‐phenylene diisocyanate (4). Prepolymers prepared by solution polyaddition were cast and successively post‐polymerized at various temperatures between 60 and 160°C for 1 h to form networks. The resultant films were transparent, flexible and insoluble. Heat distortion temperatures (Th) of the polyurethane films increased with increasing post‐polymerization temperature. The highest Th values obtained are 52, 58, 61, 69, 99, 122, 122 and 151°C for 1/5, 3/5, 2/5, 3/6, 2/4, 1/6, 1/4 and 2/6, respectively. The densities of polyurethane films also increased with increasing post‐polymerization temperature, which is comparable with an increase of Th. The X‐ray diffraction patterns of films showed two diffraction peaks, suggesting some ordered structure due to the regular networks. The network polyurethane film showed higher Th and tensile strength compared with the corresponding network polyester film, suggesting an effect of intermolecular hydrogen bonding. All films started to decompose at a temperature around 120°C due to the decomposition of unreacted terminal isocyanate groups. The thermal stability of a network polyurethane film could be remarkably enhanced by capping the unreacted terminal isocyanate group with phenol.
Optically active polymers, 2. Copolymerization of limonene with maleic anhydride
Authors: Maślińska‐Solich Jolanta , Kupka Teobald , Kluczka Mirosław , Solich Anton 
Published: April 2003

AbstractCopolymerization of maleic anhydride (MA) and (R),(S)‐limonene (LIM) was studied in various solvents, using 2,2′‐azoisobutyronitrile (AIBN) and benzoyl peroxide (BPO) as initiators and radiation (60Co γ‐source) within the temperature range of 20–70°C. Regardless of conversion or initial comonomer feed ratios, the composition of LIM‐MA copolymers ranged from about 1 : 1 to 1 : 1,6 and was dependent on the reaction conditions, leading to a formation of materials with diverse solubilities, degrees of crosslinking and molecular weights. The main product consists of a 1 : 1 LIM‐MA copolymer with pendant 4‐methyl‐3‐cyclohexenyl residues. At higher conversion these alicyclic unsaturations lead to crosslinking. No reference to cyclocopolymerization was detected.
Structural analysis of the components of Chinese lacquer “Kuro‐urushi”
Authors: Hatada Koichi , Kitayama Tatsuki , Nishiura Takafumi , Nishimoto Akira , Simonsick William J. , Vogl Otto 
Published: April 2003

AbstractThe urushiol components in Chinese lacquer “Kuro‐urushi”, which was processed by treating Chinese Raw Urushi (“Ki‐urushi”) with Fe(OH)2, were isolated by reversed‐phase liquid chromatography. A new component, which was not present in “Ki‐urushi”, was found. Structural analysis using 1H NMR and mass spectrometry showed that the component is a regioselectively formed water adduct of the original urushiol component, i. e., 3‐(11′E,13′Z‐8′‐hydroxypentadecadienyl)catechol.
Molecular mechanical analysis of polymer conformation, 2. Relation between chain conformation and birefringence of stretched non‐crystalline polyurethanes with various substituent groups
Authors: Konda Masakazu , Yamane Hideki , Kimura Yoshiharu , Kitao Toshio 
Published: April 2003

AbstractThe relationship between birefringence and polymer structure was studied both by theoretical and experimental analyses of a series of non‐crystalline polyurethanes (PU) with different side groups. The most probable steric structures of PUs were estimated by molecular mechanical calculation (MM2) of their oligomeric model compounds, and their birefringence was theoretically calculated on the structural data obtained. In addition, some of the PUs were practically synthesized and melt‐spun into thin fibers, which were drawn to a maximum draw ratio to measure the values of birefringence. The comparison of the measured and estimated values revealed that the present estimation method is effective for simulating the chain conformations and the birefringence of fully or partially extended polymer chains, which ought to be formed by drawing and melt‐flow of glassy materials. Of particular interest was that phenyl‐substituted PUs exhibit an unexpectedly larger birefringence than methyl‐substituted PUs. This fact was reasonably explained by the angular rotation of the highly polarizable phenyl group, which is energetically easily allowed and influences strongly the value of birefringence.
New catalytic systems for the fixation of carbon dioxide, 2. Synthesis of high molecular weight epichlorohydrin/carbon dioxide copolymer with rare earth phosphonates/triisobutyl‐aluminium systems
Authors: Shen Zhiquan , Chen Xianhai , Zhang Yifeng 
Published: April 2003

AbstractCopolymerization of carbon dioxide with epichlorohydrin to synthesize high molecular weight chlorine‐containing poly(carbonate‐ether) with RE(P204)3Al[CH2CH(CH3)2]3 (with RE = La, Eu, Gd, Dy, Ho, Nd, Er, Yb, Lu, Y; P204 = (RO)2POO, R = CH3(CH2)3CH(C2H5)CH2) as a catalyst was carried out for the first time. The most favorable conditions for the copolymerization were: CO2 aged Y(P204)3Al[CH2CH(CH3)2]3 as catalyst; mole ratio Al/Y = 8; reaction time 24 h; temperature 60–70°C; concentration [Y] = 3,31 · 10−2 mol/L; 1,4‐dioxane as solvent. The highest yield, intrinsic viscosity [η] and CO2 content of the copolymer obtained reached 3 945 g per mole of rare earth element, [η] = 1,49 dL/g and f(CO2) = 30 mol‐%, respectively. Results from differential thermal analysis/thermogravimetry showed that the copolymer has high thermal stability and decomposes at 320°C.
Synthesis and structure‐property relations of polymers for light emitting diodes based on isolated chromophore units
Authors: von Seggern Heinke , Schmidt‐Winkel Patrick , Zhang Chi , Schmidt Hans‐Werner 
Published: April 2003

AbstractNew fluorescent polymers for electroluminescent devices were synthesized and characterized. In order to obtain polymers for blue light emitting diodes (LEDs), two different structural concepts based on isolation of the active chromophore units within the polymer main chain were investigated. In the first approach non‐coplanar units were used to reduce the conjugation length in poly(arylenevinylene)s. In a second approach copolymers having isolated chromophore units in the polymers main chain were investigated. For this purpose, copolyesters containing isolated 1,2‐dinaphthylethene chromophore units were synthesized and characterized. The influence of the chemical structure on the photo‐ and electroluminescence is discussed. On the example of copolyester 2b, which shows bluegreen electroluminescence (λmax = 497 nm) in a LED configuration, it was demonstrated that these polyesters can be used as light emitting layer in electrooptical devices.
Thermal properties of poly(butylene isophthalate) and its copolyesters with poly(butylene adipate)
Authors: Righetti Maria Cristina , Pizzoli Maria , Munari Andrea 
Published: April 2003

AbstractThe thermal properties of uniformly random poly(butylene adipate/isophthalate) copolyesters of various composition and different molecular weight were investigated by means of differential scanning calorimetry. All copolymers were partially crystalline, and the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to pure homopolymers. The heat of fusion of 100% crystalline poly(butylene isophthalate), estimated by different methods, was found to fall within the range 22–25 kJ · mol−1. Completely amorphous samples, obtained by rapid quenching from the melt, showed a monotonic decrease of the glass transition temperature Tg and a monotonic increase of the heat capacity increment ΔCp with increasing butylene adipate content in the copolymers. The Tg‐composition dependence was found to be well fitted by the Couchman equation with no excess enthalpy correction.
Polymers by [3 + 2] cycloaddition, 6. Polyureas with novel structure elements
Authors: Maier Gerhard , Nuyken Oskar , Losert Klaus 
Published: April 2003

AbstractThe synthesis of new diisocyanates via “criss‐cross” cycloaddition between aromatic aldazines and diisocyanates as well as their conversion to polyureas is described. The new monomers and polymers contain the heterocyclic 1,3,5,7‐tetraazabicyclo[3.3.0]octane‐2,6‐dione system in their backbone. The polymers are characterized by spectroscopic techniques, DSC, thermogravimetry, and GPC. The influence of the new structure element on solubility, glass transition temperature, crystallinity, and thermal stability is discussed.
Effect of substituents on the radical copolymerization of ring‐substituted trans‐cinnamonitriles with vinyl monomers
Authors: Tanaka Hitoshi , Sakaguchi Masakazu , Kikukawa Yoshimasa , Sato Tsuneyuki , Ota Tadatoshi 
Published: April 2003

AbstractRadical copolymerizations of ring‐substituted trans‐cinnamonitriles with olefins such as styrene and acrylonitrile were studied at 60°C. The copolymerization parameters of cinnamonitriles (M1) in the copolymerizations with styrene (M2) were determined to be r1 = 0,01 to 0,30, r2 = 0,45 to 4,25, Q1 = 0,06 to 0,70, and e1 = −0,52 to 1,35. The relative reactivity, log(1/r2), showed a tendency to increase with increasing Hammett constant σ and was higher in conjugated cinnamonitriles than in less conjugated nitriles. For p‐substituted cinnamonitriles, ρ and γ values in the equation of log(1/r2) = ρ · σ + γ · ER were estimated to be 0,48 and 2,0, respectively, where ER is a resonance constant. The relative reactivity was also increased with increasing 13C NMR chemical shift of the olefinic β‐carbon of cinnamonitriles and decreasing polarity of the solvents used. In addition, the relative reactivity towards a poly(acrylonitrile) radical is higher in cinnamonitrile than in cinnamic esters. The structure of the radical generated by the attack of the 2‐methyl‐2‐propyl radical at the cinnamonitrile was examined by means of electron paramagnetic resonance (EPR) spectroscopy.
Syndiospecific polymerization of styrene by soluble alkoxytitanium catalysts
Authors: Kaminsky Walter , Lenk Stephan 
Published: April 2003

AbstractThe activity of Ti(OEt)4 (Et: C2H5) in combination with methylaluminoxane (MAO) in the syndiospecific polymerization of styrene was investigated concenrning the dependence on temperature, mole ratio of Al/Ti, concentrations of monomer, catalyst and MAO. Reaction products of Ti(OEt)4 and erythritol and sorbitol, respectively, were also used in the syndiospecific polymerization of styrene revealing that soluble Ti compounds are the active species.
Initiator efficiencies in 2,2′‐azoisobutyronitrile‐initiated free‐radical polymerizations of styrene
Authors: Buback Michael , Huckestein Brigitta , Kuchta Frank‐Dieter , Russell Gregory T. , Schmid Elisabeth 
Published: April 2003

AbstractResults are presented from a comprehensive study of the variation with conversion, temperature and pressure of the initiator efficiency of 2,2′‐azoisobutyronitrile in styrene bulk polymerizations. These efficiencies were measured using a new method involving the use of infra‐red spectroscopy to monitor directly the concentrations of various nitrile‐group containing species. Our results are shown to be satisfactorily fitted by a simple model based on the idea that initiation follows as a result of primary radical fragments diffusing away from each other. Closer microscopic inspection of the variations with temperature and pressure of the entire range of our initiator efficiencies implies the possibility that capture by monomer may also contribute as a mechanism of out‐of‐cage escape of primary radicals. Taking a wider view, the experimental method of this paper is shown to be of use for simultaneous determination of other important kinetic parameters: it yields rate coefficients of initiator decomposition, and also, when initiator decomposition is stimulated by pulse‐laser irradiation, the method is capable of delivering individual values of the rate coefficients for termination and propagation.
Radically initiated copolymers of styrene with 4‐vinylbenzylamine and its trifluoroacetamide derivative, 2. Preparation of latex particles bearing amino groups
Authors: Charreyre Marie‐Thérèse , Razafindrakoto Vanghi , Veron Laurent , Delair Thierry , Pichot Christian 
Published: April 2003

AbstractPolystyrene(PS)‐based latex particles bearing amino groups have been prepared using a two‐step process consisting of seeded copolymerization of a monomer mixture with styrene (S) and either 4‐vinylbenzylamine (VBA) or its trifluoroacetamide derivative (VBAF) in the presence of monodisperse PS latex. Poor colloidal properties and bad chemical stability were found in the case of latexes obtained with VBA. Better results were obtained with VBAF, but conversion was not completed. Surface characterization of the final latexes by 1H NMR, XPS and colorimetric titration offer some insight into the location of the VBAF monomer units within the particles.