bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transient electric birefringence of poly(sodium p‐styrenesulfonate) solutions at very low field strengths
Authors: Oppermann Wilhelm 
Published: April 2003

AbstractMeasurements of the electric birefringence were performed on dilute, aqueous solutions of a poly(sodium p‐styrenesulfonate). The concentrations were chosen to be somewhat below and above the critical concentration (c*) where, on grounds of theoretical considerations, the rod‐to‐coil transition is expected to occur. The measurements were conducted at very low field strengths E, viz. in the order of E = 104 V · m‐1, using d. c. pulses as well as 30 kHz a. c. pulses. When an a. c. field is applied, birefringence is always negative and shows a monotonous rise and decay. The same holds true for a d. c. field provided the concentration of the polymer is below c*. However, when a d. c. pulse of very low field strength is applied to a solution the concentration of which is above the critical concentration, some strange features occur: At the beginning of the pulse the birefringence is negative, but then it reverses its sign and approaches a positive steady‐state value. After cessation of the pulse the birefringence passes through a maximum before decaying to zero. The whole birefringence curve looks like a superposition of two signals with opposite signs. These features disappear at higher field strengths. On the basis of an analysis of the field‐strength dependence, it is tentatively concluded that other mechanisms besides the rotational orientation of the molecules contribute to birefringence. One such process could be migration of the macroions giving rise to flow birefringence.
Studies on planar orientation and trap depth of poly(ethylene terephthalate) film
Authors: Zhou Yigin , Zhang Jixiang , Zhang Xingyuan , Yang Jengtsong 
Published: April 2003

AbstractPoly(ethylene terephthalate) films with various degrees of planar orientation of the macromolecules were prepared by uniaxial and biaxial stretching. Fourier transform infrared spectra indicate that the content of gauche conformation decreases linearly with the degree of planar orientation, while the content of trans conformation increases linearly. A linear relationship between the trap depth calculated from Thermally Stimulated Current spectra and the degree of planar orientation was observed.
Viscoelastic properties of mixtures of polystyrene with low‐molecular‐weight poly[oxy(2,6‐dimethyl‐1,4‐phenylene)]
Authors: de Araujo Marco Aurelio , Stadler Reimund 
Published: April 2003

AbstractA series of poly[oxy(2,6‐dimethyl‐1,4‐phenylene)]s (PPE) (trivial names: polyphenylenether, polyoxyxylene, polyphenyleneoxide) with narrow molecular weight distribution were prepared by polymerization of 4‐bromo‐2,6‐dimethylphenol and subsequent fractionation. The molecular weight dependence of the glass transition temperature obeys the Fox‐Flory equation. Polystyrene (PS)/PPE blends (PS: number‐average molecular weight M̄n = 144 000, ratio of weight‐ to number‐average molecular weight M̄w/M̄n = 1,05) were prepared using PPE samples with molecular weights below the entanglement spacing of PPE, in order to obtain information about the influence of specific interactions on the linear viscoelastic properties in the plateau and terminal region. The iso‐free‐volume state turned out to be the most appropriate reference state to compare samples of various compositions. Low‐molecular‐weight PPE essentially acts as a solvent for polystyrene. The concentration dependence of the zero‐shear viscosity η0 is proportional to ϕ3,6PS, ϕPS being the volume fraction of PS, and the temperature dependence of the logarithmic shift factor log aT indicates that interactions, which are responsible for the thermodynamic miscibility in this system, do not alter the linear viscoelastic properties of PS. The concentration dependence of the plateau modulus (G(0)N ∝ ϕ1,2 for PS/PPE‐1500) blends is explained by an additional small elastic contribution of the short PPE chains to the plateau modulus at higher frequencies.
Zum Mechanismus der oxidativen Kupplung von Phenolen
Authors: Bartmann Martin , Kowalczik Udo 
Published: April 2003

AbstractIn order to make a decision between the quinone acetal equilibration/quinone acetal rearrangement and the so far discussed SET mechanism for the oxidative coupling of 2,6‐xylenol to poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) the polymerization was carried out in the presence of 5‐(2,6‐dimethylphenoxy)‐2‐methoxy‐1,3‐xylene (1) (the methylated dimer) or α‐methyl‐ω‐phenoxypoly(oxy‐1,4‐phenylene) [O‐methylated poly(phenylene ether)] (2). GC and GPC studies indicated that neither 1 nor 2 are incorporated into the polymer. These observations exclude the SET‐mechanism according to Scheme 4.
Thermal analysis of poly(butylene terephthalate) for heat capacity, rigid‐amorphous content, and transition behavior
Authors: Cheng Stephen Z. D. , Pan Robert , Wunderlich Bernhard 
Published: April 2003

AbstractThermal analysis was performed on poly(butylene terephthalate), PBT, between 210 and 560 K. By combination of experimental heat capacities with computations with an approximate frequency spectrum of 65 group and 19 skeletal vibrations, preliminary recommended ATHAS (1988) heat capacities are proposed for the solid state from 0 to 600 K. The Tarasov parameters used for the computation of the skeletal vibrations were θ1 = 542 K and θ3 = 80 K for crystalline PBT and θ3 = 40 K for amorphous PBT. The glass transition temperature of amorphous PBT was found on efficiently quenched samples to be 248 K, much lower than for semicrystalline PBT where a 310–325 K glass transition temperature is typical. The increase in heat capacity calculated for 100% amorphous samples is 107 J/(K · mol) at 248 K and 77 J/(K · mol) at 320 K. The equilibrium melting temperature is estimated to be 518 K. The unique existence of rigid‐amorphous fractions of the semicrystalline polymers is discussed with quantitative data for samples crystallized from the glass and from the melt between 275 and 490 K. The rigidamorphous fraction varies between above 0,9 for cold‐crystallized samples to 0,3 for samples crystallized at 490 K. The crystallinity varied from below 0,1 to 0,5. The crystallinity could be separated into four parts, melting at high, medium, and low temperatures, and a part crystallized on cooling after isothermal crystallization. The sequence of crystallization of differently melting crystals was established.
Crosslinking reactions in the molten state: Interpolymeric condensation reactions
Authors: Lambla Morand , Druz Jacques , Satyanarayana Nallani 
Published: April 2003

AbstractChemical reactions leading to crosslinking were followed by rheometrical studies during curing at different temperatures and compositions of compatible species. The condensation reactions between two copolymers of styrene and maleic anhydride, and several α,ω‐dihydroxyoligostyrenes, lead to an experimental variation of the elastic modulus (G′)t. A kinetic scheme is proposed, selecting the most reliable reactions, which describes the experimental behaviour adequately. According to this scheme, the rate constants of interpolymeric condensation reactions were evaluated. It appears that the values obtained for grafting and crosslinking are quite the same. They depend mainly, in absence of a catalyst, on the molecular weight of the oligomer and on the local viscosity, which is a function of composition. In presence of a catalyst, there is a large increase of the constant, indicating that the chemical step is dominating the diffusion process.
Liquid‐crystalline aromatic polyesters with phenylalkyl side chains
Authors: Brügging Wilhelm , Kampschulte Uwe , Schmidt Hans‐Werner , Heitz Walter 
Published: April 2003

AbstractThermotropic liquid‐crystalline poly(1,4‐phenylene terephthalate)s with phenylalkyl side chains were synthesized. The influence of this novel type of substituent on the thermal properties and solubility behavior is discussed. In common solvents soluble, liquid‐crystalline polyesters with low transition temperatures were obtained when the phenylalkyl substituent was introduced in combination with a bulky substituent or when both phenyl rings were substituted with phenylalkyl side chains. When poly(1,4‐phenylene terephthalate) is only monosubstituted with a phenylalkyl substituent in the 1,4‐phenylene unit, the polyesters have melting temperatures above 310°C and are only soluble in solvents such as p‐chlorophenol.
Funktionalisierung heterogen‐vernetzter polyvinylalkohol‐gele
Authors: Schott Herbert , Bretzger Waltraud 
Published: April 2003

AbstractCross‐linked poly(vinyl alcohol) beads were functionalized by derivatization of their hydroxyl groups with succinic acid anhydride, 1,6‐hexamethylene diisocyanate, 3‐aminopropyltriethoxysilane, 2‐chlorophenylbis(1,2,4‐triazol‐4‐yl) phosphate and different sulfhydryl reagents. The resulting 8 gels carry isocyanato, carboxyl, amino, phosphate and mercapto residues in concentrations of 1 to 3 mmol per gram of polymer. The derivatives obtained from the starting poly(vinyl alcohol) beads are mechanically stable, resistent to hydrolysis in the pH range between 1 and 14 and stable up to 100°C. The functionalized, cross‐linked polymer beads, applicable in aqueous systems as well as in organic solvents, should find a wide application in chromatography, as supports in the preparative solid phase synthesis and as basic carriers for polymeric reagents.
Studies on functional diene oligomers with an amino end group, 3. Synthesis of oligoisoprenes containing a secondary amino end group
Authors: Nagasaki Yukio , Higuchi Akinori , Goan Hiroki , Yoshino Norio , Tsuruta Teiji 
Published: April 2003

AbstractLithium monoalkylamide, in the presence of monoalkylamine, was found to initiate the polymerization of isoprene to form oligoisoprenes. The molecular weight distribution of products formed in the lithium isobutylamide initiated isoprene oligomerization strongly depends on the initial mole ratio [Isoprene]0/[Amine]0/[Amide]0; with an initial mole ratio of 60/1/8, oligomers with a number‐average molecular weight of about 800 were obtained. The presence of N,N,N′,N′‐tetramethylethylenediamine in the reaction system was found to be effective for the selective formation of secondary amino‐ended oligoisoprenes.
Synthesis and transport properties of 2‐ethylhexylpoly(trimethylene phosphate) – A synthetic analogue of natural teichoic acids
Authors: Wódzki Romuald , Kałużyński Krzysztof 
Published: April 2003

AbstractThe paper deals with modelling the transport of magnesium and calcium ions in the cell wall of Gram‐positive bacteria. The model compound, i. e. 2‐ethylhexylpoly(trimethylene phosphate)Structure‐based IUPAC nomenclature: α‐2‐Ethylhexyl‐ω‐hydroxypoly[oxy(hydroxyphosphonol)oxytrimethylene].
(EPTP), was synthesized in order to mimic the transport mediated by lipoteichoic acids. It was found that EPTP can transport preferentially magnesium ions in an ion exchange‐diffusion process with the counter‐transport of hydrogen ions.
Poly{[(Chloro‐2 éathyl)‐4 phéanyl]‐1 éathylène}: Synthèse, caractérisations, dégradation thermique et modifications chimiques
Authors: Boinon Bernard , Benayad Belabbas , Monthéard Jean‐Pierre 
Published: April 2003

AbstractPoly{1‐[4‐(2‐chloroethyl)phenyl]ethylene} (3) was synthesized by bulk polymerization of 4‐(2‐chloroethyl)styrene (6) in two steps from commercial products. The polymer was characterized by means of GPC (weight‐average molecular weight M̄w = 85 000 and number‐average molecular weight M̄n = 63 500), 1H NMR and 13C NMR spectroscopy. The first stage of thermal degradation begins at 290°C and ends at about 410°C. The overall activation energy was calculated to be 43 kcal · mol−1 (180 kJ · mol−1). The solid residue was crosslinked and insoluble. The volatile products, identified by gas chromatography‐mass spectroscopy (GC‐MS), were chiefly hydrogen chloride, dichloromethane and monomer. In a strongly basic medium, nucleophilic substitution of chlorine was achieved without elimination.
New functional poly(ethylene oxide)s: Synthesis and application
Authors: Kazanskii Konstantin S. , Ptitsyna Nelli V. 
Published: April 2003

AbstractPrinciples and new approaches to the synthesis of functional poly(ethylene oxide)s (PEO) are considered. It could be shown that quantitative functionalization during initiation or deactivation of living polymers cannot be reached independently of the demands to achieve a desired molecular weight of the polymer. This is illustrated by the data of the synthesis of dinitrophenyl derivatives of PEO (molecular weights from 3 · 103 to about 105) which are synthetic immunogenes. Vinyl ether macromonomers of PEO with molecular weights in the range of 750–3000 were also synthesized by anionic polymerization of ethylene oxide with trimethylamine as initiator. These macromonomers were used for effective grafting of PEO onto a solid surface, grafted PEO being able to selectively binding alkali salts from the solution. Values of binding constants were evaluated.
Functionalization of polysiloxanes by esterification of pendant epoxy groups: Cross‐linkable liquid polymers containing photo‐dimerizable ester units
Authors: Hajaiej Adel , Coqueret Xavier , Lablache‐Combier Alain , Loucheux Claude 
Published: April 2003

AbstractPhoto‐dimerizable carboxylic acids were grafted onto linear silicone copolymers by amine catalyzed esterification of pendant epoxypropyl groups. The epoxy‐carboxy reaction was found to surpass in experimental simplicity, chemical selectivity and reproducibility, the modification methods involving the hydrosilylation of functionalized olefins. Liquid, photo‐crosslinkable polymers (8a and 8b) were finally obtained after acetylation of the hydroxy‐ester groups resulting from the addition of functional carboxylic acids, and no unwanted side‐reaction was detected. The practical sensitivity of photo‐reactive polysiloxanes of various average molecular weights containing 5–17 mol‐% of sensitive units, was measured by photoresist type insolubilization tests. The ultimate acetylation reaction was shown to have little or no influence on the dimerization process of 2‐cyano‐5‐phenyl‐2,4‐pentadienoic derivatives (8a), but to increase the rate of disappearance of trans‐cinnamic groups (in 8b) submitted to UV light irradiation.
Stereochemistry of anionic oligomerization, 22. Effects of chain length and stereochemistry on the kinetics of addition of 1,1‐diphenylethylene to oligomeric models of living poly(2‐vinylpyridine)lithium
Authors: Helary Gerard , Fontanille Michel , Khan Ishrat M. , Hogen‐Esch Thieo E. 
Published: April 2003

AbstractRate constants and equilibrium constants were determined for the addition of 1,1‐diphenylethylene to living trimers of 2‐vinylpyridine in THF having either a meso or a racemic diad adjacent to the carbanion center. The racemic isomer was shown to be slightly more reactive (≈40%) compared with the meso isomer and slightly less than the corresponding dimer. The living dimer of 2‐vinylpyridine in turn is slightly more reactive than the meso trimer, but is five times less reactive compared to the lithio salt of 2‐ethylpyridine. The changes in equilibrium constant were quite dramatic, the constant for lithio‐2‐ethylpyridine being about 100–200 times larger than for the living oligomers and about 2 600 times larger than that of the living polymer.
Gas‐phase copolymerization of ethylene with propene and with 1‐butene using supported chromium‐ and titanium‐containing catalysts
Authors: Zakharov Vladimir A. , Yechevskaya Lyudmila G. , Bukatov Gennadii D. 
Published: April 2003

AbstractThe gas‐phase copolymerization of ethylene with propene and 1‐butene using supported Cr‐containing catalysts of different composition and supported Ti‐Mg catalysts was studied. Comonomer reactivity ratios for 8 different catalyst systems were determined. A lower regiospecificity of the chromium oxide catalyst as compared with the titanium‐magnesium catalyst was observed, according to 13C NMR measurements.
Small‐angle X‐ray diffraction study of the monoclinic modification of poly(3,3‐dimethyloxetane)
Authors: Pérez Ernesto , Bello Antonio , Fatou José G. , Rausell‐Colom José A. 
Published: April 2003

AbstractThe long spacings of several samples of poly(3,3‐dimethyloxetane) (PDMO) were determined by small‐angle X‐ray diffraction as a function of molecular weight and crystallization temperature, in the interval where only the monoclinic modification is produced. The equilibrium melting temperature and the basal interfacial free energy of the mature crystals were determined from the correlation between long spacings and melting temperatures. Finally, an estimation of the critical sizes of the nuclei was made from nucleation theory, and the results were compared with the actual sizes of the crystallites, assuming a two‐phase model. Our results show that both the nuclei and the mature crystals have rather small sizes, which is attributed to the high under‐coolings involved in the crystallization of PDMO.
Polymerisation durch [3+2]‐cycloaddition, 2. Reaktionen von hexafluoracetonazin mit substituierten diolefinen
Authors: Nuyken Oskar , Maier Gerhard , Burger Klaus 
Published: April 2003

AbstractHexafluoroacetone azine reacts with esters of 1,6‐heptadien‐4‐ol to form polymers 1 containing 4,4,8,8‐tetrakis(trifluoromethyl)‐1,5‐diazabicyclo[3.3.0]octan‐2,6‐diyl groups linked with trimethylene chains with acyloxy side groups. Due to these ester functions the polymers are completely soluble in common solvents. DSC measurements proved these polymers to be partly crystalline.
Polymere aminoschutzgruppen auf basis von tert‐butoxycarbonyl‐ und benzyloxycarbonylfunktionen enthaltenden polymethacrylamiden
Authors: Rehse Henning , Ritter Helmut 
Published: April 2003

AbstractThe synthesis of tert‐butoxycarbonyl‐ and benzyloxycarbonyl‐modified monomers was performed by the addition of p‐chlorophenyl isocyanate or benzyl isocyanate to the free OH groups of N‐(2‐hydroxy‐2‐methylpropyl)methacrylamide (1), N‐(2‐hydroxy‐2‐methylpropyl)‐6‐methacrylamidohexanamide (2) and N‐β‐hydroxyphenethylmethacrylamide (3). The monomers were homopolymerized and copolymerized with MMA. The kinetics of acidic‐induced amine cleavage from the new amino‐protecting groups was followed by NMR spectroscopy and it became evident that the polymers are suitable amino‐protecting groups. Ca2+ ions enhance the rate of amine cleavage considerably. Neighboring group effects, the influence of comonomers and spacer groups on the reactivity of the urethane groups are also discussed.
Activation of propene polymerization by hydrogen for improved MgCl2‐supported Ziegler‐Natta catalysts
Authors: Spitz Roger , Masson Patrick , Bobichon Charles , Guyot Alain 
Published: April 2003

AbstractAs in the case of the third generation MgCl2‐supported stereospecific catalysts, characterized by the use of aromatic esters as internal and external Lewis bases, the new improved family of catalysts, containing an aromatic diester as internal Lewis base and a trialkoxyphenylsilane as external Lewis base, was found to be sensitive to hydrogen. A very strong activation effect, followed by deactivation, was observed upon introduction of small amounts of hydrogen. In the present case the effect is reversible, unless rather high hydrogen pressure (2 bar) is used. The activation effect was observed with any of the cocatalysts and even in the absence of an external Lewis base. The effect is reduced or even suppressed if enough ethylene is used in the copolymerization with propene. Owing to the competition between ethylene and hydrogen for the activation, it is assumed that the step sensitive to hydrogen is that of initiation rather than propagation.
Emulsion polymerization of butadiene, 1. The effects of initiator and emulsifier concentration
Authors: Weerts Pierre A. , van der Loos Jos L. M. , German Anton L. 
Published: April 2003

AbstractThe kinetics of the emulsion polymerization of butadiene was investigated using Dresinate 214 as emulsifier and three dissociative initiators, viz. potassium peroxodisulfate, 4,4′‐azobis‐(4‐cyanopentanoic acid) and 2,2′‐azoisobutyronitrile. All experiments were conducted in the presence of a thiol as chain transfer agent, as usual in diene‐polymerizations. The polymerization rate in interval II, Rpol, was found to be highly insensitive to changes in the initiator concentration (Rpol ∝ [I]0,08). Primary radicals are generated in large abundance in interval I as compared with the final particle number, indicating that the initiator efficiency with regard to particle nucleation is very low. The development of particle number as a function of conversion at several emulsifier concentrations shows that limited coagulation is occurring in the present system. Rpol depends on the emulsifier concentration with an exponent of 0,61, while the final particle number after cessation of coagulation depends on the emulsifier concentration to the 1,6th power. As a consequence the average number of radicals per particle must be a function of particle size, because the monomer concentration in the latex particles is approximately constant in interval II. A certain analogy in behaviour between the emulsion polymerization of various polar monomers, kinetically dominated by radical desorption, and the emulsion polymerization of butadiene, suggests that similar events determine the kinetic course in the present system.
Emulsion copolymerization of acrylonitrile and butyl acrylate, 10. Effect of 1,1‐diphenyl‐2‐picrylhydrazyl on the polymerization process
Authors: Capek Ignác 
Published: April 2003

AbstractThe emulsion copolymerization of acrylonitrile with butyl acrylate, initiated by ammonium persulfate in the presence of disodium dodecylphenoxybenzenedisulfonate and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH), was kinetically investigated at 70°C by conventional GLC and gravimetric methods. The copolymerization under batch conditions was conducted to both low and high conversion. In the presence of a small amount of DPPH the molecular weight of the copolymer is little decreased when compared with that prepared without DPPH. In addition, the rate of copolymerization unexpectedly decreases with increasing emulsifier concentration. The radical scavenger was found to decrease the average particle size. In the interval 2 the rate of polymerization is approximately proportional to the 0,35th power of the emulsifier concentration and to the 0,5th power of the initiator concentration (without DPPH). The dependence of the rate of polymerization on the final particle number and of the final particle number on the emulsifier concentration also deviates from the simple micellar theory predictions. The results can be explained by a coagulative nucleation mechanism.
Polymer diffusion and mobility in mixtures of polystyrene and polymethylstyrenes
Authors: Lang Sibylle , Sillescu Hans 
Published: April 2003

AbstractTracer diffusion coefficients D* of both components were measured in mixtures of polystyrene with poly(o‐methylstyrene), poly(p‐methylstyrene), and a commercially available random copolymer of p‐ and m‐methylstyrene, respectively. D* values were determined by applying the holographic grating technique where between 5 and 10% of the respective polymer component was labelled at the end group with a photoreactive dye. For molecular weights between 15 000 and 37 000 and temperatures between 175 and 200°C, the D* values differed relatively slightly when compared at equal molecular weight and equal temperature distance T–Tg from the glass transition temperature Tg. The differences were compared with those of monomeric friction coefficients obtained from dynamic mechanical experiments.