bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relative importance of side reactions in the RLi‐acrylonitrile — dimethylformamide system
Authors: Denisov Viktor M. , Yakimansky Alexander V. , Novoselova Anna V. , Erussalimsky Boris L. 
Published: April 2003

AbstractThe probability of interaction of anionically growing poly(acrylonitrile) chains with dimethyl‐formamide (DMF) in the acrylonitrile (AN)‐RLi‐DMF system was investigated by means of NMR data, poly(acrylonitrile) synthetized with various ROLi initiators does not contain traces of DMF fragments. Quantum chemical calculations were carried out taking CH3CH2CH(CN)Li as a model compound and simulating the anionic active site of AN. The results obtained show that the interaction of this compound with AN is highly preferred (by 100 kJ/mol) to that with DMF. Qualitatively similar results are related to the butyllithium(BuLi)‐AN and BuLi‐DMF systems. However, the reaction between BuLi and DMF is exothermic (in contrast to that between the active site of the model compound with DMF). This fact is in agreement with the effective addition of BuLi to DMF in the absence of any competing compound.
Formation and degradation of 1,4‐polybutadiene via metathesis: new results concerning cyclic oligomers
Authors: Thorn‐Csányi Emma , Hammer Jens , Pflug Kai P. , Zilles J. Ulrich 
Published: April 2003

AbstractThe ring‐opening metathesis polymerization (ROMP) of cyclic oligomers of butadiene (c,c‐1,5‐cyclooctadiene — COD —, t,t,t‐1,5,9‐cyclododecatriene — CDT —), the acyclic diene metathesis (ADMET) of 1,5‐hexadiene and the intramolecular metathesis degradation of 1,4‐polybutadiene (1,4‐BR) were studied using stable tungsten and molybdenum carbene complexes as well as conventional metathesis catalysts. The determination of cyclic oligomers up to rings containing eight butadiene units shows, compared to the literature, different results regarding the distribution, concentration and cis/trans ratio. Kinetic studies of the ROMP of COD and the intramolecular metathesis of 1,4‐BR allow to explain the discrepancy. The ROMP product spectrum for the cyclobutene system known and accepted until now in the literature as ring‐chain equilibrium is controlled kinetically and far apart from thermodynamic equilibrium according to our results.
Block copolymers with bipyridine containing segments: Synthesis and self‐organization by Cu(I) complexation
Authors: Eisenbach Claus D. , Göldel Andreas , Terskan‐Reinold Monika , Schubert Ulrich S. 
Published: April 2003

AbstractThe synthesis and properties of segmented ABA triblock and (AB)n multiblock copolymer systems with 6,6′‐disubstituted 2,2′‐bipyridine (bpy) building blocks B and poly(oxytetramethylene) soft segments A are described. The access to the disubstituted bipyridines in large scale quantities was achieved by modification of conventional synthetic routes. In the presence of copper(I) ions these polymers formed mononuclear [Cu(I)(bpy)2] complexes in solution through self‐assembly. The complexed copolymers were microphase separated systems in bulk with nano to mesoscopic superstructures consisting of copper‐bpy complex aggregates in a polyether matrix. The thermal, mechanical and elastomer properties of the block copolymers varied with composition.
New copolyamides based on adipic acid, aliphatic diamines and amino acids: Synthesis, characterization and biodegradability, 5
Authors: Arvanitoyannis Ioannis , Nikolaou Eleftherios , Yamamoto Noboru 
Published: April 2003

AbstractNovel series of biodegradable copolyamides were synthesized via melt copolymerization. The statistical copolymides were produced by reaction of the salt of adipic acid (AA) and bis(para‐aminocyclohexyl)methane (PACM) or isophoronediamine (IPD)/α‐amino acids at 250°C. Elemental analyses, density, viscosity, differential thermal analysis (DTA) and gelpermeation chromatography (GPC) measurements and FT‐IR spectroscopy were employed for the characterization of these copolyamides. The semicrystalline (AA/PACM/α‐amino acids) or amorphous (AA/IPD/α‐amino acids) nature of these copolyamides was shown with DTA and wide angle X‐ray diffraction patterns. Several methods were used in order to investigate and assess their biodegradability such as alkaline hydrolysis (10% w/v NaOH, 80°C), burial in soil (microbial and bacterial attack) and enzymatic hydrolysis (α‐trypsin and α‐chymotrypsin). The degradation of the copolyamides was evaluated with the aid of GPC and DTA measurements and correlated to the α‐amino acid content. These copolyamides could eventually find applications in the field of food packaging and agriculture (disposable plastics) and medicine (sutures).
NMR investigations on a liquid‐crystalline side‐chain siloxane polymer with a wide biphasic region
Authors: Hempel Günter , Hänsge Heiko , Metzner Bernd , Krücke Bernd 
Published: April 2003

AbstractA polysiloxane bearing two different kinds of side chains has been studied by nuclear magnetic resonance and relaxation investigations. Both side chains contain the same mesogenic core but differ in their connection to the main chain: one of them is bound directly to the backbone, the other is linked to it via a (CH2)3 spacer. In this sample, the isotropic and mesomorphic phases coexist over a relatively wide range of temperatures. We have tried to explain this phenomenon by microphase separation. For the sA –sB transition a similar biphasic behaviour could not be observed with our methods. The order parameter has been estimated selectively for carbons in different parts of the side chain (spacer, wing group, mesogenic core). The behaviour of the order parameter in the mesomorphic regions of the biphase was observed, and a possible explanation is given.
Characteristics of permeation and separation for aqueous ethanol solutions through methyl methacrylate‐dimethylsiloxane graft copolymer membranes
Authors: Miyata Takashi , Takagi Toru , Kadota Takeshi , Uragami Tadashi 
Published: April 2003

AbstractPoly(methyl methacrylate) with oligodimethylsiloxane grafts (MMA‐g‐DMS) was prepared by copolymerization of a dimethylsiloxane (DMS) macromonomer with methyl methacrylate (MMA). Two glass transition temperatures (Tg) were observed at about 120°C and − 127°C and in all graft copolymer membranes. Transmission electron micrographs demonstrate that the MMA‐g‐DMS membranes show microphase separation. When an aqueous solution of 10 wt.‐% ethanol was applied to permeations through the MMA‐g‐DMS membranes by pervaporation, the ethanol concentration in the permeate and the permeation rate increased drastically with the DMS content in the copolymer. Especially, while at a DMS content of less than 40 mol‐% preferentially water permeates from an aqueous solution of 10 wt.‐% ethanol, the membranes with more than about 40 mol‐% of DMS show ethanol‐permselectivity. The relationship between the microphase‐separated structures and the permeation characteristics for an aqueous ethanol solution is discussed.
A new temperature‐ and pH‐responsive copolymer for possible use in protein conjugation
Authors: Chen Guohua , Hoffman Allan S. 
Published: April 2003

AbstractThe temperature‐ and pH‐sensitive copolymers of N‐isopropylacrylamide (NIPAAm) with 4‐pentenoic acid (PAc) were synthesized and the monomer reactivity ratios were estimated. The effects of polymer composition, pH and ionic strength of the aqueous solution on the lower critical solution temperature (LCST) of the copolymers were investigated. It was found that the LCSTs of these unusual copolymers can be either lowered or raised compared to the LCST of poly(N‐isopropylacrylamide) by changing the pH.
Relaxation of holographic gratings in liquid‐crystalline side chain polymers with azo chromophores
Authors: Bieringer Thomas , Wuttke Roland , Haarer Dietrich , Geßner Uwe , Rübner Joachim 
Published: April 2003

AbstractThe relaxation of holographic phase gratings was examined to obtain some information about the involved photochemically induced changes. The studies were performed with statistical liquid‐crystalline side group copolymers having different concentrations of the azobenzene dye. The formation of mesophases, which normally exist in the thermodynamic equilibrium, was prevented during the sample preparation by quenching the polymer films. Two relaxation processes were found in this glassy state of the polymers. The faster one could be described by a dispersive stretched exponential function and was attributed to relaxation processes which are related to the amorphous phase of the sample, while the slower one, corresponding to a single exponential process, correlates with the formation of light‐induced liquid‐crystalline microstructures. The latter are believed to be the main cause for the modulation of the refractive index.
On the anionic polymerization of dialkylaminoisoprenes, 3. A nuclear magnetic resonance study of the structure of oligo[5‐(N,N‐diisopropylamino)isoprenyllithium]
Authors: Petzhold Cesar , Kolshorn Heinz , Stadler Reimund 
Published: April 2003

AbstractThe structure of oligo[(5‐N,N‐diisopropylamino)isoprenyllithium] (number‐average degree of polymerization Pn = 1‐2) prepared by reaction of alkyllithium with 5‐(N,N‐diisopropylamino)‐isopreneSystem. name: N,N‐diisopropyl‐2‐vinylallylamine.
in nonpolar (benzene) and polar (tetrahydrofuran) solvents has been studied by 1H and 13C NMR spectroscopy. In tetrahydrofuran, as expected, the negative charge at the terminal chain unit is more delocalized than in benzene and, consequently, the carbon‐lithium bond has a more ionic character. In both solvents the living chain end shows a cisoid‐4, 1‐structure. No cistrans isomerization could be detected. This independence of the carbanion structure of the solvent polarity is explained by the complexation of the Li+ counter ion to the amino group of the terminal monomer unit and by the bulkiness of the isopropyl side groups, which hinder isomerization and favour the cisoid conformation of the living chain end.
Regio‐ and stereospecificity in propene polymerization with MgCl2‐supported Ziegler‐Natta catalysts: effects of hydrogen and the external donor
Authors: Chadwick John C. , Van Kessel Gerard M. M. , Sudmeijer Olof 
Published: April 2003

AbstractInvestigation of the effects of hydrogen and different external donors on the stereoregularity and chain‐end distribution of polypropylene prepared using MgCl2/TiCl4/phthalate ester‐AlEt3‐alkoxysilane catalyst systems has not only confirmed the importance of regiospecificity in relation to hydrogen activation but has also indicated a significant effect of stereospecificity. Alkoxysilanes giving high isospecificity also give high molecular weight polypropylene. Polymer stereoregularity also increases with increasing hydrogen concentration in polymerization. These effects indicate that not only regioirregular but also stereoiregular insertion slows down chain propagation. In each case the probability of chain transfer with hydrogen is higher than that following a stereoregular insertion, and in each case chain transfer with hydrogen leads to the regeneration of isospecific propagation.
Continuous polymer fractionation of poly(methyl vinyl ether) and a new Kuhn‐Mark‐Houwink relation
Authors: Petri Hans‐Michael , Stammer Andreas , Wolf B. A. 
Published: April 2003

AbstractContinuous polymer fractionation (CPF) — a new large‐scale method — was applied to the technical poly(methyl vinyl ether) (PVME) using toluence as solvent and petroleum ether as non‐solvent. Two different devices served as fractionation apparatus, namely a column packed with glass beads and a set of mixer‐settler extractors. Advantages and draw‐backs of these devices are discussed. The experiments yielded numerous PVME fractions, varying in molar mass from 22 to 87 kg/mol and in molecular non‐uniformity U = (M¯w/M̄n) – 1 from 0,25 to 0,41 according to gel‐permeation chromatography as compared with ca. U = 1,30 for the starting material. The following Kuhn‐Mark‐Houwink relation was established for PVME in ethyl methyl ketone at 30°C: [η]/(mL/g) = 2,6 . 10−3M̄0,86.
The effect of side groups on the dielectric relaxation of poly(methylhydrogensiloxane)
Authors: Goodwin Andy A. , Beevers Martin S. 
Published: April 2003

AbstractThe α‐relaxation of a linear poly(methylhydrogensiloxane) has been investigated as a function of temperature and frequency using dielectric relaxation spectroscopy. Replacement of the hydrogen with a hexyl group increased the temperature and broadness of the α‐process, and this is interpreted in terms of a slowing of the motions of the Si—O dipoles and plasticisation of the siloxane chain by the side groups. Replacement of the hydrogen with a mesogenic group produced a side‐chain liquid crystal which exhibited dielectric relaxation behaviour characteristic of the glass and liquid crystalline states.
2‐Perbromomethyl‐2‐oxazoline: a novel trifunctional initiator for the ring‐opening polymerization of 2‐methyl‐2‐oxazoline
Authors: Bera Tushar Kanti , Sivaram Swaminathan 
Published: April 2003

AbstractPolymerization of 2‐methyl‐2‐oxazoline was carried out using a trifunctional initiator, 2‐perbromomethyl‐2‐oxazoline. The degree of polymerization (DP) of the resulting polymer was very close to the feed mole ratio of the monomer to initiator. The number‐average molecular weight M̄n increased linearly with conversion, indicating the living nature of the propagating chain end. 1H NMR and end‐group analyses results are consistent with the proposal that the polymer possesses a star‐shaped structure.
Data evaluation for unified multi‐detector size exclusion chromatography — molar mass, viscosity and radius of gyration distributions
Authors: Reed Wayne F. 
Published: April 2003

AbstractThe output of a size exclusion chromatography (SEC) system was connected to a single capillary viscometer, a multi‐angle laser light scattering detector (MALLS) and a refractive index detector (RI). This provides absolute distributions of molar mass, radius of gyration and reduced viscosity, which are valuable both for practical polymer characterization and as tests of physical polymer theories. The instrument interfacing is described, along with the method of data analysis. A quantitative investigation of systematic and random sources of error and their influence on polymer characterization is made. An experimental example using a biopolyelectrolyte (hyaluronate), including complete error analysis, is presented, along with other data. Although the emphasis here is on aqueous SEC, most of the principles should carry over to organic phase SEC. A simultaneous, in‐line comparison of a low‐angle laser light scattering (LALLS) detector and MALLS detectors was also made. The dangers of ‘universal calibration’ for hydrosoluble polymers are also illustrated.
A triple‐bonds‐containing poly(ether/ester): synthesis, characterization and cross‐polymerization
Authors: Denchev Zlatan , Dudevski Ivo , Petrova Jordanka , Fakirov Stoyko 
Published: April 2003

AbstractA segmented poly(ether/ester) multiblock copolymer containing acetylene groups within the hard segment was synthesized starting from poly(ethylene glycol) with a number‐average molecular weight M̄n = 1000, 2‐butyne‐1, 4‐diol and terephthaloyl dichloride. Thermal and spectroscopic data suggest a blocky structure of the copolymer prepared. Nuclear magnetic resonance spectroscopy shows an average degree of polymerization of the hard segments of about 6. By heating in the presence or absence of a catalyst, the monoacetylene units in the hard segments are cross‐polymerized below and above their melting temperature. The crosspolymerized material reveals a maximum gel fraction of 93,5 wt.‐%, does not crystallize and shows reversible deformability in contrast to the starting polymer. In accordance with previous reports it is concluded that cross‐polymerization is possible only in a polymer distinguished by some degree of chain ordering.
Morphology, phase transitions and viscoelastic properties of poly(oxybisdimethylsilylene). A mesophase in a silicon analogue of a polyether
Authors: Pluta Miroslaw , Pakula Tadeusz , Kryszewski Marian , Kurjata Jan , Chojnowski Julian 
Published: April 2003

AbstractPoly(oxybisdimethylsilylene) (POBDMS)System. name: poly[oxy(tetramethyldisilane‐1,2‐diyl)].
has been studied by differential scanning calorimetry, polarizing microscopy, wide‐angle X‐ray scattering and dynamic mechanical measurements. The polymer shows a weakly marked glass transition near 154 K and three first‐order transitions: a crystal‐to‐crystal transition at 256 K, a crystal‐to‐mesophase transition at 294 K and a transition to the isotropic melt at 325 K. These transitions are correlated with the mechanical relaxations measured as a function of temperature. The rheological behaviour of the polymer in the isotropic liquid state and in the mesophase has been studied, as well. The properties of POBDMS are discussed in comparison with liquid‐crystalline polymers with mesogenic groups.
Micelle formation and polyisobutylene solubilization by polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene block copolymers
Authors: Quintana José R. , Salazar Ramiro A. , Katime Issa 
Published: April 2003

AbstractThermodynamics of micellization and the structure of micelles formed by polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene block copolymers were studied. A molar mass influence on the aggregation number of micelles was found. The lower the molar mass, the higher the micelle aggregation number. The solubilization of polyisobutylene by micelles of these copolymers in methyl isobutyl ketone was also examined. The saturation concentrations of polyisobutylene solubilized by different block copolymers in methyl isobutyl ketone were determined by laser light scattering. The solubility curves found were linear and dependent on the molar mass of the polyisobutylene solubilized and the copolymer. The logarithm of the maximum amount of polyisobutylene solubilized by mass unity of the triblock copolymer varies linearly with the logarithm of the molar mass of the polyisobutylene. This variation is hardly dependent on the copolymer molar mass and strongly dependent on the type of block copolymer.
Polymers containing formamidine groups, 4. Copolyformamidines prepared from triethyl orthoformate, benzidine and various diamines
Authors: Rillich Mailk , Jehnichen Dieter , Komber Hartmut , Böhme Frank 
Published: April 2003

AbstractFully aromatic and aromatic‐aliphatic polyformamidines were prepared by high‐temperature solution polycondensation of the appropriate diamines with triethyl orthoformate (TEOF). Copolyformamidines of benzidine (4,4′‐biphenyldiamine) with p‐phenylene and trans‐1,4‐cyclohexylene units, respectively, showed liquid‐crystalline behaviour. Both series of copolyformamidines differ distinctly in crystallinity. This has been discussed with respect to sequence distribution, which was determined by 13 C NMR spectroscopy.
Ring‐closing depolymerization of poly(ε‐caprolactone)
Authors: Nelißen Marion , Keul Helmut , Höcker Hartwig 
Published: April 2003

AbstractRing‐closing depolymerization of poly(ε‐caprolactone) in toluene solution with catalytic amounts of Bu2Sn(OMe)2 results in a mixture of cyclic oligomers, the equilibrium concentration of which corresponds to the concentration predicted according to the Jacobson‐Stockmayer theory. ε‐Caprolactone, however, is absent from this reaction mixture. When poly(ε‐caprolactone) is depolymerized in the melt at 260°C in the presence of a catalyst, beside ε‐caprolactone its cyclic dimer and trimer are distilled off. The composition is dependent on the catalyst used, e.g., Bu2Sn(OMe)2 produces 95,4 wt.‐% of ε‐caprolactone and 3,7 wt.‐% of its dimer while with Ti(OiPr)4 (iPr: isopropyl) 51,4 wt.‐% ε‐caprolactone and 49,6 wt.‐% of its dimer are obtained. Block copolymers containing poly(ε‐caprolactone) result in a similar product distribution, however, the second block may influence the rate of decomposition. The activation energy of the catalysed (0,5 mol‐% Bu2Sn(OMe)2) and uncatalysed ring‐closing depolymerization were determined to be 63 kJ/mol, and 87 kJ/mol, respectively.
Polymerization of phenylacetylene with WOCl4/tetraphenyltin catalyst in benzene/1,4‐dioxane. Synthesis of high‐molecular‐weight poly(phenylacetylene)
Authors: Sedláček Jan , Pacovská Marta , Vohlídal Jiří , Grubišić‐Gallot Zlatka , Žigon Majda 
Published: April 2003

AbstractPhenylacetylene was polymerized with WOCl4/tetraphenyltin (mole ratio 1:2) catalyst in benzene and benzene/1,4‐dioxane mixtures. The resulting polymers were characterized by means of multidetector size‐exclusion chromatography and 1H NMR and IR spectroscopy. 1,4‐Dioxane used as a co‐solvent was found to increase both the content of cis units and the molecular weight of poly(phenylacetylene) (PPhA); a weight‐average molecular weight of M̄w = 1 · 106 was reached. In spite of the high mole ration monomer: catalyst (1260:1) used in the polymerizations high yields of PPhA were attained. No effect of an alteration in PPhA microstructure upon its degradation in tetrahydrofuran solution exposed to air has been observed.
Novel thermotropic behavior of (diphenyl/phenyl‐o‐tolyl)phosphazene random copolymer
Authors: Kojima Morio , Magill Joseph H. , Franz Uli , White Michael L. , Matyjaszewski Krysztof 
Published: April 2003

Abstract[(Ph2PN)0,76(Ph(o‐tolyl)PN)0,24] random copolymer (Ph: phenyl) was synthesized by the reaction of Ph2POCH2CF3 and Ph(o‐tolyl)POCH2CF3 with trimethylsilyl azide. Differential scanning calorimetry (DSC) measurements showed that this copolymer has a single glass transition at ≈ 80°C and transforms into a mesophase at 162 ∼ 189°C depending upon the thermal history of the specimens. Lath shaped crystals with unit cell dimensions a = 1,30 nm, b = 1,13 nm and y = 87° (Form‐I) were obtained from mixed dilute monochlorobenzene and p‐xylene solution of the copolymer. Upon heating the specimens to 140°C, the “a” parameter of Form‐I changes to a = 2,21 nm and the “b”, “y” remain unaltered (Form‐II). When the specimens are cooled (10°C/min) from above T(1), the mesophase (δ‐form) is “frozen in” and the δ‐form specimens transform into Form‐II by heating to 140°C. Another structure change (Form‐III) occurs after the δ‐form specimens were heated to 180°C followed by cooling below the glass transition temperature Tg. However, upon cooling the specimens slowly (0,2°C/min) from above T(1), Form‐III results.
Intramolecular excimer formation in naphthalene‐containing polyesters. Bichromophoric model compounds derived from phthalic, succinic or malonic acid and 2‐hydroxynaphthalene or 2‐hydroxymethylnaphthalene
Authors: Pozuelo Javier , Mendicuti Francisco , Mattice Wayne L. 
Published: April 2003

AbstractSteady state fluorescence measurements in dilute solutions are performed for bis(2‐naphthyl) phthalate, bis(2‐naphthylmethyl) phthalate, bis(2‐naphthyl) succinate, bis(2‐naphthylmethyl) succinate, bis(2‐naphthyl) malonate and bis(2‐naphthylmethyl) malonate, as models for polyesters containing naphthalene in their rigid units and flexible spacers that impose differences in the types of interactions between successive naphthalene units. The amount of intramolecular excimer in dilute solution depends on the type of flexible spacer, and also whether the compound is derived from 2‐naphthol or 2‐hydroxymethylnaphthalene. No excimer is detected from the compounds derived from 2‐naphthol, but all compounds derived from 2‐hydroxymethylnaphthalene showed excimer formation. These results are rationalized with a theoretical analysis of the conformations of the flexible spacers.