bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reaction of dicyanates with monophenols — modeling of network buildup
Authors: Bauer J. , Alla C. , Bauer M. , Bloch B. 
Published: April 2003

AbstractChemical as well as structural modifications of highly branched polycyanurates can be achieved by using the reaction of dicyanates with monofunctional phenols. The key products of this reaction are iminocarbonic esters formed by addition of cyanato and phenolic groups. Two mechanisms are discussed for the second reaction step: an addition of two cyanato groups and an iminocarbonic ester (Route A) and a stepwise addition of iminocarbonic esters (Route B). The crucial difference between the two reactions is the number of abstracted phenolic groups per formation of one triazine ring: one for Route A and three for Route B. The effects of these reaction mechanisms on the gelation behavior and network buildup are studied theoretically with the help of cascade theory as well as experimentally by the reaction of dicyanate of bisphenol A with five different monophenols. The results clearly show that only with a model which is based on Route B can both the critical conversions at the gelation threshold and the gel fractions be modeled quantitatively. Furthermore, phenols with low pKa values were found to have an increased tendency of incorporation into the network.
Effect of draw ratio on the structure of aromatic copolyimide fibers of random monomer sequence
Authors: Wu T. M. , Chvalun S. N. , Blackwell J. , Cheng S. Z. D. , Wu Z. , Harris F. W. 
Published: April 2003

AbstractX‐ray methods have been used to investigate the structure of fibers of aromatic copolyimides prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), o‐tolidine (OTOL) and p‐phenylene diamine (PPD). We have shown previously that the non‐periodic layer lines in the X‐ray fiber diagrams of these copolymers are indicative of a random comonomer sequence. In the present paper, we analyze the shifts in the layer line positions that occur with increasing draw ratio. These changes are to be understood primarily in terms of increases in the correlation lengths for the stiff chain conformation. At high draw ratios there is also evidence for the development of a more extended chain conformation, probably due to torsional variation changes in the torsion angles. It is shown that the data are sufficiently sensitive to allow quantitative analysis of these separate effects, and their dependence on comonomer ratio.
Biaxial extensional flow behavior of monodisperse polystyrene melts
Authors: Ebrahimi N. Golshan , Takahashi M. , Araki O. , Masuda T. 
Published: April 2003

AbstractBiaxial extensional flow behavior of monodisperse polystyrene melts has been investigated by using a lubricated squeezing flow method at constant strain rates. Master curves for the biaxial stress growth coefficient η are obtained by applying the time‐temperature superposition principle. The coefficient η deviates from a linear viscoelastic curve at very small strain such as 0.1, and then approaches a quasi steady state. The quasi‐steady‐state viscosity ηB,qs decreases with the strain rate ηB. At very small strain rates, the coefficient η increases again after the quasi steady state and becomes much larger than the linear viscoelastic curve. The strain rate dependence curves of ηB,qs obtained for different molecular weight samples can be superposed to give a super master curve using the weight‐average relaxation time η0 as a reducing parameter. It is found that the biaxial viscosity ηB,qs begins to decrease at much smaller reduced strain rate (ϵBτ0=0.01) compared with the shear viscosity, which begins to decrease at reduced strain rate of about 1.0.
Small‐angle x‐ray scattering from a thermotropic random copolymer during solid‐state annealing
Authors: Wilson D. J. , Seifert S. , Stribeck N. , Windle A. H. , Zachmann H. G. 
Published: April 2003

AbstractThis paper reports the effect of solid state annealing on the structure of a liquid crystalline polymer composed of 80% 4‐hydroxybenzoic acid (HBA) and 20% 2‐hydroxy‐6‐naphthoic acid (HNA) using small‐angle X‐ray scattering. Two‐dimensional diffraction patterns possessing strong meridional reflections were recorded using synchrotron radiation at temperatures of 215, 251 and 269°C. The long period increased with increasing anneal temperature, but was largely unaffected by increasing the length of time spent at the anneal temperature. The intensity of meridional scattering increased with both increasing anneal temperature and time. In order to obtain an estimate for the average crystallite thickness at the anneal temperature, the small‐angle meridional scattering was evaluated by means of the interfacial distribution function approach.
Synthesis of a photosensitive polyimide containing a diazo group and its photocrosslinking reactions via a long‐lived active intermediate
Authors: Yamashita T. , Kasai C. , Sumida T. , Horie K. 
Published: April 2003

AbstractA novel intrinsic photosensitive polyimide containing a diazo group in the main chain was prepared, and the quantum yield for the photocrosslinking reaction was determined to be 0.13 under air at room temperature by GPC measurement. The quantum yield for the photo‐decomposition reaction of the diazo group was also determined to be 0.06. These values are higher by about two orders of magnitude than those for the photocrosslinking reaction of a benzophenone‐containing polyimide, which is prepared from benzophenonetetracarboxylic dianhydride (BTDA) and methylene bis(2‐ethylaniline) (DEDPM). The reaction was found to proceed via its singlet excited state to give a long‐lived active intermediate, a carbene, which plays a great role in the increase in the photoreactivity. Characteristics of the photoreaction and the fluorescence behavior of a series of imide‐substituted diphenyldiazomethanes were also investigated, showing that the reactivity of the diazo groups is not affected by the existence of charge transfer structures of the imide groups.
Pre‐ordering state in the crystallization process of polymer blends detected by pulsed NMR
Authors: Ikehara T. , Nishi T. 
Published: April 2003

AbstractReal time measurement by pulsed NMR revealed that poly(ϵ‐caprolactone)/polystyrene (PCL/PS) blends and PCL homopolymer form a pre‐ordering state at the onset of crystal formation. The spin‐spin relaxation signals were decomposed into three components. When the intermediate phase appeared, its fractional amount was larger than that of the interfacial phase in semicrystalline polymers and the spin‐spin relaxation time was longer than that of the interface. The fractional amount decreased in the first stage of crystallization and then increased as the process proceeded. This behavior was more significant for blends with higher PS content or those crystallized at elevated temperatures. This state is assigned to a pre‐ordering state of the crystalline polymer that has to exclude the amorphous polymer on the formation of lamellae.
Dynamics of stiff‐chain polymers in multicomponent solutions: Modification of the hole theory
Authors: Fujiyama T. , Sato T. , Teramoto A. 
Published: April 2003

AbstractThe previous theory of the global motion dynamics of stiff‐chain polymers in multicomponent systems has been modified by a refined treatment of the jamming effect on the longitudinal diffusion of polymer chains along their end‐to‐end axis to derive a new equation for zero‐shear viscosity, which depends on the longitudinal diffusion coefficients through the lifetimes of entanglements between similar as well as dissimilar polymers. Along with this theoretical study, experimental data forzero‐shearviscosity of quasi‐ternary solutions containing two stiff‐chain polymers with different lengths were obtained. They were well described by the viscosity equation obtained, with only the similarity ratio(s) inherent to the respective polymer‐solvent system(s) as adjustable parameter(s).
Surface molecular motion in thin films of poly(styrene‐block‐methyl methacrylate) diblock copolymer
Authors: Tanaka K. , Takahara A. , Kajiyama T. 
Published: April 2003

AbstractThin films of poly(styrene‐block‐methyl methacrylate) diblock copolymer [P(St‐b‐MMA)] with thickness ca. 50 nm were prepared by a dip‐coating method. The surface Tg for the P(St‐b‐MMA) thin film was evaluated on the basis of the temperature‐dependent X‐ray photoelectron spectroscopic (TDXPS) measurement. The temperature at which the surface composition started to change was defined as the glass transition temperature, Tg, at the surface region. It was revealed that the surface Tg for P(St‐b‐MMA) was much lower than that for its bulk sample. Also, the depth dependence of Tg for P(St‐b‐MMA) was investigated on the basis of the combination of TDXPS and the angular‐dependent XPS (ADXPS) method. Tg for P(St‐b‐MMA) decreased with a decrease in distance from the outermost surface. The molecular weight dependence of the surface Tg for P(St‐b‐MMA) was more pronounced than that in the bulk sample, and that was expressed as a function of M.
Effect of ZnCl2 on the spontaneous copolymerization of methyl acrylate with substituted 1,3‐dienes
Authors: Mikhael M. G. , Padias A. Buyle , Hall H. K. 
Published: April 2003

AbstractThe reactions of the mildly electron‐poor olefin methyl acrylate (MA) with three electron‐rich substituted hydrocarbon 1,3‐dienes, namely 2,3‐dimethyl‐1,3‐butadiene (DMB), 4‐methyl‐1,3‐pentadiene (MPD) and isoprene (IP) were investigated in 1,2‐dichloroethane in the presence of various amounts of zinc chloride at different temperatures. ZnCl2 complexes with the ester group of MA and increases the MA's electron‐poor character and therefore its tendency towards reactions with electron‐rich dienes. In the absence of ZnCl2, no reaction occurs between the investigated dienes and MA under the used reaction conditions. Both alternating copolymers and [4+2] cycloadducts formed spontaneously in the presence of ZnCl2 even at room temperature. The structure of the diene and its nucleophilicity control the product distribution. For the DMB and IP systems, raising the reaction temperature and increasing the ZnCl2 concentration enhance the overall reaction rate and in most cases also favor the cycloaddition over the copolymerization. IP is less reactive than DMB. With MPD only copolymer is formed because the two terminal methyl groups retard the concerted [4+2] cycloaddition. These results are in agreement with a postulated mechanism involving competition between the formation of a π‐allyl 2‐hexene‐1,6‐diradical, capable of initiating free radical copolymerization, and concerted [4+2] Diels‐Alder cycloaddition.
π Electron delocalization in pristine polyfuran: from the oligomers to the polymer
Authors: Hernández V. , Veronelli M. , Favaretto L. , Navarrete J. T. López , Jones D. , Zerbi G. 
Published: April 2003

AbstractChain‐length‐dependent π electron delocalization is analyzed in pristine oligofurans and polyfuran by means of Fourier transform Raman spectroscopy. Neutral polyfuran shows a large frequency dispersion with conjugation length and it has not yet reached saturation at the level of the hexamer. In spite of such a large π electron delocalization the polymer seems to show an unexpectedly good stability in air at room temperature. Regio‐defined poly(2,5‐difurans) could be good candidates for technological developments.
Full coverage of a hydroxy‐substituted poly(para‐phenylene) with first‐ and second‐generation dendritic wedges having isocyanate focal points
Authors: Karakaya B. , Claussen W. , Schäfer A. , Lehmann A. , Schlüter A.‐D. 
Published: April 2003

AbstractSynthesis of the hydroxyethyl‐substituted poly(para‐phenylene) 2b employing Suzuki polycondensation is described. This PPP derivative is used as a matrix for the attachment of first‐ and second‐generation dendrons of the Fréchet‐type with isocyanate functions at the focal point. The degree of coverage is determined from NMR integration to be virtually 100% in both cases.
Synthesis of oligoanthrylenes and their photopolymerization in solution
Authors: Stein S. , Müllen K. 
Published: April 2003

AbstractTrianthrylene compounds with film‐forming capabilities were synthesized in a three‐step procedure by means of transition‐metal catalyzed Grignard and Suzuki coupling reactions. Upon UV exposure, photopolymerization of the model compound 1,11‐di‐(9‐anthryl)undecane was observed in solution as well in the film due to [4+4] cycloaddition of the anthracene moieties. The soluble photopolymers were characterized by NMR spectroscopy and GPC analysis. As expected, irradiation of solutions of the trichromophoric hydrocarbons afforded crosslinked photoproducts which precipitated from solution. In the case of an analogous trianthryl derivative with tetraoxyethylene spacers, formation of a gel was observed due to cycloaddition of the anthracene groups. The film‐forming capabilities of trianthryl compounds in conjunction with UV‐induced photocrosslinking can be useful for photoresist applications and will be discussed in the following paper [1].
Photobleaching of oligoanthrylenes in the film state
Authors: Paul S. , Stein S. , Knoll W. , Müllen K. 
Published: April 2003

AbstractFilms of oligoanthrylenes are readily available by spin coating. Upon UV exposure, the properties (refractive index, fluorescence and solubility) of these films are changed due to [4+4] cycloaddition of the anthracene groups. This behavior appears to be useful for information recording purposes, which is demonstrated by surface plasmon and fluorescence microscopy. Although complete photobleaching of the films is not possible, effective photocrosslinking occurs for trichromophoric systems affording relief textures after development in ethanol/methylene chloride mixtures (negative tone photoresist). Furthermore, the reversibility of the solid state photodimerization of the anthracene moieties is discussed.
Enzyme‐mediated polymerization reactions: Peroxidase‐catalyzed polyphenol synthesis
Authors: Ayyagari M. , Akkara J. A. , Kaplan D. L. 
Published: April 2003

AbstractPeroxidase‐catalyzed phenol polymerization in the presence of hydrogen peroxide has been extensively studied. The process offers many advantages over the conventional chemical process to produce phenol‐based resins. The enzymatic process avoids the use of formaldehyde and results in minimal formation of by‐products due to high specificity of the enzyme toward the reactants. A number of phenolic derivatives and aromatic amines can be polymerized in different reaction systems, such as bulk solvents, reversed micelles and Langmuir trough. The polymers produced produced exhibit morphology reflective of the templating effect of the medium used to prepare the materials. Polymer molecular weight and polydispersity can be controlled by suitable design of the reaction medium. Polymer characteristics such as structure, thermal and temporal stability, functionalization and processability are reviewed. Conductivity, nonlinear optical and related functional properties are discussed with regard to potential applications.
Synthesis and properties of interpenetrating networks from acrylates of d‐block elements
Authors: Gupta N. , Srivastava A. K. 
Published: April 2003

AbstractSystematic synthesis of interpenetrating polymer networks (IPN) from poly(chromium acrylate) (PCrA) and zinc acrylate (ZnA) using divinyl benzene (DVB) as crosslinker has been carried out. Swelling studies and scanning electron microscopy (SEM) were performed to examine the extent of crosslinking and phase behavior of the IPN. The crosslinking decreases with the increase of linear polymer concentration and its molecular weight, respectively. On the other hand, it increases with the increase of concentration of crosslinking agent and monomer II, respectively. The IPN was found to be thermally stable up to 300 °C.
Alkylthio‐substituted oligothiophenes: the influence of the alkyl chain length on the solid‐state and solution properties of 4,4′‐bis(butylthio)‐2,2′‐bithiophene
Authors: Antolini L. , Folli U. , Goldoni F. , Iarossi D. , Mucci A. , Schenetti L. 
Published: April 2003

AbstractA solid‐state (single crystal X‐ray, IR, DSC) and solution (1H NMR nuclear Overhauser effect (NOE) and longitudinal relaxation times (T1)) study of 4,4′‐bis(butylthio)‐2,2′‐bithiophene is reported. The two thienyl rings are coplanar and in an anti orientation in the solid state, whereas a low amount of syn form is present in solution. The n‐butylthio chain adopts a fully extended, nearly idealized, anti conformation in the crystal, with all the non‐H atoms of the whole molecule strictly coplanar, despite the molecular length, but does not show a preferred orientation in solution. The observed changes on passing from the solid to the solution state are indications of the potential solvatochromic and thermochromic properties of β‐butylthio‐substituted oligomers and polymers.
Copolymerization of ethyl cyanoacrylate and ethylene in the presence of zinc chloride or trifluoroacetic acid as complexing agent
Authors: Sperlich B. , Eisenbach C. D. 
Published: April 2003

AbstractThe free radical copolymerization of ethene and ethyl cyanoacrylate (ECA) in the presence of Lewis and Brønsted acids has been studied in detail. Both trifluoroacetic acid (TFA) and ZnCl2.Et2O were found to be useful complexing agents for synthesizing highly alternating copolymers of olefins and ECA. The influence of the complexing agents was quantified by determination of the copolymerization parameters r1 of ECA for ECA/ET copolymerization. The synthesized copolymers showed unusual thermal behavior with regard to their alternating structure. This was established by the semi‐crystallinity and the variation of the glass transition temperature with the degree of alternation.
Study of particle interaction in a highly concentrated latex by turbidimetry
Authors: Weiss A. , Pötschke D. , Ballauff M. 
Published: April 2003

AbstractA study of the low‐angle region of the static structure factor S(q) (q = (4π/λ) sin(θ/2); θ: scattering angle, λ: wavelength of the radiation in the medium) of a concentrated (44 wt.%) poly(methyl‐methacrylate) (PMMA) latex by turbidimetry is presented. It is demonstrated that S(0), i.e., the structure factor extrapolated to vanishing scattering angle can be obtained in excellent accuracy up to the highest concentrations. Since S(0) reflects the balance between long‐range attractive and short‐range repulsive forces between the latex particles, this quantity can be used to assess the stability of the latex against flocculation. Special attention has been paid to the influence of polydispersity on S(0). The analysis of S(q) in the vicinity of q = 0 for the system under consideration indicates the absence of attractive forces between the particles.
Polyesters based on oxygen‐organosolv lignin
Authors: Evtugin D. V. , Gandini A. 
Published: April 2003

AbstractOxygen‐organoslov lignin (namely oxygen‐acetone) was introduced as a macromonomer into polyesterification systems including diacid chlorides and, optionally, oligoethyleneoxide glycols. It was concluded that the incomplete participation of phenolic hydroxy groups of lignin in these polycondensation reactions could lead to poor crosslinking as shown by the partial solubility of the final polyesters in polar solvents. This paper presents the synthesis, characterization and some properties of these materials.
Local dynamics in a thermotropic terpolyester as revealed by dynamic mechanical analysis, 2H NMR and dielectric spectroscopy
Authors: Wiesner U. , Spiess H. W. , Müller F. , Kremer F. , Lauprêtre F. , Halary J. L. , Monnerie L. 
Published: April 2003

AbstractDynamic mechanical, 2H NMR and dielectric spectroscopy techniques were used to identify the nature of the local motions involved in the secondary relaxations of a thermotropic aromatic terpolyester prepared from para‐hydroxybenzoic acid, hydroquinone and isophthalic acid. Three secondary relaxations, denoted β, γ, and δ, were detected. A β relaxation, pointed out by dynamic mechanical measurements, is quite close to the large amplitude π‐flip processes observed by 2H NMR. Correlated motions of the para‐substituted rings and adjacent carbonyl groups may also participate in the β process. Then, at lower temperatures, a γ process is detected by both dielectric and dynamic mechanical experiments. It is assigned to small amplitude oscillations of the isophthalic acid units of the HBA33 polymer. At high temperatures, a heavy overlap of broad rate distributions for the β and γ processes observed in the measurements precludes a more detailed analysis. A dielectric relaxation, denoted δ relaxation, is observed at very low temperatures. It likely comes from motions of a very small number of water molecules trapped in the structure of the terpolyester.
Dielectric relaxation and conductivity in polyelectrolyte—surfactant complexes
Authors: Antonietti M. , Maskos M. , Kremer F. , Blum G. 
Published: April 2003

AbstractThe dielectric and conductivity behavior of some selected solid polyelectrolyte‐surfactant complexes (PE‐surf) is characterized by broadband dielectric spectroscopy in the frequency range 10−2–107 Hz. Depending on phase‐morphology and volume fraction of alkyl‐tails, electrical conductivities at room temperature of up to 10−4 S/cm are found. In addition, the behavior at low temperatures is characterized by two distinct β‐relaxations which show an Arrhenius‐like activation, and their relaxation strength depends on temperature, in contrast to the standard behavior of dielectric media. The relaxations are assigned to surfactant movements, the number or strength of which increase with temperature, which are obviously important already well below the glass transition temperature of the ionic layers. Doping of a selected complex showing a rather high basic conductivity with LiClO4 results in a decrease of the conductivity, which is explained by an increase in the glass transition temperature of the ionic layer.
Molecular imprinting: An approach to “tailor‐made” synthetic polymers with biomimetic functions
Authors: Takeuchi T. , Matsui J. 
Published: April 2003

AbstractThe recent development of synthetic polymers with biomimetic functions prepared by molecular imprinting is reviewed in this article. Molecular imprinting is based on template polymerization in which polymers are prepared in the presence of a template molecule to be imprinted. Resultant polymers record the shapes and chemical properties of the templates in their matrixes and exhibit antibody‐like and enzyme‐like activities. The most significant advantage of this technique is its simplicity: complementary sites for the target molecules which are expected to be specific binding/catalytic sites can be constructed with the aid of molecular self‐assembly and no complicated synthesis is necessary. In this article, we present typical examples of molecularly imprinted polymers and especially focus on the effectiveness of molecular imprinted polymers as artificial antibodies and the potential as substrate‐selective catalysts.
The synthesis and polymerization of oxo‐crown ethers
Authors: Peeters E. , Janssen H. M. , van Zundert M. F. , van Genderen M. H. P. , Meijer E. W. 
Published: April 2003

AbstractA novel synthetic route to and a polymerization procedure for oxo‐crown ethers 2, 11‐dioxo‐18‐crown‐6 (1), 2‐oxo‐12‐crown‐4 (2) and 2‐oxo‐21‐crown‐7 (3) are described. Cyclization of the ω‐hydroxycarboxylic acid precursors of 1—3 has been achieved by heating these precursors in the presence of a Lewis acid catalyst (CoCl2) and a template salt (MCl). Cyclization yields up to 82% were reached, using CsCl as template salt. Oxo‐crown ethers 1—3 have been polymerized using SnOct2 as catalyst, giving polymers with molecular weights of approximately 5 kg/mol and dispersities of ca. 1.8 (measured with polyethylene oxide standards). The polymerization of 2 was monitored with 1H‐NMR and SEC giving information about (a) the influence of monomer/catalyst ratio and temperature on polymerization rate and (b) the influence of temperature on molecular weight (distribution). The possibility of introducing endgroups into poly(2‐oxo‐12‐crown‐4) using SnOct2‐catalyzed polymerization was also studied.