bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on LDPE/LLDPE blends
Authors: Abraham D. , George K. E. , Francis D. J. 
Published: April 2003

AbstractSelected grades of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) were melt‐mixed and the physical, mechanical and rheological properties evaluated. The blends were found to combine the good mechanical properties of LLDPE and processing properties of LDPE. The effect of crosslinking the blends with dicumyl peroxide (1 phrParts per hundred rubber
) was also investigated. The level of crosslinking increased with increase in LLDPE content. While the mechanical properties of the crosslinked blends were more uniform, the physical properties controlled by the crystallinity of the polymer, such as density, hardness and volume loss on abrasion, decreased on crosslinking.
Synthesis and characterization of multifunctional initiators for preparation of four‐branch polymers
Authors: Menceloǵlu Yusuf́ Z. , Baysal Bahattin M. 
Published: April 2003

AbstractTetrafunctional initiators T4‐AZO4, T4‐TCE1 and T4‐IPDI4 have been synthesized by using insertion reaction of tetrakis(dimethylamino)‐titanium (T4) with 2,2′‐azoisobutyronitrile (AIBN), tetracyanoethylene (TCE) or isophorone diisocyanate (IPDI), respectively, in dry benzene under nitrogen at 35°C. T4‐AZO4 is useful for preparing four‐branch polymers from radically polymerizable monomers by decomposition of the azo groups incorporated in the related initiator. Four‐branch polyacrylonitrile can be synthesized by using the initiator T4‐TCE1. This initiator possesses titanium‐amino functionalities which are capable of initiating acrylonitrile polymerizations. The tetrafunctional isocyanate compound T4‐IPDI4 is found to be useful to prepare a model network of dihydroxy‐terminated polymers.
Synthesis, characterization and properties of oxyethylene‐oxypropylene‐styrene multiblock copolymers
Authors: Xie Hong‐Quan , Chen Xiao‐Yuan , Guo Jen‐She 
Published: April 2003

AbstractOxyethylene‐oxypropylene‐styrene multiblock copolymers were synthesized by coupling poly(ethylene glycol), poly(propylene glycol) and α, ω‐dihydroxy polystyrene with 2,4‐toluene diisocyanate. The purified copolymers were characterized by IR and 1H NMR spectroscopy and membrane osmometry and identified as multiblock copolymers. The multiblock copolymers exhibit good emulsifying properties, high water absorption capacity and good phase transfer catalysis properties in Williamson reaction. The mechanical properties of the multiblock copolymers show that they behave like a thermoplastic elastomer or a toughened plastic, depending on the composition.
Photovernetzung von siliconen, 8. Netzwerkcharakterisierung photovernetzter siliconacrylate
Authors: Müller U. , Jockusch S. , Häusler K.‐G. , Timpe H.‐J. 
Published: April 2003

AbstractDie photoinduzierte radikalische Vernetzung von Siliconacrylaten bzw. ‐methacrylaten wurde mit Hilfe von Quellungsmessungen untersucht, wobei ein modifizierter Quellungstest erlaubt, die Netzwerkbildung als Funktion verschiedener Parameter zu betrachten. Die Ergebnisse zeigen, daß die Netzwerkdichte eine Funktion der Lichtintensität, der Bestrahlungszeit, des Acrylatgehalts, der Molmasse des unvernetzten Silicons und auch der Länge der Spacergruppe zwischen Acrylateinheit und dem Siliconrückgrat ist. Sauerstoff besitzt dagegen nur einen Einfluß auf die Polymerisationskinetik, nicht aber auf die Netzwerkdichte.Aus dem Vergleich der δB, ‐Werte der vernetzten Siliconacrylate und der vernetzten Vinylsilicone kann geschlossen werden, daß die Netzwerkstruktur auch vom Typ der olefinischen Gruppen abhängt. Die χ‐Parameter besitzen jedoch im gleichen Konzentrationsbereich die gleiche Größe.Kinetische Untersuchungen zeigen, daß die Netzwerkbildung nach einem Zeitgesetz erster Ordnung verläuft. Dieses Ergebnis steht im Einklang mit der Polymerisationskinetik.Mit Hilfe der Quellexperimente ist es auch moglich, den Einfluß von H‐Siloxanzusätzen als Wasserstoffüberträger zu untersuchen.
Synthesis of novolac on the basis of bisphenol A as curing agent for epoxy resins
Authors: Strehmel Veronika , Strehmel Bernd , Arndt Karl‐Friedrich , Müller Gert , Fedtke Manfred 
Published: April 2003

AbstractBisphenol A novolacs were synthesized in a melting process using paraformaldehyde, and in a solution process using a formalin solution and oxalic acid catalyst. 1H‐NMR investigations show a higher content of methylene bridges in the novolacs synthesized in a melting process. These novolacs were analysed by HPLC, GPC, DSC and FT‐IR spectroscopy. The molecular masses were determined by vapour pressure osmometry. The results were shown to be related with the molar ratio of the components. The bisphenol A novolacs were used as curing agents for epoxy resins. There exists a dependence of the gel times on the content of methylene bridges; this dependence is influenced by temperature. The activation energy for gel formation is nearly the same in all curing reactions investigated. The networks synthesized were investigated by thermomechanical analysis.
Curing kinetics of epoxy resins based on bisphenol‐S and its derivatives
Authors: Liaw Der‐Jang , Shen Wen‐Chang 
Published: April 2003

AbstractThe curing reactions of several epoxy resins based on bisphenol‐S with amine have been investigated by differential scanning calorimetry. The overall kinetic parameters of the curing reactions, such as activation energy, curing range and the order of the reaction are estimated by using four computational methods based on a single dynamic scan over the temperature range 50 – 300°C. Epoxy resins containing oxyethylene or oxypropylene units have lower reaction order and activation energy than the diglycidylether of bisphenol‐S. This indicates that flexible epoxide resins are easier to cure.
Sulfobetaine polyurethane ionomers. Salts effects of the properties of dilute solutions and polymer films
Authors: Buruianǎ T. , Buruianǎ E. C. , Diaconu I. , Robilǎ G. 
Published: April 2003

AbstractThe viscosimetric behaviour of diluted DMF solutions of some sulfobetaine polyurethanes and also the influence of some mono‐ and bivalent metal salts were studied. The study showed that polyurethane zwitterionomers behave as polyelectrolytes.Films of these polymers complexed with bivalent metals can form, in situ, particles of metal sulfides by exposure to slow H2S flow. Preliminary results show an increased conductivity of films treated with H2S, suggesting a microphase segregation structure.
Mixtures of poly(ethylene terephthalate) and liquid‐crystalline polyesters with Y‐shaped mesogens
Authors: Rötting Oliver , Hinrichsen Georg 
Published: April 2003

AbstractSome liquid‐crystalline polyesters (LCP) with Y‐shaped mesogens, differing only in the length of their spacers, were blended with poly(ethylene terephthalate) (PET). Calorimetric measurements show significant influence of the LCP on the crystallization of PET even at low concentrations. The mixtures are spun into fibres and their mechanical properties are compared with fibres made from pure LCPs. The formation of LCP‐fibrils leads to improved values of Young's modulus and tensile strength.
Quantitative measurement of pigment dispersion and effect of processing on dispersion in high density polyethylene using a microscope photometer
Authors: Ogbobe Okoro 
Published: April 2003

AbstractA microphotometer attached to a computer‐controlled darkfield microscopy system has been used for the quantitative measurement of the degree of pigment dispersion in high‐density polyethylene extruded at specified varying processing conditions. The method distinguishes levels of pigment dispersion in extrudates obtained from subtle changes in processing conditions. Since the set‐up is comparatively inexpensive, the technique promises to be particularly useful to small‐scale manufacturers.
Kinetik der Polyphenylensulfid‐Synthese
Authors: Koschinski I. , Reichert K.‐H. , Traenckner H.‐J. 
Published: April 2003

AbstractDie Polykondensation von Na2S·3H2O und 1,4‐Dichlorbenzol im Lösungsmittel 1 ‐Methyl‐2‐pyrrolidon wurde in kleinen Hochdruck‐Kapseln aus Edelstahl mit einem Volumen von ca. 30 μl in einem Differentialkalorimeter im Temperaturbereich von 220°C bis 260°C kinetisch untersucht. Die Reaktion ist stark exotherm, bei 220°C beträgt die Reaktionsenthalpie ca. 180 kJ mol−1. Sie ist durch ein autokatalytisches Verhalten gekennzeichnet, welches mit einem Zeitgesetz 2. Ordnung in bezug auf die Konzentration der stöchiometrisch eingesetzten Monomeren und einer vom Umsatz abhängigen Reaktionsgeschwindigkeitskonstante des Kettenwachstums beschrieben werden kann. Die Aktivierungsenergie beträgt 95 kJ mol−1.
Synthesis of 2‐(2‐carboxybenzoyloxy)ethyl methacrylate and its radical polymerization and copolymerization with butyl methacrylate
Authors: Sedláková Zdena , Bouchal Karel , Ilavský Michal 
Published: April 2003

AbstractConditions of the synthesis of 2‐(2‐carboxybenzoyloxy)ethyl methacrylate (CEM) by the alcoholysis of phthalic anhydride (PA) with 2‐hydroxyethyl methacrylate (HEMA) were optimized. For the uncatalyzed, base‐catalyzed and acid‐catalyzed reaction of PA with HEMA at 50°C the respective second‐order rate constants were 4.7 × 10−6, 14.5 × 10−5 and 5.4 × 10−5 dm3 mol−1 s−1. Also, a consecutive esterification of CEM with formation of bis(2‐methacroyloxyethyl)phthalate took place under conditions of the acid catalyzed reaction. The emulsion polymerization of CEM (solubility in water 13 mmol dm−3 at 25°C) was carried out in the presence of sodium dodecyl sulfate as the emulsifier and of the redox initiation system based on K2S2O8–K2S2O5. Using the Smith‐Ewart model of emulsion polymerization, the growth rate constant of CEM, kp = 610 dm3 mol−1 s−1 at 25°C was determined. The monomer reactivity ratios and Q and e values determined for the radical copolymerization of CEM (M1) with butyl methacrylate (M2) were r1 = 0.85, r2 = 0.75, Q = 0.82, and e = 0.4.
Beeinflussung des eigenschaftsbildes von synthesekautschuk durch die polymerisationsparameter bei der emulsionspolymerization
Authors: Wendler Karin , Poltersdorf Steffi 
Published: April 2003

AbstractDie Veränderung der Polymerisationsbedingungen (Polymerisationsgschwindigkeit, Emulgatorsystem) beeinflußt die Konzentration der Regler im Latexteilchen und damit die Molmassen, die Molmassenverteilung, Kettenverzweigungen und Gelgehalte der Polymeren. Die Speicher‐ und Verlustmodul‐Frequenzabhängigkeiten für die Kautschuke und ihre Netzwerke wurden aufgenommen und im Zusammenhang mit den Strukturparametern diskutiert.
Rubber‐extender interactions surface activity of fillers and filler/rubber interactions
Authors: Vidal A. , Haidar B. 
Published: April 2003

AbstractThe properties of filled elastomers are obviously dependent on the nature of the iller/matrix interface. However, one can expect the physical or chemical interactions which are able to take place between the surface of the solid and the polymeric matrix to be controlled by the surface activity of the filler. In this respect some of the methods, which have been devised for the characterization (identification and titration of surface functional groups, measurement of the surface free energy, determination of the distribution functions of energies,…) and the monitoring (activation, deactivation,…) of he surface reactivity of reinforcing fillers, are used in view of the establishment of relationships with the reinforcing ability of the corresponding fillers.
Verträglichkeit von kautschuken ein altes und ein aktuelles problem
Authors: Schuster Robert Hans 
Published: April 2003

AbstractThe utilization of rubber mixtures is to achieve a desired combination of properties and performance spectrum of elastomers is nowadays of a considerable technological and economical importance. The successful implementation of this concept requires the knowledge of the factors governing both the phase behaviour of rubber blends and the morphology of phase separated blends. Thermodynamic theories referring to miscibility and phase separation of polymers are briefly reviewed, with a specific focus on nonpolar polymers with high chain flexibility. It can be shown on the simple lattice that this theory works qualitatively for these systems. Reliable predictions are questionable due to the lack of equation of state parameters for the polymers of interest and temperature and concentration dependence of the interaction parameter χ.Concerning the morphology of phase separated rubber blends the main influences governing the structure of the entire system (i) the interfacial tension, (ii) the viscosity of the matrix (iii) and the shear stress are discussed in more detail. It has been pointed out that for technological usability a better knowledge about the interdiffusion of polymers and the properties of the interphase, built in this would be not only of scientific interest but also beneficial for high performance elastomer blends. It would also be useful to know more about the dispersion of polymers at short mixing times and elevated temperatures. Because it has been considered until recently that polymer miscibility occurs only if strong specific segmental interaction are involved, emphasis was dedicated to oligomer/rubber‐ and rubber/rubber‐systems which exhibit miscibility and phase transitions through a convex coexistence curve into a homogeneous region. Consequences of phase transitions at high mixing temperatures for specific tire applications are suggested.
The essential role of network topology in rubber elasticity
Authors: Vilgis T. A. , Heinrich G. 
Published: April 2003

AbstractThis paper discusses various new aspects in the elasticity of rubbers and the statistics of elastomers. It is shown that the role of network topology is crucial in the statistics of rubbers. This is seen mostly on the influence of heterogeneities of crosslink density, which is also of practical interest. Strong heterogeneities lower the modulus, but do not change the stress‐strain behavior. It is also shown that if in a given network the flexible chains are replaced by rigid rods which are flexibly hinged the entropy is still of order of that of the flexible network and that the modulus is of the same order as the Gaussian one. This holds for lower functionalities, i.e. less than six. The phase behavior of crosslinked blends and interpenetrating networks is shown to be similar of the microphase transition of block copolymers. Semi IPNs demix at a critical crosslink density of the crosslinked part, or alternatively at a critical length of the free chains, even though if the chains are of the same chemical nature as the crosslink component.
Determination of crosslink densities of carbon black filled natural rubber sulfur vulcanizates by 13C NMR MAS spectroscopy and 1H NMR transversal relaxation
Authors: Hoffmann Uwe , Gronski Wolfram , Simon Gerald , Wutzler Andre 
Published: April 2003

AbstractTwo NMR spectroscopic methods were applied to carbon black filled NR vulcanizates to determine the chemical crosslink density. Both methods give corresponding results. Addition of carbon black leads to a decrease of crosslink density with increasing filler content. The influence is more pronounced at higher sulfur content.
Molekulares versagen bei der deformation von unvernetztem naturkautschuk
Authors: Fuhrmann J. , Hamel M. 
Published: April 2003

AbstractOn line investigation of molecular chain scission during mechanical loading of unfilled, unvulcanized natural rubber is possible using the “Exoemission” method. Especially, it can be shown that chain scission is force controlled, i.e. there is no significance for energy control. The emission rate, assumed proportional to the rate of chain fracture, can be described by the rate theory of Eyring[1]. The average molecular mass of a chain between two elastically effective entaglements MC, estimated by the theory of Mooney and Rivlin is linear correlated with the activation volume of the force controlled chain scission determined from the emission intensity.The experimental data further indicated a strong dependence of crystallisation kinetics and associated molecular fracture processes on the velocity of loading.
Properties of rubber elastic systems at large strains
Authors: Göritz Dietmar 
Published: April 2003

AbstractThe large increase in tensile stress at high extension ratios has previously been treated by Kuhn und Grün in the theory of entropy elasticity by using non‐Gaussian chain statistics. This effect is caused by a non‐uniform distribution in the lengths of the network chains in a real network, such that short chains are highly orientated even at low strains and make an over‐propotionate contribution to the tensile stress.It has been shown experimentally that the short chains lead to morphological changes during extension. This means that the deformation behaviour of networks may not be described correctly in terms of a homogeneous system.The structure which arises on stretching both filled and unfilled samples has been investigated by electron microscopy. In both cases the material consisted of highly drawn ribbons which formed a super‐network. The degree of orientation of these ribbons was higher than would correspond to the macroscopic elongation. By means of this concept of a double network, a number of findings could be explained, such as the change in volume, the diffusion and adsorption of gas and, in the case of natural rubber, strain‐induced crystallization.The load‐elongation behaviour could be described by the following relationship

in which the stresses due to the chemical network and the super‐network are additive. Φ is the volume fraction of the super‐network.
Etudes microlithographiques de résines négatives renfermant des unités tétrathiafulvalènes sensibles aux électrons
Authors: Giral Louis , Montginoul Claude , Mungroo Aumduth , Sagnes René , Schué François , Guibert Jean‐Charles 
Published: April 2003

AbstractPour résoudre le phénomène de gonflement qui limite la résolution des résines micro lithographiques classiques, nous nous sommes intéressés à de nouvelles résines avec lesquelles ce phénomène n'apparaǐt pas. Nous avons retenu pour notre étude les résines R qui renferment en mélange un polymère porteur de radicaux tétrathiafulvalénylcarbonyloxyméthyles et le dibromotétrachloroéthane. Afin de voir l'influence de la nature du radical porteur de l'unité tetrathiafulvalène dans le polymère sur les propriétés microlithographiques des résines R, nous nous sommes également intéressés aux polymères renfermant des radicaux tétrathiafulvalénoxyméthyles. Les résines R ont été testées sous irradiation électronique. Leurs sensibilités dépendent en outre de la valeur de la masse molaire du polymère. Des résolutions comprises entre 0,1 et 0,4 μm ont été obtenues. Ce type de résines possèdent un certain nomber de propriétés intéressantes telles que des sensibilités élevées et de bonnes résolutions.
Frequency dependence of the complex dielectric constant of sodium carboxymethyl cellulose
Authors: Nessim Refaat I. , Botros Maged G. , Saad Gamal R. , Shalaby Mohamed M. 
Published: April 2003

AbstractThe dielectric constant, ε′, and dielectric loss, ε″, were determined for three solid carboxymethyl cellulose samples having different levels of substitution and different degrees of polymerization over a frequency range of 0.1 – 10 000 kHz at temperatures from 10–60°C. In contrast to the two relaxation processes, γ and β, previously observed in native cotton cellulose, only one relaxation process within a frequency range of 0.1 – 1 kHz was identified. It was found that the dielectric properties do not only depend on the degree of substitution, but also on the weight‐average degree of polymerization and uniformity of distribution.
A redox reaction mediated by polymeric membranes containing electron carriers
Authors: Takeishi Makoto , Nakatsugawa Masahiko , Kikuchi Masayoshi 
Published: April 2003

AbstractA redox reaction was mediated by polymeric membranes which contain naphthoquinone derivatives as electron and proton carriers. When such a membrane containing vitamin K1 was placed between two aqueous solutions of potassium ferricyanide and sodium dithionite, the oxidation‐reduction of them took place, but the reaction was rather slow. Although vitamin K3 was a more effective carrier and the reaction proceeded fast, the reaction rate decreased in the repeated runs. Since the reduced form of this carrier is slightly soluble in water, a part of the carrier got dissolved in the aqueous phase from the membrane during the reaction. 2‐Alkyloxy‐1,4‐naphthoquinones such as 2‐hexyloxy‐1,4‐naphthoquinone effectively transported electrons and protons through the polymeric membranes, promoting the membrane‐mediated reaction; in these cases no retardation was observed in the repeated runs.
Possibilities for the formation and characterization of solid‐state‐structures in aromatic polyoxadiazoles
Authors: Hofmann Dieter , Leibnitz Eberhard , Schmolke Rudolf , Schulz Burkhard 
Published: April 2003

AbstractDepending on the coagulation conditions, poly(p‐phenylene‐1,3,4‐oxadiazole) in the solid state forms two modifications, as can be evidenced by FTIR spectroscopy and by wide‐angle X‐ray scattering curves (WAXS). In both cases each modification is detectable by characteristic peaks. Processing of fibers or films from solutions in concentrated sulfuric acid by coagulation in water results in the formation of a thermodynamically non‐equilibrium form, defined as β‐modification. Under special conditions it is possible to obtain the three‐dimensionally ordered equilibrium α‐structure that leads to processing products with markedly higher tenacities.
Ölfettsäremodifizierte wäßrige Polymethacrylatdispersionen
Authors: Müller Siegfried , Zekai Doris , Pohl Martina , Pohl Gerhard , Lorkowski Hans‐Joachim 
Published: April 2003

AbstractWäßrige Anstrichsysteme setzen sich in zunehmendem Maße durch. Als eine Entwicklungsvariante für diesbezüglich geeignete Bindemittel kommen autoxidativ vernet zende Polymethacfrylatdispersionen in Betracht. Es werden wesentliche Schritte der Synthese derartiger Dispersionen un dcharakteristische Eigenschaften auchvon Beschichtungen vorgestellt.Die Ölfettsäurestruktureinheiten sind im Schalenbereich der disperigierten Teilchen angereichert, und sie befinden sich außerden zu etwa 30% in der wäßrigen Phase als Substituenten eines löslichen Copolymeren.
Linear polythioesters, XX. Products of interfacial polycondensation of 4,4′‐bis(mercaptomethyl)‐biphenyl with some aliphatic and isophthaloyl dichlorides
Authors: Podkoscielny Wawrzyniec , Tarasiuk Bogdan 
Published: April 2003

AbstractNew polythioesters were synthesized by interfacial polycondensation of 4,4'‐bis(mercaptomethyl)biphenyl with selected aliphatic and isomeric phthaloyl dichlorides.To determine optimum polycondensation conditions, the influence of the following factors on reduced viscosity and yield were studied: type of organic phase, concentration of reagents, aqueous/organic phase ratio, type and concentration of hydrogen chloride acceptor, rate of acid chloride addition, reaction temperature and reaction time.A thorough examination was carried out only for the polycondensation of dithiol with adipoyl and isophthaloyl dichlorides chosen as a model system. The structures of polythioesters were confirmed by elemental analysis, X‐ray analysis and infrared spectroscopy. The temperature of initial decomposition, the percentage of its mass loss, and temperature of the fastest decomposition process from curves of differential and thermogravimetric analysis were determined. Some physicochemical, mechanical and electrical properties were determined. The molecular weights were not measured because of the low solubility of the obtained polythioesters.