bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scanning electron microscopy analysis of the structure of thermotropic LC copolymers containing 2,7‐dioxynaphthalene or vanillate units
Authors: Li Xin‐Gui , Huang Mei‐Rong 
Published: April 2003

AbstractThe morphological structure of the fibers and rods of two series of thermotropic liquid‐crystalline copolymers made of 2,7‐naphthalenediol/terephthalic acid/4‐hydroxybenzoic acid(B)/poly(ethylene 2,6‐naphthalene dicarboxylate) and vanillic acid/B/poly(ethylene terephthalate), was systematically analyzed by using a high‐resolution scanning electron microscopy (SEM) fractographic method. Based largely on the SEM micrographs and visual appearance of the fracture surfaces, the fibers and rods were found to consist mainly of highly oriented needle‐like fibrils or lamellae, at which some finely split connections appear. The uniformity of the fibrils is somewhat dependent on the copolymer composition. The macrofibrils with diameters in the range of 10–50 μm and the microfibrils with diameters in the range of 50–90 nm have been observed. No separate phase is obvious in the fibers containing no more than 70 mol‐% of the B unit which has been confirmed by differential scanning calorimetry, but in the rods containing 75 mol‐% of the B unit a few less‐deformed phases related to B‐rich phase were occasionally observed.
Flockung und Entwässerung von Klärschlamm mit Hilfe von Polyelektrolyten
Authors: Parker Sylvia , Kulicke Werner‐Michael , Böhm Nicolai , Kötz Joachim , Jaeger Werner 
Published: April 2003

AbstractEs wurde untersucht, wie ein ausgefaulter Klärschlamm durch eine optimale Flockungshilfsmittelzugabe zu mechanisch stabilen Flocken umgesetzt werden kann, so daß bei möglichst geringem Eintrag eine bestmögliche Entwässerung erzielt wird. Um dazu aussagekräftige, auf großtechnische Anlagen übertragbare Ergebnisse zu erhalten, wurde die Effektivität der Flockungshilfsmittel und der unterschiedlichen Flockungsverfahren in einer patentierten, mobilen, rechnergestützten Flockungs‐ und Entwässerungsapparatur getestet.Der Klärschlamm wurde im Mono‐ und Dualverfahren mit bezüglich ihrer chemischen Struktur, Molmasse und Ladungsdichte (LD) eingehend charakterisierten kationischen (LD: 25–55 mol‐%; Mw: 1,5 · 106– 12,9 · 106 g mol‐1) und einem anionischen (LD: 36 mol‐%; Mw: 7,6 · 106 g mol‐1) Flockungshilfsmittel konditioniert. Im Gegensatz zu anderen bereits untersuchten Trüben konnte beim Klärschlamm weder eine Verbesserung der ohnehin sehr guten Entwässerbarkeit mittels kationischer Monoflockung (Laborversuch: 95 Gew.‐% Filtratausbeute nach 4 s), noch eine Verringerung der optimalen Einsatzmengen durch die Anwendung des Dualverfahrens erzielt werden. Darüber hinaus konnte gezeigt werden, daß die chemische Struktur und die Molmasse der untersuchten kationischen Polyelektrolyte einen weit größeren Einfluß auf die Entwässerungseffektivität besitzen als die Ladungsdichte in einem Bereich zwischen 25 und 55 mol‐%. Ferner erwies sich, daß die Konditionierungseffektivität der Polyelektrolyte mit steigender Molmasse zunimmt und die chemische Struktur hauptsächlich durch die Position der ladungstragenden Gruppe einen Einfluß auf das Entwässerungsergebnis zeigt.
Low‐molar‐mass and polymeric diazosulfonates as disguised diazonium ions for application as analytical reagents in quick assays
Authors: Matusche Peter , Nuyken Oskar , Voit Brigitte 
Published: April 2003

AbstractDiazosulfonates decompose in water upon UV irradiation, forming diazonium salts as intermediates. Therefore, these compounds can be considered as diazonium ion sources, which are thermally very stable, easy to handle, and suitable for longtime storage. Several low‐molar‐mass diazosulfonates have been used in UV initiated azo coupling reactions with a large variety of phenols, naturally occuring substances, and drugs and the results were compared to those obtained with free diazonium ions. The conditions for a successful coupling reaction and the UV absorptions of the products were studied in detail. The concept could be transferred to polymers containing diazosulfonate functional groups. A preliminary application test proved the suitability of these polymers as analytical reagents in quick assays.
Makrogelierung von Polyacrylsäuredispersionen durch Vernetzung
Authors: Dauben Michael , Platkowski Kristina , Reichert Karl‐Heinz 
Published: April 2003

AbstractMit Blockcopolymeren stabilisierte Polyacrylsäuredispersionen mit ca. 100 nm großen Partikeln führen bei Reaktion mit Diglycidylethern oder Disäuredichloriden als Vernetzer ohne Schrumpfung zur Bildung von Makrogelen. Rasterelektronenmikroskopische Aufnahmen zeigen das Vorliegen einer aus den Partikeln aufgebauten dreidimensionalen Netzwerkstruktur. Die Kinetik der Vernetzungsreaktion wurde mit Hilfe der Differential‐Scanning‐Kalorimetrie untersucht. Das aufgestellte Modell berücksichtigt ein Verteilungsgleichgewicht des Vernetzers zwischen disperser und kontinuierlicher Phase und geht von einem Stofftransportprozeß der Vernetzermoleküle in das Partikelinnere aus. Mit Hilfe dynamisch‐rheologischer Messungen wurde gezeigt, daß das Gel ein kovalent vernetztes Gebilde darstellt. Frequenzabhängige Messungen der dynamischen Moduln während der Reaktion führten zu dem Schluß, daß sich das Partikelnetzwerk infolge einer reaktionskontrollierten Cluster‐Cluster‐Aggregation bildet. Mit Hilfe der dynamischen Lichtstreuung wurde festgestellt, daß kurz vor dem Gelpunkt eine Fraktion mit Clustergrößen um 1 bis 2 μm dominiert. Die zeitliche Entwicklung dieser Gebilde von Reaktionsbeginn an wurde mit Hilfe eines einfachen Modells auf Basis der stochastischen Methode beschrieben. Die Verankerung eines Palladium‐Kolloids in dem Partikelnetzwerk führte zu einem katalytisch aktiven Material.
Studies on the ultrasonic degradation of cellulose macromolecular properties
Authors: Marx‐Figini Marianne 
Published: April 2003

AbstractThe ultrasonic degradation of cellulose was investigated using a Bandelin‐Sonopuls‐HD 60 equipment with a frequency of 20 kHz and an output power of 22 W. As cellulose samples five polymeranalogous nitrates with an initial degree of polymerization DPη(0) between 400 and 7500 dissolved in ethyl acetate were used. The resulting macromolecular properties were determined viscosimetrically as well as by SEC (DPw, DPη, DPn, and distributions).The results show the following characteristics, some of them have already been known for the ultrasonic degradation of synthetic polymers:The rate of degradation is the more rapid the higher is DP0. At longer degradation times a limiting DP (DP∞) is observed. Materials with a DPη(0) < 700 do not degrade further. During degradation a very rapid narrowing of the distribution of DP takes place which is the more rapid the higher is DP0.Correspondingly the polydispersity U decreases. The distributions show one maximum only during the whole degradation. The behaviour of polydispersity and distribution gives indications about the mechanism of scission of the molecules.The possibility to use ultrasonication to produce cellulose samples with narrow distributions is discussed.
Two‐component diacrylate networks from liquid‐crystalline and non‐liquid‐crystalline monomers I. Synthesis of the monomers, phase behaviour of the binary monomer mixtures, network formation
Authors: Braun D. , Alig I. , Junker M. , Walther J. 
Published: April 2003

AbstractTwo‐component networks of diacrylate monomers were synthesized by photoinduced polymerization in the isotropic phase. In all systems one component was a liquid‐crystalline diacrylate, whereas the second component was a non‐liquid‐crystalline diacrylate, which was varied in size, geometry and polarity. The phase behaviour of the monomer mixtures has been analysed by differential scanning calorimetry (DSC). It is influenced by the melting point and the structure of the non‐liquid‐crystalline component. All samples were cross‐linked in the isotropic phase 10°C above the phase transition temperature and a modified differential scanning calorimeter was used to investigate the enthalpies of photopolymerization. The final value and the time dependence of the conversion of acrylate double bonds were calculated from the DSC curves. The final degree of conversion of the acrylate double bonds was between 53 and 71% for all samples, whereas no significant dependence of the degree of conversion on the chemical structure of the monomers or the reaction temperature has been found. In contrast, the time dependence of the conversion was influenced by the chemical structure of the non‐liquid‐crystalline component.
Two‐component diacrylate networks from liquidcrystalline and non‐liquid‐crystalline monomers II. small‐ and wide‐angle x‐ray scattering
Authors: Junker M. , Walther J. , Braun D. , Alig I. 
Published: April 2003

AbstractThe structure of single‐ and two‐component networks of diacrylate monomers which were synthesized by photoinduced polymerization in the isotropic phase has been investigated by small‐ and wide‐angle X‐ray scattering. In all systems one component was a liquid‐crystalline diacrylate whereas the second component was non‐liquid‐crystalline. The chemical structure (size, geometry, and polarity) of the second component was varied. For the single‐component networks the scattering profiles in the small‐angle regime reveal inhomogeneities of the electron density of the order of some ten nanometers. For the two‐component networks no additional scattering contribution due to composition inhomogeneities has been found. This is an evidence that no phase separation occurs during the photoinduced cross‐linking of the thermosets. This picture of an amorphous single‐phase structure is supported by the scattering profiles in the wide‐angle regime. For the single‐component networks a broad maximum is found, the corresponding characteristic length of which can be correlated with the structure of the monomers. For the two‐component networks also only one characteristic length is found which shifts with composition between the length of the single‐component thermosets. By both methods no indication for the development of a liquid‐crystalline phase during network formation has been revealed.
Application of phase transfer catalysis in the synthesis of low‐molecular‐weight epoxy resins
Authors: Pielichowski Jan , Czub Piotr 
Published: April 2003

AbstractQuaternary ammonium salts, sulfoxides and sulfoianes were used as catalysts in the syntheses of low‐molecular‐weight epoxy resins from bisphenol A and epichlorohydrin. The reaction was carried out in a polar organic solvent at room temperature. The process of synthesis of epoxy resins under phase transfer catalysis (PTC) conditions was studied. Depending on the type of the catalyst and on the reaction conditions epoxy resins with different epoxy group equivalents were obtained. Application of the PTC conditions enabled the synthesis of epoxy resins in a singlestage process, under mild conditions and with a lower amount of epichlorohydrin. It was observed that the system dichloromethane/NaOHaq in the presence of quaternary ammonium salts or sulfoxides or sulfolanes is very convenient in the synthesis of low‐molecular‐weight epoxy resins.
Heterogeneous grafting of maleic anhydride and α‐methylstyrene from atactic polypropylene
Authors: Braun Dietrich , Braun Iris , Krämer Inge , Hellmann Goetz P. 
Published: April 2003

AbstractAtactic polypropylene (PP) is an amorphous short‐chained by‐product of isotactic polypropylene (iPP). Due to its enhanced solubility, PP is a suited model polymer for kinetic studies of iPP melt reactions. The maleination of PP via radical grafting at high temperatures was investigated. Since maleic anhydride (MAA) produces discoloring oligomers, PP was grafted with a mixture of MAA and α‐methylstyrene (MS). Advantageous is that MS cannot homopolymerize at high temperatures and that MAA and MS tend to copolymerize alternatingly (to colorless products). The kinetics of the grafting process is complicated by a phase separation of PP and [MAA+MS] that is caused by the special attractions between the two monomers. As a result, two grafted PP products are obtained, of which the major is only slightly but the minor is heavily grafted. The latter graft copolymer, which is probably created in the interfaces between phase domains, carries one MAAMS graft per PP back bone chain, approximately with three MAA and five MS units.
Organic‐inorganic hybrid sol‐gel materials, 2. Application for dental composites
Authors: Yang Jen Ming , Chen Hao Sheng , Hsu Ying Gev , Lin Feng Huei , Chang Yen Hsiang 
Published: April 2003

AbstractBy incorporating poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(styrene‐co‐methyl methacrylate) (poly(St‐co‐MMA)) structure units covalently into the SiO2 glass network via a sol‐gel approach, three organic‐inorganic hybrid materials (PMMA‐SiO2, PS—SiO2, and poly(St‐co‐MMA)—SiO2) have been prepared. The three hybrid sol‐gel materials were used as filler (up to 60 wt.‐%) for dental composite resins. The effect of the three filler materials on several mechanical properties of the dental composite resins was investigated. The hardness of the filled dental composites increased with increasing filler content, whereas the bending strength decreased. The compressive strength of the composites was improved, compared with the unfilled resin, but decreased with inreasing filler content.
Mechanical and structural characteristics of phenolphthalein poly(ether sulfone)/ultra‐high molecular weight polyethylene blends
Authors: Huang Dinghai , Yang Yuming , Li Binyao 
Published: April 2003

AbstractMechanical and structural properties of blends of phenolphthalein poly(ether sulfone) (PES‐C) with ultra‐high molecular weight polyethylene (UHMWPE) were investigated using tensile and bending testing, scanning electron microscopy and transition electron microscopy. The incorporation of minor amounts of UHMWPE (2 wt.‐%) into PES‐C has a reinforcement effect. With higher concentrations of UHMWPE, the mechanical properties decrease gradually. Structural studies demonstrated that the blends are multiphasic in the whole composition range. The minor UHMWPE, dispersed uniformly and oriented along the flow direction, as well as the strong interfacial adhesion contribute to the increase of the mechanical performance of the blends. The domain size of the UHMWPE phase was found to increase with the increase of its concentration.
Adsorption of BTX compounds from aqueous solutions by water‐insoluble starch
Authors: Chan Wu‐Chung , Yang Shih‐Ping 
Published: April 2003

AbstractThe removal of benzene, toluene and p‐xylene (BTX) compounds from aqueous solutions with highly crosslinked cationic starch containing tertiary amine groups was investigated. The adsorption process has found to be initial pH‐ and initial concentration‐dependent, endothermic, and follows the Langmuir isothermal adsorption.The heats of adsorption (ΔH) at initial pH = 4 of benzene, toluene and p‐xylene compounds are 29.45 kJ mol−1, 34.41 kJ mol−1, and 35.58 kJ mol−1, respectively, those at initial pH = 10 are 30.17 kJ mol−1, 35.56 kJ mol−1, and 39.39 kJ mol−1, respectively. The order of the amount of adsorbed BTX compounds on the adsorbent is benzene > toluene > p‐xylene.
Studies of copper‐catalysed degradation of epoxy coatings and a method for improving the durability of an epoxy/copper interface after thermal aging
Authors: Gu Xiaohong , Xue Gi 
Published: April 2003

AbstractIt has been demonstrated that an epoxy‐polyamide film is susceptible to be oxidized and degraded on a copper surface at elevated temperature. The amino and amide groups in the epoxy resin are oxidized to nitriles and the polymeric backbone is thermally degraded by the catalysis of copper, resulting a sharp reduction in adhesion between the epoxy resin and copper substrate after aging at 200°C for 30 min. By pretreating the copper surface with polyacrylonitrile, the thermal stability of the coating and the interfacial adhesion can be significantly improved.
Thermogravimetric and ESR studies of polymer/metal precursors for high‐temperature superconductors
Authors: von Lampe Irene , Brückner Angelika , Götze Silke 
Published: April 2003

AbstractBi‐Sr‐Ca‐Cu complexes of poly(methacrylic acid) (PMAA) and cresol novolac, which are precursors for high‐temperature superconductors (HTSC) and Cu complexes of those polymers were investigated by ESR spectroscopy and thermogravimetry. In the PMAA samples three different kinds of Cu2+ species were detected: i) Cu2+ pairs, ii) isolated Cu2+ ions and iii) Cu2+ clusters. While Cu2+ pairs are the main species at low Cu concentrations, clusters become dominant at high Cu contents. In the novolac samples Cu2+ was only detected in isolated sites and clusters. The introduction of Cu ions lowered the thermal stability of the polymers and led to a stepwise decomposition. In the PMAA samples the first decomposition step at ≈ 220°C is caused by the Cu2+ pair complexes.
Gelpermeationschromatographie und Kalibrierung an resolischen Phenol‐Formaldehyd‐Kondensaten
Authors: Gobec Georg , Dunky Manfred , Zich Thomas , Lederer Klaus 
Published: April 2003

AbstractMehrere Resole mit einem Mengenverhältnis von Formaldehyd zu Phenol von 2,5 bzw. 1,7 und einer Katalysatorzugabe von 8 bzw. 4 Gew.‐% NaOH wurden hergestellt und mit Hilfe der Gelpermeationschromatographie (GPC) untersucht. Dabei erwies sich Tetrahydrofuran mit 0,4 Gew.‐% Trichloressigsäure als geeignetes Lösungs‐ und Elutionsmittel, das auch hochalkalische Resole zu lösen vermag. Diese Harze wurden im niedermolekularen Bereich in bis zu acht einzelne Peaks aufgetrennt, die durch Vergleich mit den Chromatogrammen von Reinsubstanzen, die bei der Resolsynthese als Zwischenprodukte zu erwarten sind, interpretiert wurden. Im höhermolekularen Bereich wurde die Kalibrierung auf der Basis von Polystyrolbzw. Polyethylenglykol‐Standards durchgeführt. Für die hüchstmolekulare Fraktion ergab sich auf Basis der Polystyrol‐Kalibrierung eine Molmasse von ca. 150 kg mol‐1. Die alternative Verwendung eines Brechungsindex‐ und eines UV‐Detektors ergab, daß im niedermolekularen Bereich der UV‐Detektor durch Spuren von Verunreinigungen weniger gestört wird.
A facile antistatic modification of polyester fiber based on ion‐exchange reaction of sulfonate‐modified polyester and various cationic surfactants
Authors: Sano Yoshiyuki , Konda Marcekazu , Lee Chan Woo , Kimura Yoshiharu , Saegusa Takeo 
Published: April 2003

AbstractA new technique for imparting antistatic properties to poly(ethylene terephthalate) (PET) fiber has been developed. In this technique, blend polyester fibers containing poly(ethylene terephthalate/5‐sulfoisophthalate) (SIP‐PET) were prepared by blend spinning and then treated with various cationic surfactants in the process of dyeing. The surfactants could effectively be immobilized on the fiber as the counter cations of the sulfonate groups of the 5‐sulfoisophthalate (SIP) units and aid the release of static electrons formed in the fiber. Thus, the half‐life time (t1/2) of leakage of static charge and the surface resistivity (Rs) of the blend PET fibers became much lower after treating. The best result was obtained with a methylated quaternary ammonium salt of a stearylamine‐ethylene oxide (EO) adduct or hydrochloride of a laurylamine‐EO adduct as the surfactant of which the number of EO units was around ten. Even after five washing cycles the t1/2 value of the fibers treated with these surfactants was kept lower than 30 s with the Rs value maintained in the order of 1013 Ω cm‐2. Therefore, the present technique could be useful for practical production of polyester fibers with “semi‐permanent” antistatic properties which can be recovered by re‐treatment even if they were lost.
Oxidation behavior and stabilization of metallocene and other polyolefins
Authors: Foster George N. , Wasserman Scott H. , Yacka Douglas J. 
Published: April 2003

AbstractEXXPOL® metallocene catalyst technology featuring very high‐productivity catalyst systems is expected to provide ethylene polymer compositions that show excellent oxidative stability based on their minimal unsaturation content and low innocuous metal residue of a non‐acidic nature. Metallocene ethylene polymers such as mLLDPE should be comparable to the most stable, commercial polyethylenes such as linear low‐density polyethylenes (LLDPE) from the UNIPOL® gas phase PE process.As background, the oxidation behavior and stabilization case of “total residue” polyolefins based on Ziegler‐Natta or Cr catalysis systems are reviewed. The interacting effects of polymer structure (i.e., tertiary hydrogen and unsaturation) and catalyst residue are discussed in terms of competing degradation reactions ‐ e.g., chain breakage, chain enlargement (or cross‐linking) and chain branching. The metal (Ti, V and Al) and chlorine residues from Ziegler‐Natta catalyst systems and the Cr residue for Cr catalyst systems can play a role in adversely affecting polymer oxidative stability. The residue levels and their nature govern whether there is an appreciable effect on oxidative stability, and therefore the stabilization requirements.Discussed are thermo‐oxidative studies under melt processing conditions which compare selected EXXPOL®/UNIPOL® mLLDPEs with several state‐of‐the‐art Ti/Mg and Cr catalyzed LLDPE from the UNIPOL® gas phase PE process and a high‐pressure, low‐density polyethylene (HP‐LDPE). Standard melt flow and discoloration tests are combined with specialized experiments using dynamic oscillatory shear rheometry and size exclusion chromatographyviscometry to illustrate performance shifts due to polymer composition differences under melt processing conditions. The advantages of dynamic melt rheometry are illustrated in terms of sensitivity to subtle degradation changes in molecular structure. EXXPOL®/UNIPOL® mLLDPE having low unsaturation and metal residue which are non‐catalytic to auto‐oxidation show excellent intrinsic oxidative stability. The discoloration resistance of EXXPOL®/UNIPOL® mLLDPE is high, comparable with HP‐LDPE and the high‐activity Cr catalyzed LLDPE. Stabilization ease for EXXPOL®/UNIPOL® mLLDPE is equivalent to product counterparts (similar MI and density) made using high‐activity, state‐of‐the‐art Cr or Ti/Mg catalyst systems designed for use in the UNIPOL® gas phase PE process.
The role of charge transfer complexes in the photodegradation of polyolefins
Authors: Gijsman P. 
Published: April 2003

AbstractAddition of HALS‐stabilisers, the cut‐off wavelength of the light source, the temperature and the oxygen pressure have an influence on the UV‐degradation mechanism of polyolefins. All these parameters influences the conversion of oxygen into polymeric carbonyls. The results are explained assuming that the initiation of the UV‐degradation of pololefins is due to substrate‐oxygen charge transfer complexes (CTCs).
Increasing the performance and permanence of polymer stabilizers
Authors: Gray Robert L. , Neri Carlo 
Published: April 2003

AbstractA new generation of polysiloxane based polymer stabilizers is examined. The flexibility and versatility of polysiloxane backbones have allowed the development of a family of products which provide outstanding radical trapping efficiency, an unexpected resistance to extraction, and a high degree of compatibility in certain polymeric systems. Functionalization with graftable moieties results in a product which can be chemically bound to the polymer itself. The key to success in this work was optimizing the balance of graft linkages and mobility of the stabilizer chain.