bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid crystalline thermosets from dimeric LC epoxy resins cured with primary and tertiary amines
Authors: Ribera David , Mantecón Ana , Serra Angels 
Published: October 2003

AbstractLiquid crystalline thermosets (LCTs) were prepared by curing difunctional LC dimeric epoxy monomers with imine moieties in the mesogenic core and central spacers of different length. Primary diamines or tertiary amines were used as curing agents obtaining materials with different characteristics. The results obtained were related to the mesogen structure, since dipolar moments in the mesogenic cores affect the ability to form ordered networks.
Polymer design for thermally stable polyimides with low dielectric constant
Authors: Goto Kohei , Akiike Toshiyuki , Inoue Yasutake , Matsubara Minoru 
Published: October 2003

AbstractWe successfully prepared a series of thermally stable polyimides (PIs) with low dielectric constant (k) by introducing bulky diphenyl fluorenylidene moieties in backbone. The lowest k was found to be 2.77 among non‐fluorinated PIs and 2.35 among fluorinated ones. In order to prove the lowest limit of k in PIs, we prepared soluble and thermally stable polyarylenes (PArs) without polar imide linkage with the same aromatic moieties by coupling polymerization. The lowest k was 2.7 without fluorine (F) and 2.2 with F atom, which showed also promising for low k materials. From these results, PIs we prepared were estimated to the lowest k values among PIs. On the basis of statistics on these results, we could express contour lines of k as a function of imide concentration and F content with high correlation factor (r= 0.96) in PIs and PArs.
New organosoluble polyimides with low dielectric constants derived from bis[4‐(2‐trifluoromethyl‐4‐aminophenoxy)phenyl] diphenylmethylene
Authors: Liaw Der‐Jang , Tseng Wen‐Tsung 
Published: October 2003

AbstractA new kink diamine with trifluoromethyl group on either side, bis[4‐(2‐trifluoromethyl‐4‐aminophenoxy)phenyl]diphenylmethane(BTFAPDM), was reacted with various aromatic dianhydrides to prepare polyimides via poly (amic acid) precursors followed by thermal or chemical imidization. Polyimides were prepared using 3,3′, 4,4′‐biphenyltetracarboxylic dianhydride(1), 4,4′‐oxydiphthalic anhydride(2), 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (3), 4,4′‐sulfonyldiphthalic anhydride(4), and 4,4′‐hexafluoroisopropylidene‐diphathalic anhydride(5). The fluoro‐polyimides exhibited low dielectric constants between 2.46 and 2.98, light color, and excellent high solubility. They exhibited glass transition temperatures between 227 and 253°C, and possessed a coefficient of thermal expansion (CTE) of 60‐88 ppm/°C. Polymers PI‐2, PI‐3, PI‐4, PI‐5 showed excellent solubility in the organic solvents: N‐methyl‐2‐pyrrolidinone (NMP), N,N‐dimethylacetamide (DMAc), N,N‐dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridkie and tetrahydrofuran (THF). Inherent viscosity of the polyimides were found to range between 0.58 and 0.72 dLg‐1. Thermogravimetric analysis of the polyimides revealed a high thermal stability decomposition temperature in excess of 500°C in nitrogen. Temperature at 10 % weight loss was found to be in the range 506‐563°C and 498‐557°C in nitrogen and air, respectively. The polyimide films had a tensile strength in the range 75‐87 MPa; tensile modulus, 1.5‐2.2 GPa; and elongation at break, 6‐7%.
HALS in polyamide 6 polymerization
Authors: Filippini Fantoni Roberto , Sanfilippo Giorgio 
Published: October 2003

AbstractThe use of Hindered Amine Light Stabilizers (HALS) directly in polyamide 6 polymerization can cause some problems. The following two problems were the focus of our project:1) We investigated, from a theoretical point of view, the results of introducing directly one of the precursors of HALS into polyamide 6 polymerization. For the investigation, 4 amino‐2,2,6,6‐tetramethylpiperidine (triaceton‐diamine or TAD) was chosen. We considered the TAD chain‐ending effects and their influence on the total amount of amino chain‐endings that can be titrated, a parameter of primary importance in the fibre field.2) We examined the amide interchange reaction in the case of an HALS containing two amide groups, using a product available on the market, N,N′‐bis(tetramethyl‐4‐piperidyl)isophtalamide. In this case we were able to generate a couple of equations that allows one to calculate the quantity of amide interchanged HALS. This was done by comparing the results (molecular weight and chain‐endings analysis) of polymerization with and without HALS.
Transfer molding imide resins based on 2,3,3′,4′‐biphenyltetracarboxylic dianhydride
Authors: Smith J.G. , Connell J.W. , Hergenrother P.M. , Ford L.A. , Criss J.M. 
Published: October 2003

AbstractPhenylethynyl containing imide oligomers have been under investigation as part of an effort to develop resins for non‐autoclave composite fabrication processes such as resin transfer molding (RTM). These high performance/high temperature composites are potentially useful on advanced aerospace vehicles such as reusable launch vehicles (RLVs). New phenylethynyl terminated imide oligomers (PETI) based upon 2,3,3′,4′‐biphenyltetracarboxylic dianhydride (a‐BPDA) were prepared and characterized primarily by rheological behavior and cured glass transition temperature (Tg). In comparison to resins from the symmetrical isomer (3,3′,4,4′‐biphenyltetracarboxylic dianhydride, s‐BPDA), a‐BPDA afforded corresponding resins with lower melt viscosities and upon curing, higher Tgs. Several resins exhibited an attractive combination of properties such as low and stable melt viscosities required for RTM composite fabrication, high cured Tgs, and moderate toughness. One resin (P10) was used to fabricate flat, void free laminates by RTM. The laminates exhibited high mechanical properties at temperatures to 288°C. The chemistry and physical properties of these new PETIs and the laminate properties of one composition are discussed.
Synthesis and characterisation of polyketanils with ether linkages
Authors: Sęk Danuta , Iwan Agnieszka , Kasperczyk Janusz , Janeczek Henryk 
Published: October 2003

AbstractA series of polyketanils from four diketones with pendant aromatic groups (i.e. dibenzoyl, p‐dibenzoylbenzene, p‐disebacoylbenzene and trans‐1,2‐dibenzoylethylene) and two diamines with flexibilizing ether linkages [4,4′‐diaminediphenyl ether, 4,4′‐(1,3phenylenedioxy)dianiline] has been synthesized using melt polycondensation (180°C, 24h). Spectral and thermal properties of the polyketanils before and after protonation with 1,2‐(di‐2‐ethylhexyl)ester of sulfophthalic acid (DEHEPSA) were investigated.
Engineering with metallo‐supramolecular polymers: linear coordination polymers and networks
Authors: Schmatloch S. , Schubert U.S. 
Published: October 2003

AbstractHere we demonstrate the synthesis of telechelics with different spacer units and different numbers of metal‐complexing units, like α‐methoxy‐ω‐(2,2′:6′,2″‐terpyrid‐4′‐yl)‐poly(ethylenoxide)78 (1), bis(2,2′:6′,2″‐terpyrid‐4′‐yl) di(ethylene glycol) (2), bis(2,2′:6′,2″‐terpyrid‐4′‐yl)‐poly(ethylene oxide)180 (3) and tris[(2,2′:6′,2″‐terpyrid‐4′‐yl)‐oligo (ethylenoxy‐)3.33]glycerin (4) utilizing 4‐chloro‐2,2′:6′,2″‐terpyridine. The complexation behaviour of a variety of metal‐salts towards the telechelics was studied and different supramolecular architectures were investigated, such as symmetric polymeric complexes and linear coordination polymers. Furthermore, attempts have been undertaken to prepare metallo‐supramolecular cross‐linked systems.
Condensation polymers containing silicon and germanium in the main chain
Authors: Tagle Luis H. 
Published: October 2003

AbstractPoly(carbonates), poly(thiocarbonates) and poly(esteres) containing silicon and/or germanium in the main chain were obtained under phase transfer conditions. Polymers were synthesized in a biphasic system NaOH/CH2Cl2 at 20°C using several phase transfer catalysts, and characterized by IR and 1H and 13C NMR. The results were evaluated by the yields and the inherent viscosity values. The process was effective observing an increase of both parameters in comparison with the essays without catalyst. The increases depended of the nature of the polymer and the catalyst. In poly(ester) synthesis there was an increase of these parameters when the NaOH concentration was increased due to a salting out effect of the diphenolate from the aqueous phase to the organic one. Also poly(amides) containing silicon or germanium were synthesized by solution polymerization.
Aromatic polymers with side oxadiazole rings as luminescent materials in LEDs
Authors: Bruma Maria , Hamciuc Elena , Schulz Burkhard , Köpnick Thomas , Kaminorz Yvette , Robison Jenifer 
Published: October 2003

AbstractAromatic polyamides and polyazomethines with side oxadiazole rings have been synthesized by using aromatic diamines containing pendent substituted oxadiazole groups and a diacid chloride having diphenylsilane or hexafluoroisopropylidene, or an aromatic dialdehyde with fluorene unit, respectively. These polymers were easily soluble in amidic solvents. Very thin films which were deposited from polymer solutions onto silicon wafers exhibited smooth, pinhole‐free surface in atomic force microscopy investigations. The polymers showed high thermal stability with decomposition temperature being above 400°C. Some of them exhibited blue photoluminescence, in the range of 450‐480 nm, making them promising candidates for future use as high performance materials in the construction of light emitting devices.
Smart nanocomposite polymer gels
Authors: Varga Zsolt , Fehér József , Filipcsei Genovéva , Zrínyi Miklós 
Published: October 2003

AbstractThe combination of polymers with nanomaterials displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The magnetic polymer gel represents a new type of composites consisting of small magnetic particles, usually from the nanometer range to the micron range, dispersed in a highly elastic polymeric gel matrix. Combination of magnetic and elastic properties leads to a number of striking phenomena that are exhibited in response to impressed magnetic fields. Giant deformational effects, high elasticity, anisotropic properties, temporary reinforcement and quick response to magnetic field open new opportunities for using such materials for various applications.
Study of the interaction polymer/organic solvents/salt in microporous PVdF separator for lithium batteries
Authors: Saunier J. , Alloin F. , Sanchez J‐Y. 
Published: October 2003

AbstractInteractions between microporous PVdF and polar liquid electrolytes have been investigated. PVdF separators are an attractive alternative to microporous apolar polyolefins, such as polyethylene, whose poor wetting by these electrolytes induces a significant resistivity increase in lithium batteries. The swelling study of polymer/electrolyte interactions has shown that the resistivity increase induced by microporous PVdF is moderate and will enable the electrolyte composition to be optimized. Existence of a shut‐down effect is an asset for the battery safety.
Swelling, elasticity and structure of hydrogels prepared via bis‐macromonomers of poly(ethylene oxide)
Authors: Dubrovskii Sergey A. , Lagutina Marina A. , Vasiljev Vitalij V. 
Published: October 2003

AbstractThe effect of swelling on the shear modulus was studied for hydrogels prepared by radical polymerization of methacrylate‐terminated poly(ethylene oxide) (PEO) bis‐macromonomers of different molecular weight. Gels made of long chains (M = 12000 or 6000) display classical softening upon swelling, whereas gels made of shorter chains (M = 4000 or 2000) remain rigid or even stiffen. The abnormal behaviour is explained by a specific character of network junctions presented by polymethacrylate chains in which each unit is linked with a PEO network chain. It is assumed that the interactions among densely grafted PEO chains result in their stretching on polymerization and non‐affine deformation on swelling, which stiffen the gel. This is verified by the data on copolymer (macromonomers ‐ 2‐hydroxyethyl methacrylate) gels that have lesser densities of PEO chains attached to the junctions and show weaker stiffening on swelling. The osmotic pressure of gels was estimated from the swelling pressure and shear modulus. Similar to the mixing pressure of equivalent PEO solutions, it varies as the 9/4 power of polymer concentration. At the same time, it is lower than the mixing pressure. This indicates that the junctions make only quantitative changes in the osmotic properties of macromonomer chains.
H‐bond in chitosan‐based hydrogels
Authors: Xin Meihua , Li Mingchun , Yao Kangde 
Published: October 2003

AbstractN‐alkyl chitosan derivatives, including N‐ethyl, butyl, heptyl and lauryl forms were prepared via Schiff's base intermediates. The study of H‐bonds in chitosan‐based hydrogel was performed by DSC, NMR, XKD and PALS. The content of unfrozen bound water increases with increasing length of the alkyl side chain and the degree of substitution. The X‐ray diffraction peak centered at 2θ=26.5° is sensitive to water. The free volume enhances in the order, chitosan (CS) < N‐ethyl CS < N‐butyl CS < N‐heptyl CS << N‐lauryl CS. Moreover the free volume of the derivatives decreases as water content rises but the situation of chitosan is opposite. The dynamic properties of water molecules within the networks were studied through the variation of the proton line width in the 1H‐NMR spectrum. The proton line width of the water peak of N‐alkyl chitosan increases in the sequence, N‐ethyl CS < N‐butyl CS < N‐heptyl CS < N‐lauryl CS. The same results arise from the spin‐lattice relaxation time (T1) for these N‐alkyl chitosan derivatives.
Controlled‐release of drugs from cross‐linked polymers containing cubane as a crosslinking agent
Authors: Mahkam Mehrdad 
Published: October 2003

AbstractTwo anti‐inflammatory drugs, indomethacin and aspirin together with cubane‐1, 4‐dicarboxylic acid (CDA) were covalently linked with 2‐hydroxyethyl methacrylate (HEMA). The drug‐linked HEMA (indomethacin‐linked HEMA) is abbreviated as HI, aspirin‐linked HEMA as HA and cubane‐1, 4‐dicarboxylic acid (CDA) linked to two HEMA group is the cross‐linking agent (CA). A difunctional spacer group was introduced between the drugs and acrylic moiety of the monomer through a hydrolyzable ester linkage. Free radical cross‐linking polymerization of the monomers with drug effect was carried out in dioxane solution at various CA ratios, using AIBN as initiator in the temperature range 60‐70°C. The compositions of the cross‐linked three‐dimensional polymers were determined by FT‐IR spectroscopy. The glass transition temperature (Tg) of the network polymers was determined calorimetrically. The hydrolysis of drug‐polymer conjugates was carried out in cellophane membrane dialysis bags containing an aqueous buffer solution (pH 8 and pH 1) at 37°C. Detection of the hydrolysis product by UV spectroscopy shows that the drugs were released by hydrolysis of the ester bond located between the drug and spacer group.
Properties of simple models of polymer networks. A Monte Carlo simulation
Authors: Sikorski Andrzej , Romiszowski Piotr 
Published: October 2003

AbstractA model polymer network was constructed from branched chains. Each chain was built on a simple cubic lattice forming a star‐branched polymer consisting of f = 3 arms of equal lengths. The fragment of network under consideration consisted of 1, 2 and 3 star polymers with different topology of connections. The only potential used was excluded volume (athermal chains). The properties of the network were determined by the means of computer simulations using the classical Metropolis sampling algorithm (local micromodifications of chain conformation). The behaviour of linear chains of the same molecular weight was also studied as a state of reference. The influence of attaching the next star‐branched chain to the network on its static and dynamic properties was studied. The short‐time dynamic behaviour of chain fragments was determined and discussed.
Water sorption properties of poly(ethyl acrylate‐co‐hydroxyethyl methacrylate) macroporous hydrogels
Authors: Vidaurre Ana , Castilla Cortázar Isabel , Meseguer José María 
Published: October 2003

AbstractSynthetic porous hydrogels are becoming more and more important in the field of biomaterials. Different studies demonstrate that the porous structure promotes the colonisation of living cells and improves the biocompatibility of the implants. The macroporous structure allows not only the control of cellular ingrowth morphology but also the mechanical integration and the regulation of nutrient and hydraulic flow in the hydrogel. In this work poly(ethyl acrylate‐co‐hydroxyethyl methacrylate) (PEA/PHEMA) copolymers were polymerized using 2% of ethylene glycol dimethacrylate as cross‐linking agent and azoiso‐botyronitrile as initiator. Five samples were prepared with the EA/HEMA weight ratios of 75/25, 50/50, 25/75 and pure PEA and PHEMA polymers, obtaining different degrees of hydrophilicity. The macroporous structure was obtained by adding poly(acrylonitrile) fibres to the monomers. After polymerization the fibres were eliminated by dissolution in dimethyl formamide. The holes are cylinders of approximately 40μm diameter and are all, more or less, in the same direction, although they are not uniformly distributed. Water sorption isotherms and diffusion properties of the macroporous samples are compared with the samples without holes.
NMR study of the synthesis of 17O‐enriched acetic acid by hydrolysis of acetic anhydride with 17O‐enriched water
Authors: Hultman Heidi M. , Djanashvili Kristina , Peters Joop A. 
Published: October 2003

Abstract17O‐enriched acetic acid (2.5% in 17O) was synthesized by hydrolysis of acetic anhydride with 17O‐enriched water. The reaction was monitored by 17O and 1H NMR spectroscopy. Acetic anhydride, 17O‐enriched in both the ether and the carbonyl oxygens, was observed as an intermediate. This can be ascribed to competition between acetic acid and water for nucleophilic attack on acetic anhydride. Copyright © 2003 John Wiley & Sons, Ltd.
Non‐empirical calculations of NMR indirect carbon‐carbon coupling constants. Part 5: Bridged bicycloalkanes
Authors: Krivdin Leonid B. 
Published: October 2003

AbstractAll possible J(C,C) of the bicarbocyclic frameworks together with J(C,H) and J(H,H) at bridgeheads in the series of six bridged bicycloalkanes, bicyclo[1.1.0]butane, bicyclo[2.1.0]pentane, bicyclo[3.1.0]hexane, bicyclo[2.2.0]hexane, bicyclo[3.2.0]heptane and bicyclo[3.3.0]octane, were calculated at the SOPPA level with correlation consistent Dunning sets cc‐pVTZ‐Cs augmented with inner core s‐functions and locally dense Sauer sets aug‐cc‐pVTZ‐J augmented with tight s‐functions and rationalized in terms of the multipath coupling mechanism and hybridization effects explaining many interesting structural trends. Copyright © 2003 John Wiley & Sons, Ltd.
25R/25S stereochemistry of spirostane‐type steroidal sapogenins and steroidal saponins via chemical shift of geminal protons of ring‐F
Authors: Agrawal Pawan K. 
Published: October 2003

AbstractA method based on the differences among the 1H NMR chemical shifts of geminal protons of ring‐F methylene resonances (H2‐23, H2‐24 and H2‐26) is proposed for ascertaining the 25R/25S stereochemistry of ring‐F unsubstituted spirostane‐type steroidal sapogenins and steroidal saponins. Copyright © 2003 John Wiley & Sons, Ltd.
A new coumarin from Perezia hebeclada
Authors: Hernández‐Carlos Beatriz , Burgueño‐Tapia Eleuterio , Joseph‐Nathan Pedro 
Published: October 2003

AbstractMethanol extracts from Perezia hebeclada roots yielded the new 8‐β‐D‐glucopyranosyloxy‐4‐methoxy‐5‐methylcoumarin (1) together with the known 4‐β‐D‐glucopyranosyloxy‐5‐methylcoumarin (2). Their structures were determined and verified, respectively, by MS and NMR studies, including 1D and 2D experiments. Two 13C NMR signals of the sugar residue of 2 were reassigned. Copyright © 2003 John Wiley & Sons, Ltd.
Assignment of 1H and 13C NMR data for diethyl 2‐ and 8‐quinolylmethylphosphonates and their palladium(II) dihalide complexes
Authors: Marinić Željko , Ćurić Manda , Vikić‐Topić Dražen , Tušek‐Božić Ljerka 
Published: October 2003

Abstract1H and 13C NMR spectral data for diethyl 2‐ and 8‐quinolylmethylphosphonates (L) and their palladium(II) dihalide complexes, trans‐[PdL2X2] (L = 2‐dqmp, 8‐dqmp; X = Cl, Br), are presented. The NMR analysis was performed on the basis of one‐ and two‐dimensional homo‐ and heteronuclear experiments including 1H, 13C, APT, 1H–1H COSY, 1H–13C COSY, HMQC and HMBC techniques. Copyright © 2003 John Wiley & Sons, Ltd.
Structure elucidation of [1,3]oxazolo[4,5‐e][2,1]benzisoxazole and naphtho[1,2‐d][1,3]‐ and phenanthro[9,10‐d]oxazoles using gradient selected gHMBC, gHMQC and gHMQC‐TOCSY NMR techniques
Authors: Katritzky Alan R. , Akhmedov Novruz G. , Wang Zuoquan , Roznyatovsky Vitaly A. , Shestopalov Aleksandr A. , Dennis Hall C. 
Published: October 2003

AbstractStructure elucidation of compounds in the benzisoxazole series (1–6) and naphtho[1,2‐d][1,3]‐ (7–10) and phenanthro[9,10‐d][1,3]oxazole (11–14) series was accomplished using extensive 2D NMR spectroscopic studies including 1H–1H COSY, long‐ range 1H–1H COSY, 1H–13C COSY, gHMQC, gHMBC and gHMQC‐TOCSY experiments. The distinction between oxazole and isoxazole rings was made on the basis of the magnitude of heteronuclear one‐bond 1JC2, H2 (or 1JC3, H3) coupling constants. Complete analysis of the 1H NMR spectra of 11–14 was achieved by iterative calculations. Gradient selected gHMQC‐TOCSY spectra of phenanthro[9,10‐d][1,3]oxazoles 11–14 were obtained at different mixing times (12, 24, 36, 48 and 80 ms) to identify the spin system where the protons of phenanthrene ring at H‐5, H‐6 and at H‐9 and H‐7 and H‐8 were highly overlapping. Copyright © 2003 John Wiley & Sons, Ltd.
Occurrence of A‐waves in F‐wave studies of healthy nerves
Authors: Puksa Leena , Stålberg Erik , Falck Björn 
Published: October 2003

AbstractA‐waves are compound muscle action potentials that follow the M‐wave with a constant shape and latency; usually they are detected during F‐wave studies. A large reference value database for F‐wave parameters from the median, ulnar, peroneal, and tibial nerves was collected from 121–196 subjects aged 14 to 95 years without known pathology involving the studied nerves. From this material, we studied retrospectively the occurrence of A‐waves. To be included, an A‐wave had to be clearly discriminated from the baseline in at least 8 of 20 traces with a jitter of less than 0.5 ms. A‐waves occurred in 25% of the tibial nerves studied and 14% of the peroneal nerves but in only 2% of median and ulnar nerves. In the peroneal and tibial nerves, the frequency of A‐waves increased with age, suggesting that A‐waves may be related to normal age‐related mild neuropathic changes of alpha motor neurons. Thus, A‐waves are frequently found in lower‐extremity nerves in healthy subjects and less commonly in upper‐extremity nerves. Their presence must therefore be interpreted with caution and cannot be taken as necessarily indicative of abnormality. Muscle Nerve 28: 626–629, 2003