bluuebunny/crossref_metadata_2025 huggingface dataset:
Liquid crystalline properties of unsegmented and segmented polyurethanes synthesised from high aspect ratio mesogenic diols
Authors: Srinivasan Kalathur Sabdham Vangepuram , Padmavathy Tallury
Published: October 2003

A series of novel tetrad high aspect ratio mesogenic diol monomers 4‐{[4‐(n‐hydroxyalkoxy)‐phenylimino]‐methyl}‐benzoic acid 4‐{[4‐(n‐hydroxyalkoxy)‐phenylimino]‐methyl}‐phenyl ester were prepared with varying alkoxy spacer length (n=2,4,6,8,10) by reacting 4‐formylbenzoic acid 4‐formylphenyl ester and 4‐(n‐hydroxyalkoxy) anilines. Two series of thermotropic main chain liquid crystalline unsegmented polyurethanes (PUs) were obtained by the polyaddition of the mesogenic diols with hexamethylene diisocyanate (HMDI) and methylene bis(cyclohexylisocyanate) (H12MDI) in dimethylformamide respectively. The effect of the incorporation of a third component namely polyol on the liquid crystalline properties of the polyurethanes was also studied. Linear segmented PUs were synthesised by a two‐step block copolymerisation method. The PUs synthesised were based on six spacer mesogenic diol chain extender, soft segments poly(tetramethylene oxide)glycol (PTMG) (Mn= 650,1000,2000) and polycaprolactone diol (PCL) (Mn=530,1250,2000) of varying molecular weights and different diisocyanates including HMDI, H12MDI and methylene bis(phenylene isocyanate) (MDI). Structural elucidation was carried out by elemental analysis, fourier transform infra red (FT‐IR), nuclear magnetic resonance (1H NMR and 13C NMR) spectroscopy. Inherent viscosity of the unsegmented polymers measured in methanesulphonic acid at 26°C was in the range of 0.13 ‐ 0.65 dL/g while the molecular weights and molecular weight distribution of the segmented polyruethanes was determined using gel permeation chromatography (GPC). Mesomorphic properties were studied by differential scanning calorimetry (DSC) and hot stage polarising optical microscopy and the thermal stability was determined by thermogravimetric(TG)analysis. The monomeric diols and the polyurethanes exhibited nematic texture and good mesophase stability. It was observed that the partial replacement of the mesogenic diol by the polyol of varying molecular weights influenced the phase transitions and the occurrence of mesophase textures. The phase transition temperatures of the investigated polyurethanes showed dependence on the chain length of the soft segment and on the content of the mesogen moiety. A higher content of mesogenic moiety was needed to obtain liquid crystalline property when the soft segment length was increased as observed in the case of PTMG. Grained and threaded textures were observed depending on the molecular weight of the soft segment, the mesogen content and the diisocyanate. The stress‐strain analyses showed that the polymers bused on high molecular weight PTMG soft segment have elastomeric property while the PCL based PUs displayed no elastomeric property.
Designing aromatic polyamides and polyimides for gas separation membranes
Authors: de Abajo Javier , de la Campa José G. , Lozano Angel E.
Published: October 2003

Aromatic polyamides and polyimides with improved gas permselectivity, can be designed and prepared by systematically changing structural elements that affect these properties. Indeed, a conscientious choosing of the chemical changes may still provide a promising approach to get better and better polymers for selective filtration of gases.

The results of this work, in which novel monomers have been used, have confirmed that gas permeability through aromatic polyamides and polyimides much higher than that of conventional polyamides and polyimides can be achieved. It has been done by introducing bulky side groups, using non‐planar monomers, and combining these elements on both monomers: diamines and dianhydrides or diamines and diacids. A theoretical study has also been made to explain the behaviour of some individual polymers, comparing experimental and calculated values of density and free volume.
New reactive polymeric systems for use as waveguide materials in integrated optics
Authors: Dreyer Christian , Schneider Jürgen , Göcks Karin , Beuster Brigitte , Bauer Monika , Keil Norbert , Yao Huihai , Zawadzki Crispin
Published: October 2003

Cross‐linked polymeric materials are used in a wide range of applications. Special compositions are used in micro‐system technologies and its utilization is extending to integrated optics. We have been working for several years in the field of polymers for optical applications.

Highly fluorinated polycyanurate systems have been proven as promising waveguide materials in integrated optics. The refractive index can be adjusted reproducibly in a wide range almost continuously. The layer quality was optimized. Low optical losses of less than 0.3 dB/cm@1550nm were obtained and working optical prototypes were developed. The birefringence had been a major problem, but this was solved by adjusting the coefficient of thermal expansion of substrate and film.

We will report in this paper on the polycyanurate ester resins and the new triazine containing polymeric systems.
Low viscous unsaturated polyester resin for monomer free UP‐resins
Authors: Hegemann Günter
Published: October 2003

It was possible to develop comonomer free unsaturated polyester resins for the application in electrical industry. By testing model compounds and mixtures of model compounds it was possible to find the optimised structure of the resin molecule with respect to the position of the copolymerizable double bonds. By choosing the proper composition of the other components of the resin, e.g. the glycols and modifying dicarboxylic acids, it was also possible to manufacture low viscous resins.
New generation of fire retardant polyester resins
Authors: Kicko‐Walczak Ewa
Published: October 2003

Smoke evolution [in a smoke chamber (750 x 750 x 1000) ± 5 mm, Polish Standard PN‐91/K‐02501 equivalent to UIC 561‐OR (1991)] was studied in, and the oxygen index flammability test (Polish Standard PN‐76/C‐89020) was carried out for, glass‐reinforced polyester (GRP) laminates obtained with unsaturated polyester (UP) resins containing chlorine and bromine in the chain. In these studies, the effect on these properties of such additives as ZnSnO3 (ZS), ZnSn(OH)6 (ZHS), Al(OH)3 or Mg(OH)2 and Sb2O3 in an amount of up to 30 mass‐% was determined. The most efficient ignition and smoke‐evolution retarder from among the investigated compounds was ZS and ZHS, whereas an essential reduction in smoke evolution was observed also with Sb2O3. GRP laminates with these additives meet the fire‐safety recommendations concerning smoke evolution from materials used in transportation means and in the building industry.
Synthesis, characterization and properties of polycarbonate containing carboxyl side groups
Authors: Zhang Ruifeng , Moore J.A.
Published: October 2003

Diphenolic Acid, DPA [bis(4‐hydroxyphenyl)pentanoic acid] can be made from cellulose‐rich waste. The t‐butyl ester was converted to homo‐ and copolycar‐ bonates (with bis‐phenol‐A, BPA). Deblocking the ester yielded polycarbonates with pendent carboxyl groups that exhibit all the properties of polyelectrolytes and retain solubility in aqueous base without degradation for long periods.
New silicon‐containing heterocyclic polyimides
Authors: Schulz Burkhard , Hamciuc Elena , Köpnick Thomas , Kaminorz Yvette , Bruma Maria
Published: October 2003

New aromatic polyimides and polyamide‐imides with phenylquinoxaline rings and dimethylsilane units have been synthesized by solution polycondensation reaction of aromatic diamines containing phenylquinoxaline units with bis(3,4‐dicarboxyphenyl)‐dimethylsilane dianhydride, or with a diacid chloride resulting from the reaction of this dianhydride with p‐aminobenzoic acid. These polymers were easily soluble in organic solvents, such as N‐methylpyrrolidinone and dimethylacetamide, and showed high thermal stability with decomposition temperature being above 440°C and glass transition temperature in the range of 245‐285°C. Very thin coatings were deposited from polymer solutions onto silicon wafers and exhibited smooth, pinhole‐free surface in atomic force microscopy investigations. Some of these polymers showed blue fluorescence in solution and films, with a maximum in the range of 415‐425 nm.
Active polycondensation: from pep tide chemistry to amino acid based biodegradable polymers
Authors: Katsarava Ramaz
Published: October 2003

New polycondensation (PC) methods of polymer synthesis using non‐traditional active derivative of dicarboxylic acids are reviewed. The new PC methods are named by general name “Active Polycondensation” (APC) to tell them from traditional low‐temperature PC. The most of these methods are based on well known in peptide chemistry approaches to the activation of carboxylic groups. In the present paper the syntheses of heterochain polymers of basic classes ‐ polyamides, polyesters, polyurethanes, polyureas, and polybenzazoles by interaction of various active diesters with di‐ and polyfunctional nucleophiles are discussed in brief. Special attention is given to the synthesis of non‐conventional heterochain macromolecular systems, in particular poly(ester amide)s (PEAs), composed of naturally occurring α‐amino acids and other non‐toxic building blocks like fatty diacids and diols ‐ synthetic analogues of naturally occurring amino acid based polymers ‐ peptides and proteins. The synthesis and properties, biodegradation, and some practical applications of PEAs are discussed in brief.
Stereochemistry driven cocrystallisation phenomena in partially cycloaliphatic polyamides
Authors: Koning Cor , Vanhaecht Bert , Willem Rudolph , Biesemans Monique , Goderis Bart , Rimez Bart
Published: October 2003

Two series of isomeric copolyamides were synthesised, viz. polyamides 12.6 for which the adipic acid residues were partially replaced by cis/trans‐1,4‐cyclohexanedicarboxylic acid (1,4‐CHDA), and polyamides 4.14 for which the 1,4‐diaminobutane residues were partially replaced by cis/trans‐1,4‐diaminocyclohexane (1,4‐DACH). A careful DSC and WAXS analysis learned that only the trans isomers of both 1,4‐DACH and 1,4‐CHDA are incorporated into the crystalline phase. During DSC analysis, an intitial high trans content is preserved in the case of the non‐isomerising 1,4‐DACH, whereas the 1,4‐CHDA residues gradually isomerise from a high initial trans content to a significanly lower trans content. Since these cis residues are not incorporated into the crystalline domains, the lower second heating melting points of the 1,4‐CHDA‐based copolyamides in comparison with 1,4‐DACH‐based copolyamides, having similar cycloaliphatic monomer contents, can be understood.
Vinyl monomers containing active hydrogen atoms are a new type of monomer for polycondensation
Authors: Rozenberg Boris A.
Published: October 2003

The latest findings in author's laboratory devoted to the understanding kinetic peculiarities and mechanism of vinyl macromonomers formation by the example of anionic polymerization of 2‐hydroxyethylacrylate (HEA) and 2‐hydroxyethylmethacrylate (HEMA) containing group with mobile hydrogen atoms are discussed. It was shown that polymerization is accompanied by proton‐transfer in each elementary propagation step, which leads to isomerization of the backbone and formation of polyester type macromonomers. Polymerization is accompanied by side transesterification reaction with formation of polyester diacrylates and polyester diols. The peculiarities of polymerization mechanism under the action of alkali metals and its alkoholates were established. Expected applications of the polymerization products are discussed.
Copolyesters based on poly(butylene terephthalate)s containing cyclohexyl groups: synthesis, structure and crystallization
Authors: Sandhya T.E. , Ramesh C. , Sivaram S.
Published: October 2003

Poly(butylene terephthalate‐co‐cyclohexylene dimethylene terephthalate) copolymers PBTCT, were synthesized by melt condensation with compositions ranging from 94/08 to 23/77. 13C NMR spectroscopy was used to study the microstructure of the copolyesters and was found to be completely random. The melting temperature, crystallization temperature on cooling, enthalpy of melting and crystallization followed an eutectic behaviour. Thermal and x‐ray diffraction studies indicated that the copolyesters in all composition could crystallize. The XRD studies further indicated that PBT rich copolyesters in the range 75 to 100% BT, crystallized in the PBT lattice while the copolyesters rich in PCT having 38 to 100% CT, crystallized in the PCT lattice.
Atypical polysaccharide physical gels: structure/property relationships
Authors: Clayer Alexandra , Vachoud Laurent , Viton Christophe , Domard Alain
Published: October 2003

Chitin and chitosan are polysaccharides produced by the biomass. They have the same general chemical structure and constitute the series of linear copolymers of linked β, (1‐>4) glucosamine and N‐actylglucosamine. We studied the possibility of forming physical gels with all the terms of this series, whatever the proportion of the two kinds of residues included in the polymer chains. We show that physical gelation is still possible through a percolating process when certain important conditions are met. Initially the concentration in polymer must be above C*; a critical value of the balance between hydrophobic and hydrophilic interactions must be achieved and gelation must occur simultaneously everywhere in the medium. These conditions were observed in several situations allowing the formation of different kinds of gels at all values of DA. In view of the rare bio‐active properties of chitin and chitosan, these gels were tested for living tissue regeneration and constitute very interesting examples in illustration of our concept of decoys for biological media.
Encapsulation of magnetic self‐assembled systems in thermoreversible gels
Authors: Guenet Jean‐Michel , Poux Sandrine , Lopez Daniel , Thierry Annette , Mathis André , Green Mark M. , Liu Weihong
Published: October 2003

We describe two different ways of encapsulating within the fibrils of thermoreversible polymer gels the filaments of a supermolecular polymer formed by self‐assembly of a bicopper complex. Heterogeneous nucleation is brought about with gels made from isotactic poly(styrene) while compound formation occurs with gels made from poly(hexyl isocyanate). These ways depend upon the interaction between the wings of the supermolecular polymer and the side groups of the polymer. In all cases, the filaments retain their 1‐D structure. Preliminary results from magnetic susceptibility measurements show a striking difference between the pure and the encapsulated supermolecular polymer.
Calcium induced volume transition in polyelectrolyte gels
Authors: Horkay Ferenc , Basser Peter J. , Hecht Anne‐Marie , Geissler Erik
Published: October 2003

The osmotic properties and the small angle neutron scattering (SANS) behaviour of fully neutralized sodium polyacrylate gels are investigated in the presence of calcium ions. Analysis of the SANS response displays three characteristic length scales, two of which are of thermodynamic origin, while the third, associated with the frozen‐in structural inhomogeneities, is static. The SANS results are consistent with direct osmotic observations which indicate that the thermodynamic properties cannot be adequately described by a single correlation length. The concentration dependence of the osmotic pressure displays a power law behaviour with an exponent that decreases with increasing calcium concentration.
Hyperelasticity and stress softening of filler reinforced polymer networks
Authors: Klüppel Manfred
Published: October 2003

Starting from an analysis of filler networking in bulk polymers, a constitutive micro‐mechanical model of stress softening and hysteresis of filler reinforced polymer networks is developed. It refers to a non‐affine tube model of rubber elasticity, including hydrodynamic amplification of the rubber matrix by a fraction of hard, rigid filler clusters with filler‐filler bonds in the unbroken, virgin state. The filler‐induced hysteresis is described by an anisotropic free energy density, considering the cyclic breakdown and re‐aggregation of the residual fraction of soft filler clusters with already broken, damaged filler‐filler bonds. Experimental investigations of the quasi‐static stress‐strain behaviour of silica and carbon black filled rubbers up to large strain agree well with adaptations found by the developed model. The microscopic material parameters obtained appear reasonable, providing information on the mean size and distribution width of filler clusters, the tensile strength of filler‐filler bonds and the polymer network chain density.
Reinforced superabsorbent polyacrylamide hydrogels
Authors: Philippova Olga E. , Zaroslov Yuri D. , Khokhlov Alexei R. , Wegner Gerhard
Published: October 2003

The ability of linear stiff‐chain poly(sodium p‐phenylenesulfonate) to self‐assemble in aqueous media with the formation of rodlike aggregates was used to immobilize it in a polyacrylamide network without covalent bonding. It was shown that polyelectrolyte rods impart simultaneously two useful properties to the gel: higher ability to absorb water and higher mechanical strength. The counterions of charged rods ensure the enhancement of the absorption capacity of the gel, while stiff elements strengthen the gel. This makes such systems potentially promising as superabsorbent materials.
Outstanding covalent conjugated gels: electrically conducting rubbers
Authors: Pépin‐Donat Brigitte , Viallat Annie
Published: October 2003

Four series of fully conjugated poly(octylthiophene) gels were prepared by oxidative copolymerization of octylthiophene with four different cross‐links (trithienylbenzenes) of functionalities f=3 or 6 and by varying the cross‐link ratio R. The gels exhibit rubber elasticity and swell in apolar solvents. The gel fraction, the swelling ratio Q, the elastic modulus, and a NMR structural parameter display master curves of variations versus the variable fR, which characterises the statistical structure of the gels. This result shows that the linear chain segments comprised between adjacent cross‐links govern the deformation properties of the networks. Transport properties were explored. The gels are photoluminescent. When doped (oxidation by iodine), they are electronically conducting both in dry and swollen states. At large Q intra‐chain hopping mechanisms govern the conductivity while at small Q, intermolecular hopping processes are predominant. Cross‐links are not a limitation to conductivity.
Polymer gels and brushes at surfaces
Authors: Vilgis T.A. , Joanny J.F. , Johner A.
Published: October 2003

We discuss the adsorption of polymer gels on flat surfaces. Even in cases of complete wetting, where the spreading power S is positive and where an equivalent liquid would spread, the elastic stresses due to the gel deformation upon adsorption oppose spreading. The competition between elasticity characterized by the bulk shear modulus G and capillarity, characterized by the spreading power S, defines a typical length scale 1 = S/G for the deformation in the gel. Macroscopic gels larger than 1 deform only at their edges over a region of size 1. Microscopic gels show a finite deformation despite the elastic stresses. These results can be compared to confined polymer brushes.
Thermal and photo‐actuation in nematic elastomers
Authors: Warner Mark , Terentjev Eugene
Published: October 2003

Mono domain nematic elastomers change shape by as much as 400% on being heated from the nematic to isotropic state. The reason is that nematic order, Q, elongates the distribution of chains and thus the network that they form. Experimental evidence for this, and simple theory is presented. A novel method to change Q, and hence obtain an analogous elastic strain, is to bend the nematic's rods by photoisomerization. On absorbing a photon, photochromes such as azo rods leave the (straight) trans state and adopt the cis (bent) form. We show data and give simple theory to explain this remarkable, reversible elastic phenomenon.
Modelling auto‐acceleration in DGEBA/diamine systems
Authors: González M. , Kindelán M. , Cabanelas J.C. , Baselga J.
Published: October 2003

Curing of epoxy resins with aliphatic diamines at low temperatures deviates from the 4EQ mechanism (catalytic and non‐catalytic dual path) at relatively low conversions, far from vitrification. Although the Horie mechanism relies on a third order reaction it is possible a more realistic approach to epoxy curing kinetics if a detailed analysis of auto‐acceleration is made. A single parameter dependent only on the nature of the amine is proposed.
Microscopic deformation of filler particles in rubber under uniaxial deformation
Authors: Belina Gábor , Urban Volker , Straube Ekkehard , Pyckhout‐Hintzen Wim , Klüppel Manfred , Heinrich Gert
Published: October 2003

Structural studies of filled polymer networks under periodic deformation are of great importance to the industries concerned with rubber. The degree of reinforcement provided by the filler depends on a number of variables: the size of the polymer‐filler interface, the size of primary particles, the size and shape of filler clusters. In the tyre industry it is necessary to optimize mechanical properties such as low rolling resistance, good wet grip and long lifetime. There have been studies of unfilled polymer networks and filler model‐systems (block copolymers),[1,2] but because their complexity, industrial rubber samples have escaped investigations. We performed SAXS, USAXS and SANS measurements on carbon black filled natural rubber (poly‐isoprene) under uniaxial deformation at ESRF ID‐02 and Forschungszentrum Jülich KWS‐2. The scattering patterns of the studied filler particles show power‐law decay over many decades in scattering vector q. At the scale of primary particles we detected surface fractal behavior and for the characteristic size of the primary particles we calculated lengths of the order of 10 nm. X‐ray scattering was used for time resolved experiments (about 10 frames per second) and neutron scattering was used to distinguish between scattering from the studied fillers and the additives (especially zinc oxide) used in industrial materials.
Arabinoxylan networks as affected by ovalbumin content
Authors: Carvajal‐Millan Elizabeth , Surget Anne , Rouau Xavier , Guilbert Stéphane , Micard Valérie
Published: October 2003

Solutions (1% w/v) of water‐extractable arabinoxylans (WEAX) from wheat were mixed with ovalbumin solutions at different concentrations in order to obtain different protein/polysaccharide ratios (0, 0.6, 2.5, 5.0, 7.5 and 10.0). These mixtures were oxidized by a laccase (Pycnoporus cinnabarinus). The kinetics of gelation was monitored by rheological measurements of the storage modulus (G′) and loss modulus (G″) at 25°C during 2 h. In the different ovalbumin/WEAX mixtures, WEAX cross‐linking occurred as shown by an increase in G′. However, final G′ decreased as a function of protein concentration from 17.2 Pa (WEAX) to 7.1 Pa (ovalbumin/WEAX=10), following a sigmoidal relationship. Ovalbumin is probably entrapped in a WEAX covalent network, which explains the changes in rheological properties, but it does not participate in the network formation. Ferulic acid oxidation and diferulic acid formation was delayed at ovalbumin/WEAX=5.0 until 40 min but not at the end of gelation. In the same mixture SH groups from ovalbumin oxidized more rapidly than the protein alone. Ovalbumin via SH groups are probably responsible for the FA oxidation delay and the weaker WEAX gel formed by blocking the enzymatically formed free radicals.
Rheological investigation of swollen gluten polymer networks: effects of process parameters on cross‐link density
Authors: Domenek Sandra , Morel Marie‐Hélène , Redl Andreas , Guilbert Steéphane
Published: October 2003

Wheat gluten samples were subjected to different thermo‐mechanical treatments. Kinetics of protein aggregation and changes in network structure were investigated through biochemical and rheological measurements. Temperature induced protein aggregation through disulphide cross‐links. Shear treatment alters the aggregation mechanism since a lower energy of activation was observed. Accumulation of aggregated protein enhances the elastic behaviour of the material. The strong correlation found between the extent of protein aggregation and the molecular weight between cross‐links reveals the important role of covalent bonds in the network connectivity.
Filler networks in elastomers
Authors: Ehrburger‐Dolle Françoise , Bley Françoise , Geissler Erik , Livet Frédéric , Morfin Isabelle , Rochas Cyrille
Published: October 2003

Elastomers are soft materials that can be reinforced by dispersing into them nanosized solid particles. Common examples of the latter are silica or carbon black aggregates. However, the mechanism of reinforcement is still not yet fully understood. Our work consists in investigating by small‐angle X‐ray scattering (SAXS) the structure of the aggregate network spreading throughout the matrix in the initial sample and its modification during and after straining (elongation). The goal is to relate the macroscopic mechanical behaviour with the structure of the aggregate network. The present paper is a qualitative overview of recent results obtained on well defined composites.
Percolation model of hyperbranched polymerization
Authors: Galina Henryk , Lechowicz Jaromir B. , Potoczek Marek
Published: October 2003

Computer simulations of the step‐growth homopolymerization of an AB2 monomer have been carried out on a square lattice. No rearrangements of units were made between reaction events. Instead, the capture radius, i.e., the maximum distance between the randomly selected unit and its reaction partner was changed. The reaction was considered as controlled either by diffusion and local concentration fluctuations or by the law of mass action (classical limit). The size distribution of polymer species and the extent of cyclization reactions in the polymerization are discussed.
Interaction of non‐ionic hydrogels with weak aromatic acids
Authors: László Krisztina , Kosik Katalin , Filipcsei Genovéva , Zrínyi Miklós
Published: October 2003

Measurements are reported of the swelling behaviour at 20°C of poly (N isopropylacrylamide) (PNIPA) gels in aqueous solutions of two weak aromatic acids, phenol and resorcinol. For solute concentrations below 45 mmol/l the uptake of these solutions is similar. Due to selective solvation phenol exhibits an excess equilibrium concentration inside the gel of 5% over that in the surrounding bath, while for resorcinol, the excess is found to be 12%. At 50 mmol/l solute concentration, both systems display a volume transition accompanied by expulsion of the solvent. The solubility limits in water of these aromatic compounds, which are significantly different from each other (870 mmol/l and 9080 mmol/l respectively), are far above this critical concentration. In the collapsed condition the expelled liquid spreads on the surface of the phenol treated gel, while an ordered arrangement of separate droplets is generated in the case of resorcinol. In the latter case an acute contact angle was observed. It is also shown by acid‐base titration that the PNIPA/water system may exhibit a slight ion exchanging character.
Evaluation of the degree of cross‐linking of cellulose‐based superabsorbent hydrogels: a comparison between different techniques
Authors: Lionetto Francesca , Sannino Alessandro , Mensitieri Giuseppe , Maffezzoli Alfonso
Published: October 2003

Three different techniques have been applied to the evaluation of the degree of cross‐linking of superabsorbent cellulose‐based hydrogels obtained from water solutions of carboxymethylcellulose sodium salt (CMCNa) and hydroxyethylcellulose (HEC), chemically cross‐linked with divinyl sulfone. These polyelectrolyte hydrogels are biodegradable and have the same sorption capacity as acrylate‐based superabsorbents on the market. A 13C solid state NMR analysis was carried out on dry samples of hydrogel to obtain the degree of cross‐linking, an important parameter that affects the swelling and mechanical properties of a hydrogel. Dynamic mechanical analysis was performed during the hydrogel cross‐linking using a parallel plate rheometer under oscillatory deformations in order to monitor the evolution of the hydrogel viscoelastic properties during the synthesis. The value of |G*| and the slope of the stress‐deformation ratio plots from uniaxial compression tests were used to evaluate the elastically effective degree of cross‐linking according to classical rubber elasticity theory. Moreover, a dynamic mechanical analysis was carried out on cross‐linked hydrogels at different degrees of swelling in order to investigate the influence of the swelling on the mechanical properties and the application of rubber elasticity theory to swollen hydrogels.
Thermodynamics of water sorption in acrylic homonetworks and IPNs
Authors: Gallego Ferrer Gloria , Monleón Pradas Manuel , Gómez Ribelles José Luis
Published: October 2003

The equilibrium thermodynamic properties of poly(hydroxyethyl acrylate) and poly(ethyl acrylate)‐i‐poly(hydroxyethyl acrylate) hydrogels are investigated starting from the water sorption isotherms of the systems. Partial enthalpy and entropy of the sorbed water in the gel differ markedly from the values of pure water at the lowest water contents, and tend to those of liquid water as saturation is approached. The residual mixing free energy is calculated, as a means of assessing the intensity of the water‐polymer interaction. Its small positive magnitude shows that water‐polymer hydrogen bonds are labile compared to water‐water and polymer‐polymer hydrogen bonds, and thus the stability of the gel state is still mainly due to the combinatorial entropic contribution to the mixing free energy. An equation correctly describing the sorption isotherms, when combined with the thermodynamic equations, can deliver the true water‐polymer interaction parameter and its dependence on the polymer volume fraction in the gel.
Ion condensation in a polyelectrolyte gel
Authors: Morfin Isabelle , Horkay Ferenc , Basser Peter J. , Bley Françoise , Ehrburger‐Dolle Françoise , Hecht Anne‐Marie , Rochas Cyrille , Geissler Erik
Published: October 2003

Anomalous small angle X‐ray scattering is used to determine the distribution of divalent ions in a neutralized polyelectrolyte gel of sodium polyacrylate in the vicinity of the volume transition. At the five different energies of the incident beam used to vary the contrast, the scattering curves have similar shapes, and are separated only by constant multiplying factors. This result, in conjunction with SANS results from the same sample, indicates that the divalent ion (strontium) is confined on the polymer backbone.
Compression elastic modulus of neutral and protonated poly(N‐vinylimidazole) hydrogels
Authors: Valencia Joaquín , Baselga Juan , Pacios Isabel E. , Piérola Inés F.
Published: October 2003

The compression modulus of poly(N‐vinylimidazole) (PVI) hydrogels synthesized by cross‐linking polymerization in aqueous solution, was measured at room temperature in several related systems: i) just after polymerization, ii) swollen at equilibrium in deionized water, iii) swollen in HCl (aq) (pH=2.5), iv) swollen in HCl (pH=2.5) and 1 M NaCl (aq) solution and v) swollen in H2SO4 (pH=2.5) (aq) solution. Samples of the first and second groups are neutral whereas hydrogels of the other three groups are ionic because of protonation of basic imidazole groups. The experimental results were fitted with the Erman‐Monnerie theory, applied to compression measurements for the first time, to determine the phantom modulus, [fph*], and the parameter κG which measures the constraining role of entanglements on the fluctuations of chains between knots.
A Monte Carlo simulation of a knotted linear chain system as an elementary network fragment
Authors: Romiszowski Piotr , Sikorski Andrzej
Published: October 2003

We present the results of the Monte Carlo simulations of the dynamics of the linear chain system. The chains were constructed on a simple cubic lattice. The simulations were carried out by means of the classical Metropolis sampling method with the excluded volume effect present. No other interactions were introduced into the system (athermal polymer case). The linear chains in the system were constructed in such a way that there were knots at certain positions. Also, some chains were threaded through the knots forming the topological constraints in the system. The system under consideration underwent a series of micromodifications during the simulation run. Then the trajectory was analysed and the dynamics of the system was described by means of the autocorrelation functions. The short‐time dynamics enabled us to investigate whether or not the knotted constraints affect the local dynamics of the chains. Also the long‐time dynamics of the system can be useful in the characterizations of the dynamical properties of the fragments of the networks.
Predicting the modulus of end‐linked networks from formation conditions
Authors: Stepto R.F.T. , Cail J.I. , Taylor D.J.R.
Published: October 2003

The application of a Monte‐Carlo (MC) algorithm to account fully for loop formation in RA2 + R′B3 and RA2 + R′B4 polymerizations is described. The resulting interpretation of experimental elastic moduli of HDI‐based polyurethane networks prepared at different dilutions shows it is essential to account for elastic losses in loop structures of all sizes. An important parameter, x, is introduced, namely the average fractional loss of elasticity per larger loop structure relative to the loss per smallest loop structure. Values of x vary between 0.50 and 0.60. Subsequent application of the MC calculations to the formation and resulting structures of MDI‐based polyurethane networks and poly(dimethyl siloxane) networks again predicts significant reductions in modulus due to loop structures. However, comparison with experimental modulus data shows that the reductions in modulus due to loops are outweighed by increases due to chain interactions and to topological entanglements.
Viscoelastic properties of polyacrylonitrile gels: dependence of sol‐gel transition on concentration and aging time
Authors: Tanaka Yutaka
Published: October 2003

Dynamic viscoelasticity was observed for polyacrylonitrile solution in dimethylacetamide in the process of sol‐gel transition. The gel was prepared by the freezing and thawing method, i.e., the solution was frozen at −50°C and then kept at 25°C so as to undergo gelation. The longer the freezing time, the shorter was the gelation time. Also the higher the concentration, the shorter the gelation time. The strength of the network, S and critical exponent n at the transition point were evaluated. The S value increased with increasing concentration and was constant in value in spite of the variation of freezing time when the concentration of the solution was constant.
Deterministic solutions for a step‐growth polymerization
Authors: Choi Sungjae , Liu Xiangdong , Timm Delmar C.
Published: October 2003

Chain topology, including branch node, chain link and cross‐link dynamics that contribute to the number of elastically active strands and junctions, are calculated using purely deterministic derivations. Solutions are not coupled to population density distributions. An eigenzeit transformation assists in the conversion of expressions derived by chemical reaction principles from time to conversion space, yielding transport phenomena type expressions where the rate of change in the molar concentrations of branch nodes with respect to conversion is expressed as functions of the fraction of reactive sites on precursors and reactants. Analogies are hypothesized to exist in cross‐linking space that effectively distribute branch nodes with i reacted moieties between cross‐links having j bonds extending to the gel. To obtain solutions, reacted sites on nodes or links with finite chain extensions are examined in terms of stoichiometry associated with covalent bonding. Solutions replicate published results based on Miller and Macosko's recursive procedure and results obtained from truncated weighted sums of population density distributions as suggested by Flory.
Properties of epoxy systems with clay nanoparticles
Authors: Zelenková Mysková Markéta , Zelenka Jiři , Spaček Vladimir , Socha Frantisek
Published: October 2003

Low molecular epoxy resin was mixed with different concentrations of montmorillonite clay with alkylamine‐modified surface. The presence of the clay nanoparticles influences the gel time of the amine cured resin as well as the mechanical properties. Toughness and modulus, both in the glass and the rubberlike region, increase with clay concentration. An increasing amount of lower mobility phase with increased clay concentration was observed.
Pyridine and aminide derivatives as ligands in 1 : 1 Rh2[tfa]4 adducts: 1H, 13C and 15N NMR study
Authors: Jaźwiński Jarosław , Duddeck Helmut
Published: October 2003

1H, 13C and 15N chemical shifts of some pyridines and mesoionic oxatriazole aminides were recorded in the absence and presence of the complex dirhodium tetrakis(trifluoroacetate). The adduct formation shifts prove that the nitrogen atom in the pyridine derivatives and the N‐6 atom of the aminides are the binding sites in the adducts. At low temperature, adduct species can be identified separately by their individual signals. The 15N chemical shift responds very sensitively even to small concentration changes in the adduct. Copyright © 2003 John Wiley & Sons, Ltd.
The advantages of forward linear prediction over multiple aliasing for obtaining high‐resolution HSQC spectra in systems with extreme spectral crowding
Authors: Reynolds William F. , Enriquez Raul G.
Published: October 2003

The resolution obtained for the highly crowded 13C–1H HSQC spectrum of a mixture of three trisaccharides using forward linear prediction is compared with that recently reported for the same mixture but using multiple (100‐fold or greater) aliasing of HSQC spectra in combination with a computer program to unfold the aliased spectra. It is shown that forward linear prediction gives slightly superior resolution while avoiding the significant sensitivity loss associated with the very narrow spectral windows and consequent long evolution times required for the multiple aliasing method. Copyright © 2003 John Wiley & Sons, Ltd.
Improvement of double pulsed field gradient spin‐echo ROESY experiments for identification of bound waters
Authors: Furihata Kazuo , Shimotakahara Sakurako , Tashiro Mitsuru
Published: October 2003

A novel pulse sequence incorporating the double pulsed field gradient spin‐echo (DPFGSE) and the gradient‐tailored excitation WATERGATE techniques is presented that has particular use for identifying bound waters in 15N‐labeled macromolecules. This sequence, DPFGSE–ROESY–HSQC, affords greater spectral sensitivity than the DPFGSE–ROESY–HMQC experiment which was previously presented and is consequently useful for rapidly obtaining reliable information for characterizing macromolecular bound water molecules. A significant enhancement in the sensitivity is achieved by using the gradient‐tailored excitation WATERGATE sequence in the reverse INEPT step as it allows the use of much higher receiver gains. Since coherence selection is not used, the sequence has improved sensitivity together with less spectral artifacts. The advantage of this pulse sequence is illustrated using 15N‐labeled ribonuclease T1. Copyright © 2003 John Wiley & Sons, Ltd.
Theoretical study on 19F magnetic shielding constants of some metal fluorides
Authors: Cai Shu‐Hui , Yu Xian‐Yong , Chen Zhong , Wan Hui‐Lin
Published: October 2003

A study is presented of 19F NMR magnetic shielding constants of MF2 (M = Zn, Cd), β‐PbF2, MF3 (M = Al, Ga, In), AMF3 (A = K, Rb, Cs, Ba; M = Mg, Ca, Li, Zn, Cd), BaMgF4, BaZnF4 and Ba2ZnF6 using the DFT/GIAO method. The aug‐cc‐pVTZ basis set was used for the fluorine atom under investigation and LanL2DZ for the remaining fluorine atoms. The 3–21G(2d) basis set was used for the aluminum atom and CRENBL for the other metal atoms. When appropriate cluster models were employed, the theoretical results obtained from the B3LYP/GIAO calculations are in good agreement with experimental measurements and may be better than those obtained from empirical calculations. The correlation coefficient and the slope of the fitting line between our theoretical predictions and the experimental observations are close to unity. Copyright © 2003 John Wiley & Sons, Ltd.
Spin label study of phase morphology and polymer segmental motion in poly(acrylic acid)–poly(ethylene oxide) complex
Authors: Tan Li , Lu Guangqiang , Chen Shiming , Ping Zhenghua , Shen Yimin
Published: October 2003

The ESR lineshapes of nitroxide radical end‐labeled on poly(ethylene oxide) (SLPEO) for the pure polymer and for different weight ratio complexes with poly(acrylic acid) (PAA) were studied as a function of temperature. For SLPEO one spectral component was detected in the entire temperature range, indicating that the spin label was in the homogeneous phase domain. For all PAA–PEO complexes two spectral components with different rates of motion, a ‘fast’ and a ‘slow’ component, were observed, which indicates the existence of microheterogeneity at the molecular level: the more mobile the PEO‐rich microphase, the more rigid is the PAA‐rich microphase. On the other hand, the SLPEO polymer segmental motion was restricted owing to the hydrogen bond interaction between the carboxyl proton in PAA and the ether oxygen in PEO. This restriction was exacerbated with increasing the PAA content in the complex, which could be further substantiated through the calculated S and τc values. Copyright © 2003 John Wiley & Sons, Ltd.
Two new asterosaponins from the starfish Asterias rubens: application of a cryogenic NMR probe head
Authors: Sandvoss M. , Preiss A. , Levsen K. , Weisemann R. , Spraul M.
Published: October 2003

We report two new asterosaponins from the Baltic starfish Asterias rubens along with their 1H and 13C NMR data. The compounds were isolated after on‐flow liquid chromatography–NMR–mass spectrometry screening indicated that they had not been identified before. The one‐ and two‐dimensional NMR experiments used to elucidate the structures were recorded using a 5 mm cryogenic probe head. The advantages of cryogenic probes for this kind of examination in comparison with conventional probe heads are discussed. Copyright © 2003 John Wiley & Sons, Ltd.
Multiple quantum NMR spectra of toluene and p‐bromotoluene partially aligned in a nematic phase
Authors: Field Leslie D. , Ramadan Saadallah A.
Published: October 2003

1H multiple quantum (MQ) NMR spectra of toluene and p‐bromotoluene, partially aligned in a liquid crystalline solvent, were acquired using gradient‐assisted methods. The MQ spectra were analysed to give the dipolar couplings (Dij) and these were used to determine the molecular shape and average orientation of the of the spin systems. Copyright © 2003 John Wiley & Sons, Ltd.
Solid‐state NMR characterization of oxygen sites in organically modified aluminosilicate xerogels
Authors: Lafuma Aurélie , Fayon Franck , Massiot Dominique , Chodorowski‐Kimmès Sandrine , Sanchez Clément
Published: October 2003

Solid‐state NMR characterization of hybrid aluminosilicate xerogels, by 17O magic angle spinning (MAS) and triple quantum magic angle spinning (MQMAS) techniques, evidences Si—O—Si and Si—O—Al oxygen sites, spectrally separated in MQMAS experiments. Inversion of the MQMAS spectra allows the measurement of quadrupolar parameters, isotropic chemical shifts, distribution of chemical shift and discussion of the mobility of the structural units. Copyright © 2003 John Wiley & Sons, Ltd.
Acetylcholine receptor distribution and synapse elimination at the developing neuromuscular junction of mdx mice
Authors: Minatel Elaine , Neto Humberto Santo , Marques Maria Julia
Published: October 2003

The pattern of innervation of the vertebrate neuromuscular junction is established during early development, when junctions go from multiple to single innervation in the phenomenon of synapse elimination, suggesting that changes at the molecular level in the postsynaptic cell lead to the removal of nerve terminals. The mdx mouse is deficient in dystrophin and associated proteins that are part of the postsynaptic cytoskeleton. We used rhodamine‐α‐bungarotoxin and anti‐neurofilament IgG–FITC to stain acetylcholine receptors and nerve terminals of the sternomastoid muscle during postnatal development in mdx and control C57BL/10 mice. Using fluorescence confocal microscopy, we observed that, 7 days after birth, 86.7% of the endplates of mdx mice were monoinnervated (n = 200) compared with 41.4% in control mice (n = 200). By the end of the second postnatal week, all endplates were innervated singly (100% mdx and 94.7% controls, n = 200 per group). These results show that dystrophic fibers achieve single innervation earlier, perhaps because dystrophin or a normal cytoskeletal complex is implicated in this phenomenon. Muscle Nerve 28: 561–569, 2003
X‐linked motor and sensory neuropathy with pyramidal signs and cerebral white matter lesions
Authors: Goto Hirofumi , Matsuo Hidenori , Ohnishi Akio , Fukudome Takayasu , Shibuya Noritoshi
Published: October 2003

We report two brothers with hereditary motor and sensory neuropathies and pyramidal signs. Electrophysiological evaluation revealed polyneuropathy and involvement of the central motor, somatosensory, and auditory pathways. Brain magnetic resonance imaging studies showed diffuse white matter lesions, and sural nerve biopsy identified a reduction in the large myelinated nerve fibers. The patients' mother and sister exhibited similar, but milder neurologic findings suggesting that the genetic defect may be X‐linked; however, a point mutation in the connexin 32 gene was negative. Muscle Nerve 28: 623–625, 2003
Mononeuropathy multiplex in association with livedoid vasculitis
Authors: Toth Cory , Trotter Martin , Clark Arthur , Zochodne Douglas
Published: October 2003

Livedoid vasculitis is a chronic dermatological disorder associated with petechiae and recurrent, unusually shaped ulcers that heal to form hyperpigmentated areas and atrophie blanche. This condition is more correctly termed a vasculopathy, rather than a vascultis, and is often associated with an underlying hypercoagulable disorder. We report a patient with livedoid vasculitis and mononeuropathy multiplex. We propose that peripheral nervous system involvement arises from multifocal areas of ischemia due to fibrin and thrombin deposition within both the wall and lumen of vasa nervorum. Muscle Nerve 28: 634–639, 2003
McArdle's disease presenting as recurrent cryptogenic renal failure due to occult seizures
Authors: Walker Adrianne R. , Tschetter Kevin , Matsuo Fumisuke , Flanigan Kevin M.
Published: October 2003

Myophosphorylase deficiency (McArdle's disease) may present with episodic renal failure following exertion. We present a case of adult‐onset myophosphorylase deficiency in which recurrent bouts of renal failure could not be associated with any exertional events until a tonic seizure was witnessed after the fourth episode of renal failure. In the absence of a clear exertional cause for myoglobinuria, an occult seizure disorder should be suspected. Muscle Nerve 28: 640–643, 2003