bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent achievements in multidimensional NMR
Authors: Griesinger C. , Brüschweiler R. , Madi Z. L. , Sørensen O. W. , Ernst R. R.
Published: March 2011

Recent developments in high resolution multidimensional NMR spectroscopy are discussed. Emphasis is laid on the extraction of structural information especially of 3D spectra. A novel 2D experiment is proposed to measure cross relaxation induced by correlated motion in macromolecules.
Spatial structure of biomolecules by nuclear relaxation and molecular modelling methods
Authors: Rossi Claudio , Picchi Maria Pia , Marchettini Nadia
Published: March 2011

Nuclear magnetic resonance spectroscopy (NMR) has become the most frequently used technique for the investigation of the structure of biomacromolecules in solution. In particular, selective relaxation techniques have been used in the analysis of homonuclear dipolar connectivities (selective and biselective proton spin‐lattice relaxation experiments) and heteronuclear couplings (selective {H} C‐NOE, biselective carbon R1 experiments). An accurate determination of selected i‐j internuclear distances has made it possible to identify the preferred solution structure. A different experimental technique based on two‐dimensional NOE spectra has made it possible to define the complex network of dipolar interactions that exists in biomacromolecules and hence the conformational properties in solution.
Carbon‐13 NMR studies of local dynamics in polymer solutions and melts
Authors: Laupretre Françoise
Published: March 2011

Carbon‐13 spin‐lattice relaxation time measurements have been performed at two experimental frequencies on a series of amorphous polymers in the bulk state at temperatures well above the glass‐transition temperatures and in solution. The high experimental values of the T1 minimum as a function of temperature cannot be accounted for only by the specific orientation autocorrelation functions developed for polymers. They indicate the existence of an additional fast anisotropic motion, which we have assigned to librations of limited but significant extent of the internuclear CH vectors about their rest position. Moreover, in most cases, the temperature dependence of the segmental motions proves that they are involved in the glass‐rubber transition phenomena.
Dynamic processes in aqueous protein systems. Molecular theory and NMR relaxation
Authors: Kimmich Rainer
Published: March 2011

A model theory is presented explaining a series of striking phenomena observed with nuclear magnetic relaxation in protein systems such as solutions or tissue. The frequency and concentration dependences of the nuclear magnetic relaxation times are discussed. It is concluded that the translational diffusion of water molecules along the rugged surfaces of proteins and ‐ to a minor degree ‐ protein backbone fluctuations are crucial processes. The rate limiting factor of macromolecular tumbling is assumed to be given by the free‐water content in a certain analogy to the free‐volume model of Cohen and Turnbull. The two characteristic water mass fractions indicating the saturation of the hydration shells and the onset of protein tumbling can be related to each other on this basis. A closed and relatively simple set of relaxation formulas is presented. The potentially fractal nature of the diffusion of water molecules on the protein surface is discussed.
Nuclear magnetic relaxation and molecular motion in solid lysozyme
Authors: Fedotov V. D. , Obuchov N. P. , Spêváček J. , Straka J.
Published: March 2011

Nuclear magnetic relaxation data for both proton and carbon‐13 nuclei in solid lysozyme are analysed together to obtain information on local internal motions in protein. For this analysis the “model‐free” approach is used. Three types of internal motion appear to determine the observed nuclear relaxation in protein. They may be attributed to local rotations of methyl groups around symmetry axes, the motion of main and side chain atoms like in rigid lattice, and large‐amplitude motions of side groups (mainly, methylene groups). Conclusions on hydrated water influence on local dynamics of protein are made.
ESR imaging of polymers and solid materials
Authors: Berliner Lawrence J. , Fujii Hirotada
Published: March 2011

EPR imaging was applied to the study of several important processes in polymers and materials. The solvent diffusion and induced swelling was visualized in the water/DMF or toluene/DMF interactions with polycarbonate or polystyrene molded rods. The cross‐sectional images revealed non‐homogeneous solute/solvent diffusion, rod expansion and crack development. The ESR lineshapes in all cases above confirmed that the nitroxide imaging agent did not interact significantly with the polymer matrix; thus the paramagnetic distribution reflected bulk solvent distribution quite well. The diffusion of an electrolyte buffer (Krebs) solution containing a nitroxide spin probe was followed in a cross‐sectional image of a polyacrylamide gel rod. A one‐dimensional radial diffusion constant was calculated for the solvent piperidinol nitroxide spin probe, TEMPOL. Lastly, solid coal rods were monitored during mild pyrolysis at 150°C in air. Here the naturally occurring organic radical composition was imaged. Even with the increase in total ESR signal and subsequent decline to ca. the initial levels, the coal rod cross‐section was essentially homogeneous in paramagnetic centers throughout the heating process. All of the imaging above utilized a homemade L‐band, flat loop surface coil spectrometer.
Charge transport in polymers studied by combining optical and electrical techniques
Authors: Bässler Heinz
Published: March 2011

Three examples are presented demonstrating the wealth of information steady state absorption and fluorescence studies can yield regarding charge transport in polymeric systems: (i) The determination of the density of intrinsic and extrinsic hopping states in polyvinylcarbazole via site‐selective fluorescence spectroscopy by drawing on the analogy between charge and energy localization in disordered organic media, (ii) the identification of inter‐chain jumps as being rate limiting for charge transport in a polydiacetylene single crystal as an example for conjugated polymers and (iii) the elucidation of polaron formation in phenylenevinylene‐type polymers.
Magnetic spin effects as a tool for studying electronic processes in solids
Authors: Frankevich E. L.
Published: March 2011

The role played by the law of the conservation of momentum in the primary processes of charge carrier generation is considered. External magnetic field is shown to be able to influence the rate constants governing spin dependent processes. Magnetic field effect and Reaction Yield Detected Magnetic Resonance on the photoconductivity of organic solids give important information on the mechanism of primary steps of charge photogeneration.
Mechanism of photogeneration of free carriers in quasi‐one‐dimensional photosemiconductors: Application tc polydiacetylene
Authors: Frankevich E. L. , Sokolik I. A. , Lymarev A. A.
Published: March 2011

The dependence of the quantum yield of free charge carriers on the electric field strength in quasi‐one‐dimensional photosemiconductors is rationalized. The occurrence of the trapping and nongeminate recombination in the bulk of the material is shown to be responsible of nonzero yield at zero external field. Current i vs. excitation intensity g plot obeys the law i∼g2/3 for polydiacetylene single crystal as expected from theory presented.
Resonance raman spectroscopy of conjugated polymers what can we learn?
Authors: Kuzmany H.
Published: March 2011

This paper gives a review on the use of resonance Raman spectroscopy to analyse electronic and molecular structures of π‐conjugated and σ‐conjugated polymers. It starts with a short introduction into the present state of research in the field of conducting polymers and with a very short introduction into the principles of resonance Raman spectroscopy. Then the potentialities of the technique are demonstrated for the examples of the analysis of conjugation length in polyacetylene, for studying the thermochromic phase transition in polysilanes and in polyalkylthiophenes, for a sudy of the doping processes in polyaniline and finally for an analysis of the ground state in the narrow gap system polyisothianaphthene. Advantages and pitfalls for such analyses are outlined.
Photoconducting composite, polyester polymer‐cds powder
Authors: Kuczkowski Andrzej
Published: March 2011

The relation between electrical, photoelectrical and electrophotographical properties of polyester polymer–CdS composites as a function of component weight ratio, electric field strength and light intensity were investigated. Cl and Cu activated CdSa powder as well as unactivated CdS powder were added to polyester polymer. It has been shown that the composite containing from 60 to 70 wt‐% of CdSa has the best photoelectric properties. The electrophotographical layers of this composite exhibited a photosensitivity as high as 1.25 (Lx · s)−1. The results have been explained in terms of the reduction in interparticle barrier height assisted by the localized trapping of photoexcited or field‐excited holes.
New mechanism of the formation of superconductive ferromagnetic structures in elastomers without conjugation in the backbones
Authors: Grigorov L. N. , Andrejev V. M. , Smirnova S. G.
Published: March 2011

A quantum‐mechanical model of charge condensation is proposed for non‐conjugated polar elastomers It was found that the stability of the bi‐ and multi‐polaron state may be achieved if the dielectrical permeability of the matrix is high enough. It is shown that the multi‐electron unit, called as superplaron, should have a linear structure and possess ferromagnetic properties. The one‐dimensional character of the conductivity of a superpolaron leads to the formation of electron pairs and to the appearance of high temperature superconductivity of superpolarons. A lot of experimental data confirms the real existance of superconductivity at some polar elastomers at 300 K.
Nonlinear optical properties of thin organic films
Authors: Bubeck Christoph , Neher Dieter , Kaltbeitzel Anke
Published: March 2011

A brief survey is given on our recent work on the linear and nonlinear optical properties of thin films of polymers with a conjugated π–electron system. Third harmonic generation and degenerate four wave mixing experiments are used to study magnitude and response time of the third order nonlinear optical susceptibility of poly(p‐phenylenevinylene) and poly(phenyl acetylene). Phthalocyanine derivatives show a strong influence of the intermolecular electronic coupling on the response time of transient gratings. The influence of energy transfer on the relaxation process is discussed.
Nonlinear optical properties of poly(arylenevinylene) polymers
Authors: Bradley D. D. C.
Published: March 2011

This paper concerns investigations of the third order nonlinear optical response of poly(arylene vinylene) polymers and in particular precursor route poly(p‐phenylene vinylene) [PPV]. Results for photoexcitation measurements provide information on the response time and the nature of the nonlinearity in the single‐photon resonant excitation regime. Transmission third harmonic generation [THG] measurements yield complimentary information on the single‐photon non‐resonant regime.
Fracture resistance in rubber‐toughened polymers
Authors: Bucknall C. B.
Published: March 2011

The effects of rubber content, particle size and interparticle spacing on the fracture behaviour of toughened polymers over a range of strain rates and temperatures are discussed with particular reference to high‐impact polystyrene and rubber‐toughened nylons. It is concluded that the limiting factor in determining fracture resistance is a kinetic one: the rate at which the matrix polymer can respond to stress by forming oriented fibrils. Fibrillation can occur either by multiple crazing, in which case the preferred particle diameter D is about 1 μm; or as a result of cavitation within the rubber particles followed by shear yielding, which requires smaller inter‐particle spacings. An extension of the Argon‐Salama model for crazing is proposed to explain the interparticle spacing effect. Morphology is less critical in controlling fracture at low strain rates or higher temperatures.
Lyophilic polymer‐polymer emulsions in vicinity of the phase separation point
Authors: Kuleznev Valerü N. , Klykova Valentina D.
Published: March 2011

Experimental and theoretical results of the investigation of the laws governing the lamination process in polymer‐polymer systems in the transient region between binodal and spinodal have been systematized. The causes of the viscosity decrease in the phase separation region have been explained. An assumption has been made that the laws observed result from differences in the conditions of segregation of macromolecules of polymers forming a mixture and segments of the same molecules in interphase layer.
A comparison of theoretical predictions and experimental evidences of miscibility for poly(ethylene oxide)‐based blends
Authors: Cimmino S. , Martuscelli E. , Saviano M. , Silvestre C.
Published: March 2011

Mixtures of poly(ethylene oxide)/atactic poly(methyl methacrylate) (PEO/At‐PMMA) blends and poly(ethylene oxide)/poly(ethylene‐co‐vinylacetate) (PEO/EVAc‐1) blends were prepared by casting from a common solvent and were found miscible. The applications of the Solubility Parameter Theory, Patterson Theory and the Equation of State Theory of Flory are reported. The miscibility predictions obtained are discussed and compared to experimental miscibility evidence.
Interactions between polymers
Authors: Rätzsch Manfred , Haudel Gottfried
Published: March 2011

The main part of this report deals with the thermodynamic fundamentals of one‐ and multi‐phase polymer blends and the presently reached state of a theoretical prediction is estimated. Potentialities and limits of the thermodynamic theories are discussed. Furthermore, a theoretical conception, basing on interfacial tensions between polymers and successfully used for the theoretical description of polymer alloys, is considered. The second topic of this report is the development of highly impact resistant thermoplastics and thermoplastic elastomers. In connection with it, the technological parameters necessary for the realization of multi‐phase polymer blends by mechanical mixing in the melt, are discussed. The experimental methods for the determination of the distribution are presented. The practical importance of multi‐phase blends is substantiated, the role of the interfacial energies revealed and discussed. In the third part the possibilities of the increase of compatibility are given forth and in further part demonstrated by examples.
Thermodynamics of miscible polymer blends studied by inverse gas chromatography
Authors: Munk P. , Hattam P. , Abdel‐Azim A‐A. A. , Du Qiangguo
Published: March 2011

Use of inverse gas chromatography for the investigation of polymer‐polymer interactions is compromised by a dependence of the measured polymer‐polymer interaction coefficient, B23, on the chemical nature of the probe in contradiction to theory currently used. We have developed a procedure whereby the “true” B23, may be extracted from the probe dependent data. Additionally a theory of mixing based on a multidimensional solubility parameter approach has been developed. The new theory has been used to predict the polymer‐polymer interaction coefficients and these are compared with experimentally determined values on several miscible blends.
Miscibility and mechanical properties of polymer blends
Authors: Pukánszky Béla , Tüdõs Ferenc
Published: March 2011

The tensile properties of 16 blends prepared from 12 different polymers were investigated in the whole composition range. The composition dependence of Young's modulus has shown less, while that of the yield and ultimate properties exhibited more significant variations with miscibility. The quantitative evaluation of the yield stress and tensile strength data resulted in a parameter, which could be related to the interfacial tension and miscibility.
Compatibility and thermodynamic interaction in random copolymer blends
Authors: Shiomi Tomoo , Imai Kiyokazu
Published: March 2011

Some random copolymer blends have been found to be miscible in a certain range of copolymer composition even though any combinations of their corresponding homopolymers are not miscible. The opposite case may exist. These two types of miscibility behaviors have been called miscibility and immiscibility windows, respectively. Such two miscibility behaviors were discussed by application of the equation‐of‐state theory to copolymer systems. The equation‐of‐state theory gives two kinds of temperature dependences of the interaction parameter X: (a) a U‐shaped curve which is always positive regardless of temperature and (b) a function increasing monotonically from negative to positive values. Infinite molecular weight polymer blends are immiscible over all the temperature in the case (a), while in the case (b) two polymers are miscible below a temperature at which X=0. Applying the equation‐of‐state theory to random copolymer blends in which miscibility changes with the copolymer composition at a certain temperature to be immiscible → miscible → immiscible, two types of dependences of the temperature‐X curve can be obtained: (1) (a) → (b) → (a) dependent on the copolymer composition and (2) (b) regardless of the copolymer composition. For the blends in which miscibility changes with the copolymer composition to be miscible → immiscible → miscible, there can be two types: (3) (b) → (a) → (b) and (4) (b) regardless of the copolymer composition. It may be concluded that socalled miscibility and immiscibility windows should be defined by the types (1) and (3), respectively. The equation‐of‐state theory for random copolymer systems was applied to the real systems. The blends of poly(vinyl acetate‐co‐vinyl chloride) and poly(ethylene‐co‐vinyl acetate) were of the type (1), while it was suggested that the blends of poly(vinyl acetate‐co‐vinyl chloride) and poly(isobutyl methacrylate‐co‐ butyl methacrylate) may be of the type (4) though this system behaved like an immiscibility window at a certain temperature.
Condis‐crystal structure of flexible‐chain polymers in polymer blends
Authors: Antipov E. M. , Borisenkova E. K. , Kulichikhin V. G. , Platé N. A.
Published: March 2011

When heated above the melting point, a thermodynamic equilibrium mesophase of conformationally disordered crystal type (so‐called condis state) has been found in some flexible‐chain polymers (not containing mesogenic groups) dispersed in a matrix of another polymer. Typical organic and inorganic polymers such as polyethylene (PE) and poly[bis (2, 2, 2‐trifluoroethoxy) phosphazene] (PPh) were taken as main components of the polymer blends under investigation. The most interesting situation is realized if two mesophase polymers are used in the same binary blend.
Gelation mechanism of ionic polysaccharides
Authors: Gamini A. , Civitarese G. , Cesàro A. , Delben F. , Paoletti S.
Published: March 2011

Experimental results obtained by membrane equilibria, osmotic pressure, viscosity and circular dichroism measurements on alginate and pectate solutions in the presence of Ca2+ ions are presented. From equilibrium dialysis data both electrostatic and cooperative interactions seem to describe the binding process of Ca2+ ions onto polymer chains. An increase of the number‐average molecular weight M̄n for both poly‐saccharides with calcium ion concentration is observed. An increase of polymer dimensions can well account for the observed increase of the intrinsic viscosity [η] with bound Ca2+ ion concentration at several ionic strengths.
Amylose gelation in low‐concentration conditions
Authors: Doublier J. L. , Llamas G. , Choplin L.
Published: March 2011

Amylose gels of low concentration (1–2 wt.‐%) were studied by means of a rheological method and turbidity measurements. The effects of temperature and concentration were investigated. The kinetics of turbidity evolution and of the storage modulus G' variations were strongly dependent of both parameters. The overall gelation process could be described in three steps: first, an induction period, followed by a sharp variation of G' and turbidity, and finally a slow variation of G'. These observations confirm that amylose gelation proceeds through a phase separation process.
Thermodynamic properties of gels of lithium poly(alkyl borates)
Authors: Dmitrieva Z. T. , Tikhonova L. D.
Published: March 2011

The temperature‐viscosity dependence of structured solution (gel) of [t‐C4H9OB(OR)3]Li · mROH and [B(OR)4]Li in heptane, where R = n‐C4H9, n‐C7H15, n‐C10H21; m = 0, 1, 2, has been studied in the range of threshold shear stress. Energy, heat and entropy of activation values have been obtained for the elasto‐viscous flow of gels of complexes. The energies of activation determined for the flow of gels of complexes are unaffected by the temperature in a temperature range of 293–343 K, while the heat of activation increases with temperature.
State diagrams of perfluorocarbon/solvent systems
Authors: Dobnik E. , Borchard W.
Published: March 2011

The phase behaviour of perfluorocarbons in various solvents has been investigated. In case of perfluorohexadecane the state diagrams with trichlorotrifluoroethylene (CF2Cl‐CFCl2) known also as Freon F113 and hexafluorobenzene (C6F6) as solvents could be determined in the total concentration range and also at temperatures far below the melting temperatures of the pure components. Beside the normal melt transitions in this binary systems some not yet known intramolecular phase transitions were found. From the course of the liquidus curve the Flory‐Huggins interaction parameter of these systems could be determined. So statements about the quality of these solvents can be made. The investigated substances are suitable solvents for all perfluorocarbons which are actually available. The high molecular polytetrafluoroethylene (PTFE) cannot entirely be dissolved by these solvents, although traces are soluble. The reason is that the boiling points and critical temperatures of the solvents lie below the temperatures of the liquidus curve of the polymer of the considered system.
Relaxation phenomena near the sol‐gel transition
Authors: Martin James E. , Adolf Douglas , Odinek Judy
Published: March 2011

Near the sol‐gel transition, relaxation phenomena exhibit a form of critical slowing down that is manifest in a variety of microscopic and macroscopic dynamical phenomena. For example, quasielastic light scattering studies (QELS) of the relaxation of thermally induced density fluctuations in critical silica sol‐gels reveal a self‐similar dynamics wherein decay processes occur on all time scales (fractal time), and average decay times diverge. Likewise, time‐ and frequency‐dependent viscoelastic phenomena of critical gels are described by power laws and both the viscosity and recoverable equilibrium creep compliance diverge. These unusual relaxation phenomena appear to be associated with the connectivity divergence that occurs at the sol‐gel transition. Light scattering studies of this sol‐gel transition reveal fractal clusters whose size diverges as a power law, in reasonable accord with the predictions of percolation theory. Based on these structural observations, we have developed a scaling description of the dynamics that relies on a length‐scale‐dependent viscosity and the geometrical self‐similarity of the sol‐gel transition. When percolation exponents are used in these expressions, a good description of the viscoelastic phenomena and the relaxation of density fluctuations near the gel point is obtained. Finally, it is shown that the dynamic scaling treatment of the viscoelastic properties can be summarized in a Time‐Cure Superposition principle, which predicts certain universal axes for frequency‐ or time‐dependent properties near the gel point.
Frequency dependence of viscoelastic properties of some physical gels near the gel point
Authors: Cuvelier Gérard , Launay Bernard
Published: March 2011

The sol‐gel and gel‐sol transitions of three biopolymer gelling systems (gelatin, iota‐carrageenan and xanthan‐carob) have been studied by dynamic measurements. At the gel point a power law dependence of the storage (G') and loss (G”) moduli on frequency is observed, with an exponent varying from 0.5 to 0.65. The variation of log(tgδ = G”/G') versus the gelation (or melting) parameter (time or temperature) at different frequencies leads to a precise determination of the gel point.
Network formation and properties: Rate theory description of effects of ring formation on elastic shear modulus of RA2 + RB3 networks
Authors: Rolfes Heidi , Stepto Robert F. T.
Published: March 2011

The rate theory of RA2+RB3 polymerization has been developed to enable the concentrations of the smallest inelastic loops and the resulting reductions in elastic shear modulus at complete reaction to be evaluated. Reduction in modulus is expressed as Mc/M°c, the effective molar mass of chains between elastically active junction points (Mc) relative to that for the perfect network for given reactants (M°c). Calculations have been carried out for stoichiometric reaction mixtures and the concentration of loops is characterized by λ, a ring‐forming parameter. λ = Pab/CAo, where CAo is the initial concentration of A‐groups and Pab = (3/(2πvb2))3/2/NAv, with v the number of bonds in the chain forming the smallest loop, b the effective bond length of the chain, and NAv Avogadro's number. Pab is equal to the mutual concentration, assuming Gaussian statistics, of the A‐ and B‐groups at the two ends of the linear sub‐chain of v bonds. Loop formation increases as λ increases, that is, as the initial concentration of reactive groups (CAo) decreases, or, at constant CAo, as the molar mass of reactants (v) or their chain stiffness (b) decreases. Comparison with existing experimental data on two series of polyurethane networks formed from hexamethylene diisocyanate and two polyoxypropylene triols at different initial dilutions shows that the values of Pab decrease with increases in initial dilution and molar mass of triol. The decrease with molar mass is entirely accounted for by changes in v and the variation with dilution shows that the approximation of counting only smallest loops improves as dilution increases.
Molecular aspects of polymer network deformation ‐ small angle neutron scattering and NMR studies
Authors: Gronski W. , Forster F. , Pyckhout‐Hintzen W. , Springer T.
Published: March 2011

Poly(1,4‐butadiene) networks obtained by a 4‐functional random cross‐linking reaction over a broad range of polymer concentration were studied by small angle neutron scattering(SANS), 2H NMR and Monte Carlo(MC) simulation in the isotropic and uniaxially deformed state. The defect structure of the networks has been characterized by MC simulation of the cross‐linking reaction. The anisotropy of the radius of gyration in deformed networks determined from SANS has been analyzed by the theory of Ullman. It was found that the number of active cross‐links per chain is in agreement with MC and that the chain deformation follows phantom behaviour. The local orientation as measured by 2H NMR is related to the global anisotropy of the network by a MC calculation of oriented chains. The 2H NMR line shape of the deformed network is analyzed in terms of two relaxation processes arising from interior parts of the chains and from segments at chain ends. The mobility of both decrease with strain. It was found that the orientation connected to the first process shows the classical strain dependence of rubber elasticity, whereas the second exhibits a weaker dependence on strain.
Direct evidence of crosslinks by metathesis degradation
Authors: Hummel Klaus , Hubmann Ewald
Published: March 2011

The degradation of unsaturated polymers by olefin metathesis has already been applied to the investigation of crosslink structures. In the present paper, crosslinks in poly(butadiene‐alt‐propene), obtained by partial bromination with N‐bromosuccinimide and reaction with 1,4‐bis(bromomagnesium)butane, were investigated by this method. Metathesis degradation was carried out with (E)‐4‐octene using the catalyst WCl6‐Sn(CH3)4. The low‐molecular‐weight products were identified by combination of gas chromatography (GC) and mass spectrometry (MS).
Study of structure and dynamics of gelatin gels by temperature ramped holographic relaxation spectroscopy
Authors: Wu Chi , Schrof Wolfgang , Lilge Dieter , Lüddecke Erik , Horn Dieter
Published: March 2011

A technique combined temperature ramp with holographic relaxation spectroscopy (HRS) is used to investigate on the structure and dynamics of gelatin gels. Two kinds of photochromic probes are used. The first is the gelatin molecule covalently labeled with fluorescein‐isothiocyanate. After gelation, some of the labeled gelatin molecules will form the gel and the rest will still be in the sol. Therefore, the mobility of labeled gelatin molecules in the sol and the gel are probed. The translational diffusion coefficient of gelatin molecules in the sol, the gel content and the gel melting temperature at different gelatin concentrations ranging from 1 to 15 weight‐% are measured. The second probe is the small fluorescein molecule in the gelatin gel as a tracer. The mobilities of the tracer in the “gel” are probed. An HRS curve with double peaks is observed. It is experimentally proven that this “anomalous” HRS curve is related to the structure of the gelatin gels. During a normal cooling process (2 C/min), two kinds of networks are found. A “coarse” one is formed through the aggregation of collagen‐like triple‐stranded helices and a “fine” one is formed simply by entanglements between gelatin molecules.
Phase behaviour of poly(vinyl methyl ether)‐cross‐polystyrene semi‐interpenetrating networks
Authors: Felisberti Maria Isabel , Krieger Volker , Stadler Reimund
Published: March 2011

Semi‐interpenetrating polymer networks of varying composition are prepared by crosslinking polystyrene containing a small number of maleic anhydride groups (4.8 mol% of MA units) with hexamethylene‐diamine (HMDA) in the presence of linear poly(vinyl methyl ether) (PVME). Lightly crosslinked samples are homogeneous at room temperature and show a phase behaviour similar to uncrosslinked blends, i.e. lower critical solution temperature (LCST) behaviour. The influence of crosslinking on the phase behaviour has been studied by small angle light scattering (SALS) and turbidity measurements. The cloud point strongly depends on the heating rate. The presence of the network reduces the stable single phase region in agreement to theory. In systems showing spinodal decomposition, it is expected that some concentration fluctuations will grow more rapidly than others resulting in a separated phase system which shows high degree of connectivity with characteristic dimensions. Using temperature jump experiments, SALS can be used to estimate parameters of the phase separation kinetics and the characteristic dimensions of the phases. In temperature jump experiments into the spinodal region a maximum in the scattered light intensity is observed with time at a certain scattering vector. However, the semi‐IPN's develop no scattering maximum. This is explained by a damping of the thermodynamical dominant wavelength in spinodal decomposition in the network.
Fracto‐emission accompanying adhesive failure in a model fiber pull‐out system
Authors: Dickinson J. T. , Zhen‐Yi Ma
Published: March 2011

Fracto‐emission (FE) is the emission of particles and photons during and after fracture of materials. The observed emission includes electrons, negative and positive ions, neutral species in both ground states and in excited states, and visible photons. This emission can often serve as a sensitive probe of crack growth and may prove to be a useful tool for investigating molecular and microscopic events accompanying crack growth and for studying the details of failure modes in a variety of materials. Here, we examine photon and electron emission during failure of axially loaded stainless steel fixtures (e.g., rods) embedded in epoxy. These experimental data provide time resolved information on the sequence of events leading to interfacial fracture proceeding pullout. In addition, we examine the emissions during frictional pullout which over a large range of strain rates exhibits stick‐slip behavior. Relations of these emissions to the fracture and pullout processes are discussed.
Electron emission during deformation of polymers
Authors: Zakrevskii V. A.
Published: March 2011

Electron emission was detected during deformation of both carbochain and heterochain polymers in vacuum. It was found that the features of emission are similar to those observed in molecular scissions under drawing of unoriented and oriented polymers. This fact indicates that there is a relationship between the fracture process and electron emission under deformation of polymers. This relationship is also obvious from the experiments with interruption of loading when electron emission during the repeated loading does not begin immediately at the moment of load application, but can be recorded only at the degree of deformation which is higher than that reached during the first loading. The interconnection between deformational electron emission and molecular scissions allowed visualization of the fracture process in the subsurface layers of polymers using an electron‐optical convertor which gives a mechanoemission image of a stretched sample. It is supposed that the deformation‐induced electron emission of polymers is caused by ionization of stressed macromolecules resulting from tunnel transitions of electrons into deep traps. During deformation, the traps are destroyed and a part of electrons escapes in vacuum.
Crazing and shear deformation of polymer alloys
Authors: Narisawa Ikuo , Kuriyama Takashi , Ojima Kennichiro
Published: March 2011

Crazing and/or shear yielding mechanisms in multiphase polymer alloys play a critical role in toughening. The present paper describes the use of finite element models (FEM) to simulate the crazing and shear deformation behaviour around the particles embedded in brittle or ductile matrices. The FEM simulation results on the stress distribution reveal that the dilatational stress within the rubber particles is high enough to cavitate. The stability of craze growth can be reached when the compliant particle is incorporated in a brittle matrix. On the other hand, shear yielding around the particle occurs in the equator of the particle/matrix interface when the stress locally exceeds the yield stress of the matrix. This yield‐initiation stress increases with the increase in the elastic modulus and Poisson's ratio of the particles. The toughening mechanism, that cavitation occurs first followed by shear yielding to form a neck between the particles, is discussed based on the simulation results for the two‐particle model.
Some aspects of the control of physico‐mechanical properties of polymer compositions with elastomeric inclusions
Authors: Rozenberg B. A.
Published: March 2011

The paper reviews the author's works on the regulation of physico‐mechanical properties of polymer compositions with elastomeric inclusions. The factors, determining the modification efficiency of elastomeric inclusions in epoxy matrices, are analyzed. The regularities of the phase separation in curing system and the control of the interface interaction and morphology of epoxy polymers with elastomeric inclusions are considered.
Some monomers, oligomers and polymers with conjugated triple bonds
Authors: Giesa Reiner , Klapper Markus , Schulz Rolf C.
Published: March 2011

In the first part new monoaminodiacetylenes with different numbers of CH2‐groups, the formation of Perowskit‐type Mn complexes and their polymerizability are described. Symmetrical diaminodiacetylenes and some derivatives therefrom have also been prepared. The second part deals with different types of polymers with diacetylene units in the backbone. Under irradiation color formation and crosslinking take place. Well‐defined low molecular weight model compounds of polydiacetylenes is the subject of the third part. Finally rod‐like but soluble polymers with alternating p‐phenylene and acetylene units are described.
Molecular dynamics in low‐molar and polymeric ferroelectric liquid crystals
Authors: Kremer Friedrich , Vallerien Sven Uwe , Zentel Rudolf , Kapitza Heinrich
Published: March 2011

Broadband dielectric spectroscopy covering the frequency range from 10−1 Hz to 109 Hz was employed to study the molecular dynamics in low‐molar and polymeric ferrroelectric liquid crystals. At frequencies below 106 Hz the ferroelectric modes, soft and Goldstone mode are observed. In the frequency regime from 106 Hz to 109 Hz a fast relaxation process is found, which is assigned to the hindered rotation of the mesogens around their long molecular axis. It turns out that the molecular dynamics is not principally different between low‐molar and polymeric systems.
High‐resolution optical spectroscopy of polymers: Molecular potentials and internal fields
Authors: Haarer D. , Kador L.
Published: March 2011

Photochemical hole burning is a spectroscopic method which creates, via laser irradiation at low temperatures, narrow persistent dips in the inhomogeneous absorption bands of solids which are doped with appropriate dye molecules. Especially in amorphous samples, the spectral width of these dips can be several orders of magnitude smaller than that of the total inhomogeneous bands. This does not only provide an enormous increase in spectral resolution, but in addition it allows to select very small subsets of absorbers in the sample with accidentally degenerate transition frequencies. It can be shown that by applying external fields, material parameters and molecular potentials can be probed.
ON peculiarities of the influence of oxyaromatic compounds on physico‐mechanical properties of nylons
Authors: Arzhakov M. S. , Volkov A. V. , Volynskii A. L. , Bakeyev N.Ph.
Published: March 2011

The physico‐mechanical properties of nylons modified by oxyaromatic compounds (OAC) have been studied. It has been shown that such modification results in an increase of the Young's modulus and glass transition temperature and in a decrease of water sorption. A noticeable improvement of the elastic properties of the modified nylons in a humid atmosphere is assigned to a shift of glass transition temperature towards higher values of humidity and moisture content. Mechanism of the OAC reinforcing action on polymers involves an increase of energy of intermolecular interaction and a decrease of kinetic mobility of macromolecules in the modified polymer system due to the formation of the strong hydrogen bonds between phenol hydroxyls of OACs and Ny‐6 amide groups in the amorphous polymer regions.
The preparation of poly(aryl ether ketones) by the use of trifluoromethanesulfonic acid
Authors: Risse Wilhelm , Sogah Dotsevi Y. , Boettcher F. Peter
Published: March 2011

Two synthetic routes were used for the preparation of aromatic poly(ether ketones): Friedel‐Crafts acylation and aromatic nucleophilic substitution. The first route involved the reaction of diphenyl ether and terephthalic acid dichloride in trifluoromethane‐sulfonic acid. The addition of trifluoromethanesulfonic anhydride or phosphorus pentoxide resulted in increased molecular weights. The second synthetic route involved the synthesis of an amorphous tert ‐butyl‐substituted poly(ether ketone) prepolymer. Subsequently, the tert ‐butyl groups were removed by a reversed Friedel‐Crafts alkylation reaction yielding the crystalline polymer PEEK. The dealkylation reaction was performed in trifluoromethanesulfonic acid. The addition of a tert ‐butyl group acceptor resulted in high dealkylation conversions.
Synthesis and properties of alternating copolymers of acrylics and olefins
Authors: Eisenbach Claus D. , Bülow Ulrich , Lieberth Wolfgang
Published: March 2011

The free radical copolymerization and terpolymerization of acrylic monomers with olefins in the presence of Lewis acid complexing agent for the acrylic monomer has been investigated. The course of the polyreaction is in agreement with the features of a radical chain growth reaction, and the polymer properties can be varied by changing the composition of the reaction mixture and the reaction conditions. The alternating copolymers are usually amorphous materials, and only the alternating ethylene/acrylonitrile copolymer can be obtained as a material of relatively high crystallinity. The degree of crystallinity can be varied through terpolymerization of complexed acrylonitrile with ethylene/propylene comonomers. The basic features of the polyreaction and the polymer structures as well as some of the physical and material properties of the copolymers have been studied.
Kinetics of curing reaction and properties of polymeric materials based on epoxy resins
Authors: Privalko V. P. , Kramarenko V.Yu. , Feinleib A. M.
Published: March 2011

Base epoxy oligomers of Bisphenol A type were cured by aliphatic and aromatic amines, as well as by anhydride and isocyanate hardeners. The glassy networks obtained were characterized by scanning calorimetry, linear dilatometry, IR spectroscopy and electron microscopy.
Reversed micelles as matrix microreactors for chemical processing of macromolecules
Authors: Alexander V.Kabanov
Published: March 2011

Being solubilized in the systems of the surfactant reversed micelles (RM), the macromolecules incorporate into the inner cavity of RM, whose size can be changed by varying the surfactant hydration degree Wo, i.e. [H2O]/[Surfactant] molar ratio. The conjugates of macromolecules (protein‐protein, protein‐linear polyelectrolyte) are synthesized in RM of AOT (Aerosol OT, sodium bis[2‐ethylhexyl]sulfosuccinate) in octane. The yield critically depends on the hydration degree: the reaction does not proceed at low Wo, but at Wo exceeding threshold value (which differs for various macromolecules) the yield increases sharply and reaches 100%. Using the ultracentrifugation it was demonstrated that at Wo lower than threshold the polyelectrolyte represents a compact globule compressed by the micellar matrix in the RM inner cavity. Under these conditions there is no space for the protein in the RM, containing polyelectrolyte, and therefore reaction does not proceed. At Wo higher than threshold RM become large enough to entrap the conjugated macromolecules simultaneously. The possibility of regulation of the conjugate composition by variation of Wo (size of micellar matrix) was demonstrated. The RM are applied as universal matrix microreactors, for modification of macromolecules with water insoluble reagents and for regulation of supramacromolecular composition of oligomeric enzymes.
Synthesis and characterization of molecular ribbons
Authors: Blatter K. , Godt A. , Vogel T. , Schlüter A.‐D.
Published: March 2011

This paper describes a recently developed route to obtain soluble, fully characterizable and high‐molecular‐weight ladder polymers with perfect molecular structures. It is based on Poly‐Diels‐Alder ‐Additions of suitable bifunctional building blocks.
Concentration fluctuation effects for dynamics of polymer solutions
Authors: Semenov A. N.
Published: March 2011

Dynamics of concentration fluctuation in a semidilute polymer theta‐solution in the regime of entanglements is studied theoretically. A number of relaxation modes is predicted, the largest amplitude corresponding to a reptation mode with the time , where q is the wave vector, the static correlation length, R the size of a polymer coil. A mode with a “superlong” time N2q−2 is predicted for . It is shown also that fluctuations of molecular field result in a substantial decrease of macromolecular curvilinear diffusion constant. The same effect gives rise to an increase of zero‐shear viscosity of the solution; the dependence of viscosity on number of links per chain, N, is much stronger than N3 in the regime of high N.
Sol ‐ gel transition in biopolymers
Authors: Axelos M. A. V. , Kolb M.
Published: March 2011

Rheological measurements have been performed on pectin biopolymers close to the sol‐gel transition. From these measurements scaling exponents were determined independently for the viscosity, s = 0.82(5), for the elastic modulus, t = 1.93(8), for the frequency‐dependent modulus, Δ = 0.71(2), and for the relaxation times below and above the transition, vz = 2.67(12) and vz' = 2.65(9). The exponents satisfy the scaling relations predicted by the theory and their numerical values agree with those from scalar elasticity percolation.
Gelation and vitrification of epoxy resins monitored by ultrasonic measurements
Authors: Lairez D. , Durand D. , Emery J. R.
Published: March 2011

Ultrasonics measurements were performed during the cure of epoxy resins. The results show some different comportments if there is only the gelation process which passes through the frequency window of the study or if there is also a vitrification phenomenon. The last case occurs with a high glass transition temperature epoxy resin like DGEBA‐DDS. with which the increasing glass transition temperature of the resin is rapidly higher than the study temperature. The former case happens for low Tg epoxy resin like BDGE‐HMDA. But in any case the method is very sensitive to the mechanical properties evolution of the material.
Anhydride curing of epoxy resins via chain reaction
Authors: Trappe V. , Burchard W. , Steinmann B.
Published: March 2011

In contrast to common curing reactions, the anhydride curing of epoxies follows a living anionic chain growth. The resulting consequences of this mechanism, i.e. (1) DPn = a[Mo]/[Io], (2) first‐order kinetics and (3) Poisson chain‐length distribution were tested with the phenyl glycidyl ether/phthalic acid anhydride system, using l‐methyl imidazole. Overall agreement was found and the observed deviations could be explained with a modified Poisson process.

Conformational properties of the resins were measured by static and dynamic light scattering and by viscometry. These were compared with the quantities of a corresponding branched system prepared with a mixture of phenyl glycidyl ether and bisphenol‐A diglycidyl ether. Typical deviations to smaller dimensions were observed at high molar masses as a result of increasing branching.
Relaxation of entangled polymers in melts
Authors: des Cloizeaux J.
Published: March 2011

The stress relaxation function of a monodisperse or polydisperse melt, and the corresponding viscosity, have been calculated in the entanglement domain by applying the Doi‐Edwards theory which relies on the reptation concept introduced by P. G. de Gennes. Though the theory has been considered as successful, the agreement with precise experiments is only qualitative, and strong anomalies remained to be explained. A new theory is presented here: it is obtained by introducing simple approximations derived from elementary but novel considerations. This theory is shown to be in good agreement with experiments on monodisperse and polydisperse melts. In particular, it explains the well‐known fact that the viscosity of a monodisperse polymer melt of molecular mass M seems to increase proportionally to M3,4 when M is large.
Continuous time simulation of transient polymer networks: Rheological properties
Authors: Biller Peter , Petruccione Francesco
Published: March 2011

In this work the rheological properties of a concentrated polymer solution or melt are investigated. The polymeric material is described as a transient network and the specific model is of the Yamamoto type with configuration dependent creation and loss rates. For the solution of the model a continuous time simulation approach is used which is based on the stochastic interpretation of the fundamental equations of the theory. The qualitative predictions for the rheological behaviour turn out to be very good. For a quantitative test the unknown configuration dependence of the loss rate function is extracted from experimental data as the solution of an inverse problem. The comparison of experimental data for planar elongational flow with the simulation results using the fitted loss rate function shows that the agreement is satisfactory, but not yet perfect. A possible reason for this finding is given.