bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigations of anomalous photo‐current in poly(n‐vinylcarbazole)/trinitrofluorenone in regarding dipole relaxation
Authors: Wünsche Peter , Althausen Dietrich 
Published: March 2011

AbstractMeasurements were carried out of the change of polarity of photo‐current after a laser flash on poly(N‐vinylcarbazole) with trinitrofluorenone (PVK/TNF). This experimental results could be interpreted by taking into consideration dipol‐relaxations. A model for estimation is presented.
Vibrational spectra of polyacetylenes
Authors: Dellepiane Giovanna , Piaggio Paolo , Cuniberti Carla , Fuso Silvano , Musso Gianfranco , Rui Marina , Tubino Riccardo 
Published: March 2011

AbstractA considerable amount of information about optical and electronic properties of polyacetylenes has been obtained during the last decade from vibrational spectroscopy. In this lecture several basic points not yet fully understood will be discussed and a new method for evaluating the vibrational density of states for random defects will be presented.
Electrical properties of poly(tetrathiafulvalenes)
Authors: Gruber Harald , Roth Hans‐Klaus , Patzsch Jörg , Fanghänel Egon 
Published: March 2011

AbstractResults of conductivity measurements on undoped and iodine or bromine doped poly(tetrathiafulvalenes) are reported. At higher temperatures the temperature dependence of the d.c. conductivity can be best described by σd.c. = °o. exp(T/To)1/4, typical for variable range hopping. The a.c. conductivity follows the general law °(ω) ∼ ω2 for frequencies higher than a critical frequency. A description of the frequency dependent conductivity is given by the extended pair approximation (EPA). At lower temperatures a deviation from linearity of the function in σ versus T−1/4 is observed.
Conditions for the formation of superconductive polymers and possibilities for their realization
Authors: Grigorov L. N. 
Published: March 2011

AbstractGeneral principles of the creation of superconductivity at the polymers are considered. It is shown that high temperature superconductivity may be produced only at really one‐dimensional conducting materials. It is also shown that conjugated polymers cannot have onedimensional conductivity. The new class of nonconjugated polar elastomers is proposed as a perspective one for the creation of high temperature superconductive structures–superpolarons–which appear as a result of internal selfionization of the polymer matrix and a consequent selforganization of free polarons. The practical methods of the formation of superpolarons are shown for the films of oxidized atactice polypropylene. Evidences are given which show the existence of superconductive structures in oxidized polypropylene at room temperature.
Structure and electronic properties of ladder polymers. A new class of conducting polymers
Authors: Wuckel L. , Lehmann G. 
Published: March 2011

AbstractTheoretical calculations have been applied to design novel synthetic polymers which show metallic conductivity without doping. Some selected highly conjugated structures were calculated using a HUCKELMO method extended by introducing elastic sigma bonds. A group of highly conjugated aromatic ladder polymers is promising in this context. Another interesting group consists of laddered heteroaromatic structures in which carbon atoms are replaced by nitrogen.Ionization potentials, electron affinities, band widths, band gaps as well as oxidation and reduction potentials were calculated. Small, band gaps were obtained for polyacene, polyperinaphthalene and polypyridinopyridine. The values are in good aggreement with that obtained on the basis of the VEH method. This paper reports also some efforts to prepare polyacene, polyperinaphthalene and polypyridinopyridine, and to investigate their electronic properties.Concerning their electrochemical properties high specific capacities and good electrochemical stability has been found in aprotic lithium cells.
Dynamics of uv excimer laser ablation of pmma, caused by mechanical stresses theory and experiment
Authors: Kitai M. S. , Popkov V. L. , Semchishen V. A. 
Published: March 2011

AbstractA quantitative model of PMMA ablation was developed. Photochemical reactions, heating of the polymer and mechanical stresses were taken into consideration. The increasing of the optical absorption during the photochemical reaction caused by ArF laser radiation was investigated. The developed model allowed to evaluate the ablation parameters.
Structuring of polymer blends in simple shear flow
Authors: Lyngaae‐Jørgensen J. , Valenza A. 
Published: March 2011

AbstractA simplified model for the formation of steady state structure of discrete domains in polymer blends is established for simple shear flow. It is assumed that the domain size distribution, which results from an equilibrium between breakup processes and coalescence processes, may be divided in small and stable spherical domains and large and unstable ellipsoidal domains. Based on simplified rate balances and an expression for domain deformation rate the volume fraction of large domains and the large and small semiaxes of the ellipsoids are expressed as functions of volume fraction and shear rate/shear stress. The ability of the model to simulate actual behaviour is tested against quantitative data for polystyrene/poly(methyl methacrylate) blends. It is concluded that the Taylor type behaviour is approached at low volume fraction and low shear stress. The aspect ratio, P, shows a maximum in a plot against shear stress with volume fraction as discrete variable. For certain concentrations P seems to approach infinity thus forming infinitely long fibers.
Interpenetrating polymer networks, the state of the art
Authors: Sperling L. H. , Fay J. J. , Murphy C. J. , Thomas D. A. 
Published: March 2011

AbstractInterpenetrating polymer networks are combinations of two crosslinked polymers. Often, they exhibit dual phase continuity, meaning that both phases extend continuously throughout the sample. Recent research on IPNs has shown that both nucleation and spinodal decomposition mechanisms are important in the kinetics of phase separation.If the polymers are almost miscible, a microheterogeneous morphology will develop. Under these conditions, the glass transition of the IPN may be very broad, extending the range between the glass transition of the two homopolymers. Such materials are useful for sound and vibration damping. The loss and storage modulus, and tan δ behavior of polymers and IPNs in the glass transition region were evaluated on a quantitative basis, in order to characterize their damping behavior better. Corrections for background in dynamic mechanical spectroscopy studies will be discussed. The storage modulus of polystyrene at 25°C was selected as a standard. The development of a group contribution analysis of the integral area under the linear loss modulus‐temperature curves, the loss area, LA, is reviewed, and applied to a number of acrylic, styrenic, and vinyl statistical copolymers and IPNs. Each moiety in a polymer is shown to contribute to LA on a simple, additive basis.New research emphasizes the role of morphology and phase continuity in determining LA. The system cross‐poly(vinyl methyl ether)‐inter‐cross‐polystyrene was selected, because its phase diagram in the blend state is well known, and it has become both a model and interesting system to investigate. Midrange IPN compositions exist as two phases at room temperature, as illustrated by dynamic mechanical spectroscopy.
Reactive processing and blending of polymers making use of mechanoradicals
Authors: Geuskens Georges 
Published: March 2011

AbstractThe grafting of various vinyl monomers on polyethylene and on ethylene‐propylene copolymers has been initiated by mechanoradicals in an internal mixer. This is possible if the polymer has been slightly cross‐linked by γ‐radiation before processing or is dynamically cross‐linked by peroxides during processing. Some properties such as adhesion to metals or impact resistance of blends containing the modified polymers are improved.
Controllable specific interactions and miscibility in polymer blends, 2. A brief description of the main results
Authors: Jiang Ming , Cao Xianyi , Chen Wenjie , Xiao Hong , Jin Xiaoling , Yu Tongyin 
Published: March 2011

AbstractIn this paper, we briefly report the main results of our work on the effect of introducing specific interaction on the miscibility of otherwise immiscible polymer blends. A strong proton‐donating unit (CF3)2(OH)C‐ was incorporated into polystyrene (PS(OH)). A series of blends of PS(OH) with one of polyacrylates such as PBA, PMMA, PEMA and PBMA was studied. The infrared spectra of the blends present convincing evidence of the formation of hydrogen bonding. The frequency shift of the OH stretching band due to H‐bonding is independent of the structure and composition of the hydroxyl‐containing polymers, but clearly dependent on those of the counterpolymers. Both excimer and nonradiative energy transfer (NRET) fluorescence techniques have proved effective for monitoring the variation of the degree of molecular interpenetration with the density and strength of the hydrogen bonds in the blends. TEM observations reveal clear and regular variation in the morphology of the blends with the content of hydroxyl‐containing groups. The morphological features of this kind of blends are almost controllable since the structure and/or amount of the introduced groups forming hydrogen bonding are readily adjusted in chemistry. NRET and viscosity measurements of solutions of polyacrylate and PS(OH) with relatively high hydroxyl contents in toluene provide evidence of the intermolecular complexation. In addition, the effect of introducing simultaneously crosslinking and intermolecular hydrogen bonding into blends of PS and PBA on miscibility was studied. It is concluded that single phase IPN can be prepared, but much higher content of the proton donor is needed in comparison with the blends of the corresponding linear polymers. The interlocking structure of the networks appears unfavourable to forming miscible IPN.
Processing and properties of blends with liquid crystal polymers
Authors: La Mantia Francesco Paolo , Valenza Antonino 
Published: March 2011

AbstractExperimental data on the processing behavior and on the rheological and mechanical properties of blends with a liquid crystal polymer as one component are presented. The blends with low amounts of LCP show easier processability and lower viscosity than the thermoplastic matrix. The elastic modulus is also improved. The reduction of viscosity has been attributed to the lower pressure entry, due to the formation of fibrils and to the immiscibility of the two phases.
Phase behaviour of ordered polymer solutions
Authors: Koningsveld R. , Stockmayer W. H. , Nies E. 
Published: March 2011

AbstractRules for equilibrium phase behaviour, laid down long ago on the basis of the two laws of thermodynamics, appear to be valid also for many polymer systems in which aggregates of various topology occur. The phase rule offers a useful tool for the construction and understanding of phase diagrams for systems in which order of some kind is prevalent in certain ranges in the diagram. ‘Double sickle’ type phase diagrams, found for surfactant solutions, microemulsions as well as block‐copolymer solutions can be traced back to the considerable loss of translational entropy which accompanies aggregation.
Phase separation in the poly (γ‐benzyl‐α, l‐glutamate)/benzyl alcohol system
Authors: Horton J. C. , Donald A. M. 
Published: March 2011

AbstractWe describe phase separations seen in the poly (γ‐benzyl α, L‐glutamate) (PBLG)/benzyl alcohol (BA) system. At temperatures below about 60°C, this system gels. Possible explanations of the system's rigidity include both crystallisation and spinodal decomposition. Recent work on atactic polystyrene (a‐PS) gels has suggested these are the result of a phase separation arrested by vitrification. An analogy between a‐PS and PBLG gels is suggested whereby crystallisation (in the latter) plays the rǒle of vitrification in the former.
Ligand‐exchange chemistry of Cr13‐polyacrylamide gels
Authors: Burrafato Giovanni , Albonico Paola , Bucci Silvia , Lockhart Thomas P. 
Published: March 2011

AbstractEvidence that ligand‐induced de‐gelation of Cr(+3)/polyacrylamide (PAAm) gels involves simple extraction of Cr(+3) from the gel matrix has been obtained from rheological studies. Kinetic experiments provide evidence that de‐gelation involves dissociative ligand exchange at Cr(+3). On the basis of de‐gelation results acetate is suggested to be a poor thermodynamic model for the bonding of PAAm to Cr(+3) and it is hypothesized that Cr(+3)/PAAm complexation may involve bonding to both a polymer carboxylate and a neighboring amide group.
The structure of poly(ethylene oxide)‐poly(dimethyl‐siloxane) triblock copolymers in solution
Authors: Maassen H.‐P. , Yang J. L. , Wegner G. 
Published: March 2011

AbstractA series of triblock copolymers consisting of oligomeric segments of poly(ethylene oxide)(PEO) and poly(dimethylsiloxane) (PDMS) were synthesized. These amphiphilic polymers have the general structure (PEO)n‐Z‐(PDMS)m‐Z‐(PEO)n or inversely (PDMS)m‐Z–(PEO)n‐Z‐(PDMS)m where “Z” is the group linking the chains of different polarity. n and m varied in the range m, n < 77. These polymers spontaneously form lyotropic mesphases if mixed with water. The phasediagrams and symmetry of the phases were determined. Moreover, photoreactive groups were attached at exactly and only the positions “Z” of the block copolymers. When photocrosslinking was induced in a particular lyotropic mesophase, the arrangement of the molecules in this phase structure was fixed. Although the phase structure collapsed when the systems were freed from water, the structure returned on reswelling. Some rules concerning the tendency of such molecules to self‐organize as a function of the molecular structures are obtained.
Colloid structure in polyethylene‐wax/n‐paraffin mixtures
Authors: Sawodny Michael , Asbach Gerd‐Ingo , Kilian Hanns‐Georg 
Published: March 2011

AbstractThe spherulite structure and its genesis in WAX PE130 are discussed on the basis of DSC, X‐ray small‐angle and raster‐electron‐microscopical measurements. Modifications of this superstructure in the presence of a low‐molecular‐weight solvent are shown. The role of thermodynamics and kinetics is reflected. Conclusions are drawn which imply general aspects that governs the growth of spherulites.
Ion complexation of biopolymers: Macromolecular structure and viscoelastic properties of gels
Authors: Axelos M. A. V. 
Published: March 2011

AbstractThe effect of charge density and solvent conditions have been explored on sodium pectinate–calcium system undergoing gelation. Viscosity and shear modulus were determined respectively before and after the transition. More than 55% of sugar residues need to be charged to build a network. The amount of calcium required increases dramatically with the decrease of pH and ionic strength. Pectins in salt–free solutions are rapidly connected by calcium ions but the crosslink density remains lower than in NaCl‐rich solutions. Small angle X‐ray scattering indicates that the junction zones may be viewed as rod‐like cylinders whose cross–section radius increases from 3 to 6 and 8 Å when the ratio R = 2 (Ca2+)/(COO−) changes from 0 to 0.5 and 0.75.
Monte Carlo calculation of a partial reaction in radical cross‐linking of 1,4‐polybutadiene
Authors: Martl Michael G. , Saf Robert , Hummel Klaus 
Published: March 2011

AbstractIn simulation of radical cross‐linking of 1,4‐polybutadiene the formation of cross‐links is assumed to occur in the following steps: Formation of radicals from a low‐molecular‐weight compound, hydrogen abstraction from the polymer chain resulting in polymer radicals and finally mutual substitution of two polymer chains. The reaction is complicated by a coupled partial double‐bond shift. The frequency distribution of the fraction of C atoms between cross‐links is investigated as a function of the probability of double‐bond shift and the degree of substitution. This distribution depends significantly on the extent of the double‐bond shift. The discussion of network structures considering only physical network theories is therefore insufficient and should also include chemical aspects.
Enhancement of inhomogeneities in gels upon swelling and stretching
Authors: Bastide Jacques , Mendes Eduardo , Boué François , Buzier Martine , Lindner Peter 
Published: March 2011

AbstractIn this paper, it is shown how a percolation process can be used to describe the inhomogeneities of polymer concentration, appearing in gels prepared by random crosslinking of a semi‐dilute solution, and how they are modified by swelling or stretching of the network. Neutron scattering experimental data are compared to the predictions of this model in the isotropic and anisotropic cases. A good agreement is found. In particular, “abnormal” butterfly patterns in the iso‐intensity curves have been detected, as expected from the model.
Chain orientation in deformed networks via NMR
Authors: Poon Chi‐Duen , Samulski Edward T. , Nakatani Alan I. 
Published: March 2011

AbstractWe quantitatively simulate the deuterium NMR linshapes that result when labelled poly(dimethyl siloxane)‐d6 networks are uniaxially strained. The inferred microscopic reorientational processes that the chain segments exercise in (deformed) networks are indicative of dynamic heterogeneity wherein different parts of the network average the residual quadrupolar interaction to different degrees. The higher the molecular weight between crosslinks, the larger the fraction of slow reorienting species suggesting that chain disinterpersion may be the rate‐limiting contribution to segmental motion in long chains. Our depiction of the network at ambient temperature is that of a liquid wherein motionally distinct segmental domains are characterized by different rotational correlation times. However, under uniaxial extention the fluid network is similar to an anisotropic liquid having macroscopically homogeneous (nematic‐like) segmental orientational order that is characterized by a single order parameter. Order parameters extracted from the NMR simulation are discussed in terms of classical descriptions of how macroscopic strain induces microscopic orientational order in Gaussian networks.
Structure of filled and unfilled elastomers: Thermoporometric measurements
Authors: Pouchelon A. , Soria M. , Moll L. 
Published: March 2011

AbstractThe thermoporometry has been applied to the determination of the crosslink density of silicone elastomers. Significant effort was devoted to the choice of the solvent, only the 2‐butanone leads to the desired thermoporometric effect. The problem of the physical state of the polymer at the temperature of the experiment was pointed out. Nevertheless, the obtained results expressed by the distribution of the molecular weigth between crosslinks and their average values are compatible with those of the usual techniques and they well explain the mechanical properties of the elastomers.
Slow crack growth in polyethylene ‐ a review
Authors: Brown Norman , Lu Xici , Huang Yan‐Ling , Qian Ruzheng 
Published: March 2011

AbstractSlow crack growth in a wide variety of polyethylenes have been investigated. The quantitative relationship between: (1) the external variables such as stress, temperature, stress intensity and J‐integral; (2) the morphological variable such as density and crystal size and (3) molecular variables such as molecular weight, branch density and branch distribution and the rate and time to failure for slow crack growth will be presented. The kinetics of slow crack growth is correlated with the microstructural changes. A fundamental description of slow crack growth is given in terms of tie molecules and the stress field on the boundary of the craze from which fracture initiates.
Chain relaxation capability and service life of polymeric materials
Authors: Brostow Witold 
Published: March 2011

AbstractBehavior of polymers in creep, stress relaxation, stress‐strain curve determination, impact tests and under dynamic periodic loads are analyzed. Rapid crack propagation and slow crack propagation are considered in relation to service performance and life time. All essential aspects of mechanical behavior of polymeric materials and components have a common denominator: competition between chain relaxation capability (CRC) and destructive processes. For a given force (magnitude, rate, direction, duration) the outcome of this competition depends largely on the amount of free volume.
The effect of different hardeners on the ageing of crosslinked epoxy resins
Authors: Förster P. , Hauschildt K. R. , Wilhelm D. 
Published: March 2011

AbstractPolymers based on epoxies are widely used in the industrial production of materials for different applications. The crosslinking is often done with hardeners like aliphatic or aromatic amines, with dicarboxylic acid anhydride or anionically. The resins containing mineral fillers possess similar thermal mechanical properties. On thermal oxidative ageing, however, the systems behave very differently. An account is given of the thermal mechanical behaviour and of the weight loss on ageing above the glass transition temperature. By using semiempirical molecular orbital calculations we have been able to identify a possible reason for the different thermal oxidative stability of epoxy resins crosslinked with different hardeners.
Computer simulations of thin polymer layers
Authors: Khalatur P. G. 
Published: March 2011

AbstractMolecular dynamics calculations are used to explore the structure of dense monolayers of long‐chain molecules supported on a planar surface. As a model we consider ensembles of flexible chains consisting of N segments (N=32, 64 and 128) in a box with lateral (x, y) periodicity conditions. The effect of surface coverage on the conformational properties of chains is studied. At high coverages, the results of the simulations show that each chain is strongly stretched along the normal to the surface and the mean layer thickness is linear in N. The segment density distribution along the normal is found to be an universal function A2/3 f (zA1/3 N), where A is the surface area per chain. The high‐coverage distribution has a well defined broad plateau, in agreement with the so‐called blob model. In contrast to the predictions of this model, however, we observe that the chains are strongly stretched at all space scales. Differences between the results of simulations and those predicted by the mean‐field theory are also discussed.
Hydrophilic membranes based on poly(vinyl methyl ether‐crosslinked‐polystyrene) semi‐interpenetrating networks
Authors: Felisberti Maria Isabel , Stadler Reimund 
Published: March 2011

AbstractMicroporous membranes were prepared from poly(vinyl methyl ether ‐ crosslinked‐polystyrene) (PVME‐cross‐PS) semi‐IPN's by extraction of poly(vinyl methyl ether) (PVME) with water. Membrane morphology and properties are fixed during the process of swelling, phase separation, PVME extraction and vitrification which occurs upon immersing the samples in water. The membranes are characterized by swelling (water uptake), the relative amounts of free and bound water, and their permselectivity towards KCI solution.
Photoconductivity in polymers. Chemical structures and physical mechanisms
Authors: Strohriegl Peter , Haarer Dietrich 
Published: March 2011

AbstractSynthesis and photoconductivity measurements are presented for two different types of photoconductors: i) polymers with pendant carbazolyl groups and ii) conjugated polymers. The temperature‐ and field dependence of the effective carrier mobility has been measured in a series of polymethacrylates with pendant carbazolyl groups and is discussed in relation to theoretical models. Time‐of‐flight measurements show that conjugated polymers like poly(methylphenylsilane) and poly(1,4‐phenylenevinylene) exhibit extremely high carrier mobilities.