bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrolytically initiated vinyl polymerization
Authors: Olaj Oskar Friedrich 
Published: March 2011

AbstractAfter a short outline of the historic development of electroinitiated vinyl polymerization and a description of the early work in this field a survey is given on the most important initiation systems. The difficulties and problems which arise, in addition to conventional initiation of vinyl polymerization, are analyzed. Among others, these comprise the spatial heterogeneity of active particle production, the necessity of dissolving the electrolyte in the polymerization system, which preferably also should be a solvent for the polymer formed, the susceptibility of the electrode process to impurities, the eventual termination of the growing chains by the products of the process taking place at the counter‐electrode, and the possibility of simultaneous initiation of anionic and free radical polymerization at the cathode and of cationic and free radical polymerization at the anode. Some examples show that in spite of these numerous difficulties precise kinetic measurements are possible in some free radical as well as in some ionic initiation systems. While the initiation of free radical polymerization processes suffers from disappointingly low current yields (≈︁10−3), throughout which makes this initiation much inferior to any conventional one, there are some positive features inherent in the electroinitiation of ionic polymerization. Especially, it is the possibility to carry out cationic polymerization exclusively in presence and under control of such counterions which are known to have favorable polymerization characteristics (this is to lead to high rates and molecular weights), however, the corresponding anhydrous acids of which do not exist, by merely oxidizing the monomer in presence of salts of these counterions (e.g. AgSbF6). Due to the non‐availability of the corresponding anhydrous acid HSbF6 this cannot be accomplished in a direct manner by conventional techniques.
Phenol electropolymerization in acid medium
Authors: Mengoli Giuliano , M. Musiani Marco 
Published: March 2011

AbstractAn overview is given of phenol electro‐polymerization in oxalic acid media, as a method of corrosion protection for Fe substrates. The work focuses on the electrical and/or chemical parameters of the system which mainly determine the growth and/or corrosion resistance of the organic‐inorganic films thus obtained. Quantitative evaluation of the barrier to corrosion provided by the coatings was carried out by the ac impedance technique.
Neutron scattering studies of the structure of amorphous and crystalline polymers and of polymer blends
Authors: Fischer E. W. 
Published: March 2011

AbstractThe technique of neutron scattering for studying both the structure and dynamics of polymer systems is now well established. In the case of amorphous flexible polymers in most cases the bulk chain dimensions agree rather well with those of the unperturbed coil. Some newer results concerning for example side‐chain liquid‐crystal polymers and segmented polyurethane elastomers are described. Neutron small‐angle scattering can also be used for the investigation of the molecular deformation mechanism during the drawing process of polymers.In the case of semicrystalline polymers the way in which a single macromolecule traverses the crystalline and amorphous phases can also be evaluated by neutron scattering. A method has been proposed for the evaluation of the neutron scattering data without introducing detailed structural models. The only assumption made is that the molecular structure can be described as consisting of “clusters” of crystalline stems which belong to the same molecule. It is shown that this cluster model can be verified experimentally for the cases of poly(ethylene oxide), polypropylene and polyethylene.The structure factor S(q) in compatible polymer blends is usually treated by the random phase approximation according to de Gennes. The temperature dependence of S(q) displayed by some systems, however, appears to be anomalous within this approximation. A new method is presented for evaluating the neutron scattering data which takes into account that the Flory‐Huggins interaction parameter χ is not a point‐function χδ(τ), but can be interpreted in terms of a structure model χ(τ) which consists of spatially separated positive and negative contributions within a 1–10 å range.Finally the application of neutron scattering to diblock copolymers is discussed and it is shown that the results for the case of polystyrene‐poly (p‐methylstyrene) are in good agreement with the theoretically expected behaviour.
Reactive oligomers and polymers: Synthesis and application for polymer modification
Authors: Fedtke Manfred 
Published: March 2011

AbstractThe classification of reactive oligomers and some aspects of their reactivity in crosslinking systems is discussed, and related to three experimental attemps to contribute to a better understanding of epoxy network modification by reactive oligomers and polymers.The synthesis and modification of telechelic oligomers with functional groups at the chain end as starting materials for modified epoxies proved to be successful only when all the mechanisms occurring below gel point had been investigated by model reactions on the one hand and, on the other, when the actual determination of their influence on the network structure had been established.Ethylene‐vinylalcohol copolymers with a controllable amount of hydroxylic groups are a convenient model system. The reaction of OH‐groups with acid anhydrides produces carboxylic groups attached onto the polymer chain which are useful as hardeners for epoxy resins. The mechanisms of the synthesis and of the crosslinking reactions are more complex than might be expected.More information is now available about the amount of oligoether sequences in epoxies prepared by anionically and cationically induced crosslinking of glycidyl ethers. Using model compounds, several different types of oligomers have been found which depend on the initiating agent.
Instruments and methods for small‐angle scattering with synchrotron radiation
Authors: Koch M. H. J. 
Published: March 2011

AbstractSome aspects of small‐angle X‐ray scattering (SAXS) instrumentation for synchrotron radiation (SR) are considered below. The basic layout of instruments as well as some of the problems arising from the nature of the source and of the type of experiments are discussed. Further, a survey of the instruments available at major SR facilities is given.
Elastic light scattering from nonspherical and polydisperse particles in the size range from 100 to 2000 NM
Authors: Glatter Otto , Hofer Michael 
Published: March 2011

AbstractIn the case of monodisperse dilute systems it is possible to calculate the distance distribution function for homogeneous and inhomogeneous particles of arbitrary shape. The distance distribution function enables one to find a rough classification of the shape and to determine the size of the particle. This function can be deconvoluted to the radial polarization density profile for particles with spherical symmetry.A number, mass or intensity distribution can be calculated from the light scattering data from polydisperse systems if the distribution can be described by a single parameter and if it is possible to calculate the shape factor of the particles, as it is the case for spheres and spheroids. The range of applicability of the method depends on the experimental set‐up, but is in most cases in the size range from 100 nm to several micrometers.
Polymer blends
Authors: Higgins Julia S. 
Published: March 2011

AbstractSmall angle neutron scattering may be used to provide information on the thermodynamic basis of polymer‐polymer miscibility via the temperature and concentration dependences of the observed interaction parameters. The kinetics of the phase separation process may also be followed and this in turn gives further information about the blend compatibility as well as providing tests of current theories of spinodal decomposition in binary mixtures.
Structure studies of langmuir‐blodgett films
Authors: Feigin Lev A. , Lvov Yurii M. 
Published: March 2011

AbstractA method of small‐angle X‐ray investigation of the structure of Langmuir‐Blodgett (L‐B) films on substrates is developed. Experiments were carried out using a small‐angle X‐ray diffractometer with a position‐sensitive detector. X‐ray patterns contain 10–15 reflections with spacings from 50 Å up to 250 A and a number of ripples in the inner parts of the curves. An analysis of these ripples revealed integral parameters of L‐B films (thickness 100 ‐ 2000 A, a number of monolayers: 1–50). The Fourier‐synthesis of the structural amplitudes gave electron density profiles across the films. These profiles demonstrated the successive realization of pre‐programmed sequences of alternating bilayers in L‐B superlattices.
Small‐angle scattering as a tool for the study of microemulsion structure
Authors: Kaler Eric W. 
Published: March 2011

AbstractMicroemulsions are equilibrium dispersions of oil and water stabilized by a surfactant‐rich sheet at the internal oil‐water interfaces. The domains of oil and water have characteristic dimensions of a few hundred Ångstroms, and so are appropriate for study with small‐angle scattering. The scattering from droplets of oil in water or water in oil may be modelled well with modern representations of the structure of colloidal suspensions, but the structure of microemulsions containing comparable amounts of oil and water is likely bicontinuous and is well represented as a disordered lamellar structure. Recent theoretical and experimental results are reviewed and extended.
In‐situ small‐angle studies of microstructural changes in polymers
Authors: Schultz Jerold M. 
Published: March 2011

AbstractA series of experiments in which small‐angle x‐ray scattering (SAXS) is used to follow microstructural changes in situ is reviewed. The work relates to primary and secondary crystallization, to melting and to physical aging. SAXS curve shapes are used to define whether primary crystallization occurs through the growth of “skeletal” or of “dense” spherulites. The integrated intensity is used to establish whether primary and secondary crystallization occur simultaneously. The ratio of second‐ to first‐order peak intensities, the absolute intensity, and reversible peak shifts are used to study the nature of secondary crystallization in polyethylene, poly(vinylidene fluoride) and a polysiloxane. The last two of these exhibit reversible peak shifts which are not consistent with simple models and it is concluded that thorough replacement of existing structures occurs during this process. SAXS peak shape changes in PE indicate that melting occurs by the random loss of crystals throughout the material. Finally, it is shown that SAXS can be a useful tool for monitoring physical aging in semicrystalline polymers.
Small angle neutron scattering (SANS) studies of diffusion in bulk polystyrene near the glass transition temperature (Tg)
Authors: Anderson James E. , Jou J.H. 
Published: March 2011

AbstractUltraslow diffusion in bulk polymers has been measured by SANS. The experiment begins by measuring scattering from heterogeneous specimens containing domains of protonated‐and deuterated‐polymers at temperatures far below Tg. The samples are subsequently held [annealed] above Tg for a known time‐interval, then cooled below Tg where SANS is measured again. Scattering changes, from before to after annealing, are analysed to obtain diffusion coefficients. The recent Summerfield ‐ Ullman procedure is used to deconvolute portions of the scattering curve that decrease and increase with annealing time. Because of SANS sensitivity to small distances, the method yields D ≈ 10−18 to 10−15 cm2/s after annealing times of 1–24 h. Data analysis is complicated by “smearing effects” which produce apparent Q‐dependent diffusion coefficients. Representative experimental results on polystyrene at 108°–130°C are discussed.
Small‐angle X‐ray scattering characterization of inorganic glasses
Authors: Walter G. , Kranold R. , Lembke U. 
Published: March 2011

AbstractSmall‐angle X‐ray scattering is a powerful tool in glass science. The present paper reviews the characterization of inorganic glasses by means of this technique, with specific concern for four areas; (A) the correlations between structure and properties; (B) the middle‐range order; (C) the kinetics of phase separation; and (D) the techniques of glass preparation. SAXS studies on various glass systems, e.g. vitreous silica, phosphate glasses, colour glasses, photochromic glasses, and glass‐ceramic‐forming systems, are described in terms of this approach.
Development of polymer blend phase morphology during processing
Authors: White James L. , Min Kyonsuku 
Published: March 2011

AbstractWe investigate the mechanics of formation of polymer blends both from the view of (i) the technology and flow characteristics in batch and continuous compounding machinery as well as from (ii) the mechanistic perspective of the formation and evolution of dispersed phases. Special attention is given to internal mixers and to intermeshing co‐rotating twin screw extruders. The role of interfacial tension and viscosity ratio in affecting phase morphology is described. We also discuss the development of polymer chain orientation in the different components of an immiscible polymer blend during processing.
Study and control of polymer blends morphology and related properties
Authors: Teyssié Ph. , Fayt R. , Jérôme R. 
Published: March 2011

AbstractIt will be shown how a combination of techniques allows to gain a rather precise idea of the (un)miscibility situation in polymer blends at different size scales (i.e. from ca.20 A up to lμ); typical examples include simultaneous use of TEM, SEM, NRET and ss. NMR.On these bases, interesting blends have been studied and tailored, in which both morphology and interfacial adhesion have been controlled (in particular by the use of diblock copolymers) to provide for a better spectrum of properties. A number of situations will be described, implying commodity and engineering polymers, but also different types of fillers; their optimization has led to interesting applications in the field of better emulsion dispersions, very high impact resins, economical engineering plastics, controlled migration, filled materials,.
Digital image analysis of polymer blends morphology
Authors: Nishi Toshio , Hayashi Takafumi , Tanaka Hajime 
Published: March 2011

AbstractApplication of digital image analysis (DIA) to polymer blends morphology is discussed with examples. Various operations in DIA including two‐dimensional Fourier transformation (2DFT), intensity distribution, recursive region extraction, etc. are applied to morphology of polymer blends due to spinodal decomposition (SD), nucleation 6 growth (NG), and eutectic solidification (ES). Merits and drawbacks of DIA to study polymer blends morphology are discussed and the possibility of future development is presented.
Crystallization, morphology, structure and miscibility of poly(ethylene oxide) based blends
Authors: Cimmino S. , Martuscelli E. , Silvestre C. 
Published: March 2011

AbstractResults of an investigation on the morphology, structure, isothermal crystallization, thermal behaviour and miscibility of poly(ethylene oxide) (PEO) based binary blends are reported. In particular poly(vinyl acetate)(PVAc), poly(methyl methacrylate) (PMMA) at different tacticity and poly(ethyl methacrylate) (PEMA) were added to PEO.It was found that with the only exception of isotactic poly(methyl methacrylate) (IPMMA), the addition of the above cited components causes a depression in both the spherulite growth rate and the overall kinetic rate constant. The experimental G and Kn were analyzed by means of the latest kinetic theory in order to determine the influence of composition on the process of surface secondary nucleation. The optical microscopy of thin films of the sample revealed that the blends crystallized with volume filling crystals at least up to 50/50 blend composition. The small angle X‐ray scattering curves were analyzed using a recently developed methodology. The structural properties of the blends were attributed to the presence of the non crystallizable material in the interlamellar or interfibrillar regions of PEO. From the glass transition temperature it has been deduced that an homogeneous amorphous phase is present for all the blends except for the PEO/IPMMA amorphous system. For the system PEO/atactic poly(methyl methacrylate) (APMMA) the miscibility was also predicted by theoretical approaches.
Brittle‐tough transition temperatures in impact tests on rubber‐toughened plastics
Authors: Bucknall Clive B. 
Published: March 2011

Abstract— In notched impact tests, rubber‐toughened plastics show abrupt transitions in toughness with increasing temperature. Typically, there are two such transitions, one just above the Tg of the rubber phase, and the second some tens of degrees higher. The factors affecting the positions of these transitions are discussed. The relaxation behaviour of the rubber phase is a key factor, but rubber content and particle size are also important. Examples of impact transitions in high‐impact polystyrene (HIPS) and toughened nylon are discussed.
Solvent effect on the miscibility of polymer blends
Authors: Bui Van Tam , Baril Daniel , Vu Thanh Long 
Published: March 2011

AbstractStarting from the Flory‐Huggins theory applied to a polymer/polymer/solvent solution, an expression has been derived showing the overall effect of solvent on the composition of the polymer blend in the final solid state. This expression has been experimentally verified by investigating the miscibility of two polymer blends: polystyrene/poly(α‐methylstyrene) cast from tetrahydrofuran and cyclohexane, and polystyrene/poly (methyl methacrylate) obtained from tetrahydrofuran and chloroform. Besides the usual differential scanning calorimetry technique, thermogravimetric analysis might be helpful for detecting the miscibility of polymer blends.
Small‐angle neutron scattering study of homopolymer blends and blockcopolymers of polystyrene/polyparamethylstyrene
Authors: Jung W. G. , Fischer E. W. 
Published: March 2011

AbstractSmall angle neutron scattering (SANS) experiments were carried out at one mixture and two block copolymers of polystrene (PS) and poly(p‐methylstyrene)(PpMS) at different temperatures ranging from 107 to 295°C. Both block copolymers show a maximum in scattering intensity, which increases with decreasing temperature approaching the spinodal point. Theoretical curves from Leibler's mean field theory agree very well with the experimental points with (XN) as the only fitting parameter, where χ is the Flory‐Huggins interaction parameter and N is the degree of polymerization. The reciprocal value of I(qm)−1 of the maximum intensity for the block copolymers as well as the reciprocal intensity at zero scattering vector (I(q=0)−1) for the mixture obey well the ansatz I = A + B/T within the experimental temperature range. The spinodal values of (XN)S are in good agreement with the theoretical values from Leibler.
Block copolymer‐homopolymer blends in the disordered state: Determination of the interaction parameter using small angle neutron scattering
Authors: Marie Pascal , Selb Joseph , Rameau Alain , Gallot Yves 
Published: March 2011

AbstractThe aim of this study was to determine the interaction parameter xAB and its variation with temperature from the intensity scattered By pure block copolymer (A‐B) and block copolymer‐homopolymer (B) blends where A is polydeuteratedstyrene and B polybutadiene. SANS experiments on pure copolymers of low molecular weight have shown that the scattering curve exhibits a peak of intensity related to the correlation hole effect. χAB was determined by fitting the experimental curves using Leibler's theory and the law of variation of χAB versus temperature was established. In the case of copolymer‐homopolymer blends, the scattering spectrum is modified because of a new and additional long range correlation effect (mixing effect) which dominates in the low q range and leads to strong forward scattering. We have not found any significant variation of χ with blend composition.
Microstructure of miscible polymer blends
Authors: Vesely D. , Finch D. S. 
Published: March 2011

AbstractThe purpose of this work is to describe the application of new electron microscopy techniques to the study of polymer blends with very fine dispersion of phases (miscible blends). Blends of PVC with PMMA, PCL, POM and SAN were prepared by high temperature mixing on a two roll mill, or by solvent casting. Thin sections (or cast films) were investigated in the scanning transmission electron microscope and small phases were identified in most blends. The contrast was enhanced by electronic combination of bright and dark field signals, by an irradiation and staining technique and by differential mass loss. The specimens were further characterized by measurement of mass loss, resulting from electron beam damage. The non linear changes in the mass loss rate with concentration were interpreted as being influenced by partial solubility and molecular interactions.
Relaxation behaviour of stretched polymer melts
Authors: Verbraak C. L .J. A. , Te Nijenhuis K. , van Der Vegt A. K. 
Published: March 2011

AbstractThe relaxation behaviour of stretched polymer melts is described with the aid of the Lodge‐model, in which a finite deformation time is incorporated. The theoretical predictions, based on this model, are in fair agreement with experimental results, at least for relatively small deformations. A simple shift factor is introduced to fit the theoretical and experimental curves in the case of larger deformations.
Recognition hysteresis of the acetylcholine receptor of torpedo Californica
Authors: Neumann Eberhard , Boldt Elvira , Rauer Barbara , Wolf Hendrik , Chang Hai Won 
Published: March 2011

AbstractThe nicotinic acetylcholine receptor (nAcChR) of the electric organ of Torpedo californica fish exhibits a pronounced hysteresis loop in the high affinity binding of the neurotransmitter acetylcholine (AcCh). When increasing amounts of AcCh are added (pulse mode) an extremely long‐lived, metastable conformer distribution is obtained (lower hysteresis branch) between low affinity AcCh binding states (Rl) and high (Rh) and very high (Rvh) affinity states. Dialysis conditions always lead to the equilibrium binding curve (upper hysteresis branch; K̄A = 5 × 10−9M, 4°C; one A bound to the R‐monomer of Mr ≈ 290 000). Cyclic, pulse mode addition and dilution of AcCh results in scanning loops within the main hysteresis.The kinetic analysis of the changes in free and bound AcCh during the open‐system conditions of dialysis, that releases the metastability, shows that the AcCh (A) binding proceeds along an induced‐fit pathway according to A+Rh ⇋ ARn ⇋ ARvh. The rate constant of the step ARh → ARvh is k2 = 6 × 10−3s−1 and that of the reverse step is k−2 = 3 × 10−4s−1. Direct binding of A to free Rvh can be excluded. Therefore, the state Rvh does not preexist, it is induced and only stable, as ARvh, by bound AcCh. The metastability can be described in terms of long‐lived ARvh ·R1 hybrid dimers.Physiologically, the metastable hybrid may be viewed as a saving device: the functionally important, channel‐active R1 conformer is, at low AcCh‐concentrations [A] < 1μM, prevented to convert to the desensitized states Rh and ARvh. Furtheron, AcCh enhances the phosphorylation of phosphatidyl inositol and the auto‐phosphorylation of the receptor. If the AcCh binding hysteresis causes a phosphorylation hysteresis the desensitized nAcChR may serve as a memory molecule of the transsynaptic information signalling of the neurotransmission.