bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ferrocene containing polymers
Authors: Nuyken Oskar , Burkhardt Volker , Pöhlmann Thomas , Herberhold Max 
Published: March 2011

AbstractPolymers with pendent ferrocene units are synthesized by radical and anionic methods. It has been demonstrated that polymer‐analogous reactions are an attractive alternative to prepare those polymers. Polymers with ferrocene units in the main chain are available from interfacial condensation reaction between ferrocene‐1,1′‐dicarbonic acid dichloride with α, ω‐diamines. Addition of ferrocene‐1,1′‐dithiol onto norbornadiene yields a polymer with repeating units from ferrocene disulfide and norbornene and nortricyclane end‐groups. End‐capping reactions of α, ω‐dimercapto‐telechelics with vinylferrocene yield polymers with ferrocene end‐groups.
Synthesis and investigation of new organometallic polymers on the basis of polyacrylonitrile
Authors: Valetsky P. M. , Bronstein L. M. , Loginova T. P. 
Published: March 2011

AbstractThe regularities of complex formation of PAN nitrile groups with hexacarbonyls of VIB group metals were studied. PAN metal carbonyl complexes with various degrees of complexation were synthesized. Thermal transformations of PAN metal carbonyls were investigated. It was shown that the thermal changes of PAN chromium carbonyls are anomalous, but this does not prevent from the formation of polyconjugated areas and the enchancement of conductivity.
Theory of steric stabilization of colloid systems by grafted polymers
Authors: Ekaterina B.Zhulina , Oleg V.Borisov 
Published: March 2011

AbstractAn analytical mean‐field theory of steric stabilization of dispersions by non‐charged polymer chains grafted at one end onto the surface of colloid particles has been developed. The chains were assumed to be grafted densly, so that the neighboring coils overlap and form a single stabilizing layer. In the case of low‐molecular‐weight dispersing medium and relatively loose stabilizing layers the shape of the potential curve of interparticle interaction is determined by the value of magnified image is the Hamaker constant and Γ is the surface concentration of stabilizing polymer) and the quality of the dispersing medium as a solvent for polymer chains. Depending on the value of γ the system may exhibit the stability of both thermodynamic ( α<1 ) and kinetic ( α> 1 ) character. When the molecules of the dispersing medium are short polymer chains the increase in their length leads to a drastic decrease in the stability range of the system and to its destabilization.
Growth process of polymers near the gelation threshold
Authors: Adam M. 
Published: March 2011

AbstractWe will review experimental results obtained recently on the determination of the laws governing the growth process of polymer clusters as the gel point is approached. The exponent γ which characterizes the increase of the mean weight‐average molecular weight Mw as the gel point is approached and the exponent τ which characterizes the mass distribution were measured on different chemical systems. They were found to be independent of the chemical system (within experimental error) and very close to exponent values calculated by computer simulations following the percolation model. Therefore, the sol‐gel transition is a critical phenomenon of connectivity belonging to the same class of universality as percolation.
The evolution of viscoelasticity near the gel point of end‐linking poly(dimethylsiloxane)s
Authors: Scanlan James C. , Winter H. Henning 
Published: March 2011

AbstractThe linear viscoelasticity of polymers near the gel point can be described by two scaling laws. The material at the gel point has a power‐law linear viscoelastic relaxation modulus, and the relaxation exponent has been found to vary with the composition of the precursor materials, i.e., it is not universal for gelation. A second scaling law describes the evolution of the linear viscoelastic properties through the gel point. The rate of change of the dynamic mechanical modulus/viscosity is observed to scale as a power‐law function of frequency. This power‐law function defines a dynamic critical exponent, and this has been found to be independent of precursor composition for end‐linking poly(dimethylsiloxane) polymers and equal to κ = 0.21 ± 0.02. This exponent may be a universal measure of gelation. The technique of Time Resolved Mechanical Spectroscopy is used to observe the evolution of linear viscoelastic properties of crosslinking polymers in situ in the rheometer. A stretched exponential relaxation modulus describes the evolution of mechanical properties in the vicinity of the gel point very well. The exponents which characterize the divergence of the zero‐shear viscosity and the equilibrium modulus are not universal, since they are related to the relaxation exponent and the dynamic critical exponent.
Demixing and polymerization in systems of anisotropic globular particles: A molecular dynamics simulation study
Authors: Brugè F. , Martorana V. , Fornili S. L. , Palma‐Vittorelli M. B. 
Published: March 2011

AbstractWe report a first set of results of Molecular Dynamics simulations of phase separation in a two‐dimensional system of identical particles bearing attachment sites at their surface. Morphology of regions of aggregation so obtained appear similar to images of biologically self‐assembled structures. Also, they evidence the relevance of the region of thermodynamic instability and of the presence and range of interaction of specific attachment sites. Particles of our system are apt to represent indifferently, though grossly, globular proteins or rigid cells, bearing specific and fixed adhesion sites at their surface. Results illustrate some basic aspects of the origin of the morphology of extended biomolecular/cellular structures, self‐organized from initially homogeneous solutions.
Crosslinking index, molar mass distribution and rubber equilibrium shear modulus during polyfunctional crosslinking: Part II: Application to real systems
Authors: te Nijenhuis Klaas 
Published: March 2011

AbstractIn a previous paper a theory was presented concerning gels formed by polyfunctional crosslinks in a polydisperse primary polymer. The equilibrium shear modulus as well as the crosslinking index were obtained as functions of the functionality of the crosslinks and of the sol fraction. In this paper the theory is applied to gelatin gels (known functionality of crosslinks) and to poly(vinyl chloride) gels (known number of crosslinks).
Boundary conditions for ionotropic gelation of polyuronides
Authors: Braudo Evgenij E. , Yuryev Vladimir P. 
Published: March 2011

AbstractThe determination of reagent concentrations sufficient for gelation in the course of a crosslinking reaction in solution enables characterization of macromolecular coil dimensions as a function of solvent quality and calculation of the apparent equilibrium constant and the reaction order with respect to polymer. Interactions of polyuronides with polycoordinative metal ions are discussed.
Diffusion through rubbery and glassy polymer membranes
Authors: Blume I. , Smit E. , Wessling M. , Smolders C. A. 
Published: March 2011

AbstractMass transport of a number of organic vapors through polydimethylsiloxane films (PDMS) and carbon dioxide through a variety of polyimides based on a hexafluorotetracarboxylic acid unit (6FDA) were investigated. Vapor diffusion through PDMS films strongly depends on the concentration of the penetrant molecules in the network. For chloroform, increasing diffusivity at lower upstream activities occurs due to network plasticization, while a decreasing diffusion coefficient at larger concentration is supposed to stem from penetrant molecule clustering. The diffusion of carbon dioxide in 6FDA‐based polyimides was modelled on a molecular basis. An exponential relation was found between Δcp and the diffusion coefficient and the permeability, respectively. This relation holds also for on‐chain modifications.
Self‐diffusion of azo dyes in poly(vinyl chloride) gels and solutions: Dye‐polymer interactions
Authors: Griffin William G. , Griffin Mary C. A. 
Published: March 2011

AbstractMeasurements of the self‐diffusion coefficients of two azo dyes in poly(vinyl chloride)/bis(2‐ethylhexyl) phthalate gels and solutions by the forced Rayleigh scattering technique are reported. The dependence of dye diffusion coefficients on polymer concentration and temperature has been determined and it is observed that both dyes seem to bind reversibly to the polymer. The energetics of dye binding are analyzed and the apparent dependence of the equilibrium dye‐binding coefficients on the polymer concentration is discussed.
X‐ray scattering studies of fatty acid films on water and on Cdcl2 solutions
Authors: Kjaer K. , Als‐Nielsen J. , Kenn R. M. , Böhm C. , Tippmann‐Krayer P. , Peterson I. R. , Bibo A. M. , Helm C. A. , Möhwald H. , Leveiller F. , Jacquemain D. , Weinbach S. , Leiserowitz L. , Deutsch M. 
Published: March 2011

AbstractX‐ray diffraction methods for Langmuir films on the surface of water are briefly presented, together with recent results for docosanoic acid monolayers on pure water and for eicosanoic acid monolayers on an ionic subphase.
Fluorescence microscopy studies of layer/substrate interaction during the Langmuir‐Blodgett transfer: Fractional condensation and local layer modification in lipid monolayers at the three‐phase line
Authors: Spratte Karl , Riegler Hans 
Published: March 2011

AbstractTransfer fluorescence microscopy reveals the substrate‐mediated fractional condensation and phase‐selective deposition of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylethanolamine (DMPE) monolayers during the LB‐transfer. Preferentially the higher ordered liquid‐condensed (LC) state is transferred onto the substrate during the transfer of a monolayer in the LC/LE (liquid/expanded) coexistence state on the water subphase. This is manifested in the directly observable attraction of LC‐domains towards the three‐phase line and observation of a domain‐free gap as consequence of the segregation of the fluorescent probe into the floating monolayer adjacent to the three‐phase line. Fingering domain growth nucleating at the three‐phase line and the substrate‐mediated pressure deposition of probe‐free material corroborate the preference of the solid substrate for the higher condensed phase. These observations are caused by changes in the free energy of the monolayer due to the replacement of the aqueous interface by the solid substrate surface.
Ice nucleation by monolayers of aliphatic alcohols
Authors: Popovitz‐Biro R. , Gavish M. , Lahav M. , Leiserowitz L. 
Published: March 2011

AbstractMonolayers of aliphatic long chain alcohols (CnH2n+1OH) were found to induce nucleation of ice at temperatures approaching O°C in contrast to water‐soluble alcohols which are efficient antifreeze agents. The corresponding fatty acids and alcohols with bulky hydrophobic groups, induce ice nucleation at temperatures lower by as much as 12°C. The freezing point induced by the amphiphilic alcohols was found to be sensitive not only to area per molecule but also to chain length and parity, reaching higher temperatures for monolayers with n odd. Grazing incidence X‐ray diffraction studies performed on some of these alcohols at the air/water interface (at 5°C and at zero pressure), demonstrated the formation of crystalline two‐dimensional clusters with a distorted hexagonal cell whose dimensions resemble those of hexagonal ice. The catalysis of ice nucleation by these alcohol monolayers may be rationalized in terms of the structural match between the monolayer domains and the ab layer of hexagonal ice.
A study of microgel star amphiphile monolayers
Authors: Shen Jiacong , Zhang Xi , Cha Xiao , Yin Rui 
Published: March 2011

AbstractThis paper reports on the synthesis of a microgel star amphiphile and on the behaviour of its monolayers both on the water surface and on solid substrates. On the water surface, the monolayer surface pressure relaxes at constant area, leading to a “duckweed”‐type structure. The hydrophilic groups play an important role in this process. On solid substrates, Langmuir‐Blodgett films can be fabricated from it with unit transfer ratio and good laminar structure.
A compact Raman microprobe/microscope: Analysis of polydiacetylene Langmuir and Langmuir‐Blodgett films
Authors: Batchelder D. N. , Cheng C. , Müller W. , Smith B. J. E. 
Published: March 2011

AbstractA compact Raman microprobe/microscope has been developed which contains no wavelength dispersive elements. Multilayer dielectric filters, tuned by rotation, provide sufficient wavelength selectivity for taking Raman spectra and forming Raman images of samples as small as 1 μm in diameter. The application of the instrument is demonstrated by Raman spectra and images of polydiacetylene Langmuir and Langmuir‐Blodgett films.
Amphiphilic dyes for NLO in LB‐films
Authors: Laschewsky A. , Paulus W. , Ringsdorf H. , Lupo D. , Ottenbreit P. , Praß W. , Bubeck C. , Neher D. , Wegner G. 
Published: March 2011

AbstractThe influence of structural variations of phenyl‐hydrazones and stilbazium salts on monolayer behaviour and second‐harmonic generation in LB‐monolayers is discussed. In contrast to the stilbazium salts the variation of the substituents of the phenylhydrazones does not influence the absorption maximum of the dyes in resonance enhancement of the nonlinearity. This allows a direct comparison of the substitution pattern on SHG.
Thermodesorption of LB‐multilayers of metal stearates
Authors: Höhne U. , Möhwald H. 
Published: March 2011

AbstractThermodesorption of stearate multilayers containing different metal ions was investigated by Interference‐enhanced Reflection (IeR) and Nomarsky microscopy. Heating of samples in air leads to desorption of stearyl chains and to formation of metal oxide clusters.A new approach to build controlled structures was made by preparing a surface with neighbouring hydrophobic and hydrophilic areas. It is shown that arranging inorganic particles in a predetermined way is possible.
Composition and lateral distribution of self‐assembling monolayers containing surfactant and dye
Authors: Quint P. , Möhwald H. 
Published: March 2011

AbstractNew methods to prepare monolayers with defined lateral distribution of the components are described. These methods make use of different principles: (1) H‐type dye aggregates in an OTS‐matrix and fatty acid domains in a NBD‐dye matrix are prepared by the self‐assembling technique. This is demonstrated by fluorescence microscopy and UV/Vis‐spectroscopy. (2) If the support is structured by photolithography, adsorption and desorption occur preferentially on one of the two types of surface. It is shown that by this method dyes can be distributed laterally with an accuracy of better than 0.5 μm.
Discotic liquid crystals at the air water interface
Authors: Karthaus Olaf , Ringsdorf Helmut , Urban Claus 
Published: March 2011

AbstractThe monolayer properties of two types of discotic liquid crystals, hexasubstituted triphenylenes 1 and azo derivatives of phloroglucinol 5, were examined. First investigations show that these discotic liquid crystals form stable monolayers. It could be shown that electron acceptors insert into the monolayer of 1. Azo discs display a packing behaviour at the monolayer that is ascribed to a side‐on packing of the molecules.
Mono‐ and multilayers from preformed polymers‐influence of molecular weight
Authors: Matzenbach A. , Ottenbreit P. , Prass W. 
Published: March 2011

AbstractAmphiphilic homopolymers have been prepared which are able to form ordered monofilms at the gaswater interface and which can be transferred onto solid substrates. The monofilm and LB‐multilayer properties of these compounds were investigated as function of molecular weight. In monofilms a small but distinct dependence of molecular weight on the properties in the fluid phase of the monofilm was observed for molecular weights (weight average) below 70 000 dalton. In LB‐multilayers, however, no such influence could be detected.
Raman‐spectroscopy and ‐imaging with surface‐plasmon polaritons
Authors: Knobloch H. , Knoll W. 
Published: March 2011

AbstractWe report on surface plasmon field—enhanced Raman imaging investigations of Langmuir—Blodgett multilayer assemblies of cadmium arachidate. This new method is a combination of Plasmon surface polariton field—enhanced Raman scattering with an optical multichannel detection scheme. The imaging capabilities of a CCD—camera are used to spatially resolve the Raman—spectral information of a heterogenous sample.
A novel configuration for the optical characterization of waveguiding layers
Authors: Alberti B. , Peterson I. R. 
Published: March 2011

AbstractWhen a transparent layer of sufficient thickness is suitably coated on both sides with metal, the structure supports one‐dimensionally bound optical modes which propagate in two dimensions but which can be detected externally in a very simple manner. We show that this configuration can be used to determine the optical constants of the layer.
Synthesis and characterization of topologically interesting vinyl polymers
Authors: Hogen‐Esch T. E. , Sundararajan J. , Toreki W. 
Published: March 2011

AbstractA series of macrocyclic poly(2‐vinylpyridine)&s were synthesized by high dilution (∼10−5 M) coupling of the two‐ended living precursor dianions with 1, 2‐ and 1, 4‐bis‐(bromomethyl)benzene (1, 2‐ or 1, 4‐DBX). SEC measurements indicate that the macrocycles contain less than 5% linear precursor and that the hydrodynamic size of the macrocycles is substantially (∼30%) less than that of the linear precursor. At very low MW, the sizes of macrocyclic and linear polymers differ less, particularly for the case of the 1, 2‐DBX product. Viscometry measurements in THF of linear and macrocyclic polymers also indicated substantial size differences of linear and macrocyclic P2VP.The values of the glass transition temperature (Tg) for both the 1, 2‐ and 1, 4‐DBX macrocycles were found to increase with decreasing MW as qualitatively predicted by entropy calculations. Thus, as the degree of polymerization decreases, the macrocyclic chains become conformationally stiffer and this is reflected by higher Tg values. The differences in Tg between linear and macrocyclic P2VP are quite large (∼40K) around a DP of 40 and decrease to values of a few degrees at a DP of around 200. These differences are diagnostically useful in estimating the linear content of the macrocycles below a DP of 100.
New polymers by homogenous zirconocene/aluminoxane catalysts
Authors: Kaminsky W. , Bark A. , Arndt M. 
Published: March 2011

AbstractWith homogenous catalysts on the basis of chiral metallocenes and methylaluminoxane it has become possible to polymerize cyclic olefins like cyclobutene, cyclopentene or norbornene. No ring opening reaction occurs. The crystalline polycycloalkenes show extremly high melting points between 400 and 600°C. Copolymers of cyclopentene with propene are amorphous. They have a low molecular weight and glass transition point. On the other hand the glass transition temperature of norbornene/ethene copolymers exceeds 130°C. These copolymers could be used as materials for optical discs and fibers.
Synthesis of block and graft copolymers of tetrahydrofuran and cyclic acetals
Authors: Franta Emile , Reibel Léonard 
Published: March 2011

AbstractThe polymerization of tetrahydrofuran under a living form allows quantitative functionalisation as well as the formation of copolymers. Cyclic acetal polymerization is more complex but through the “Activated‐Monomer Mechanism” approach, it is possible to prepare telechelic polymers as well as block and graft copolymers with particular emphasis concerning amphiphilic ones.
Living and apparently living carbocationic polymerizations
Authors: Sigwalt Pierre 
Published: March 2011

AbstractSome years ago, the occurrence of living carbocationic polymerization had not generally been expected to be possible, since it is well known that most carbocationic species are quite unstable and have very short lifetimes, and since transfer to monomer had been shown to be important, particularly near room temperature. However, during the last years, many reports of living carbocationic polymerizations have been made. They were based on the observation of various features usually linked to living polymerizations, such as a linear increase of mol. wts. with conversion, sometimes even after several monomer additions, which was attributed to the absence of termination and transfer. In some cases, narrow mol. wt. distributions were also obtained.There seems to be now a general agreement that in these polymerizations a reversible termination occurs, making eventually further growth possible on all macromolecules. Another general feature of those apparently living systems is that the ratio of propagation rate and initiation rate is not too high, so that the concentration of macromolecules is approximately equal to that of the initiator.But the experimental data do not necessarily imply, as this has been generally assumed, that transfer is absent and that the nature of active sites is completely different from those in more classical systems. It is shown that the values of transfer constants already measured in these last ones are compatible with the results obtained in the apparently living systems. A perfectly linear relationship between number‐average degree of polymerization (D̄P̄n) and polymer yield may be observed even up to mol. wts. of about 2.104 with transfer constants ktrM/kp as high as 5.10−4 in apparently living systems. Termination and transfer might be, however, reduced in some cases by various means that are examined, such as the presence of polar additives, a lowering of temperature and the presence of excess monomer. The distinction between systems obeying all the main criteria for living polymerization and those which are only apparently living is discussed.
Exchange reactions in the living cationic polymerization of alkenes
Authors: Matyjaszewski Krzysztof , Lin Chih‐Hwa 
Published: March 2011

AbstractLiving cationic polymerization of alkenes is discussed in terms of rapid dynamic equilibration between carbenium ions and either covalent species or onium ions. Rates of exchange between these species have strong effect on polydispersities of the synthesized polymers. In the discussed living systems, rates of exchange are faster than rates of propagation. Propagation proceeds via classic carbocationic mechanism.
Aluminium complex of a schiffs base as new initiator for oligomerization of heterocycles
Authors: Vincens Valérie , Le Borgne Alain , Spassky Nicolas 
Published: March 2011

AbstractA chiral aluminium complex of a Schiff&s base is a new initiator for the preparation of defined (number‐average degree of polymerization, functionality) oligomers derived from heterocyclic monomers (oxiranes, β‐lactones).
Emulsion polymerization of vinyl chloride, 2 potassium persulfats decomposition in the presence of PVC latex
Authors: Georgescu Cecilia‐Speranta , Sarbu Adriana , Butucea Victor 
Published: March 2011

AbstractThe decomposition rate of potassium persulfate (KPS) in aqueous solutions, in the presence of sodium dodecyl sulfate (SDS) and poly(vinyl chloride) latex (PVC) was studied. The dissolved SDS increases the decomposition rate constant (kd) while the SDS aggregation as micella and/or its adsorption on the polymer hydrophobic surface results in a decreasing kd. The emulsifier ‐ free surface of the polymer particles increases the decomposition rate. A reaction mechanism based on emulsifier ‐ emulsifier and emulsifier ‐ polymer hydrophobic interactions is put forward.