bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoreactive Langmuir–Blodgett–Kuhn multilayer assemblies from functionalized liquid crystalline side chain polymers. II. Structural characterization of homo‐ and copolymers containing azobenzene and phenylbenzoate moieties
Authors: Schmidt A. , Sawodny M. , Knoll W. , Urban C. , Ringsdorf H. , Ahuja R.C. , Möbius D. 
Published: April 2003

AbstractLiquid crystalline side chain polymers containing photoreactive azobenzene chromophores in the dark‐adapted trans form and phenylbenzoate groups as co‐mesogens have been prepared and investigated as monomolecular layers at the water/air interface and as multilayer assemblies deposited onto solid supports by the Langmuir–Blodgett–Kuhn (LBK) technique. Pressure area isotherms at variable temperatures together with reflection absorption spectra and Brewster angle microscopic pictures have been taken and analyzed (i) to derive information about the structural order and the packing properties of the mesogenic side groups within the monolayers of different homo‐ and co‐polymeric systems and ii) to optimize the conditions for the transfer of the monolayers.The resulting multilayer assemblies were primarily characterized by X‐ray reflectometry studies, which yield the film thickness, the electron density modulations indicative of any internal (double) layer periodicity, and two roughness parameters characterizing the substrate/film and the film/air interfaces, respectively. These investigations were complemented by surface plasmon, UV‐vis and IR spectroscopic measurements which provided further information as to the optical/structural properties of the samples.It was found that those systems containing only azobenzene side groups (or a high percentage of them) are composed of metastable double layer subunits which can be easily assembled to thicker films even capable of carrying waveguide modes. The azobenzene chromophores forming various types of aggregates have an average tilt angle of 36° relative to the film normal presumably with a broad angular distribution.If the azobenzene mesogens are diluted by phenylbenzoate co‐mesogens in the radio 1:2, only the first few dipping cycles show a good monolayer transfer so that only thin multilayer assemblies can be built up. Moreover, all these preparations though deposited in the Y‐type mode show no indication of a doublelayer structure in the transferred film, but instead exhibit the so‐called mesogen peak with a smectic periodicity corresponding to only a single monolayer. A structural model with interdigitating side groups is proposed to account for these experimental results.
Photostructuring of a polymer containing anthrylene‐bisacrylate subunits
Authors: Paul S. , Stein S. , Knoll W. , Müllen K. 
Published: April 2003

AbstractA new polymer P containing anthrylene‐bisacrylate subunits is presented which allows the preparation of spin‐cast films of high optical and geometrical homogeneity. Upon irradiation of these films with UV light, both a change in the optical thickness (= geometrical thickness d × refractive index n) and a decrease of the solubility can be induced due to photocrosslinking of the polymer chains. These features make the new polymer a promising material for both optical information storage and photolithography and/or for a possible combination of the two effects.
Permeation of polymers — a computational approach
Authors: Müller‐Plathe Florian 
Published: April 2003

AbstractThis article reviews the progress that has been made in recent years in computer modelling of the transport of small atoms, molecules and ions through synthetic polymers. We discuss the physical concepts behind phenomena such as sorption, diffusion, permeation and ionic conductivity and the techniques to study them by computer simulation: molecular dynamics and Monte Carlo simulation with atomistically detailed force fields as well as coarse‐grained lattice models. Important results have been obtained at both the qualitative and quantitative level. The mechanisms underlying the diffusion of gas molecules and the mobility of ions could be observed in simulations and are now unambiguously established. Short‐time irregularities in the motion such as anomalous diffusion have been found. Some quantities can be calculated very accurately (e.g.gas diffusion coefficients for low‐barrier polymers), where for others only trends and relative orderings can be estimated (e.g.gas solubilities, ionic conductivities) at a semiquantitative level. Where possible, the range of applicability of various methods is indicated. Coarse‐grain approaches are presented which extend the results obtained by atomistic models to longer length scales and thereby allow the treatment of heterogeneous materials such as semicrystal‐line or filled polymers. We believe that computer simulation has enough to offer to make it a useful tool when studying or designing polymer membranes.
Morphology, structure and lattice defects in thin films of syndiotactic polystyrene
Authors: Kestenbach H.‐J. , Petermann J. 
Published: April 2003

AbstractThe morphologies developed during crystallization of syndiotactic polystyrene (sPS) in thin films, were investigated by transmission electron microscopy (TEM) and electron diffraction. Special emphasis was put on the diffraction contrast, which is very sensitive to crystal defects. While the defocus contrast gives an overall picture of the morphologies, the darkfield diffraction contrast may image lattice defects such as dislocations, stacking faults, and ordered domains, among others.Three different morphologies were found:

Single‐crystal‐like morphologies.
Edge‐on stacked lamellar morphologies.
Spherulitic morphologies.
Due to different imaging conditions for those morphologies in the dark‐field imaging mode, different types of lattice defects were detected. Because the dark‐field images are not a direct visualization of the defects, the nature of the contrasts is discussed with respect to the disorder of the molecules creating the defects.
Synthesis and conversion kinetics of some new “Durham” polyacetylene precursors
Authors: Saunders R. S. , Cohen R. E. , Schrock R. R. 
Published: April 2003

AbstractA new “Durham” polyacetylene precursor monomer (substituted tricyclo[4.2.2.02,5]deca‐3,7,9‐triene) was synthesized, and improved synthetic pathways to two existing precursor monomers were developed. Polymers of these three precursor monomers, as well as a bis‐trifluoro substituted precursor monomer, were synthesized using ring opening metathesis polymerization (ROMP) with a tungsten alkylidine initiator. The kinetics of conversion (precursor polymer to polyacetylene) were studied for each of the four precursor polymers using differential scanning calorimetry (DSC). Percent age conversion vs. time data were fit to the Avrami expression often used to describe the kinetics of bulk of crystallization of polymers. The parameter K of the Avrami expression was assumed to depend on temperature according to an Arrhenius expression. In this way, an equation with three constants was obtained that completely describes the kinetics of conversion of a particular polyacetylene precursor polymer. Values for the constants depended on the type of substituent on the precursor polymer. Because the kinetics are well described by the Avrami expression, it is proposed that “nucleation” and “propagation” processes are involved in the conversion of the precursor polymers to polyacetylene.
Synthesis and characterization of liquid crystalline polyesters containing crown ether units in the mesogens
Authors: Fischer H. , Karasz F. E. 
Published: April 2003

AbstractLiquid crystalline polyetheresters with crown ethers in the mesogenic unit have been synthesized using the DB‐[18]‐C‐6 crown. This compound was then transferred to the diacetyl‐, dicarboxy‐ and dicarboxydichloride derivatives. After incorporation of the crown ether moiety into the mesogens of main chain polymers, the liquid crystalline phase of the polymers obtained was observed. The appearance of an unordered smectic phase (smectic A or smectic C) was proved by combining optical investigations, X‐ray diffraction and DSC measurements.
Soluble parts in gelatin/water gels
Authors: Cölfen H. , Borchard W. 
Published: April 2003

AbstractSo‐called soluble parts were extracted from gelatin/water gels by means of deswelling caused by application of a swelling pressure. The soluble parts were characterized by FTIR spectroscopy, time‐of‐flight mass spectrometry, analytical ultracen‐trifugation and amino acid analysis. The results are compared with literature data. The extracted gelatin has a composition similar to the original gelatin. The extract has a much lower molar mass than the soluble parts obtained by different extraction procedures reported in the literature. This supports the conclusion that there must be at least two types of soluble parts. Soluble part of type 1 has molar masses up to 4000 g/mol, has composition similar to the original gelatin and shows virtually no gelling abilities, although an association of the molecules occurs. Soluble part of type 2 consists of a significant amount ofa2(I) chains of type (I) collagen or their fragments and probably has weak gelling abilities.
Characterization of polymers based on quantitative aspects of blob theory
Authors: Dondos A. 
Published: April 2003

AbstractUsing an equation derived from blob theory we calculate the number of statistical segments of which one blob consists (Nc). The same characteristic number can also be directly determined from the Mark–Houwink–Sakurada (MHS) representation. The above characteristic number depends only on the quality (i.e., properties) of the solvent and is found to be the same for different polymers if these polymers are dissolved in solvents for which the exponent in the MHS equation is the same. Based on the above determination of Nc, we calculate the adjustable parameter nα of thermal blob theory. The obtained value lies near a mean value of 10. Knowing the Θ temperature for a number of polymer‐solvent systems, we propose a relation giving the Θ temperature as a function of the rigidity of the polymers and the properties of the solvents. Combining relations derived either from the two‐parameter theory or from blob theory, we propose relations that give the adjustable parameter C relating the number of blobs of a chain to its excluded‐volume parameter z. Knowing the adjustable parameter C (mean value 36) and using a relation derived also from the combination of the two‐parameter theory with blob theory, we obtain the long range interaction parameter B of any polymer‐solvent system. The obtained values are almost the same as the values obtained directly from the Stockmayer–Fixman–Burchard representation.
Aggregation and microstructure of ethylene‐propylene copolymer viscosity improving additive
Authors: Kucks M. J. , Ou‐Yang H. D. , Rubin I. D. 
Published: April 2003

AbstractStatic light scattering measurements of ethylene‐propylene random copolymer revealed that solvophobic ethylene segments were responsible for both aggregation and cluster density variations over temperature. By changing the molar ratio of ethylene to propylene, as well as the solvent, we controlled the degree of solvophobicity. This caused markedly different combinations of aggregation and density variations with temperature. Combinations observed from 50 to −10°C included: (a) constant aggregation and density for an E/P ratio of 60/40 in methylcyclohexane, (b) increased aggregation at −10°C combined with a constant cluster density for an E/P ratio of 60/40 in tetralin and an E/P ratio of 80/20 in methylcyclohexane, (c) increased aggregation and density at −10°C for an E/P ratio of 80/20 in tetralin. We also show how these combined microstructural changes are related to intrinsic viscosity measurements made from 50 to −10°C in these same solvents.
IR spectroscopic analysis of complexes between high molecular weight polyethylene oxide and salts of alkaline metals
Authors: Bogdanov B. , Uzov Chr. , Gavrailova G. 
Published: April 2003

AbstractIon‐binding complexes between high molecular weight polyethylene oxide (PEO) and NaSCN, KSCN and NaI were studied by low and high temperature infrared (IR) spectroscopy (from −130°C to 200°C) within the interval from 2200 cm−1 to 700 cm−1.It is shown that absorption maxima of the stretching vibration of COC bonds in PEO are shifted towards lower wave‐numbers in the IR spectra of the complexes because of the decreasing electronic density of these bonds due to electrostatic interaction of the metal cation (Me+) with the ether O atom.Characteristic changes in the IR spectra of the complexes were observed in the absorption regions of the stretching vibration of COMe+ bonds. They can be explained by structural changes in the systems when they are heated and cooled. Possible conformation states of CC and CObonds in the ethylene oxide units in the complexes between PEO and alkali metal salts which are similar to the conformations of these bonds in molten PEO are suggested.
Small‐angle X‐ray and light scattering from randomly branched polycyanurates
Authors: Bauer J. , Dingenouts N. , Ballauff M. 
Published: April 2003

AbstractA study by small‐angle X‐ray and light scattering of dilute solutions of randomly branched polycyanurates is presented. By combining the scattering intensities of the two methods on an absolute scale, the range from 4 x 10−3 to 7 nm−1 of the wave vector q was available for data analysis. The scattering curves of polymers with different weight‐average molecular weights could be well fitted using an experssion for the form factor derived from the theory of mass fractals. The analysis of the data obtained by combination of the two scattering experiments gave reliable results for the molecular weight, radius of gyration, and fractal dimension of the polycyanurate samples that match the results of viscometry and size‐exclusion chromatography of the same polymeric system.
A new apparatus for simultaneous observation of optical microscopy and small‐angle light scattering measurements of polymers under shear flow
Authors: Kume T. , Asakawa K. , Moses E. , Matsuzaka K. , Hashimoto T. 
Published: April 2003

AbstractA new apparatus which makes it possible to measure flow small‐angle light scattering (“flow‐SALS”) and to observe the development of the supramolecular structure by an optical microscope (“shear microscopy”) has been developed in our laboratory. It simultaneously provides information on reciprocal space from SALS and on real space from optical microscopy. Therefore, the development of the supramolecular structure in systems such as polymer solutions and polymer mixtures as well as liquid crystals and colloidal systems under shear can be investigated in depth. Shear‐induced phase separation and shear‐induced homogenization of some polymer solution systems were investigated using this apparatus.
Thermodynamic and kinetic aspects of cocrystallization and phase segregation phenomena of polyethylene blends between the D and H species as viewed from DSC, FTIR and synchrotron X‐ray scattering
Authors: Tashiro K. 
Published: April 2003

AbstractCocrystallization and phase segregation phenomena of polyethylene (PE) blends between fully deuterated high‐density PE (DHDPE) and hydrogeneous PE with various degrees of ethyl branching have been investigated on the basis of DSC, FTIR, synchrotron X‐ray scattering, and neutron scattering measurements. When the blend between DHDPE and linear‐low‐density PE [LLDPE(2) with 17 ethyl branches/1000 carbons is cooled slowly from the molten state, it exhibits an almost perfect cocrystallization of the D and H species in the same crystalline lamellae. For the blends of DHDPE with LLDPE(3) with higher branching content (41 branches/1000C) or with HDPE without branching, the cocrystallization and/or phase segregation phenomena have been observed to vary systematically depending on the D/H content and on the crystallization condition. The spatial arrangement of the D and H stems in the lamella, the aggregation state of the lamellae in the spherulites, etc. were investigated for these blend samples. Differences in crystallization behavior between the meltcooled sample and the solution‐grown sample were clarified on the basis of DSC, FTIR, and X‐ray diffraction data. The time‐resolved FTIR and small‐angle X‐ray scattering measurements have revealed that the crystallization rate is one of the important factors to govern the cocrystallization and phase segregation phenomena in addition to the thermodynamic stability of the blends.
Influence of channel diameter on the dynamics of polyethylene in its inclusion complex with perhydrotriphenylene
Authors: Zhang N. R. , Mattice W. L. 
Published: April 2003

AbstractThe influences of channel size and structure on the molecular dynamics of polyethylene at 300K have been studied using the inclusion complex of n‐tetracontane with perhydrotriphenylene. The diameter of the channel in the real physical system is enlarged by 1 or 2 Å to provide alternative sizes. The content of gauche (G) states rises from almost nil in the real physical channel to a value in the channel enlarged by 2 Å that is nearly half of the result seen with the free unperturbed chain. The population of G±TG± triplets is much larger than the population of G±TG± triplets (T denotes the trans state). Translation of the center of mass along the channel shows that n‐tetracontane senses the molecular structure of the perhydrotriphenylene in the walls when the channel is enlarged by 1 Å, but not when the channel is enlarged by 2Å. Rotation of the n‐tetracontane as a rigid body about its long axis is primarily responsible for the decay of the orientation autocorrelation functions for the C‐C and C‐H bonds.
Polymer adsorption between a rough surface and a flat surface for an ideal long chain
Authors: Xu Xuetong , Sun Xin , Yang Yuliang 
Published: April 2003

AbstractWe have studied the adsorption of an ideal long polymer chain between a rough surface and a flat surface. The two surfaces are basically parallel to each other and penetrable for the polymer chain. The rough surface is modeled as a sinusoidal grating and the chain is assumed to be long enough so at the ground state dominance is tenable. By solving the diffusion equation for a polymer chain in an external field, we have investigated the related eigenvalue problem and obtained the ground state energy (the lowest confinement energy) of the system. The monomer density distributions on the two surfaces are obtained and their relations to the four relevant characteristic lengths: the separation between the two surfaces h, the confinement thickness D, the surface roughness amplitude z0 and the grating wavelength λ, are discussed.
Effect of crystallization, poling and ageing conditions on the FIR, dielectric and pyroelectric properties of hot‐pressed PVDF and P(VDF/TFE)‐(0.98/0.02)
Authors: Kulek J. , Hilczer B. , Kamba S. , Petzelt J. 
Published: April 2003

AbstractWe studied the influence of hot‐pressing temperature as well as poling and ageing conditions on the amount of polar phase of hot‐pressed PVDF and P(VDF/TFE)‐(0.98/0.02) foil. FIR transmission spectra of hot‐pressed homopolymer and copolymer films were measured in the 30‐450 cm—1 range as a function of hot‐pressing temperature Thp and poling temperature Tp. The FIR studies show that homopolymer and copolymer consist of both polar and nonpolar modifications of PVDF. The content of the polar phase tends to decrease with Thp and increase after poling. The FIR spectra of our samples exhibit a strong absorption peak near 100 cm—1 absent in the biaxially oriented Solef samples, which is believed to be due to the amorphous phase in our samples. Four thermally stimulated current (TSC) maxima are attributed to the relaxation in the amorphous region (∼40°C), to the dipolar relaxation in the nonpolar (∼60°C) and polar (∼80°C) phase, and the space charge relaxation (dependent on the poling temperature). The pyroelectric coefficient of the homopolymer and copolymer thermoelectret foil prepared by hot‐pressing is of the same order as that of the PVDF thermoelectret foil produced by Solvay and can be influenced by the hot‐pressing conditions. The dielectric response of the hot‐pressed PVDF‐type foils can be described by the Kohlrausch‐–Williams‐Watts function and is characteristic of a heterogeneous system.
Influence of nucleation promoters on the crystallization of poly(ethylene terephthalate)
Authors: Wang Xiaohui , Zhu Zhangxing , Bu Haishan 
Published: April 2003

AbstractA series of N‐alkyl‐p‐toluenesulfonamides (ATSA) were synthesized and identified. The measurement of solution viscosity of poly(ethylene terephthalate) (PET) proved that ATSA does not react with PET during the melting process of PET/ATSA mixtures, and consequently does not cause any decrease of molecular weight of PET. The compatibility of ATSA with PET was investigated by polarized light and scanning electron microscopy. Phase separation could not be found to a 0.5 μm level. The investigation of crystallization of PET/ATSA mixtures by means of differential scanning calorimetry revealed that ATSA significantly accelerates the crystallization rate of PET, and that ATSA is more effective when increasing the length of alkyl chains within ATSA. The increase of crystallization rate of PET is proposed to be caused by the improvement of molecular motion of chains, which can be proved by the depression of glass transition temperature when ATSA is added.
Monte carlo simulation of emulsion polymerization — linear, branched, and crosslinked polymers
Authors: Tobita H. 
Published: April 2003

AbstractA new Monte Carlo approach for the kinetics of emulsion polymerization is discussed. The diameters of polymer particles produced in emulsion polymerizations are in the submicrometer range; therefore, it is straightforward to simulate the formation processes of all polymer molecules in each polymer particle by application of the Monte Carlo method with a well‐designed algorithm. In the Monte Carlo technique, virtually any kinetic event, such as the desorption of oligomeric radicals, chain‐length‐dependent reaction kinetics, branching and crosslinking reactions, can be accounted for. In principle, neither idealizations nor approximations, which are usually required in the analytical approaches, are not necessary. As a consequence one can observe the structure of each polymer molecule directly; therefore, very detailed information can be obtained easily, including the full distributions of the dead and live polymer molecular weights, and the spatial distribution of the branched and crosslinked polymer chains in the case of nonlinear polymerizations. Monte Carlo simulations promise to provide greater insight into the complex molecular processes which occur during emulsion polymerizations.
Synthesis and solid‐state properties of comb‐like ionenes
Authors: Wang J. , Meyer W. H. , Wegner G. 
Published: April 2003

AbstractA series of comb‐like ionenes with aliphatic side chains of different length and organic main chain spacer groups of different size have been synthesized by the step‐growth polymerization of long aliphatic chain‐substituted diamines with α,ω‐dibromoalkanes. Highly ordered films of layered structure have been obtained by solution casting. The long side chains crystallize with an interdigitating hexagonal packing perpendicular to the film plane. The perfection of the side chain packing is related to the size of the spacer group in the main chain as well as to the valence of the counterions, but also depends on the thermal history of the samples. It is in all cases comparable to the quality of aliphatic chain packing in LB multilayers of surfactants. The comb‐like ionenes exhibit liquid‐crystalline textures above their side chain melting transition.