bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of interparticle distance in maximizing the toughness of high‐impact thermoplastics
Authors: Michler G. H.
Published: April 2003

For the two groups of rubber modified thermoplastics (toughness by multiple crazing as in HIPS and ABS polymers or by multiple shearing as in high‐impact PA) the local processes of plastic deformation have been studied by different techniques of electron microscopy, including scanning, transmission and high voltage electron microscopy. The processes have been investigated dependent on the morphology, in particular on the diameter D of the rubber particles and their interparticle distance A. For both groups critical values for the interparticle distance exist: a minimum critical value Amin (which has the same physical reason for both and is connected with the coupled movements of segments of the interconnected macromolecules) and a maximum critical value Amax (which is of a different nature in the two cases).
Conformation and shape of rigid‐rod polyesters substituted with flexible side chains as revealed by small‐angle neutron scattering
Authors: März K. , Lindner P. , Urban G. , Ballauff M. , Kugler J. , Fischer E. W.
Published: April 2003

A small‐angle neutron study of liquid crystalline main chain polyesters with flexible side chains is presented. Investigations in solution have been performed using protonated material dissolved in deuterated tetrahydrofuran and deuterated nitrobenzene. To determine the conformation in bulk, mixtures of deuterated and protonated material have been investigated at ambient and at elevated temperature. For this purpose, a route for the synthesis of fully deuterated polyesters has been developed. It is shown that the form factor measured in solution is compatible with an extended, rod‐like conformation. Investigations in bulk show that a plate‐like conformation is adopted under these conditions. This observation is in full agreement with earlier findings from structural studies which indicate that in bulk the side chains of a given main chain are located in a plane; i.e., the polyester molecule assumes a plate‐like shape. Thus the present investigation demonstrates that there is a pronounced change of conformation when going from solution to bulk. The reason for this change are the packing constraints exerted by the neighbouring molecules in the bulk.
Dilute solution properties of alternating copolymers from acrylonitrile and α‐methylstyrene
Authors: Cincu C. , Ion L. , Trifan M.
Published: April 2003

Kuhn‐Mark‐Houwink‐Sakurada relations were obtained in various solvents for alternating copolymers from acrylonitrile and α‐methylstyrene. The values of the unperturbed dimension and the conformational parameter were determined using usual extrapolation techniques. The values of the unperturbed dimensions are dependent on the solvent and are quite different from the values calculated on the basis of additivity rules from the unperturbed dimensions of the parent homopolymers.
Biodegradable polymers. 8th comm. On the kinetics of ring‐opening polymerization of 1,3‐dioxane‐2‐one (trimethylene carbonate)
Authors: Rafler G.
Published: April 2003

The ring‐opening polymerization of 1,3‐dioxane‐2‐one was investigated in dependence on the most important reaction parameters. It was found that the monomer conversion is above all determined by the polymerization temperature and the initiator concentration. The molecular weight of the formed polycarbonate is determined not only by the kinetics of the polymerization reaction, but also by the extent of competitive side reactions. High molecular weight products are only obtained by high polymerization rates.
Small‐angle x‐ray analysis of latex particles using contrast variation
Authors: Dingenouts N. , Ballauff M.
Published: April 2003

A study of a core‐shell latex consisting of a polystyrene core and a polymethylmethacrylate (PMMA) shell by small‐angle x‐ray scattering is presented. Since the electron density, i.e., the contrast of both polymers, can be easily matched by addition of sucrose to the dispersing agent water, the internal structure of the particles can be studied by contrast variation. The scattering intensities obtained at different contrast are all compatible with a concentric core‐shell model which exhibits a finite nonuniformity of the thickness of the shell. The present analysis furthermore reveals that the interfacial region between the polystyrene and the PMMA phase must be very small.
Increased biodegradation of LDPE with nonionic surfactant
Authors: Albertsson A.‐Chr. , Sares Chr. , Karlsson S.
Published: April 2003

LDPE's with and without 0.5% nonionic surfactant (Tween 80) were subject to biodegradation in salt solutions with Pseudomonas aeruginosa. The degradation of LDPE was greater in samples with Tween 80 than in pure LDPE as observed by ATR‐FTIR, DSC and chemiluminescence (CL) measurements. In light microscopy a larger number of bacteria were observed on the surface of LDPE with Tween 80 incubated with Pseudomonas aeruginosa for 60 days than on the surface of pure LDPE. The results indicate a greater susceptibility to biodegradation in the LDPE samples with surfactant than in the corresponding pure LDPE.
Simultaneous measurements of small angle X‐ray scattering, wide angle X‐ray scattering and heat exchange during crystallization and melting of polymers
Authors: Bark M. , Zachmann H. G.
Published: April 2003

Experimental equipment was constructed for simultaneous measurements of wide angle X‐ray scattering (WAXS), small angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC) using synchrotron radiation as a strong source of X‐rays. The crystallization occurring during heating of an initially amorphous sample with constant heating rate was investigated. Poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN), poly(ethylene terephthalate) (PET) and the copolymer PEN‐co‐PHB (90:10), where PHB stands for poly(p‐hydroxybenzoic acid), were used as materials. By comparing the change of the degree of crystallinity as measured by WAXS and DSC with the change of the SAXS power Q, it was shown that the primary crystallization, during which morphological units like spherulites axe growing, is followed by a secondary crystallization during which the degree of crystallinity with the lamellar stacks in the spherulites is increased. Assuming a two‐phase system for the semicrystalline structure, consisting of crystals and amorphous regions, three different processes were shown to be responsible for this increase: The formation of new crystal lamellae within the already existing lamellar stacks, the thickening of already existing crystals at the expense of the amorphous regions, and the complete melting of crystals followed by formation of new, thicker, crystals.
Structural aspects of oligothienyl series from X‐ray powder diffraction data
Authors: Porzio W. , Destri S. , Mascherpa M. , Brückner S.
Published: April 2003

The structures of the series of oligothienyls (T4‐T5‐T6) have been determined and refined from X‐ray powder diffraction data using the Rietveld full‐profile analysis. Unlike polythiophene, all the molecules in the isomorphous series display no internal symmetry, being only approximately planar within 12°. Packing is always achieved through a common molecular disposition, which is usually defined as a herringbone arrangement, with an angle between mean planes of adjacent molecules which spans from 60° to 70°.
The orientation distribution in an industrial sample of poly(p‐phenylenetere‐phthalamide) determined by two‐ and three‐dimensional NMR techniques
Authors: Wilhelm M. , de Lacroix S. Féaux , Titman J. J. , Schmidt‐Rohr K. , Spiess H. W.
Published: April 2003

Two new solid‐state NMR methods for measuring orientation distributions in partially ordered solids are applied to high tensile‐strength fibre polymers. Both methods use the anisotropy of the carbon‐13 chemical shift tensor as a probe for local molecular directions, but they differ in the manner in which the information is extracted and complement one other. The spectral resolution is higher in the ORDER (ORientation Distributions with Enhanced Resolution) experiment, which employs rotor‐synchronized three‐dimensional magic angle spinning (MAS) NMR, while the angular precision with which the orientation distribution can be determined is higher in the DECODER (Direction Exchange with Correlation of Orientation Distribution Evaluation and Reconstruction) experiment. The utility of the two techniques is demonstrated by their application to the study of industrially produced poly(p‐phenyleneterephthalamide) fibres. Both give the same result for the width (χ = 13°) and the order parameters (=0.85, =0.57, =0.34, =0.14) of the orientation distribution.
Thermal graft copolymerization of 4‐vinyl pyridine onto ethyl cellulose in homogeneous media. 1. Influence of ammonium persulfate
Authors: Abdel‐Razik E. A.
Published: April 2003

Graft copolymerization of 4‐vinyl pyridine(4‐VP) onto ethyl cellulose (EC) using ammonium persulfate (APS) as free radical initiator was studied in the toluene: DMSO (4:l v/v) solvent system. The weight conversion, grafting percentage and grafting efficiency were determined as functions of the polymerization temperature and of the concentration of monomer, ethyl cellulose and initiator. The homopolymerization of 4‐VP in the presence ofAPS was also investigated. The graft copolymers were characterized by thin layer chromatography, IR spectroscopy, nuclear magnetic resonance and intrinsic viscosity measurements. The highest rate of propagation of graft copolymerization of 4‐VP onto EC in the presence of APS observed was 0.06 %/min. A suitable mechanism of grafting reaction is discussed.
New polyelectrolyte materials based on smectite polyoxyethylene intercalation compounds
Authors: Aranda P. , Ruiz‐Hitzky E.
Published: April 2003

The intercalation of poly(ethylene oxide), PEO, into homoionic phyllosilicates of the smectite group (montmorillonite and hectorite) gives composite materials able to act as solid polyelectrolytes. The synthesis and the structural characterization of new intercalation compounds belonging to this class of materials have been investigated. The resulting compounds exhibit good chemical and thermal stability, preserving their ion‐exchange properties. PEO intercalation produces an enhancement of the electrical conductivity associated with the interlayer cations compared to the parent silicates. Ionic conductivity determined by impedance spectroscopy measurements of different polyoxyethylene compounds (PEO and crown‐ethers) into homoionic 2:1 charged phyllosilicates reveals that the conductivity values can be correlated with the oxyethylene‐cation strength interaction.
Crystallinity of cellulose and its accessibility during deuteration
Authors: Loelovitch M. , Gordeev M.
Published: April 2003

The accessibility of cellulose samples with different supermolecular structure during deuteration has been studied by NMR. It has been established that the content of accessible regions is higher than the content of amorphous regions determined by the X‐ray method. A modified crystalline–amorphous model of cellulose structure is proposed to explain this result. According to this model, thin surface layers of crystallites are less ordered and are accessible during the deuterium exchange. The quantitative ratio between the accessibility and the crystallinity of cellulose has been established.
Neutron spin echo studies on the segmental diffusion behavior in the different chain sections of high molecular weight poly(dimethylsiloxane) melts
Authors: Ewen B. , Maschke U. , Richter D. , Farago B.
Published: April 2003

Using neutron spin echo spectroscopy, the dynamics of high molecular weight poly(dimethylsiloxane) in the melt (T=473 K) was investigated. In order to decide whether the lateral constraints are uniform or nonuniform with respect to the contour of a test chain, chains were labeled either completely or partially by a corresponding proton‐deuterium exchange. It was found that the central and the terminal chain sequences experience the same amount of lateral confinement, which–in the framework of the reptation or tube model–can be characterized by a tube diameter dt of about 70 Å. Nearly the same dt value is obtained from the plateau modulus of rheological measurements, too. Thus, these experiments show unambiguously that the lateral constraints, responsible for the reptational chain dynamics, are quite homogeneous, even in the case of extremely large tube dimensions.
General formulation of the statistical mechanics of multicomponent polymer systems
Authors: Vilgis T.A. , Haronska P.
Published: April 2003

This paper summarizes different approaches to strongly interacting polymer systems. The first part of the paper discusses repulsive systems, i.e. polymers in a good solvent, polymer melts and blends. Corresponding field theories are reviewed and critically revisited from different points of view. The second part of the paper is devoted to attractive systems, i.e. polymers in a poor solvent, ionomers, polyelectrolytes under certain conditions, etc. New types to field theories have to be developed as theories for repulsive polymer systems no longer lead to the appropriate physics. The technical approaches used in the paper are field theory and path integrals. Novel possibilities for a microscopic theoretical description of these systems are reported.
Liquid‐crystalline perylene oligomers: Synthesis and phase behavior
Authors: Pressner D. , Göltner C. , Spieß H‐W. , Müllen K.
Published: April 2003

Two selectively deuterated, liquid‐crystalline oligomers of different topology, containing the deep‐violet perylene mesogen 1, were prepared by two‐fold polymer‐analogous reaction of a suitable pre‐oligomer or by polycondensation of an ester‐functionalized monomer. The materials obtained were investigated by optical microscopy, DSC, X‐ray diffraction, and solid‐state 2H NMR spectroscopy. The structural changes in the mesophases formed and the dynamic phase behavior are discussed, and the results are compared with those obtained from low molecular weight model compounds.
Temperature evolution of the structure of a thermotropic main‐chain liquid crystalline copolyester
Authors: Antipov E.M. , Stamm M. , Abetz V. , Fischer E.W.
Published: April 2003

X‐ray diffraction, differential scanning calorimetry and dynamic mechanical analysis are used to study the temperature evolution of the structure of the thermotropic copolyester poly[(phenyl‐pphenylene)‐co‐(terephthalate)‐co‐(p‐hydroxybenzoate)] (PES) prepared from terephthalic acid, phenyl‐hydroquinone and p‐hydroxybenzoic acid (molar ratio 45/45/10). Needle‐like crystals are developed in the quenched as‐spun fibers despite the random sequence of the monomers of the copolyester. Moreover, two other crystalline phases are observed at elevated temperatures, which may be explained by a phase separation process. X‐ray diffraction experiments show a significant temperature dependence of structural features, indicating some conformational disorder and mobility in this class of “rigid‐rod” liquid crystalline polymers. Changes in the X‐ray pattern are observed on heating, starting immediately above the glass transition temperature of the copolyester. Melting of PES reveals a two‐step character with transitions at 300 °C and 320 °C. The material becomes isotropic at 400 °C or higher.
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

Liquid 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

A 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

This 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

The 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

A 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

Liquid 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

So‐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

Using 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

Static 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

Ion‐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

A 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

A 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

Cocrystallization 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

The 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

We 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

We 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

A 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

A 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

A 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.
Reaction of dicyanates with monophenols — modeling of network buildup
Authors: Bauer J. , Alla C. , Bauer M. , Bloch B.
Published: April 2003

Chemical as well as structural modifications of highly branched polycyanurates can be achieved by using the reaction of dicyanates with monofunctional phenols. The key products of this reaction are iminocarbonic esters formed by addition of cyanato and phenolic groups. Two mechanisms are discussed for the second reaction step: an addition of two cyanato groups and an iminocarbonic ester (Route A) and a stepwise addition of iminocarbonic esters (Route B). The crucial difference between the two reactions is the number of abstracted phenolic groups per formation of one triazine ring: one for Route A and three for Route B. The effects of these reaction mechanisms on the gelation behavior and network buildup are studied theoretically with the help of cascade theory as well as experimentally by the reaction of dicyanate of bisphenol A with five different monophenols. The results clearly show that only with a model which is based on Route B can both the critical conversions at the gelation threshold and the gel fractions be modeled quantitatively. Furthermore, phenols with low pKa values were found to have an increased tendency of incorporation into the network.
Effect of draw ratio on the structure of aromatic copolyimide fibers of random monomer sequence
Authors: Wu T. M. , Chvalun S. N. , Blackwell J. , Cheng S. Z. D. , Wu Z. , Harris F. W.
Published: April 2003

X‐ray methods have been used to investigate the structure of fibers of aromatic copolyimides prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), o‐tolidine (OTOL) and p‐phenylene diamine (PPD). We have shown previously that the non‐periodic layer lines in the X‐ray fiber diagrams of these copolymers are indicative of a random comonomer sequence. In the present paper, we analyze the shifts in the layer line positions that occur with increasing draw ratio. These changes are to be understood primarily in terms of increases in the correlation lengths for the stiff chain conformation. At high draw ratios there is also evidence for the development of a more extended chain conformation, probably due to torsional variation changes in the torsion angles. It is shown that the data are sufficiently sensitive to allow quantitative analysis of these separate effects, and their dependence on comonomer ratio.
Biaxial extensional flow behavior of monodisperse polystyrene melts
Authors: Ebrahimi N. Golshan , Takahashi M. , Araki O. , Masuda T.
Published: April 2003

Biaxial extensional flow behavior of monodisperse polystyrene melts has been investigated by using a lubricated squeezing flow method at constant strain rates. Master curves for the biaxial stress growth coefficient η are obtained by applying the time‐temperature superposition principle. The coefficient η deviates from a linear viscoelastic curve at very small strain such as 0.1, and then approaches a quasi steady state. The quasi‐steady‐state viscosity ηB,qs decreases with the strain rate ηB. At very small strain rates, the coefficient η increases again after the quasi steady state and becomes much larger than the linear viscoelastic curve. The strain rate dependence curves of ηB,qs obtained for different molecular weight samples can be superposed to give a super master curve using the weight‐average relaxation time η0 as a reducing parameter. It is found that the biaxial viscosity ηB,qs begins to decrease at much smaller reduced strain rate (ϵBτ0=0.01) compared with the shear viscosity, which begins to decrease at reduced strain rate of about 1.0.
Small‐angle x‐ray scattering from a thermotropic random copolymer during solid‐state annealing
Authors: Wilson D. J. , Seifert S. , Stribeck N. , Windle A. H. , Zachmann H. G.
Published: April 2003

This paper reports the effect of solid state annealing on the structure of a liquid crystalline polymer composed of 80% 4‐hydroxybenzoic acid (HBA) and 20% 2‐hydroxy‐6‐naphthoic acid (HNA) using small‐angle X‐ray scattering. Two‐dimensional diffraction patterns possessing strong meridional reflections were recorded using synchrotron radiation at temperatures of 215, 251 and 269°C. The long period increased with increasing anneal temperature, but was largely unaffected by increasing the length of time spent at the anneal temperature. The intensity of meridional scattering increased with both increasing anneal temperature and time. In order to obtain an estimate for the average crystallite thickness at the anneal temperature, the small‐angle meridional scattering was evaluated by means of the interfacial distribution function approach.
Synthesis of a photosensitive polyimide containing a diazo group and its photocrosslinking reactions via a long‐lived active intermediate
Authors: Yamashita T. , Kasai C. , Sumida T. , Horie K.
Published: April 2003

A novel intrinsic photosensitive polyimide containing a diazo group in the main chain was prepared, and the quantum yield for the photocrosslinking reaction was determined to be 0.13 under air at room temperature by GPC measurement. The quantum yield for the photo‐decomposition reaction of the diazo group was also determined to be 0.06. These values are higher by about two orders of magnitude than those for the photocrosslinking reaction of a benzophenone‐containing polyimide, which is prepared from benzophenonetetracarboxylic dianhydride (BTDA) and methylene bis(2‐ethylaniline) (DEDPM). The reaction was found to proceed via its singlet excited state to give a long‐lived active intermediate, a carbene, which plays a great role in the increase in the photoreactivity. Characteristics of the photoreaction and the fluorescence behavior of a series of imide‐substituted diphenyldiazomethanes were also investigated, showing that the reactivity of the diazo groups is not affected by the existence of charge transfer structures of the imide groups.
Pre‐ordering state in the crystallization process of polymer blends detected by pulsed NMR
Authors: Ikehara T. , Nishi T.
Published: April 2003

Real time measurement by pulsed NMR revealed that poly(ϵ‐caprolactone)/polystyrene (PCL/PS) blends and PCL homopolymer form a pre‐ordering state at the onset of crystal formation. The spin‐spin relaxation signals were decomposed into three components. When the intermediate phase appeared, its fractional amount was larger than that of the interfacial phase in semicrystalline polymers and the spin‐spin relaxation time was longer than that of the interface. The fractional amount decreased in the first stage of crystallization and then increased as the process proceeded. This behavior was more significant for blends with higher PS content or those crystallized at elevated temperatures. This state is assigned to a pre‐ordering state of the crystalline polymer that has to exclude the amorphous polymer on the formation of lamellae.
Dynamics of stiff‐chain polymers in multicomponent solutions: Modification of the hole theory
Authors: Fujiyama T. , Sato T. , Teramoto A.
Published: April 2003

The previous theory of the global motion dynamics of stiff‐chain polymers in multicomponent systems has been modified by a refined treatment of the jamming effect on the longitudinal diffusion of polymer chains along their end‐to‐end axis to derive a new equation for zero‐shear viscosity, which depends on the longitudinal diffusion coefficients through the lifetimes of entanglements between similar as well as dissimilar polymers. Along with this theoretical study, experimental data forzero‐shearviscosity of quasi‐ternary solutions containing two stiff‐chain polymers with different lengths were obtained. They were well described by the viscosity equation obtained, with only the similarity ratio(s) inherent to the respective polymer‐solvent system(s) as adjustable parameter(s).
Surface molecular motion in thin films of poly(styrene‐block‐methyl methacrylate) diblock copolymer
Authors: Tanaka K. , Takahara A. , Kajiyama T.
Published: April 2003

Thin films of poly(styrene‐block‐methyl methacrylate) diblock copolymer [P(St‐b‐MMA)] with thickness ca. 50 nm were prepared by a dip‐coating method. The surface Tg for the P(St‐b‐MMA) thin film was evaluated on the basis of the temperature‐dependent X‐ray photoelectron spectroscopic (TDXPS) measurement. The temperature at which the surface composition started to change was defined as the glass transition temperature, Tg, at the surface region. It was revealed that the surface Tg for P(St‐b‐MMA) was much lower than that for its bulk sample. Also, the depth dependence of Tg for P(St‐b‐MMA) was investigated on the basis of the combination of TDXPS and the angular‐dependent XPS (ADXPS) method. Tg for P(St‐b‐MMA) decreased with a decrease in distance from the outermost surface. The molecular weight dependence of the surface Tg for P(St‐b‐MMA) was more pronounced than that in the bulk sample, and that was expressed as a function of M.