bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric relaxation in liquid crystalline siloxane copolymers
Authors: Novotna E. , Kresse H. , Krücke B.
Published: April 2003

Dielectric relaxation measurements have been carried out in the frequency range from 1 Hz to 100 kHz on copolymers with different molar ratios of two liquid crystalline parts. Two dielectric relaxation ranges were detected which are related to the two respective parts. The copolymers show an increasing molecular mobility with respect to the homopolymers. The results are discussed in relation to the phase diagram and to dielectric data on low molecular liquid crystals.
Side chain liquid crystalline polymethacrylates with three‐ring azobenzene groups
Authors: Krüger H. , Wolff D. , Zschuppe V.
Published: April 2003

The influence of three aromatic rings in the azobenzene mesogenic moities on the LC character of side chain polymethacrylates is described. The three‐ring azobenzene groups exhibit some retardation and inhibition effect during the radical methacrylate polymerization. Therefore the polymerization conditions had to be modified. Dimethylformamide was found to be a solvent realizing high polymer yields and satisfactory molar masses. The phase behaviour of the obtained SCLC polymethacrylates and of their monomers is characterized by X‐ray, DSC and polarizing microscopy in dependence of spacer length. The polymethacrylates with three‐ring azobenzene mesogens show significant higher glass transition and clearing temperatures than two‐ring analogues. The change in the liquid crystalline phase arrangement from smectic C to smectic B with increasing spacer length is explained by the better movability of the mesogens.
Comparative characterization of solvent spun cellulose and high wet modulus viscose fibres by their long periods
Authors: Lenz J. , Schurz J. , Wrentschur E.
Published: April 2003

The evaluation of the long periods and crystallite lengths of original and pretreated solvent spun cellulose fibres revealed that they consist of about 90% crystalline cellulose in the direction of the fibre axis. In the case of high wet modulus viscose fibres this percentage is only 50–60%. The intensity of the long period of solvent spun fibres is lower than that of the high wet modulus viscose fibres corresponding to a smaller difference between their crystalline and amorphous orientation factors. There is existing a significant correlation between this difference and the intensity of the long period.
Characterization of the cationic polyelectrolyte poly(diallyl dimethyl ammonium chloride) by ultracentrifugation methods
Authors: Wandrey C h. , Görnitz E.
Published: April 2003

The characterization of polyelectrolytes is demonstrated by combination of different ultracentrifuge methods with laboratory as well as technical poly(diallyl dimethyl ammonium chloride) samples. Low speed sedimentation equilibrium in an analytical ultracentrifuge was used to determine the molecular weight averages Mw and Mz. The method was shown to be applicable even in case of partly aggregated solutions and the amount of aggregates was established. Equilibrium sedimentation in a density gradient of a preparative ultracentrifuge allows to separate linear and branched parts. While structural uniform polymers are distributed in a Gaussian band, nonuniformities lead to deformations of distribution curves. With mathematical curve analysis structural portions can be determined.
Third‐order concentration corrections to the shear viscosity of hard‐sphere suspensions
Authors: Schlacken H.
Published: April 2003

The contribution of three and four scattering events to the third‐order concentration coefficient k3 is evaluated up to order 0(11) of the reciprocal particle distance. A value of k3=6.091 is obtained.
Determination of the parameters of the relaxation spectrum of polymers from the results of calorimetric measurements
Authors: Yanchevsky L. K. , Levandovsky V. V.
Published: April 2003

A method is suggested which allows the determination of a complex of relaxation characteristics describing the process of glass transition of amorphous polymers from the results of calorimetric measurements in one single experiment.
Orientation dynamics of side chain polymers subject to electric fields. Part I. Steady state
Authors: Hoffmann C. L. , Man H.‐T. , Fuller G. G.
Published: April 2003

Many polymeric glasses must be orientationally ordered for the materials to exhibit useful characteristics. The objective of this work was to understand the dynamics of the orientation and relaxation processes and to relate these behaviours to the structural characteristics of the polymeric material. In this study we considered materials suitable for nonlinear optical applications. In particular, thin polymer films, either doped with nonlinear optical chromophores or films with the chromophores covalently bonded to side groups were studied. Orientation of these chromophores was achieved by the application of an external electric field. Ellipsometry was used to measure the birefringence resulting from chromophore orientation and the steady state and transient behaviours were studied. Materials characteristics studied included method of chromophore incorporation, chromophore concentration, spacer length, and molecular weight. Our results showed that the polymer structure, specifically the tacticity, was the dominant factor determining the steady state and transient behaviours. The relationship between monomer and polymer structure and the resulting effect on the orientation dynamics is discussed. Qualitative agreement with theoretical predictions was obtained for the simpler guest/host system, but the model was shown to be inadequate to explain the behaviours of the more complex systems studied. The results reported here have provided valuable insight into the molecular processes that occur during the chromophore orientation and relaxation, and the effects of structural characteristics of the polymers on these mechanisms.
Palladium and nickel catalyzed polycondensation ‐ The key to structurally defined polyarylenes and other aromatic polymers
Authors: Schlüter A.‐D. , Wegner G.
Published: April 2003

This article provides an overview on a new and easy to perform Ni‐and Pd‐catalyzed polycondensation of various kinds of homo‐ and heteroaromatic monomers. It allows the regiospecific coupling of these monomers at predetermined positions to furnish the corresponding structurally perfect polyarylenes, which up to now have only been known as ill‐defined, generally insoluble and infusible materials. The compatibility of this method towards functional groups is excellent. The achievable degrees of polymerization range from 20 to 60. The solubility and characterizability of the polymers is ensured, if necessary, by the attachment of flexible alkyl, tert.‐butyl, or alkoxy chains to the monomers. Results of initial physicochemical measurements with some of the polymers and their respective model compounds are briefly discussed. They do not only give vital clues to the intrinsic properties of poly‐ and oligoarylenes but also disclose exciting, unprecedented properties of these materials.
Determination of the pore size distribution of membranes by gel permeation chromatography
Authors: Weigel Th. , Albrecht W. , Paul D.
Published: April 2003

Polyacrylonitrile membranes with different separation ranges are prepared and characterized by gel permeation chromatography. The determination of the pore size distribution of the ultrafiltration flat membrane (upper ultrafiltration range) and of the microfiltration hollow fiber membrane (lower microfiltration range) is affected by different measuring procedures. A comparison of the parameters of separation performance is obtained by making use of aqueous poly(ethylene glycol) (PEG) mixtures with broad molecular weight distribution, or the application of single PEG test substances is performed. The obtained results are discussed in connection with the separation range of membranes and the molecular weight of test solutions.
Study of the crystallization kinetics of a thermotropic liquid crystalline polymer
Authors: Zhao S. R. , Schaper A. , Ruland W.
Published: April 2003

The isothermal crystallization kinetics of a thermotropic liquid crystalline (LC) polymer has been studied using the integral intensity of a selected X‐ray reflection as a measure of the crystallinity. The starting conditions for the crystallization have been varied by isothermal annealing of the polymer in the LC state during various time intervals. Using the Avrami equation to interpret the crystallization kinetics, Avrami exponents increasing from 0.66 to 2.1 have been obtained with increasing annealing time. This observation can be explained by simultaneous heterogeneous nucleation from ID (centers of disclinations) and 2D (domain walls) nuclei. Using a modified form of the Avrami equation, the contributions of the two types of nuclei can be separated. Avrami exponents smaller than 1 appear to be related to the finite size of the domains. Time resolved studies of the crystallization process using a polarization microscope and bright field transmission electron microscopy observations corroborate the interpretation of the Avrami plots.
Grain boundary morphology of lamellar microdomains
Authors: Nishikawa Y. , Kawada H. , Hasegawa H. , Hashimoto T.
Published: April 2003

The grain boundary morphology of lamellar microdomains in block copolymers was investigated by means of transmission electron microscopy. A variety of patterns which can be successfully reproduced by the computer simulation using Scherk's first surface or deformed Scherk's first surfaces as a calculation model were observed. This implies that the microdomains with lamellar morphology which locally have only two‐dimensional continuity are topologically continuous in three dimensional space as a whole through the grain boundaries, but the lamellae are essentially flat within the grains.
A fast membrane osmometer based on a porous glass membrane: first results
Authors: Köhler W. , Kühn A. , Motsch A.
Published: April 2003

The prototype of a fast and versatile membrane osmometer based on a capillary shaped porous glass membrane has been developed and successfully tested with solutions of polystyrene in toluene. The coaxial design of the cell is ideally suited both for batch and continuous flow operation. Time constants on the order of several seconds are observed with membranes of 10 nm and 20 nm nominal pore size. Important design criteria are discussed and first results for the cut‐off molar mass are reported.
In‐situ absorption studies of nonlinear optically active side‐chain polymers during corona poling
Authors: Wedel A. , Strohriegl P. , Danz R.
Published: April 2003

Absorption measurements in the wavelength range from 300 to 700 nm are used to study the orientation of nonlinear optical side groups in an acrylic polymer oriented by corona poling inside a spectrophotometer. The poling and relaxation behavior of these films are measured. The in‐situ poling process produces efficient orientational order in acrylic side‐chain polymers, which can be described by an order parameter.
Orientational measurements on a crosslinkable thermotropic main‐chain copolyester using FTIR spectrometry
Authors: Sahre K. , Eichhorn K.‐J. , Reichelt N. , Hummel D. O.
Published: April 2003

The orientation capability of thin solution‐cast films of a new synthesized crosslinkable thermotropic main chain copolyesterwith itaconoyl units was demonstrated by means ofpolarized FTIR spectrometry. The isotropic films with a thickness of about 10 μm were drawn uniaxially and annealed to get a preferential alignment of the polymer backbone in the drawing direction and an increase of the state of order. The resulted state should be fixed by a following crosslinking reaction of the itaconoyl unit to obatin a thermostable polymeric material with reduced anisotropy of mechanical properties. The orientation effects of mesogenic units dominate in the drawn films of the ternary copolyester. WAXS and DSC results show that annealing of the films produce an increase in crystallinity. More ordered regions in the solid polymer are formed which cause typical changes in the IR spectra.
The kinetics of cellulose fiber degradation and correlation with some tensile properties
Authors: Testa G. , Sardella A. , Rossi E. , Bozzi C. , Seves A.
Published: April 2003

Cellulosic degradation of cotton and flax yarns caused by light, heat and heterogeneous acid‐catalyzed hydrolysis was studied. These processes were followed by measuring changes in intrinsic fluidity (1/DPw): two principal stages, characterized by different zero‐order kinetics, take place. A relation between changes in intrinsic fluidity with some mechanical properties of the same yarns during the degradation process was found.
Structural investigation of phthalocyaninatopoly(siloxane) Langmuir–Blodgett films by X‐ray diffraction
Authors: Albouy P.‐A. , Schaub M. , Wegner G.
Published: April 2003

The structure of Langmuir–Blodgett (LB) films of a rigid rod phthalocyanatopoly(siloxane) substituted by alkoxy side chains has been investigated by X‐ray diffraction using thin silicon wafers as a substrate for deposition. Freshly prepared samples do not possess a truely periodic multilayer structure. The polymer backbones lie flat in the substrate plane and are preferentially oriented along the dipping direction. Each macromolecule is surrounded by parallel adjacent rods and a first‐neighbor distance is found in every direction. This structure recalls the local organization of a nematic liquid crystal. Short annealing of the as‐deposited films leads to a highly oriented hexagonally dense packing as of cylinders. The alignment of the backbones along the dipping direction becomes nearly perfect and the most densely packed plane is oriented in the substrate plane. A helical order within the macromolecules of the annealed samples is suspected from extra reflections appearing in the diffraction pattern.
Polyphenothiazinobisthiazole: A novel polymer for third‐order nonlinear optics
Authors: Kistenmacher A. , Soczka Th. , Baier U. , Ueberhofen K. , Bubeck Chr. , Müllen K.
Published: April 2003

The synthesis and the optical properties of the novel polymer polyphenothiazinobisthiazole (PPT) are described. The design of this polymer was planned taking into consideration several aspects that were anticipated to lead to a material with an enhanced nonlinear optical susceptibility (χ(3)). Monomer 16 was prepared in a five‐step synthsis starting from N‐dodecyl‐3,7‐diaminophenothiazin (11). 16 was reacted with terephthaloyl chloride to yield the precursor polyamide 17. This precursor polyamide was subjected to a thermal cyclization at 300°C under vacuum leading to the title polymer PPT (18). PPT shows UV/vis absorption maxima at λ=282 nm, 305 nm and 463 nm. The macroscopic nonlinear optical susceptibility χ(3)(−3ω;ω,ω,ω,) of a thin film of PPT was determined with a third harmonic generation (THG) technique at a fundamental laser wavelength λL=1064 nm. The results show that PPT exhibits nonlinear optical properties comparable to those of poly‐p‐phenylenevinylene (PPV).
Dihydroanthracene dimers as novel bifunctional initiators for anionic polymerization
Authors: Bartz Th. , Klapper M. , Müllen K.
Published: April 2003

Anionic polymerizations initiated with an alkylene bridged dihydroanthracene dimer as a bifunctional initiator are described as a synthetic route to polymers containing the dianthryl species in the center of the macromolecular chain. The approach taken herein involves the twofold deprotonation of 1,3‐di‐(9,9′,10,10′ ‐tetrahydro‐9,9′ ‐anthryl)propane and the initiation of methyl methacrylate polymerization at both anionic sites. The synthesis of ABA block copolymers by addition of tert‐butyl acrylate as a second monomer is described. Polymer analogous aromatization of the initiator generates the corresponding polymer with two anthracene units in the main chain. The synthezised homo‐ and block copolymers have been fully characterized by GPC, UV and NMR measurements.
Chain stiffness of poly‐methoxypropyl[1.1.1]propellane
Authors: Lassale I. , Schmidt M. , Schlüter A. D.
Published: April 2003

The chain stiffness of a methoxypropyl‐substituted poly[1.1.1]propellane in solution is investigated by static and dynamic light scattering. The Kuhn statistical segment length is determined aslk=150Å utilizing the Kratky–Porod wormlike chain model. It is, however, not yet clear whether the derived Kuhn length characterizes the chain stiffness of a perfect polypropellane chain or rather originates from “kinks” in the polymer backbone due to the presence of possible side reactions during polymerization.
Redox active LC ionomers: LC ionomers as materials for compatible blends with amorphous ionomers
Authors: Wiesemann A. , Zentel R. , Lieser G.
Published: April 2003

Redoxactive liquid crystalline (LC) side group polymers were prepared by copolymerization of liquid crystalline acrylates and ferrocene‐containing acrylates. The corresponding liquid crystalline ionomers were synthesized by a reversible redox reaction. The incorporation of tetra‐alkylated ferrocene derivatives leads to LC polymers with reduced redox potential. These polymers can be oxidized under mild conditions to the corresponding ionomers, which are much more stable in solution than LC ionomers containing monoalkylated ferrocenium ions. Dynamic mechanical measurements and small angle X‐ray scattering (SAXS) perfomed on LC ionomers prove the existence of ionic superstructures (clusters) which are typical for ionomers and a gelation of the LC ionomers.

In biphasic polymer blends consisting of liquid crystalline and amorphous ionomers (partially sulfonated polystyrene) we investigated the influence of the concentration of ionic groups in the LC component on the size of phase separated regions. It was found that blends without ionic interactions are macroscopically phase separated. In blends consisting of two ionic components, microphase separated regions of approximately 100 nm were found. The size of phase separated regions decreases continuously with increasing concentration of ionic groups in the LC component and can therefore be adjusted by a reversible redox reaction.

The incorporation of ionic groups in LC polymers leads on a macroscopic scale to a combination of the liquid crystalline properties of the LC component with the elastic behavior of the amorphous ionomer. Therefore microphase separated ionomer blends show homogeneous liquid crystalline textures and behave mechanically like reversible crosslinked ionomers.
Preparation and characterization of cellulose/glycidyl methacrylate/acrylic acid cation exchange composites
Authors: Ibrahim N. A. , Abo‐Shosha M. H.
Published: April 2003

Acrylic acid (AA)/glycidyl methacrylate (GMA) mixtures were bulk polymerized in the presence of cellulose in order to prepare cellulose/GMA/AA cation exchange composites using sodium persulfate as an oxidant, alone or in conjunction with sodium sulfite, sodium thiosulfate, sodium metabisulfite or glucose as a reductant. The presence of the reductant has the effect of shortening the polymerization time, expressed as the solidification time (ST), with little improvement in the polymerization extent, expressed as percentage total conversion (%TC), as well as the percentage yield and the carboxyl content of the crude and the purified composites. Sodium sulfite was selected as the the reductant that can achieve best polymerization. The effect of the concentrations of “sodium persulfate/sodium sulfite, redox system, acrylic acid and glycidyl methacrylate” and temperature on the formation of the composite were investigated. Four cation exchange composites were prepared and characterized by investigating their potentiometric titration, water solubility and swellability as well as durability.
Surface orientation of liquid crystalline poly(alkylsilanes)
Authors: Factor B. J. , Russell T. P. , Toney M. F. , Miller R. D.
Published: April 2003

X‐ray diffraction measurements on thin films of poly(hexyl‐pentylsilane) cast on silicon substrates are presented. The polymer chains pack in a hexagonal lattice which is oriented such that the chains lie parallel to the surface. In addition, a remarkable degree of orientational order was found with the planes containing the neighbor molecules lying in the surface plane. Parallel to the film surface, the average crystallite size is 600 Å, while perpendicular to the surface, there is nearly perfect interchain stacking of the polymers throughout the thickness of the film.
Polymers of 1‐azabicyclooctane[4,2,0]. Part 3. Modification of polystyrene‐block‐poly‐1‐azabicyclooctane[4,2,0]
Authors: Mühlbach K. , Schulz R. C.
Published: April 2003

Polystyrene‐block‐poly‐1‐azabicyclooctane[4,2,0] has been modified by protonation or alkylation of the polyamine moiety. Short chain alkyl iodides lead to quantitatively quarternized products while longer alkyl chains or alkyl‐bromides give incomplete conversion. The viscosimetric behavior of the charged blockcopolymers is dominated by the polyelectrolyte block although the polyelectrolyte effect is drastically reduced by the presence of the polystyrene block.

The blockcopolymers are insoluble in water, but concentrated solutions of the polymers in DMF can be diluted with any amount of water without any precipitation. Although the blockcopolymers have an amphiphilic structure they do not exhibit any surface activity. In a water/DMF (9/1) solution the polymers have a core‐shell micelle‐like structure of collapsed polystyrene block which is solubilized by the surrounding polyelectrolyte block.
Aspects of thermal grafting of acrylonitrile onto ethyl cellulose in homogeneous media
Authors: Abdel‐Razik E. A.
Published: April 2003

Homogeneous thermal graft copolymerization of acrylonitrile (AN) onto ethyl cellulose (EC) by using ammonium persulfate (APS) as free radical initiator was carried out in the toluene: DMSO solvent system. Many variables affecting the grafting parameters were studied. The effect of using comonomer pairs of acrylonitrile and acrylamide on the grafting yield was examined. Different techniques such as IR and NMR were used. A Trommsdorf effect was observed in certain systems. The rate of graft copolymerization of acrylonitrile onto EC was determined as Rp=0.16% min—1. The higher carbonyl content of thermooxidized EC showed lower grafting yield. The mechanism of the grafting reaction is discussed.
Electrochemical solution properties of poly(vinylbenzyltrialkylammonium) salts
Authors: Wandrey C. , Zarras P. , Vogl O.
Published: April 2003

Poly(vinylbenzyltrialkylammonium) salts with alkyl groups having 1 to 8 carbon atoms on the ammonium nitrogen atom were synthesized. The polymers are soluble in water but have different solubility when low molecular salts such as sodium chloride are added. The reduced solution viscosity in water showed typical polyelectrolyte behavior. Larger alkyl groups make the polymers much less soluble and even insoluble in water. The polymers are still soluble in methanol. To study the counterion‐polyion interactions in semidilute and dilute solution the electrical conductivity and counterion activity were investigated in a range of low polyelectrolyte concentration (10−6<cp10−3 monomol/l). With decreasing concentration, below the overlap concentration, a rapid increase of the equivalent conductivity occurred followed by a maximum. The electrochemical solution properties were found to be influenced by the size of the substituents of the cationic group.
Study of polytetrafluoroethylene crystallization
Authors: Ferry L. , Vigier G. , Vassoille R. , Bessede J. L.
Published: April 2003

Crystallization of polytetrafluoroethylene (PTFE) from the melt state has been studied by wide angle X‐ray scattering (WAXS), small angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC) experiments, supported by scanning electron microscopy (SEM) observations. Isothermal crystallization of PTFE (between 315 °C and 325 °C) is analyzed and compared with PTFE cooled at 1 °C/min taken as the reference. We establish a TTC (time, temperature, crystallization) diagram and point out the time and temperature dependence of both crystallite thickness and crystallinity. It appears that the crystallization occurs in a very narrow temperature range. We assign the morphological changes to different crystal growth regimes in the range of study.
On the deformation of hard elastic polymers — applicability of the coil‐strand‐transition model
Authors: Wittkop M. , Kreitmeier S. , Göuritz D.
Published: April 2003

The applicability of the coil‐strand‐transition model to describe the deformation of hard elastic polymers was studied by deformation and relaxation tests of hard elastic polyethylene and hard elastic polypropylene samples in different liquids. It was found that within the model the calculated values of the fibril diameter, the contribution of surface stress and the total stress are in agreement with measurements. The dominance of energetic contributions to the stress was also confirmed.
Reaction of glycidyl ethers with ε‐caprolactam
Authors: Tänzer W.
Published: April 2003

Phenyl glycidyl ether (PGE) as well as ε‐caprolactam (CL) can be polymerized by cationic initiators. For the present work, Mg(ClO)4ċ2 H2O was used. The formation of different oligomer structures depends strongly on the reaction conditions if both monomers are oligomerized in a one‐pot reaction. HPLC,13C‐NMR and FT‐IR studies showed that not only were homooligomeric products of PGE formed, but also products from phenyl glycidyl ether and ε‐caprolactam. Homopolymerization of CL does not occur. Mixtures of diglycidyl ether of bisphenol A (DGEBA) and CL in the presence of catalytic amounts of magnesium perchlorate yield clear and homogeneous castings withTg=96 to 100°C. These networks include <10% dioxane‐ and water‐extractable products.
Structural and dynamical studies of 13C‐labeled polyethylene adsorbed on the surface of silica gel by high‐resolution solid‐state 13C NMR spectroscopy
Authors: Inoue D. , Kurosu H. , Chen Qun , Ando I.
Published: April 2003

13C CP/MAS NMR spectra of 10% 13C‐labeled polyethylene adsorbed on the surface of silica gel were measured by means of high‐resolution solid‐state 13C NMR. From these experimental results, it was found that adsorbed polyethylene has immobile and mobile parts. In the immobile part, the polyethylene takes the trans conformation as the major conformation and gauche as the minor conformation, and in the mobile part fast transition between trans and gauche conformations occurs. Futhermore, in order to elucidate the dynamics of the polyethylene, 13C spin‐lattice relaxation times T1 were measured. It was found that the molecular motion of the polyethylene in the mobile part is strongly restricted, compared with the noncrystalline component of polyethylene in bulk.
Optically active and highly threodiisotactic poly(triphenylmethyl crotonate) with conformational chirality
Authors: Ute K. , Asada T. , Nabeshima Y. , Hatada K.
Published: April 2003

Polymerization of triphenylmethyl crotonate with a 9‐fluorenyllithium/(S,S)‐(+)‐2,3‐dimethoxy‐1,4‐bis(dimethylamino)‐butane complex in toluene at −78°C gave a highly threodiisotactic polymer. The polymer had a trimodal distribution of molecular weight (MW); the highest‐MW part showed a small negative optical rotation and the other two showed positive rotation. The middle‐MW fraction (DP=21.5, M̄w/M̄n=1.07) had an [α]D of +53.3°. The optical rotation of this fraction decreased gradually in chloroform at 60°C while the GPC curve of the fraction remained unchanged. The loss of optical activity was ascribed to the racemization through helix sense reversal of the polymer chain. The rate of the decrease in optical rotation obeyed first‐order kinetics. From the rate constants at 50 and 60°C, the activation enthalpy for the helix reversal was determined to be 28.4 kcal/mol.
Catalysis on polymer supports
Authors: Schlick S. , Bortel E. , Dyrek K.
Published: April 2003

We present an overview of the synthesis, physical characterization and catalytic properties of polymer‐supported reagents and consider the major advantages and drawbacks in the use of polymeric supports for synthesis and catalysis. The most important development in recent years appears to be the characterization of polymeric supports by thermal analysis, advanced spectroscopic and scattering methods, and electron microscopy. As a result, the mechanism of catalytic activity is better understood; the challenge remains to prepare supported catalysts with good mechanical properties, and high chemical stability at elevated temperatures, and to prevent the loss of often pricey catalysts such as rhodium during numerous catalytic cycles.
Glass transition in ethylene‐vinylacetate copolymers analyzed by combined dielectric and X‐ray scattering experiments
Authors: Holzer B. , Strobl G.
Published: April 2003

We studied the peculiarities of the glass transition in semicrystalline polymers by simultaneous temperature‐dependent small angle X‐ray scattering experiments and dielectric relaxation studies on ethylene‐vinylacetate statistical copolymers. Properties of the β‐relaxations, which represents the glass transition of these systems, change systematically with the comonomer content and the temperature. The broadening of the dielectric loss spectra, indicative of large variations in the sequence mobility in the amorphous regions, increases with the crystallinity, and on approaching Tg also explicitly with decreasing temperature. While the first effect is due to the special structure of the disordered regions, where the presence of fixed entanglements and loops results in motional restrictions, the temperature effect near Tg may reflect the increase in the correlation length of the β‐process.
The structure of the hard domains in trans,trans‐HMDI‐based polyurethane elastomers
Authors: Nigar M. , Blackwell J. , Chvalun S. N. , Seneker S. D. , Schmelzer H. G.
Published: April 2003

X‐ray methods have been used to investigate the structure of the hard domains in polyurethane elastomers based on trans, trans‐dicyclohexylmethane 4,4′‐diisocyanate (HMDI) with butanediol as the chain extender. The crystalline hard segments become oriented on stretching the films at room temperature, although the degree of crystallinity remains relatively low. The ordering is improved considerably by annealing the films for several hours at 130–190°C: the fiber diagram contains 25 sharp Bragg reflections which are indexed by a triclinic unit cell with dimensions a=5.1 Å, b=10.2 Å, c=37.5 Å, α=115.2°, β=84.9°, and γ=94.2°. The cell contains dimer units of two chains which are probably staggered along the c axis direction in the bc plane. In the samples annealed for shorter periods of time, a second less abundant crystal structure is observed that coexists with the first. This second structure is also triclinic with a more extended fiber repeat of c=41.3 Å and is slowly converted to the contracted form on further annealing. Molecular models show that in the extended form the butanediol units have the all‐trans conformation, whereas in the contracted form they probably have the tg+tg−t or tg−tg+t conformations, which have lower potential energies than the all‐trans form. The chains in both the extended and the contracted conformations are able to form a network of intermolecular hydrogen bonds, and in this regard the structures are very similar to those reported previously for the analogous diphenylmethane diisocyanate (MDI)‐based elastomers. Thus the higher melting points for the HMDI‐based hard segments are most likely due to hydrophobic interactions between the dicyclohexyl methanes that are stronger than those between the diphenyl methanes of the MDI‐based elastomers.
Surface modification of polyethylene fibers treated in an oxygen microwave plasma
Authors: Plawky U. , Londschien M. , Michaeli W.
Published: April 2003

The surface modification of a commercial polyethylene fiber treated in an oxygen low temperature microwave plasma was investigated. The change in surface chemistry was analyzed with electron spectroscopy for chemical analysis. A controlled state of oxidation of the fiber surface was reached by variation of gas flux, process pressure and microwave energy. The oxygen was incorporated into the fiber surface in the form of functional groups. In the determined treatment range, a change in surface morphology as a result of the plasma treatment was not observed with electron microscopy. The higher oxygen content in the fiber surface increased the fiber‐matrix adhesion as shown by mechanical tests.
Chemical aspects of the radiation‐induced conductivity in polymers
Authors: Tyutnev A. P. , Sadovnichii D. N. , Boev S. G.
Published: April 2003

It has been demonstrated that radiation‐induced conductivity (RIC) is strongly dependent on the chemical structure of the macromolecules, this dependence being influenced by the position of the active molecular group acting as a hopping center for charge carriers: main chain vs pendant case. Both RIC magnitude and its nature (free ion vs geminate) are affected. Annealing of the radiation‐induced conductivity (RIC) in four common polymers (PS, PET, LDPE and PTFE) continuously irradiated in vacuum to doses of about 5 × 104 Gy has been studied. While substantial recovery (up to 75%) has been observed in PS and PET, only steady degradation of RIC has been encountered in LDPE and especially in PTFE (annealing at elevated temperatures has been fulfilled only in air). Unlike other polymers tested, PS shows recovery that depends critically on the surrounding atmosphere (air or vacuum). To describe these results one relies heavily on the radiation‐induced oxidation as a chain radical process with degenerate branching (a case of LDPE and PTFE) and catalytic recombination of macroradicals (as in PS).
FTIR spectroscopic studies on the interfacial reactions of oxazoline‐functionalized polymers
Authors: Schäfer R. , Kressler J. , Mülhaupt R.
Published: April 2003

The interfacial reaction of immiscible polymeric systems containing oxazoline and carboxylic acid groups, respectively, has been studied by FTIR spectroscopy and FTIR microscopy. A poly(butadiene‐co‐acrylonitrile) rubber, where the nitrile groups are partially converted to oxazoline groups, is thermally annealed in a two‐layer specimen with poly(ethene‐co‐methacrylic acid). The formation of the esteramide in the interface is measured quantitatively by FTIR difference spectroscopy. Evaluating the formation of the amide I band leads to reaction rate constants ranging from 0.0125 to 0.022 s−1 in the temperature range from 170 to 230°C. It can be shown by FTIR microscopy that this system is immiscible because there is no interdiffusion across the interface. Also the formation of an esteramide in the interfacial reaction of the system poly(ethene‐co‐methacrylic acid)/bis(1,3‐oxazoline‐2‐yl)‐terminated poly(dimethylsiloxane) is monitored qualitatively by FTIR spectroscopy.
Graft copolymerization onto wood fibers. Ozone‐activated hydrophobization of pretreated wood pulp
Authors: Daneault C. , Sain M. M. , Lavoie C.
Published: April 2003

Despite the fact that graft copolymerization is a favored reaction for cellulose xanthate, a significant part of the cellulose and lignin component is subject to undesired degradation reaction. Exposure of thermomechanical pulp to ozone followed by grafting by the xanthation method further degrades the cellulose and decreases graft yield. Graft yield can be improved by introducing chemical crosslinks to the cellulose backbone before or after ozone exposure. It is suggested that crosslinking with formaldeyde recombines some of the degraded chains of hydroxylated cellulose after ozone exposure and also helps to prevent degradation of cellulose chain during grafting of cellulose xanthate. Sizing of pulp with dispersed and saponified rosin—Al complexes slows down the grafting reaction and decreases the polymer add‐on percentage significantly. An exposure to ozone before or after the sizing process improves grafting efficiency and graft yield and the copolymer formation is the preferred reaction. The surface morphology of sized pulp has practically no influence on the grafting parameters. Unlike the sizing mechanism, the chemical nature of the sizing agent influences the grafting process. Sizing of pulp with an alkyl ketene dimer significantly decreased the copolymer formation by preventing reactive cellulose hydroxyl group from reacting.
The sorption of N‐cetylpyridinium chloride on leacril fibers. Electrokinetic properties
Authors: Espinosa‐Jiménez M. , Giménez‐Martín E.
Published: April 2003

An experimental investigation on the streaming potential and sorption of N‐cetylpyridinium chloride on Leacril fibers has been carried out. The results reveal that the uptake of N‐cetylpyridinium chloride on Leacril fibers takes place by means of electrostatic attraction between the cation of the surface‐active agent used and both the sulphonate and the sulfate end‐groups of the Leacril.

Given the hydrophobic character of Leacril and the amphiphilic nature of the N‐cetylpyridinium chloride molecules, hydrophobic attractions between the fiber and the hydrophobic part of the surfactant might account for the interaction, explaining the sorption of N‐cetylpyridinium chloride even when it is hindered by electrostatic repulsion.

The electrical characterization of Leacril fibers has been carried out and the methods employed for the determination of zeta potentials of Leacril fibers are discussed, on the basis of streaming potential technique. In our case for this hydrophobic fiber, the linear model of Goring and Mason of a bundle of capillaries gives the most precise values of zeta potential. Also discussed is the behavior of the surface conductance of the system in the above process of sorption.
Investigation of the structure of low molecular weight polybutadienes and epoxides made therefrom
Authors: Maenz K. , Möllhoff M. , Stadermann D.
Published: April 2003

Model calculations on low molecular weight polybutadienes (PCILO, MM2) lead to statements about preferred conformations and, therefore, about the secondary structure of these polymers. The results of the calculations enable a better interpretation of experimental results obtained in epoxidation reactions of the polybutadienes.
Search for conducting doped polymers with great chemical stability: Regiospecific poly(3,3″‐dihexyl‐2,2′:5′,2″‐terthiophene)
Authors: Magnoni M. C. , Gallazzi M. C. , Zerbi G.
Published: April 2003

Previous calculations have suggested that the formation and the stability of charge transfer bonds in doped polyconjugated systems may be maximized by a favored topology of the dopant molecule. The preferred site of attack is found where the steric hindrance is minimized. Following these principles, regiospecific poly(3,3″‐dihexyl‐2,2′:5′,2″‐terthiophene) was synthesized and doped with FeCl3. The time and temperature dependence of the dedoping process has been studied by the analysis of the doping induced infrared spectrum. This material in the doped state shows an extremely great stability (in air, even at relatively high temperatures) never previously reported for any other doped system.
Surface enrichment in thin films of PVC and PMMA
Authors: Kunze K. , Stamm M. , Hartshorne M. , Affrossman S.
Published: April 2003

The surface enrichment in thin bilayer films of poly(vinyl chloride) (PVC) and deuterated poly(methyl methacrylate) (PMMAd) was studied by neutron reflectometry, X‐ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS). In a layer system, where the PVC film is placed on top of a thin PMMA film, the PMMA chains migrate to the surface, although annealing of the films is performed below the glass transition temperature of PMMA. In addition, the surface segregation in blends of these materials was studied by XPS and SSIMS. In all cases PMMA is enriched at the surface. Results from the different techniques, probing different, sample depths, are consistent, if an exponential concentration profile of PMMAd at the surface is assumed. Concentration profiles at the surface are discussed with respect to theoretical models and diffusion coefficients are estimated.
Crystal structure and morphology of bromo‐substituted fully aromatic liquid crystal polyesters
Authors: Liu J. , Geil P. H. , Huh S.‐M. , Lin J.‐I.
Published: April 2003

The bromo‐substituted main chain liquid crystal polyesters poly(3‐bromo‐4‐oxybiphenylene‐4′‐carbonyl) (PBOBC) and poly(5‐bromo‐6‐oxy‐2‐naphthoyl) (PBONY) have been polymerized as lamellar single crystals using the confined thin film melt polymerization (CTFMP) technique. Electron diffraction indicates a triclinic (pseudo‐orthorhombic) unit cell with a12.71, b3.85, c10.50 Å, αβγ90° for PBOBC and a monoclinic unit cell with a13.02, b4.06, c17.15 Å, β101° for PBONY. The crystal structures of the two polymers have been simulated by the Cerius2 program and are suggested to have space group P for PBOBC and space group P121/c1 for PBONY. DSC measurements indicate that these two bromo‐substituted fully aromatic polyesters have crystal‐mesophase transition temperatures (Tk‐m389°C for PBOBC and 429°C for PBONY) with TGA indicating the onset of degradation at similar temperatures (400 and 420°C). The Tk‐m are between those of the corresponding non‐substituted and phenyl‐substituted aromatic polyesters. Possible reasons for the Tk‐m differences are considered in detail.
Novel aspects of the microstructure of poly(ethylene oxide) as revealed by microhardness: Influence of chain ends
Authors: Calleja F. J. Baltá , Cruz C. Santa
Published: April 2003

The microhardness (H) of a series of melt crystallized samples of poly(ethylene oxide) (PEO) was investigated as a function of molecular weight and crystallization temperature (Tc). It is shown that for a given molecular weight, H and the crystal hardness (Hc) increase with Tc, following a thermodynamic approach which takes into account the dependence of Hc upon crystal thickness (ℓc). A combined analysis of H‐data and DSC results reveals that, both the surface free energy (σe) and the hardness‐derived parameter b of the samples of unaffected by Tc. The microhardness of the PEO samples was markedly affected by molecular weight. Furthermore, it is shown that the molecular weight variations produce changes in the surface free energy due to variations in the number of chain ends on the crystal surface, giving rise to a parallel variation in the b parameter. As a consequence, the melting temperature and the crystal hardness exhibit a similar dependence on crystal thickness.
Synthesis in microemulsion and characterization of low charge density ampholytic terpolymers
Authors: Neyret S. , Candau F. , Selb J.
Published: April 2003

High molecular weight and low charge density ampholytic terpolymers based on acrylamide (AM), as a neutral monomer, and sodium 2‐(acrylamido)‐2‐methylpropanesulfonate (NaAMPS) and [2‐(methacryloyloxy)ethyl]trimethylammonium chloride (MADQUAT) as charged monomers have been prepared by a microemulsion polymerization technique. An optimization of the process for the selection of the different components of the microemulsion has been achieved by applying criteria based on the hydrophile‐lipophile balance (HLB) and cohesive energy ratio concepts. Composition‐conversion curves were determined for samples containing different monomer feeds. The drifts observed in the terpolymer compositions with conversion were compared to those calculated from the reactivity ratios determined in binary copolymerizations performed in solution and in microemulsion. The results show that the reactivity of the monomers in ternary systems depends on the ionic strength, i.e. on the monomer feed composition.
Seeded emulsion polymerization of butylacrylate: “Zero‐one or pseudo‐bulk?”
Authors: Zirkzee H. F. , Van den Enden M. J. W. A. , Van Kilsdonk W. T. , Van Herk A. M. , German A. L.
Published: April 2003

The kinetics of the emulsion polymerization of butyl acrylate at 20°C in Smith‐Ewart interval III were investigated using a redox initiator system peroxodisulfate–bisulfite–copper. The aim of this work was to obtain more basic knowledge about the kinetic behavior of the butyl acrylate system. Monomer conversion into polymer was based on gravimetrically calibrated online densitometry. The experimentally obtained conversion versus time curves for these seeded reactions were fitted by a linear regression procedure (slope and intercept) as well as by a nonlinear regression procedure based upon zero‐one kinetics. The conclussion is that the emulsion polymerization of butyl acrylate may reflect zero‐one kinetics up to a particle size of approximately 130 nm. The rate coefficients for entry and exit can be obtained fairly accurately with the slope and intercept procedure and with the nonlinear regression method if the propagation rate coefficient is accurately known. However, this is not the case. Therefore the development of universal procedures for obtaining the propagation rate coefficients is essential, since this parameter is of paramount importance in all further model calculations concerning emulsion polymerization.
Polymerization of styrenes and acrylates carrying dendrons of the first and second generation
Authors: Neubert I. , Klopsch R. , Claussen W. , Schlüter A.‐D.
Published: April 2003

The synthesis of dendronized acrylate and styrene monomers with Fréchet‐type as well as urethane‐based dendrons of the first and second generation and their radically initiated polymerization to the high molecular weight dendrimers 6(G‐1,2) and 8a(G‐2) is reported. The latter polymer carries four THP‐protected hydroxy functions per repeat unit whose quantitative deprotection is also described.
Trends in polymer chemistry 1996
Authors: Frey H. , Kressler J. , Richtering W. , Mülhaupt R.
Published: April 2003

Important advances have been made in controlled radical polymerization, particularly in the application of the new technique for the preparation of novel block copolymers. CO‐copolymers are becoming increasingly popular. Increasing research efforts are also being devoted to discrete supermolecular structures as well as the preparation of nanometer‐size noble metal clusters in polymer matrices. MALDI‐TOF continues its triumph in synthetic polymer chemistry.
NMR imaging of the competitive vulcanization of natural rubber and polybutadiene blends
Authors: Klei B. , Koenig J. L.
Published: April 2003

NMR imaging was used to study the spatial heterogeneity of the molecular mobility of the competitive vulcanization of natural rubber and high‐cis polybutadiene blends. The NMR images showed the presence of domains of widely different molecular mobilities. This heterogeneous mobility reflects differences in the crosslink density internal to each component of the blend. The differences in the internal crosslink density probably arise from differences in diffusion and solubility of the curatives. Additionally, overall, the poor dispersion of sulfur and accelerator due to inadequate mixing also contributes to the heterogeneity.
Anthracenol[2,3‐C:6,7‐c′]difuran, a new monomer for diels—alder polyaddition reactions
Authors: Kintzel O. , Schlüter A.‐D.
Published: April 2003

The anthracenedifuran precursor 7 was obtained in a short sequence from its lower homologue 1. On thermal treatment, 7 generates the highly Diels‐Alder (DA)‐active anthracenodifuran “8”. Its bisdiene character is proved by trapping with diquinone 9, which gives the [9]cyclacene derivative 10 and oligomeric material.