bluuebunny/crossref_metadata_2025 huggingface dataset:
Zum einfluß von düsenverzug und plastischer reckung auf die eigenschaften von naßgesponnenen polyoxadiazolfäden
Authors: Stark W. , Remde H. , Leonhardt R. , Strauß K.‐H. , Strubl R.
Published: April 2003

Polyoxadiazol, ein aromatisches heterocyclisches Polymer, ist aufgrund seiner hohen thermischen Stabilität für eine Reihe von Einsatzzwecken interessant. Mit einer Laborspinnanlage wurden die Spinnbedingungen Düsenverzug und Grad der plastischen Reckung variiert und deren Einfluß auf die Materialparameter wie Bruchdehnung, Festigkeit und Modul untersucht. Zur Erreichung höherer Festigkeiten und Moduli erwiesen sich ein mittlerer Düsenverzug von 2 und ein eher niedriger plastischer Reckgrad von 1,5 bis 2 als günstig. Ebenfalls untersucht wurde die Längenzunahme der Fäden bei lastfreier Temperung. Je nach Düsenverzug und plastischem Reckgrad wurden sowohl positive als auch negative Längenänderungen gefunden, die mit der überlagerung von spontaner Dehnung und Schrumpf erklärt werden.
Polyanion‐polycation‐complex formation of charged microgels and latices with oppositely charged polyelectrolytes in solution
Authors: Kötz J. , Paulke B. , Philipp B. , Denkinger P. , Burchard W.
Published: April 2003

Employing cationic, covalently crosslinked polyallylamine‐based highly swollen microgels and anionic latices obtained by copolymerization of methacrylic acid and epoxypropyl methacrylate, the interaction of these polymer colloids with oppositely charged linear macroions is investigated by potentiometry, conductometry and turbidimetry. The microgels behave similar to linear macroions in symplex formation, if the components are reacted in the neutralized state, while in a “free acid – free base” titration only the easily accessible sites of the microgels are primarily involved in the interaction. With the more compact polymer latices a stable dispersion is formed, while with the microgels flocculation occurs. The results are discussed with regard to the influence of physical structure of the polymer colloids on stoichiometry and state of dispersion of the symplexes formed.
Indications of the excluded volume effect in the core of a polymer colloid particle
Authors: Pekcan Ö.
Published: April 2003

The phosphorescence intensity of naphthalene groups labelled to the poly(methyl methacrylate) phase of a colloid particle is studied in dependence of temperature. The peculiar structure in the phosphorescence spectra around −126 °C is attributed to the theta point conditions of the colloid dispersion. The results are interpreted in terms of the excluded volume effect.
The sorption of ethyl xanthogenate on polyester fibres. II. Kinetics and thermodynamics
Authors: Espinosa‐Jiménez M. , Cano‐Suárez A.
Published: April 2003

Data on the kinetics and thermodynamics of absorption of potassium ethyl xanthogenate onto polyester fibres at different temperatures are presented. It is established that the increase in temperature of the system increases the uptake of ethyl xanthogenate ions by the fibres. Adsorption equilibria, specific rate constants, diffusion coefficients, activation energy and enthalpy of reaction were determined. From the results the conclusion can be derived that the adsorption of ethyl xanthogenate ions on the polyester fibre in the investigated temperature interval takes place with establishment of strong chemical bonds.
Dielectric investigation by time domain spectroscopy of vinyl chloride/vinylidene chloride copolymer solutions
Authors: Menge H. , Feldman Yu. D. , Polygalov E. , Fedotov V. D. , Schneider H.
Published: April 2003

Dielectric time domain spectroscopy measurements were performed on vinyl chloride/vinylidene chloride copolymers in solution over a frequency range of 1 to 104 MHz. The dielectric absorption and dispersion have been studied at temperatures from −20°C to +20°C. The data were analyzed by using the Havriliak‐Negami equation and related to the motional behaviour. The dielectric correlation function was compared with those from different motional models used in NMR experiments.
Synthesis and substituent distribution of Na‐cellulose sulphates via O‐trimethylsilyl cellulose as intermediate
Authors: Wagenknecht W. , Nehls I. , Stein A. , Klemm D. , Philipp B.
Published: April 2003

Sulphation of cellulose was performed in an homogeneous aprotic system with SO3 or CISO3H, resp., via O‐trimethylsilyl celluloses as reactive intermediates. Na‐cellulose sulphates completely soluble in water and showing small chain degradation could be obtained at DSs≥ 0.25. The DSs in the range between 0.2 and 2.5 as well as the distribution of the sulphate half‐ester groups within the AGU were regulated via the DSsi at one hand, the type and amount of sulphating agent at the other. Sulphation was performed either with the isolated and redissolved trimethylsilyl cellulose in N,N‐dimethylformamide or tetrahydrofurane, or starting with an activated cellulose suspension, by achieving silylation and subsequent sulphation in one system of reaction. Obviously, the silyl group acts as a reactive group in subsequent sulphation, and the sites previously silylated are preferentially sulphated in the subsequent step of reaction, and the DSs is limited by the degree of silylation (DSsi) previously obtained. The homogeneous sulphation of trimethysilyl cellulose indicates a reactivity of silyl ether groups in the order of C‐6 > C‐2 ≫ C‐3.
Synthesis of nanoparticles for brain cell labelling in vivo
Authors: Paulke B.‐R. , Härtig W. , Brückner G.
Published: April 2003

Different types of latices were synthesized by emulsion copolymerization that differ in particle size, polymer hydrophilicity and surface coverage with functional groups. All of these particles were equipped with intensive fluorescence by inclusion polymerization, covalent bonding during particle formation and growth or surface modification of pre‐fabricated latices, respectively. Concentrated particle suspensions were injected into the brain tissue of mice. The filling of glial cells by phagocytosis and the retrograde labelling of neurons with two kinds of beads could be shown in brain sections.
Pure and modified polycyanurates ‐ polymers with great future as adhesives, casting resins, and binders for laminates
Authors: Bauer M.
Published: April 2003

Pure and modified polycyanurates are known for about 20 years. Up to now an important number of different special products was developed. Composites which base on polycyanurate resins show a high thermostability, stability against humidity and chemicals, and excellent electrical insulating properties. The resins are used as adhesives, binders for laminates, casting resins, and for other applications.
Thermodynamics of blends of poly(vinyl methyl ether) and polystyrene
Authors: Troeger J. , Kammer H. W.
Published: April 2003

Light scattering is employed to determine cloud point curves of polystyrene (PS)/poly(vinyl methyl ether) blends over a large range of PS molecular weights. All blends investigated display lower critical solution temperature (LCST) behaviour. The LCST shifts to lower temperatures and smaller PS contents with ascending disparity of the constituent's molecular masses. Thermodynamics of the blends has been rationalized in terms of an equation‐of‐state theory. Relevant parameters can be calculated. Both enthalpy of mixing and excess volume turn out to be negative.
Dielectric relaxation of amorphous random copolymers of poly(ethylene terephthalate) and poly(ethylene‐2,6‐naphthalene dicarboxylate)
Authors: Ezquerra T. A. , Baltà‐Calleja F. J. , Zachmann H. G.
Published: April 2003

The dielectric constant and dielectric loss values have been determined in the 103‐106 Hz frequency range for amorphous random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene‐2,6‐naphthalene dicarboxylate) (PEN). The dielectric behaviour has been interpreted in terms of the Havriliak‐Negami formulation. On this basis the variation of the dielectric properties with temperature has been qualitatively related mainly to two processes: The α process which is associated to the glass transition of the polymer and depends on the molar ratio of PET and PEN. The β process which is assigned to a local motion of the ‐COO groups attached to the aromatic rings. The existence of a β* process in between the α and the β processes has been observed in PEN at low frequencies. The relaxation time spectrum has been discussed in terms of molecular structure alterations. Finally, the temperature variation of the relaxation time is analyzed in the light of various predictions.
Rotational dynamics of substituted phthalocyaninatopolysiloxanes as measured by 2D solid‐state NMR spectroscopy
Authors: Schwiegk S. , Werth M. , Leisen J. , Wegner G. , Spiess H. W.
Published: April 2003

The rotational dynamic behaviour of a polymer of the hairy rod type has been investigated in the solid state. Octa‐(alkoxy)‐phthalocyaninatopolysiloxanes have been synthesized selectively deuterated at the aromatic core positions for this study. They form a hexagonal columnar structure without any phase change in the temperature range from 170 to 470 K. Thermally activated uniaxial rotation involving the phthalocyanato moiety around the long axis of the polymer is detected by solid‐echo 2H‐NMR spectroscopy. Two‐dimensional NMR spectroscopy shows that the motional process involves 90° jumps with considerable broadening of the reorientation potential, reflecting the four‐fold symmetry of the repeat unit. This indicates that the siliconphthalocyanine moieties can rotate around their covalent Si‐O bond within a single macromolecule, rather than the molecules as a whole around their columnar axes.
Tracer‐diffusion in quenched lamellar phases
Authors: Fredrickson G. H.
Published: April 2003

A theory is presented to describe the tracer‐diffusion properties of surfactant molecules embedded in quenched, disordered lamellar phases, such as those encountered in concentrated solutions and melts of block copolymers. We demonstrate that for weak anisotropy of the local diffusion tensor Dij, the average diffusion coefficient of an isotropically disordered sample is slightly larger than (1/3)∑iDii and is independent of the geometrical and statistical details of the quenched pattern. For large anisotropy of Dij, transport of a tracer molecule will in general become dependent on the population and type of topological defects that characterize the quenched sample and thus on its preparation and history. In such instances, sub‐diffusive transport can be achieved.
Investigation of stress distributions in filled polysiloxane by NMR imaging
Authors: Blümler P. , Blümich B.
Published: April 2003

NMR imaging is applied to industrial poly(dimethylsiloxane). Samples were investigated in the strained and unstrained state with and without a cut, and compared with two model compounds. Inhomogeneous filler distributions cause variations in the magnetic susceptibility and lead to contrast in gradient‐echo images.T2‐parameter images revealed distributions in segmental mobility associated with the filler inhomogeneities as well as with the cut. The images were recalibrated to give strain and stress images by use of integral stress andT2values determined for macroscopic uniaxial strain. The effects of filler inhomogeneities appear larger in the NMR images than in polarization micrographs because of magnification by magnetic field distortions from susceptibility differences in gradient‐echo images, and because changes in segmental mobility of surrounding polymer chains are detected rather than the filler itself. The methods can also be applied to 3D imaging of nontransparent rubbers.
Synthesis, electrical conductivity and electroluminescence of poly(p‐phenylene vinylene) prepared by the precursor route
Authors: Gmeiner J. , Karg S. , Meier M. , Rieß W. , Strohriegl P. , Schwoerer M.
Published: April 2003

We present a detailed experimental procedure for the synthesis of poly(p‐phenylene vinylene) by the precursor route. Special emphasis is given to the conditions of the thermal elimination reaction that leads from the processable precursor polymer 4 to PPV. We found that a temperature of 320°C is necessary to remove sulphur and chlorine containing defect structures which are probably formed by nucleophilic substitutions during thermal elimination. PPV prepared by our procedure contains 0.12% of chlorine and 0.15% of sulphur. With this material we are able to prepare large area light emitting diodes (LED) which work at driving voltages as low as 2 Volts in an ITO/PPV/Al configuration. The low threshold results in an improved device performance: So a LED continuously driven with a current density of 20 mA/cm2 emits light for one week at ambient conditions and for more than four weeks if operated in a glove box at room temperature.
The formation of polymer‐solvent complexes of polyacrylonitrile from organic solvents containing carbonyl groups
Authors: Bashir Z. , Church S. P. , Price D. M.
Published: April 2003

The crystallisation behaviour on cooling of concentrated solutions of polyacrylonitrile (PAN) in two organic solvents, gamma butyrolactone (gBL) and ethylene carbonate (EC), was investigated. gBL is a liquid but EC is a crystalline solid at 20°C. Wide angle X‐ray diffraction studies showed that the peaks from the solvent‐containing gel films were different from those in the dry PAN powder. Polarised‐infrared spectroscopy measurements conducted on uniaxially‐drawn gel films indicated not only preferential orientation of the nitriles perpendicular to the draw direction but also orientation of the residual solvent in such a way as to suggest pairing of the gBL or EC molecule with the nitriles on the chains. It is suggested that the X‐ray diffractograms of the gels may be due to the formation of polymer‐solvent complexes during crystallisation of PAN from solvents with carbonyl groups. Differential scanning calorimetry showed gel‐melting endotherms on heating and crystallisation exotherms on cooling.
Atomistic details of disordering processes in superheated polymethylene crystals
Authors: Liang G. L. , Noid D. W. , Sumpter B. G. , Wunderlich B.
Published: April 2003

Atomistic details of disordering in superheated polymethylene crystals have been studied using molecular dynamics simulations. Superheating causes a quick development of large‐scale disorder throughout the crystal, including reorientation, translation, and the destruction of crystal symmetry, followed ultimately by surface melting. Crystallization‐centers with hexagonal packing are found in the superheated, unconstrained crystals. On cooling during the simulation, a recrystallization process competes with the disordering resulting in a reorientation of the molecular chains and reorganization of the crystal.

“The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. DE‐AC05‐84OR‐21400. Accordingly, the U.S. Government retains a nonexclusive, royalty‐free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.”
Correlation between structure and electrical conductivity of soluble polyphenylenes
Authors: Simitzis J. , Tzevelekis D. , Stamboulis A. , Hinrichsen G.
Published: April 2003

Polyphenylenes were prepared by using biphenyl‐AlCl3‐CuCl2 according to cationic oxidative polymerization. The chlorobenzene soluble fraction was doped with 10% (w/v) solution of FeCl3 in acetonitrile. The alternating electrical conductivity, X‐ray diffractograms and the FTIR‐spectra of both undoped and doped polyphenylenes were measured. The proportion of the components used for the preparation of polyphenylenes strongly influences their structure as well as their conductive properties. The undoped polyphenylenes were found to be insulators, but most of them became semiconductors after doping. The increase of the alternating electrical conductivity σ' (resulting from the real part of the admittance‐vector) of the doped polyphenylenes has been explained considering the factors that influence the polyphenylenes structure: the high ratio of para/meta, the presence of both amorphous and crystalline regions, and the presence of polynuclear structures. On the other hand, the presence of aliphatic structures interrupts the conjugation system, leading to lower σ' values.
Effects of the crystallinity on the β relaxation of poly(ethylene terephthalate)
Authors: Fulchiron R. , Gauthier C. , Vigier G.
Published: April 2003

The β relaxation of PET is studied as a function of its crystallinity. The variation of the magnitude of tan Φ is explained taking into account the mechanical coupling of crystalline and amorphous phases by means of a series‐parallel model which is intermediate between the purely parallel and series ones. The adjustable parameter which is considered in such a model is related to the amorphous volume fraction which ensures the mechanical coupling and which appears to be proportional to the reciprocal long period. The morphology analysis shows that the variation of the crystalline fraction (between 0.32 and 0.53) during treatments carried out for one hour between 120°C and 230°C affects mainly the crystalline lamellae thickness while the long period evolves much less. Therefore, the coupling fraction remains almost unchanged. Moreover, an important feature of this work is that the β relaxation in semicrystalline polymers does not linearly evolves with the crystallinity while β relaxation does not exist in the crystalline part.
Towards rigid‐rod polyelectrolytes via well‐defined precursor poly(paraphenylene)s substituted by 6‐iodohexyl side chains
Authors: Rau I. U. , Rehahn M.
Published: April 2003

A synthetic strategy is presented which opens up an efficient access to readily soluble poly(para‐phenylene) (PPP) electrolytes of well‐defined molecular constitution and conveniently determinable degree of polycondensation (DP). By means of PPP derivatives substituted by carboxylic acid functionalities, a four‐step precursor route has been developed which consists of (a) the Pd‐catalyzed synthesis of PPPs with 6‐phenoxyhexyl pendant groups, followed by (b) the cleavage of the 6‐phenoxyhexyl ethers using trimethyliodo silane. The latter conversion produces exclusively 6‐iodohexyl pendant groups, the reaction of which with sodium 4‐ethylcarboxylatophenolate (c), followed by ester hydrolysis (d) yielded the desired rigid‐rod polyelectrolytes. Under appropriate reaction conditions all steps (a–d) occur highly selectively and almost quantitatively, and no degradation of the polymer backbone occurs, as is shown by high resolution NMR spectroscopy and osmometric investigations. Thus, structurally homogeneous carboxylated PPPs of well‐known DP are available by that reaction sequence. Essentially, this success is due to the excellent solubility of all intermediates involved as well as the advantageous reactivity of the 6‐iodohexyl‐substituted PPP intermediate.
Side chain polyrotaxanes: 2. Functionalized polysulfone with non‐covalently anchored cyclodextrins in the side chains
Authors: Born M. , Koch Th. , Ritter H.
Published: April 2003

The synthesis of a new side‐chain polyrotaxane containing β‐dimethyl cyclodextrin rings is described. The rotaxane side groups are attached via amide functions at an aromatic polysulfone. Some characteristics of the polyrotaxane are compared with those of a corresponding guest model compound. It is found that the Tg value, the solubility in chloroform and acetone, some 1H‐NMR shifts and the GPC maximum are significantly influenced by the non‐covalently anchored cyclodextrin rings.
Design and synthesis of a convergent and directional molecular antenna
Authors: Xu Zhifu , Moore J.S.
Published: April 2003

A phenylacetylene monodendron having a smooth gradient in electronic energy from the periphery to the core has been synthesized. The focal point terminates in a perylene luminophor. This design is suggested to contain the essential features of an efficient exciton antenna, manifested in the form of a light energy conversion device.
Abiotic degradation products from enhanced environmentally degradable polyethylene
Authors: Albertsson A.‐C. , Barenstedt C. , Karlsson S.
Published: April 2003

Abiotic degradation products from LDPE with starch + pro‐oxidant, LDPE with starch only and pure LDPE were determined as a step towards establishing products resulting from environmental degradation. The samples were subjected to thermal ageing in water at 95°C for 6 weeks or alternatively pre‐heated and subsequently immersed in aqueous environments at ambient temperature for 10 months whereafter the water phase was analyzed for degradation products. Altogether over 50 degradation products were identified by GC‐MS, mainly ketones, alcohols, aldehydes, lactones and carboxylic acids, the last being most represented. The amount of degradation products formed from the different samples correlated to their molecular weight reductions as measured by SEC but was also dependent on the permeability of the sample, i.e. its ability to allow formed degradation products to diffuse out to the surrounding environment. The addition of both starch and pro‐oxidant significantly increased the susceptibility to degradation, while the addition of starch alone gave a noticeable but smaller increase.
Modified polyacrylonitrile for adsorption applications
Authors: Simitzis J.
Published: April 2003

Polyacrylonitrile (PAN) was produced by redox polymerization of acrylonitrile and then was modified with 50% aqueous solutions of H2SO4 or NaOH. Copolymers of acrylonitrile with acrylic acid, acrylamide or methylenebisacrylamide were prepared by radical polymerization. The structures of these polymers based on PAN were studied by IR‐spectroscopy in order to determine their characteristic groups. The cation exchange capacity is higher in polymers containing more acidic groups (COOH), and for the examined cases the adsorbability was Cu2+ > Zn2+ (ion exchange selectivity).

The discoloring ability of the examined polymers was studied with aqueous solutions of three dyes, i.e. methylene blue (cationic or basic dye), congo red (direct dye having similarities with anionic dyes) and alizarin yellow (acid dye or anionic monoazo dye). The results are interpreted in terms of electron donor‐acceptor (EDA) interactions between the main groups of the polymers and the dyes. The presence of CONH2 (having polar character) in the polymers based on PAN, produces favorable interactions with the groups (electron donor or acceptor) of the molecules of the three dyes. The design of new polymer materials based on PAN with increased adsorption ability, could be performed with such a discoloring investigation, especially for methylene blue and alizarin yellow.
Light scattering studies on long‐range density fluctuations in a glass‐forming polymer
Authors: Kanaya T. , Patkowski A. , Fischer E.W. , Seils J. , Gläser H. , Kaji K.
Published: April 2003

Static and dynamic light scattering measurements were performed on a glass‐forming polymer, poly(methyl‐p‐tolylsiloxane) (PMpTS; Tg=−17°C), in a temperature range of 30°C to 120°C. It was found that long‐range density fluctuations, so‐called clusters, are observed in this polymer. They are characterized by “excess” angular‐dependent isotropic scattered intensity and additional slow decay in the photon correlation function. These properties are generally observed in low molecular weight glass formers as well as in glass‐forming polymers. In addition, we found that the clusters completely disappear above about 90°C. The kinetics of the cluster growth was also studied by temperature jump experiments. During the cluster formation process after the temperature jump, we measured the angular‐dependent polarized scattered intensities, and the photon correlation function as a function of annealing time. We discuss the cluster growth kinetics based on these results, especially the time evolution of the correlation length ξOZ evaluated using the Ornstein‐Zernike formula, the isotropic scattering intensity IOZ(0) at q=0, and the correlation time τcl of the cluster decay. Finally, we briefly discuss some properties of the equilibrated clusters, which are well reproducible.
Polymer conformational structure and dynamics at the glass transition studied by multidimensional 13C NMR
Authors: Zemke K. , Schmidt‐Rohr K. , Spiess H.W.
Published: April 2003

In a variety of amorphous polymers such as poly(propylene), poly(vinyl acetate) and poly(isobutylene), various backbone conformations are detected by magic‐angle‐spinning (MAS) NMR in the solid state, exploiting the γ‐gauche effect on the isotropic chemical shifts. In poly(propylene), the populations of the conformations are related to specific configurations determined from solution 13C NMR. Above the glass transition temperature, dynamical exchange between the conformations is observed. The non‐exponentiality of the correlation functions and the motional rates are similar of those of the diffuse reorientations observed by 2D exchange NMR with slow MAS or on static samples at the same temperatures. Although trans and gauche define the preferred conformations within the distribution of rotational angles for poly(propylene), the dynamics are not suitably described by motions of the atoms on a diamond lattice. This is demonstrated in particular by the absence of long term orientational memory in 3D exchange NMR experiments. To characterize the nature of the motion further, correlation functions of orders L = 2 and L = 4 have been calculated from 2D exchange spectra without MAS. A behavior intermediate between large‐angle jumps and isotropic rotational diffusion is observed.
Dielectric studies of the α‐relaxation in miscible polymer blends and its relation to concentration fluctuations
Authors: Zetsche A. , Fischer E.W.
Published: April 2003

The α‐relaxations in homogeneous polymer blends are often compared with the corresponding relaxations in their pure components, an effect that has long been associated qualitatively with concentration fluctuations. A novel “fluctuation model” describes very accurately the observed dielectric relaxation curves measured in polyvinylmethylether/polystyrene. From this analysis of measured α‐relaxations the mean square concentration fluctuations 〈(δϕ)2〉 can be evaluated as functions of temperature and average concentration ϕ0. In the description of concentration fluctuations in terms of the wellknown random phase approximation, the relevant parameter for the temperature dependence of 〈(δϕ)2〉 is the reference volume element V. For fluctuations calculated from the dielectric α‐relaxation this volume was found to be identical with a “cooperatively rearranging domain” which has been discussed in theoretical treatments concerning the glass transition.
Ordering kinetics in a symmetric diblock copolymer
Authors: Floudas G. , Pakula T. , Fischer E.W. , Hadjichristidis N. , Pispas S.
Published: April 2003

Small angle X‐ray scattering (SAXS) and rheology are employed to study the microphase separation transition in a symmetric poly(styrene‐b‐isoprene) diblock copolymer. The order‐disorder transition temperature TODT has been identified with a good precision (TODT=359 K) and the interaction parameter is extracted using mean field theory at temperatures well above TODT. The kinetics of microphase separation have been studied by means of rheology in a small temperature range below the order‐disorder transition, following a quench from the disordered state. The time evolution of the storage and loss moduli exhibited shapes which are reminiscent of the crystallization isotherms of semicrystalline materials (of the Avrami type). For shallow quenches, we find a temperature range of 3 K below TODT where the ordering proceeds by heterogeneous nucleation and growth of three‐dimensional objects with lamellar microstructure. At higher undercooling, the kinetic curves change in form, indicating a different mechanism of structure formation. Our results are compared with theoretical predictions for the ordering kinetics of symmetric diblocks.
X‐ray analysis of the structure of a wholly aromatic polyester with alkoxy sidechains
Authors: Biswas A. , Blackwell J. , Deutscher K. , Wegner G.
Published: April 2003

X‐ray diffraction has been used to determine the structure of the poly(p‐phenylene 2,5‐di‐hexadecyloxy‐terephthalate), which is one of a series of polyesters with stiff aromatic mainchains and flexible aliphatic sidechains currently being studied by this laboratory. The X‐ray data for oriented melt quenched films show that this polymer adopts an interesting and novel structure, in which the backbones and sidechains form separate incommensurate lattices. The backbones are fully extended, and adopt a monoclinic structure with unit cell dimensions: a=26.2Å, b=7.3Å, c=12.6Å, and α=130°C. They are in contact along the b axis, thereby forming stable sheets that are separated by intercalated, highly extended sidechains, which point along the a axis. The sidechains are packed in a columnar, approximately hexagonal structure that is similar to the hexagonal form of linear alkanes. The repeat for the sidechain lattice along the backbone direction is c=13.2Å, and thus the two lattices are incommensurate. We envisage a small disordered boundary layer between the backbone and sidechain lattices, containing some of the inital and final carbons of the sidechain, and accommodating any conformational isomerism. This allows an independent lattice to be formed by the central sections of the sidechains, but this cannot propagate indefinitely because of the different c dimension and the restrictions imposed by covalent linkage to the backbones. As a result, the sidechain crystallites are only approximately 50Å wide, compared to approximately 200Å for those formed by the backbones. Simulated X‐ray patterns for the above incommensurate structure show good qualitative agreement with the observed data.
Molecular order in a homlogous series of liquid‐crystalline side group polymers from multidimensional carbon‐13 and silicon‐29 NMR spectroscopy
Authors: Titman J.J. , Tzou Der‐Lii , de Lacroix S. Féaux , Boeffel C. , Spiess H.W.
Published: April 2003

The variation in the degree of orientational order as a function of molecular site is investigated in a homologous series of liquid‐crystalline side group polymers based on a polysiloxane backbone using multidimensional carbon‐13 and silicon‐29 NMR spectroscopy. Significant differences in ordering behavior are observed amongst the members of the series as the length of the flexible spacer group is increased. In particular the degree of order on the polymer backbone and the size of the order gradient away from the aligned mesogen are correlated with the parity of the spacer chain.
Blue light‐emitting diodes based on ladder polymers of the PPP type
Authors: Huber J. , Müllen K. , Salbeck J. , Schenk H. , Scherf U. , Stehlin T. , Stern R.
Published: April 2003

The blue emission of ladder‐type poly(para‐phenylene) films is unstable under heat treatment due to the formation of aggregates that emit yellow light. Novel statistical copolymers possessing ladder‐type oligo(para‐phenylene) segments connected via twisted phenylene spacers are used to suppress the formation of these aggregates and to obtain blue emission stable under annealing.
Relation between structure and elastic constants of man‐made cellulosic fibers: I. A two phase anisotropic model with contiguity parameter
Authors: Ganster J. , Fink H.‐P. , Fraatz J. , Nywlt M.
Published: April 2003

Mechanical properties of cellulosics were calculated taking into account a two‐phase system of crystalline and non‐crystalline regions and a contiguity parameter as a mechanical coupling variable according to McCullough et al. In doing so, the simplified orientational averaging procedure has been shown to be valid also for crystal symmetries lower than orthorhombic. Performance maps were derived to demonstrate the dependence of longitudinal and transverse Young's moduli as well as the axial and transverse shear moduli on crystallinity, on crystalline and non‐crystalline orientation and on the contiguity factor as an additional materials design parameter.
FTIR spectroscopic studies on the heterogeneous transformation of cellulose I into cellulose II
Authors: Fengel D. , Strobel C.
Published: April 2003

The heterogeneous transformation of cellulose I into cellulose II via Na‐cellulose I was performed by an alkali treatment of cotton linters followed by stepwise washing. Two experimental series were carried out, one with NaOH/H2O and the other with NaOD/D2O. Changes in the cellulose structure were studied by FTIR spectroscopy. Various reactions such as the inclusion of alkali and water in the cellulose lattice, splitting and new formation of inter‐ and intramolecular hydrogen bonds are discussed regarding the absorbance variations and wavenumber shifts of several bands.
Photoinitiated curing of multifunctional monomers
Authors: Decker C.
Published: April 2003

This article provides an overview of the different types of photocurable systems currently used in radiation curing applications and reports the remarkable performance of some newly developed multifunctional monomers. Light‐induced crosslinking polymerization has been studied by real‐time infrared spectroscopy, which records directly conversion versus time profiles, thus allowing the important kinetic parameters to be evaluated for reactions occurring within a fraction of a second. Acrylate monomers bearing a carbamate or oxazolidone function exhibit an unexpectedly high reactivity. The curing reaction was shown to develop with long kinetic chains (up to 50 000 mol per initiating radical), because of a high value of the propagation rate constant and a low value of the termination rate constant and a low value of the termination rate constant. The UV‐curing performances of different types of vinyl ether based systems are described, special emphasis being given to the kinetic and mechanistic aspects. Highly crosslinked polymer materials having quite different structures have ben synthesized by acting on the formulation composition and on the selected photoinitiators and co‐monomers. The light‐induced polymerization of a triacrylate monomer has been carried out in a polymer matrix to generate a semi‐interpenetrating polymer network. In low‐modulus binders, such as polyurethane or natural rubber, the UV‐cured polymer combines the properties of the elastomeric polymer and of the glassy acrylate network. Dual polymer networks have been created by polymerizing photochemically a rubber bearing both epoxy and acrylate groups in its main chain.
Polyaniline dispersions 4. Polymerization seeded by polyaniline particles
Authors: Stejskal J. , Špírková M. , Kratochvíal P.
Published: April 2003

Aniline hydrochloride was polymerized in water and in 1 M hydrochloric acid by oxidation with ammonium persulfate. The macroscopic precipitation of polyaniline was prevented by the presence of poly(vinyl alcohol). The change of pH occurring during the reaction were recorded. Their relation to color transitions is discussed. The reaction was accelerated by introduction of seed polyaniline particles. The properties of resulting dispersions were not affected by seeding. The particle diameter was about 310 nm for polymerization in water and about 420 nm in 1 M hydrochloric acid.
Copolymerization of a polyhydrocarbon macromonomer with methyl acrylate and acrylonitrile in the presence of a lewis acid
Authors: Lee H.‐Y. , Herman M. S. , Padias A. B. , Hall H. K. , Tack R. D.
Published: April 2003

The free radical copolymerization of a vinyl‐terminated hydrocarbon macromonomer, namely poly‐l‐butene with molecular weight 1,000, with methyl acrylate (MA) led to copolymers with broad molecular weight distributions, and even bimodal character. In the presence of alkylaluminum chloride Lewis acids, higher incorporation of MA was obtained. The polymer MW and mole% MA in the copolymer increase with their decreasing Lewis acid strength. The best result was obtained in the presence of 25 mole% Et2AlCl versus MA at 60°C which led to 82% of the polyhydrocarbon chains being derivatized and unimodal MW distribution. For the copolymerization of the polyhydrocarbon macromonomer and AN, the best results were obtained without Lewis acid in toluene using a free radical initiator at 125°C. The model compound 2,2,4‐trimethyl‐1‐pentene copolymerizes with both MA and AN in standard free radical conditions and the copolymerization parameters were determined.
Alternating copolymerization of cyclic imino ethers with aryl α,β‐unsaturated carboxylates: A new method for synthesis of poly(ethyleneimine‐co‐acrylic acid)
Authors: Kadokawa J. , Nishizawa S. , Kobayashi S.
Published: April 2003

This paper describes an alternating copolymerization of cyclic imino ethers with aryl α,β‐unsaturated carboxylates, which occurs without added catalyst. In the combinations of 2‐methyl‐2‐oxazoline (1a) with phenyl acrylate derivatives (2a‐c), 1:1 alternating copolymers were produced. In other systems examined, 1:1 copolymers were not produced except for the combination of 2‐methyl‐5,6‐dihydro‐4H‐1,3‐oxazine (1b) with p‐cyanophenyl or p‐nitrophenyl acrylate (2b or c). The copolymerization mechanism was explained by the zwitterion intermediates. The present copolymerization let to a new synthesis of poly(ethylenamine‐co‐acrylic acid), a poly(amino acid) derivative, via the alkaline hydrolysis of the copolymer.
X‐ray investigation of epitaxial growth of trans‐polyoctenylene on isotactic polypropylene
Authors: Wenig W. , Gehrmann R.
Published: April 2003

The epitaxial crystallization of trans‐polyoctenylene (TOR) on isotactic polypropylene (iPP) in thin iPP/TOR films in the concentration range from neat iPP to a 50/50 wt.% blend has been investigated by X‐ray analysis of annealed and unannealed samples. Due to the big differences of the melting temperatures of the two components, epitaxial growth of TOR lamellae on polypropylene can already be observed in unannealed samples. The TOR lamellae show rotational symmetry relative to the c‐vector of the PP, and it can be shown that the (110)‐TOR plane is the contact plane to the polypropylene crystals. The TOR lamellae make an angle of 40° with the PP lamellae. Tilt angles were determined both experimentally and theoretically. The calculated angles are Φ111PP = 49.3° and Φ010TOR = 43.1°.
Dielectric investigations on novolac phenol‐formaldehyde resin
Authors: Holland C. , Stark W. , Hinrichsen G.
Published: April 2003

Permittivity ϵ′ and dielectric loss ϵ″ of novolac have been determined in the temperature interval from —150 to 150°C and in the frequency interval from 102.5 to 106 Hz. Novolac exhibits a main and a secondary relaxation process. For the main relaxation a master curve of ϵ″ was calculated, the shape of which was described by the Havriliak—Negami function (HN). The parameters of the HN fit were interpreted by a model that relates the values to the polymer structure. Furthermore, the temperature dependence of the dielectric relaxation times was analyzed by a WLF approach for the main relaxation and an Arrhenius approach for the secondary relaxation. The dielectric relaxation times of the main relaxation were correlated with the electrical conductivity and the melt viscosity.
Dendritic polymers: from aesthetic macromolecules to commercially interesting materials
Authors: Voit B. I.
Published: April 2003

Dendritic polymers, perfectly branched dendrimers as well as hyperbranched materials, are discussed in some detail. The variety of the synthetic routes to perfect dendrimers and some highlights of the achieved structures document the rapid increase of activity in this field. Much information on growth, defects, dimensions, and properties of these globular macromolecules has be gained with special characterization techniques and their differences to linear polymers have become obvious. Hyperbranched polymers, which can be prepared in a one‐step synthesis, cover almost the same structures as their perfect analogs and an interesting comparison of their properties can be made. High solubility and functionality, small dimensions, globular structure, and interesting viscosity behavior qualify both types of dendritic polymers for new applications. The transition from aesthetic macromolecules to commercially interesting materials is discussed with some examples.
Sequence distribution and miscibility of SMA copolymers
Authors: Pionteck J. , Reid V. , Macknight W. J.
Published: April 2003

We have investigated the miscibility of poly(styrene‐co‐maleic anhydride) (SMA/SMA) blends, i.e. blends of two SMA copolymers which have different maleic anhydride (MA) contents. 33 SMA copolymers with MA contents between 2 and 29 vol.% were used. The MA contents were determined by two different techniques: FTIR using a titration technique for calibration and DEPT NMR, which was also employed to determine the triad sequence distribution of the SMA copolymers investigated. The miscibility was determined by the single Tg criterion as measured by DSC after annealing at 220°C for 2 min. After normalization of the polymerization degree to N=1000 (χcr=0.002), we found miscibility for such blends (1:1 by weight) where the difference in the MA contents Δ[MA] is less than or equal to 2.5 vol.%. At higher differences in MA content the copolymers are immiscible. The miscibility is independent of the overall MA content. The resulting interaction parameter χs, MA is equal to 3 at 220°C. A comparison of the miscibility window determined experimentally with calculated miscibility windows where special interaction energies are assigned to the different triad‐–triad combinations does not show any evidence for an influence of the sequence distribution on the miscibility of SMA/SMA blends.
Surface effects on polymer blends and block copolymer melts: Theoretical concepts of surface enrichment, surface induced phase separation and ordering
Authors: Binder K.
Published: April 2003

Surfaces have a profound effect on the structure and related properties of multiphase polymeric materials, such as polymer mixtures and block copolymer mesophases. In particular, phase transitions in the bulk (unmixing, microphase separation, etc.) may be complemented by surface‐induced transitions (formation of wetting layers, surface‐directed spinodal decomposition, surface‐induced ordering). This review gives a brief introduction to the phenomenological theories of such phenomena, emphasizing the simplest approach based on Flory—Huggins—de Gennes free energy functionals and associated Monte Carlo simulations. More sophisticated theories and recent experiments are mentioned briefly.
Chromatographic characterization of complex polymer systems with thermal field‐flow fractionation
Authors: Antonietti M. , Briel A. , Tank C.
Published: April 2003

Thermal field‐flow fractionation (TFFF) coupled with multi‐angle laser light scattering (MALLS) is a promising quantitative method for determining the molecular‐weight distribution (MWD) of complex polymers and their aggregates. This paper describes the application of TFFF‐MALLS to linear polystyrene as well as highly cross‐linked microgel and sulfonated polystyrene samples. In addition, the chromatographic characterization of block copolymer micelles with different core chemistry is performed. The dependence of retention volume on the mass diffusion coefficient D and the thermal diffusion coefficient DT was confirmed. It is shown that DT, as predicted by theory, depends only on the solvent, being independent of both molecular weight and structure.
Morphological and thermal investigations of nylon‐6‐poly(sulfone ether)‐nylon‐6 triblock copolymers
Authors: Schnablegger H. , Kaufhold W. , Kompf R. T. , Pielartzik H. , Cohen R. E.
Published: April 2003

Three triblock copolymers of nylon‐6 (Ny6) and aromatic poly(sulfone ether) (PSuE) were investigated relative to their morphology and their thermal properties. Generally, the nylon blocks of the three Ny6‐PSuE‐Ny6 samples were very short (between 5 and 16 monomer units). Heterogeneous, microphase‐separated morphologies could be observed for all samples, independent of the processing conditions, i.e., solvent casting or melt cooling. However, the process conditions were highly influential on the formation of the supramolecular structures (i.e., spherulites), especially when the crystallizable block was short.
Modification of properties of epoxy polymers by high hydrostatic pressure
Authors: Beloshenko V. A. , Pacter M. K. , Varyukhin V. N.
Published: April 2003

A study was made of the changes in density, thermal resistance and mechanical and dielectric properties of a number of epoxy polymers cured at high hydrostatic pressure. The possibility of controlling characteristics under pressure is shown. The most important is the change in the glass‐transition temperature; the effect of pressure on the mechanical properties and thermal resistance is small.
Self‐consistent field theory of block copolymers and block copolymer blends
Authors: Whitmore M. D. , Vavasour J. D.
Published: April 2003

This paper reviews the numerical, self‐consistent field theory of block copolymers and blends in which they are a major component, and the relationship of this approach to analytic theories of the weak and strong segregation limits. The major topics of interest are microphase separation and, in blends, its interplay with macrophase separation. The paper contains a brief summary of the existing theory in a form which is generalized to include various architectures and blends, and applications to amorphous copolymers, semi‐crystallizable copolymers, copolymer/solvent mixtures, and binary and ternary copolymer/homopolymer mixtures. Phase diagrams, and the scaling of microdomains with molecular weights, temperature and concentration are analyzed and compared with experiment. The distributions of components between and within subdomains, which are calculated directly, provide the basis for understanding and identifying different segregation regimes. Of particular interest are the limitations of the theory.
Continuous fractionation of an ionene containing cycloaliphatic moieties and the dependence of the glass transition temperature on molar mass
Authors: Schultes K. , Wolf B. A. , Meyer W. H. , Wegner G.
Published: April 2003

About 340 g of a cycloaliphatic ionene (see formula given in the introduction) were fractionated by a continuous counter‐current extraction method (CPF). The efficiency of the separation was checked by viscometry and gel permeation chromatography (GPC). Ten different fractions with number average molecular masses between 16 000 and 29 000 D were obtained and their glass transition temperatures Tg determined by differential scanning calorimetry (DSC) for their bromide and tetrafluoroborate salts. No molecular weight dependence of Tg was found, in contrast to recently reported results with aliphatic ionenes, where — in case of the bromide — Tg increases with rising molecular weight.
Local ac current contrast on carbon fiber surfaces imaged by scanning force microscopy
Authors: Sturm H. , Schulz E.
Published: April 2003

After a delamination process in a C‐fiber reinforced polymer composite, the identification of the polymer residue of poly‐(phenylene sulphide) on carbon fiber surfaces gives important information on the composite failure mechanism. Using scanning force microscopy (SFM) in its lateral force imaging mode or with the stiffness imaging mode, it is almost impossible to distinguish the two composite components owing to a very low material‐based contrast of the local friction and compliance. The new technique using contrast based on a local AC current measurement allows a clear identification of the conducting carbon fiber and the non‐conducting polymer coverage.
New synthetic approach to oh‐functionalized poly(p‐xylylene)s by coupling of aromatic dialdehydes and diketones in the presence of smi2
Authors: Wege V. U. , Greiner A.
Published: April 2003

1,2‐dihydroxysubstituted poly(p‐xylylene)s were synthesized in the presence of samarium(II)‐iodide. The structure and endgroups of the polymers were verified by spectroscopy and chromatography. The structure—property relationships of the poly‐1,2‐diol structures obtained were investigated. Polymer analogous transformations were carried out for poly‐(1,4‐phenylene‐1,2‐ethanediol). The reaction parameters were investigated with respect to degrees of polymerization. Although some of the polymers were soluble, precipitation was found to be the reason for limited molecular weights.