bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of the crystallinity on the β relaxation of poly(ethylene terephthalate)
Authors: Fulchiron R. , Gauthier C. , Vigier G. 
Published: April 2003

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractAbiotic 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

AbstractPolyacrylonitrile (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

AbstractStatic 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

AbstractIn 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

AbstractThe 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

AbstractSmall 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

AbstractX‐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

AbstractThe 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

AbstractThe 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

AbstractMechanical 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

AbstractThe 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

AbstractThis 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

AbstractAniline 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

AbstractThe 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

AbstractThis 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

AbstractThe 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

AbstractPermittivity 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.