bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anhydride‐cured epoxy resins toughened with diol‐ and bis(4‐hydroxybenzoate)‐terminated poly(tetrahydrofuran) liquid rubbers. Part II. Phase separation
Authors: Läuger J. , Albert P. , Kressler J. , Gronski W. , Mülhaupt R. 
Published: April 2003

AbstractThe structure formation via spinodal decomposition is monitored by transmission electron microscopy (TEM) and small angle light scattering (SALS) using hexahydrophthalic anhydride cured bisphenol A diglycidyl ether mixed with bis(4‐hydroxybenzoate)‐terminated poly(tetrahydrofuran) segmented poly(hydroxyether). The poly(tetrahydrofuran) (PTHF) segment has a number average molecular weight of 4500 g/mol. There is good agreement between the particle—particle spacing obtained from the maximum of SALS traces and the digital image analysis of TEM micrographs. Time‐resolved SALS measurements are used to study the phase separation kinetics in the epoxy/diol‐terminated PTHF system.
Scanning force microscopy of high modulus polyethylene fibers
Authors: Wawkuschewski A. , Cantow H. ‐J. , Magonov S. N. , Hewes J. D. , Kocur M. A. 
Published: April 2003

AbstractSurfaces of commercial ultrastrong polymer fibers Spectra® 900 and Spectra® 1000, which are produced by gel‐spinning of ultrahigh molecular weight polyethylene (UHWM PE), were examined with scanning force microscopy (SFM). Measurements were conducted in water in order to minimize surface damage caused by the tip‐sample interactions. Different types of imperfections (arbitrarily oriented fibrils, ends of fibrils and discontinuities in surface layers) were found on the fiber surface. These features interfere with the dominating fibrillar structure aligned along the fiber direction. Within the fibrillar structure were found domains of ribbon‐like features with a width of 30‐–110 nm. These ribbons are oriented perpendicular to the fiber direction and were assigned to lamellar platelets overgrown on oriented nanofibrils. SFM images in the nanoscale (1‐–100 nm) showed that nanofibrils 5‐–7 nm wide are the elementary construction elements of polymer fibers. They are combined into larger fibrils of 40‐–50 nm width. Needle‐type crystallites 10‐–30 nm wide were also found on the fiber surface. An extended chain molecular order was detected on surfaces of nanofibrils, needle crystallites, and within the central part of lamellar ribbons. Local regions with long period features having a repeat distance of 15‐–25 nm were found on the fiber surface. Etching of the fiber surface by elemental fluorination damaged the surface fibrillar structure, and produced deep pores tens of nanometer in diameter in the surface layer.
Formation of colloidal PMMA particles via free radical and group transfer dispersion polymerization of methylmethacrylate and methylmethacrylate/ethyleneglycoldimethacrylate
Authors: Hölderle M. , Mülhaupt R. 
Published: April 2003

AbstractNon‐aqueous dispersions of colloidal PMMA microparticles with average sizes ranging from 70 to 330 nm were prepared by living polymerization of methylmethacrylate (MMA) and methylmethacrylate/ethyleneglycoldimethacrylate (EDMA) in n‐heptane diluent using 2‐methyl‐1‐methoxy‐1‐trimethylsilyloxy‐prop‐1‐ene (MTS) as initiator in the presence of tetrabutylammonium fluoride (TBAF) or tetrabutylammonium cyanide (TBAC) as catalyst, and polystyrene‐block‐poly‐(ethene‐alt‐propene) (SEP) as dispersing agent. The influence of process parameters such as concentrations of MMA, EDMA crosslinking agent, TBAF, and SEP on conversion, molecular weight, particle size, and molecular weight and particle size distributions has been investigated. In contrast to GTP in solution, group transfer dispersion polymerization (GTDP) was markedly slower and accompanied by agglomeration and drastic broadening of both molecular weight and particle size distributions with increasing MMA conversion. In a new GTDP process colloidal PMMA microparticles, obtained by free radical dispersion polymerization, were added as seeds, thus affording much narrower particle size distribution and high MMA conversion.
Effects of water on the mechanical relaxation in polyamide 4
Authors: Bellinger M. A. , Ng C.‐W. A. , Macknight W. J. 
Published: April 2003

AbstractThe relaxation behavior of polyamide 4 was investigated as a function of absorbed moisture using dynamic mechanical measurements. Two relaxations, α at 81 °C and γ at — 111°C, were observed in the “dry” sample at a frequency of 1 Hz. The addition of water resulted in the depression of the α relaxation (αw) of the “wet” polyamide and the appearance of a second α relaxation (αd), slightly depressed from that of the “dry” specimen, reflecting the movements of the polymer chains after water has evaporated during the heating scan of the experiment. A second run was performed, resulting in the appearance of a single relaxation peak (α) at temperature very close to that of “dry” polyamide 4. Additionally, a β transition was observed whose temperature decreased with increasing water content. Similar results were obtained for specimens of polyamide 6. From plots of the depression of the glass transition temperature, ΔTg, as a function of the ratio of the number of water molecules to the number of accessible amide groups in the amorphous regions, R, one observes a sharp depression in the glass transition temperature with increasing water content up to some critical value, above which additional water molecules do not significantly change the glass transition temperature. Based on existing models for the sorption of water in polyamides, we propose a model whereby the environment of the polymer—water complex varies with the amount of water added to the system. At low water contents, both loosely and tightly bound water exist at the sorption centers, or amide groups. Above the critical water concentration, additional water molecules form clusters at these sorption centers. Additional aspects of the model explain the appearance of two α or primary relaxation peaks (αw and αd) due to the changing environments as a consequence of the heating scan of the dynamic mechanical measurements.
Linear viscoelastic behavior of branched polybutadiene: A fractional calculus approach
Authors: Friedrich C. 
Published: April 2003

AbstractA rheological constitutive equation for complex polymeric materials is derived starting from a special formulation of the Laplace transformed relaxance. Material functions such as the complex modulus G*(ω), the relaxation modulus G(t) and the relaxation time spectrum H(λ) are derived. These material functions contain six material parameters, which divide these functions into three characteristic regions: the plateau region, which is in fact a power law region with a small slope, and, towards smaller frequencies, two additional power law regions with different slopes.The comparison of the measured dynamic moduli of modified polybutadienes with the predictions of the proposed phenomenological model shows good agreement. Due to the fact that the mentioned material functions can easily be used, this model represents a tool for the quantitative description and discrimination of certain materials showing intermediate power law regions.
Time‐resolved small‐angle and wide‐angle X‐ray scattering apparatus using the imaging plate as a two‐dimensional detector
Authors: Hashimoto T. , Okamoto S. , Saijo K. , Kimishima K. , Kume T. 
Published: April 2003

AbstractWe report an application of the imaging plate, which contains phosphor crystals photostimulable by an X‐ray beam, as a two‐dimensional (2D) detector for time‐resolved small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD) studies especially designed for use with a rotating anode X‐ray generator as an incident X‐ray beam source. The detector constructed has the shape of an octahedral cylinder, and to each face is attached an imaging plate of 200 mm width and 100 mm height. Each plate consists of 800 × 1600 pixels with an area of 125 × 125 μm2/pixel. Time‐resolved data acquisition of SAXS and WAXD patterns on the 2D detector is performed by changing the plate face with time either by a rotation of the drum or by shifting a face of the plate in the drum with respect to the incident beam. The detection (which consists of writing and reading) of scattered X‐ray intensity distributions with the plates as well as erasure of the scattering patterns stored on the plates can be continuously performed by rotating the drum. The reading rate for the scattering patterns recorded onto the plate is 25 μs/pixel or 300 s/plate. The time required for changing the plate face from one to another by rotating the drum is 2 s, which corresponds to a minimum dead time for the time‐resolved study with an effective area of 100 × 200 mm2. When necessary, especially to shorten the dead time for the measurements, each plate can be further divided into N sections by shifting the drum with respect to the incident beam, the time required for the shifting being 25 ms/mm. Thus when the plate of 200 × 100 mm2 is divided into sections of (200/N) × 100 mm2, the minimum dead time is reduced to 25 × (200/N) ms.
Influence of a brushed polyimide surface on photoinduced reorientation processes in dye‐containing liquid crystalline polymers
Authors: Pfaadt M. , Boeffel C. , Spiess H. W. 
Published: April 2003

AbstractInfrared spectroscopy is used to study the influence of the polarization of the irradiating light and the substrate surface treated with polyimide on the reorientation process of dye‐containing liquid‐crystalline side‐group copolymers. The depolarization of the linearly polarized light on brushed polyimide surfaces affects the reorientation process and as a consequence the irradiation direction becomes the new order axis after irradiation. Relaxation processes are observed after short irradiation times, since a new stable equilibrium state has not been reached. In contrast, complete reorientation, achieving changes in order parameter of 0.9, is observed after long irradiation times. The system is then stabilized in the new orientational distribution and no relaxation processes occur. The relaxation processes can be explained by a combination of matrix response and thermal cis‐trans back relaxation of the azobenzene.
Crystallization of amorphous polyamides from the glassy state
Authors: Androsch R. , Stolp M. , Radusch H.‐J. 
Published: April 2003

AbstractThe general crystallization behavior of amorphous polyamides during heating treatment was measured by wide angle X‐ray scattering (WAXS) and differential scanning calorimetry (DSC) to get information on (1) the temperature range where the crystallization in an anisothermic process takes place and (2) the type of the crystalline phases (α or γ) considering the Brill transition and the state of order in the α‐crystal. Various polyamides (PA 6, 6.10 and 6.6) were quenched and cooled to 200 K and then heated until they melted. During heating from the glassy state the crystallization starts rapidly at the glass transition temperature and then the crystallinity slowly increases until the melting point. The crystallinity was calculated on the basis of the separation of the amorphous and crystalline scattering by profile fitting. The angular position of the amorphous halo and so the density of the amorphous phase is higher in the presence of the crystalline phase compared to the completely amorphous state. The crystalline structure (α or γ), which is difficult to distinguish at higher temperatures due to the Brill transition, was determined by quenching the samples from elevated temperatures to room temperature after heating. The perfection of the α‐crystal, i.e. the crystal perfection index, increases with temperature during continuous heating.
Synthesis and characterization of interpenetrating polymer networks based on polyacrylate and epoxy
Authors: Tan Su‐sheng , Zhang Dong‐hua 
Published: April 2003

AbstractThe synthesis and properties of simultaneously interpenetrating networks (SINs) based on poly(polyethylene glycol diacrylate) (PEGDA) and epoxy (diglycidyl ether of bisphenol A, DGEBA) were studied. The effect of compositional variation on the morphology and properties of products was investigated. The swelling coefficient, densities, glass transition behavior, and thermal stability of these interpenetrating networks (IPNs) are discussed. Microphase separation morphological structures were found in all PEGDA/DGEBA IPNs. Decreased swelling ratios compared to the calculated swelling coefficients based on the weight additivity of the components were obtained after the formation of IPNs. Increased density and thermal stability were also obtained in these IPNs, implying the existence of interpenetration (topological entanglements) among the component networks.
Silver nanocluster formation within microphase‐separated block copolymers
Authors: Sohn B. H. , Cohen R. E. 
Published: April 2003

AbstractSilver cluster formation in bulk block copolymer films (static‐cast) and in thin films (microtomed or spin‐coated) was investigated by transmission electron microscopy. In all cases, the silver clusters were formed predominantly within the original silver‐containing microdomains. A greater degree of control of cluster formation and a narrower cluster size distribution were achieved in the thin films of block copolymers. The interfaces between domains of the heterogeneous copolymers and the free interfaces of the thin film specimens all played an important role in nucleation and growth of clusters.
Stabilization of colloidal palladium particles by a block copolymer of polystyrene and a block containing amide sidegroups
Authors: Roescher A. , Hempenius M. , Klok H.‐A. , Möller M. 
Published: April 2003

AbstractA block copolymer of polystyrene and poly(tert‐butylmethacrylate) was prepared by anionic polymerization. The ester groups of the poly(tert‐butylmethacrylate) were hydrolyzed, after wich the remaining carboxyl groups were reacted with pyrrolidine. The resulting block copolymer with amide sidegroups was used for stabilization of a palladium colloid in toluene.
Nanofibrillar surface structures of gel‐drawn UHMW‐polyethylene tapes
Authors: Sheiko S. S. , Möller M. , Kunz M. , Deckmann H. 
Published: April 2003

AbstractThe fibrillar structure of gel‐drawn ultrahigh molecular weight polyethylene was studied by scanning force microscopy (SFM), transmission electron microscopy (TEM) and 2H‐NMR. Periodically striped 20—50 nm wide nanofibrils were depicted at the surface of the ultradrawn tapes. A periodicity of about 25 nm was observed independently of the draw ratio in the range 10 ≤ λ ≤ 70. This is consistent with the long period derived from SAXS experiments. The stripes were more pronounced at low draw ratios and a short range interfibrillar correlation was detected in that case. Based on variations in the 2H‐NMR relaxation times and segment orientation, it is concluded that structural defects are concentrated within small domains inside the crystallites and that the striped structure originates from defect layers within the fibrillar crystallites.
Dynamic mechanical properties of interpenetrating polymer networks based on polyacrylates and epoxy
Authors: Tan S. , Zhang D. , Zhou E. 
Published: April 2003

AbstractInterpenetrating polymer networks (IPNs) based on polyacrylate (poly(polyethylene glycol diacrylate), PEGDA) and epoxy(diglycidyl ether of bisphenol A, DGEBA) were prepared simultaneously. Dynamic mechanical properties of the SINs (simultaneous interpenetrating networks) with various compositions were studied. Enhanced mechanical properties were found in this case. From the point of view of pre‐swollen networks, all of the PEGDA/DGEBA IPNs were composed of the individual pre‐swollen networks. A micro‐phase segregation system was produced in the SIN. Glass transition temperatures shifted inward, which was attributed to molecular packing effects or mutual‐entanglements of molecular segments among the individual pre‐swollen networks. In accordance with the additivity of properties, namely the parallel model, the entanglement density between the two polymer networks reached its maximum at 50/50 PEGDA/DGEBA IPN.
Poly(P‐xylylene)s: Synthesis, polymer analogous reactions, and perspectives on structure–property relationships
Authors: Greiner A. , Mang S. , Schäfer O. , Simon P. 
Published: April 2003

AbstractA critical overview of different synthetic approaches to poly(p‐xylylene)s (PPXs) is coupled with perspectives on particular structure–property relationships and challenging applications. An attempt is made to emphasize the potential of different synthetic approaches to PPXs focused on different applications. Additionally, the synthesis and polymer analogous reactions of PPXs without leaving groups and functionalized PPXs (with leaving groups in the a‐position) serving as processable precursors for non‐processable polymers are evaluated.
Alkynes bearing furan rings. 1. Synthesis and polymerization with Mo‐based catalysts
Authors: Méalares C. , Costa G. , Gandini A. , Valenti B. 
Published: April 2003

AbstractThis paper describes the preparation of new alkynes bearing furanic substituents and their polymerization by catalytic systems based on transition metal halides in order to obtain novel materials with original properties because of the presence of both furan moieties and alternate single and double bonds. However, difficulties arising from the specific reactivity of the heterocycle in our experimental conditions led us to envisage an indirect way to obtain well‐defined products, using an aromatic polymer as the precursor.
Novel fluorinated block copolymers for the construction of ultra‐low energy surfaces and as dispersion stabilizers in solvents with low cohesion energy
Authors: Antonietti M. , Förster S. , Micha M. A. , Oestreich S. 
Published: April 2003

AbstractBlock copolymers consisting of polystyrene and a block containing long fluorinated side chains are made by two very effective polymer analogous reactions from commercially available polystyrene‐b‐polybutadiene block copolymers. Since these polymers consist of two mutually immiscible blocks with hydrophobic and very hydrophobic character they form micelles in a wide range of media down to very hydrophobic solvents, e. g. toluene, tetrahydrofurane (THF), perfluorohexane, perfluoro(methylcyclohexane), hexafluorobenzene and 1,1,2‐trichlorotrifluoroethane (Freon 113). First indications that our polymers are useful as effective steric stabilizers in such solvents are given by characterization of some polymer dispersions made in the solvents via precipitation polymerization.In the solid state, mesophase formation typical for block copolymers is observed and characterized by quantitative small angle X‐ray scattering (SAXS). The surface of such films is controlled by the fluorinated block and exhibits an ultra‐low surface energy of the order of γSV = 15 mN/m, below that of polytetrafluoroethylene (PTFE) or polydimethylsiloxanes (PDMS). Unlike PTFE, the blocky nature of the presented polymer enables thermoplastic processing and dissolution in standard solvents, which is of practical relevance. Gas‐permeability measurements on membranes coated with these copolymers exhibit some interesting selectivities.
X‐Ray investigation of the structure of polyurethane elastomers based on 1,5‐naphthalene diisocyanate
Authors: Androsch R. , Blackwell J. , Chvalun S. N. , Festel G. , Eisenbach C. D. 
Published: April 2003

AbstractThe structure of the crystalline hard domains of polyurethane elastomers based on 1,5‐naphthalene diisocyanate (NDI) has been investigated by X‐ray methods. The specimens were pressed films prepared from NDI and 1,4‐butanediol (chain extender), with poly(oxytetramethylene) as the soft segments. Small angle X‐ray data show that the hard domains are lamellae oriented preferentially with their planes parallel to the film surface. The corresponding wide angle data show that the hard domains are crystalline, and that the degree of crystallinity can be more than 60%. The hard segment chains are relatively extended and are oriented perpendicular to the film surface: they probably form a staggered array in which they are linked in sheets by hydrogen bonds. Molecular models suggest that the hydrogen bonds are shorter, and hence stronger, than those formed in the hard domains of equivalent elastomers based on diphenylmethane diisocyanate (MDI) or dicyclohexylmethane diisocyanate (HMDI). In addition, the stacking of the naphthylene units is unencumbered by the presence of the bridge methylene groups in the latter systems, and these structural features probably account for the higher melting temperature of the hard domains.
Polypropylene growth on silica‐supported metallocene catalysts: A microscopic study to explain kinetic behavior especially in early polymerization stages
Authors: Steinmetz B. , Tesche B. , Przybyla C. , Zechlin J. , Fink G. 
Published: April 2003

AbstractThe polypropylene growth on metallocene/MAO catalysts supported on a silica carrier has been examined by scanning electron microscopy. The kinetic induction period in early polymerization stages can be explained by the formation of a discrete polymer layer only on the outer surface of the catalyst particle. Differences in the fragmentation process at later stages are pointed out, depending on the supporting procedure of the catalyst system.
Comparison of polydipentylsilylenes and ‐siloxanes containing chiral groups
Authors: Schwegler L. A. , Molenberg A. , Möller M. 
Published: April 2003

AbstractPolydipentylsilylene and ‐siloxane copolymers, containing bis[(S)‐(+)‐2‐methylbutyl]silane units have been synthesized. Thermal analysis demonstrated for both types of copolymers that crystallization was hindered on incorporation of the 2‐methylbutyl groups. Optical rotation measurements in various solvents yielded a much stronger optical activity of the polysilylene copolymers, compared to the polysiloxanes. This effect has been explained by the formation of a chiral supramolecular structure in the case of the polysilylenes. The measurements have indicated that the solvent quality can be employed to enhance the formation of this structure at relatively low 2‐methylbutyl contents.