bluuebunny/crossref_metadata_2025_split huggingface dataset:
Processing of product forms for the large‐scale manufacturing of advanced thermoplastic composites
Authors: Cutolo D. , Savadori A. 
Published: April 2003

AbstractIn the field of large‐volume applications today, injection‐moldable polymers, reinforced with short or long fibers, are used for semi‐structural components. Additional use is made of glass mat thermoplastic sheets, for which the processing technologies have already been established in a large number of applications. Advanced thermoplastic composites based on highly aligned, continuous fibers represent, with their high fiber content, a big step in terms of mechanical performance and offer thermoplastic polymers the chance to become structural components. In spite of a great deal of work carried out in this category of materials, in particular with carbon fiber‐based products for defense and aerospace applications, the business is still at an early stage of development due to the high price of intermediate products (small plants and not fully optimized production processes) and to embrionic manufacturing technologies for mess production applications.Conversion of the various continuous fiber reinforced thermoplastic materials into useful parts and components is dependent on the intermediate product forms: boardy tape, flexible two, fabric or sheet. Some general technologies exist for the thermoplastic composites and their subsequent processing methods; however, in many cases because of the peculiarity of these products (i.e. fabric deformation under stamping) they require different approaches.The scope of this work is to describe those methods that are most promising for large‐volume applications, in particular products forms (containing powder) for post‐shaping impregnation, and to analyze some of the fundamental mechanisms of flow and deformation that drive the processing behavior.
Photogeneration and transport of charge carriers in polysilylenes
Authors: Nešpůrek Stanislav , Kmínek Ivan , Pfleger Jiří , Brynda Eduard , Cimrová Věra , Schnabel Wolfram 
Published: April 2003

AbstractThe attachment of π‐conjugated chromophores that absorb the radiation with long wavelengths to poly(methylphenylsilylene) (1) via reactions of its formylated derivative is described. Some of the polymers obtained show improved photostability and higher quantum photogeneration efficiency in comparison with the parent polymer. Photoconductive ultra‐thin layers can be prepared from polar derivatives of (1) by the Langmuir–Blodgett technique.
Orientation and order in thin films of a combined liquid crystalline polymer
Authors: Henn Guido , Poths Holger , Stamm Manfred 
Published: April 2003

AbstractThe order in thin films of a combined liquid crystalline polymer is studied by X‐ray reflection. Films of thicknesses of less than 200 nm on float glass are investigated as a function of temperature. The polymer with mesogenic groups in the main and side‐chains exhibits smectic and cholesteric mesophases. Measurements in the smectic phases show a Bragg peak and smectic layers are oriented parallel to the substrate. The sample is thus macroscopically ordered by the influence of substrate and free surface. The film surface is very smooth after spincoating; surface roughness is typically 0.8 nm. First annealing of samples leads to a significant roughening of the free surface; roughness increases to 2.1 nm. Order as a function of film thickness depends on the interaction of the polymer with the substrate and free surface. These interactions give rise to a typical correlation length of perturbations in smectic ordering.
Striking selectivity of anion incorporation into polypyrrole by competitive doping: perchlorate versus hexafluorophosphate
Authors: Walton D. J. , Hall C. E. , Mure J. M. , Pyle A. , Thomas C. , Viney I. V. F. 
Published: April 2003

AbstractIn the electro‐oxidative preparation of polypyrrole films from electrolyte media containing both perchlorate and hexafluorophosphate anions a striking selectivity towards ClO4 was observed, with a three‐fold preference for this anion in films from aqueous medium and a greater than ten‐fold preference from MeCN. This result is of benefit towards the production of polypyrroles containing complex functionalized dopant anions, since the presence of PF6 to bolster electrolysis parameters will less readily carry over into the final polymer. PF6 is particularly useful for this purpose in MeCN, where ClO4 is inappropriate, being itself too readily incorporated into the polymer from this solvent system.
Hydrogenation of aldehydes and ketones catalyzed by a polysulfosiloxane–platinum complex
Authors: Tang Li‐Ming , Lu Ying , Huang Mei‐Yu , Jiang Ying‐Yan 
Published: April 2003

AbstractAn acidic inorganic polymer, polysulfosiloxane, has been prepared and used as ligand for preparing a polysulfosiloxane–platinum complex. It has been found that such a complex could catalyze the hydrogenation of aldehydes and ketones to alcohols, giving as much as 100% yield at room temperature and under atmospheric pressure. Temperature, S/Pt molar ratio in the complex and solvents greatly influenced the reaction. This complex was very stable and could be used several times without any change in catalytic activity.
Oxygenation of 3‐pentanol to 3‐pentanone catalyzed by polymer–platinum complex
Authors: Yang Xiao‐Tun , Yin Shu‐Pu , Huang Mei‐Yu , Jiang Ying‐Yan 
Published: April 2003

AbstractA new inorganic polymer–platinum complex, silicasupported polysilazane–platinum complex, has been prepared and found to be capable of catalyzing the oxygenation of 3‐pentanol to 3‐pentanone in 100% yield at moderate temperature and under atmospheric oxygen pressure. Water is the best solvent for this reaction. This inorganic polymer complex is very stable in the reaction and can be reused several times without any appreciable change in catalytic activity.
Thermal elimination reaction in polyparaphenylene vinylene synthesis from the soluble sulfonium salt precursor route
Authors: Massardier Valérie , van Hoang Tran , Guyot Alain 
Published: April 2003

AbstractThe thermal conversion of poly(p‐xylyidene tetrahydrothiophenium) chloride into polyparaphenylene vinylene has been studied by Fourier transform infrared spectroscopy (FT‐IR), thermogravimetry, and HCl and tetrahydrothiophene analyses, in the temperature range 20–250°C. Using this system, almost complete elimination can be obtained after only 1 hr heating at 180°C. A side reaction, with the transient formation of C–Cl bond is observed during the heat treatment. After doping with oleum, a stable conductivity is obtained that is not very‐sensitive to the elimination temperature.
Recent theories of gas sorption in polymers
Authors: Barbari T. A. , Conforti R. M. 
Published: April 2003

AbstractTheories and models are presented for gas sorption in polymers above and below the glass transition temperature. With the exception of predictive theories that do not represent the data well, the models are fit to data for the carbon dioxide/silicone rubber and carbon dioxide/polycarbonate systems for the purposes of comparison. During the past decade, a number of new models and theories have been proposed specifically for gas sorption in glassy polymers. Each new model attempts to incorporate aspects of the gas sorption process that are unique to polymers below the glass transition temperature. This review discusses these recent advances, the assumptions used in their development and their advantages and disadvantages.
Sorption and permeation in elastic solids: applicability to gas transport in glassy polymeric materials
Authors: Lipscomb G. Glenn , Banerjee Tapan , Chhajer Mukesh 
Published: April 2003

AbstractA thermodynamic analysis of sorption and transport in elastic solids is presented. The penetrant's chemical potential in the solid is calculated from the free energy changes that accompany deformation of the solid to accommodate the penetrant and mixing of the deformed solid and penetrant. Sorption isotherms are obtained by equating this chemical potential to that of that of the gas phase. The penetrant diffusivity is determined from a statistical mechanical analysis described in the literature. Both pure and mixed gas solubility, diffusivity and permeability are predicted. Mixed gas behavior is predicted using material parameters obtained from pure gas data only. The results suggest certain relationships between the dual mode model parameters that are found experimentally. Comparison with several experimental gas–polymer systems indicate the elastic solid analysis can reproduce pure gas data and predict mixed gas data well with physically realistic material parameters. The results provide a basis for investigating the relationships between the mechanical, volumetric, gravimetric and thermodynamic processes that give rise to transport.
Crystallization behavior of polyethers containing odd numbers of methylene spacers from the isotropic and liquid crystalline states
Authors: Yandrasits Michael A. , Chen Jianhua , Arnold Fred E. , Cheng Stephen Z. D. , Percec Virgil 
Published: April 2003

AbstractA series of thermotropic polyethers synthesized from 1‐(4‐hydroxyphenyl) ‐ 2 ‐ (2 ‐ methyl ‐ 4 ‐ hydroxyphenyl) ‐ ethane and α,ω‐dibromo‐n‐alkanes with odd numbers of methylene units (MBPE‐n = odd) shows monotropic mesophase behavior. In isothermal differential scanning calorimetry (DSC) experiments, two—sometimes even three—exothermic transition processes can be observed when the crystallization temperature is below the mesophase transition temperature, while only one exothermic process is present above the mesophase transition temperature. The melting behavior of the crystals grown from the mesophase and from the isotropic melt states is different. The crystals grown from the mesophase state exhibit a larger overall heat of transition and a higher transition temperature compared with those grown from the isotropic melt. This may be attributed to the molecular interfacial connections between the crystal and amorphous regions when MBPEs crystallize from the mesophase state. The difference in morphology between the crystals grown from the different states has also been studied with polarized light microscopy (PLM) and transmission electronic microscopy (TEM). The structures of the crystals grown from the different states are, however, the same, as evidenced through wide‐angle X‐ray diffraction (WAXD) measurements. From the banded morphology of MBPE samples observed from PLM, the defect textures observed through TEM and the results of WAXD experiments, this mesophase can be identified as a nematic liquid crystal state.
Acid treatment for functionalizing polyethylene fiber surfaces for enhanced adhesion to epoxy resins
Authors: Ravichandran V. , Obendorf S. K. 
Published: April 2003

AbstractThe utility of high‐strength, high‐modulus polyethylene fibers in fiber‐reinforced composites is limited due to its poor interfacial adhesion to various polymeric matrices. One way to overcome this limitation is to introduce reactive functionalities on the fiber surface capable of covalently bonding to matrix resins. Ultra high‐strength polyethylene (UHSPE) fibers were treated with chlorosulfonic acid. The surface acid groups were found to considerably improve the interfacial adhesion between polyethylene fibers and epoxy resins as shown by the microbond test. These surface functionalities were found to improve the fiber wettability, as shown by contact angle measurements using the Wilhelmy balance method. Colorimetric measurements of methylene blue absorption were used to quantify the surface concentrations of the acid groups. It was possible to functionalize the UHSPE fiber surfaces using this method to obtain fibers that formed a stronger adhesive bond with epoxy resins; this was achievable without sacrificing other fiber mechanical properties.
Surface‐grafting onto aramid powder: reaction of acyl chloride groups on the surface with functional polymers having terminal hydroxyl or amino groups
Authors: Tsubokawa Norio , Oyanagi Takashi 
Published: April 2003

AbstractThe surface‐grafting of polymers onto aramid, poly(p‐phenylene terephthalamide), powder surface by the reaction of acyl chloride groups on the surface with functional polymers having terminal hydroxyl and amino groups was investigated. The introduction of acyl chloride groups onto the aramid powder surface was achieved by the reaction of the aramid powder with adipoyl dichloride: the acyl chloride group content of the surface was estimated to be 1.14 mmol/g (0.17 mmol/m2) by elemental analysis. It was found that by the reaction of acyl chloride groups on the surface with functional polymers, such as terminal diol‐type poly(propylene oxide) (PPG) and terminal diamine‐type poly(dimethylsiloxane) (SDA), these polymers were grafted onto the aramid powder surface; the percentage of surface grafting of PPG and SDA onto the aramid powder was 16.7 and 22.4%, respectively. The thermogravimetric curve of PPG surface‐grafted aramid powder exhibited an initial weight loss at about 250°C and a second weight loss at about 500°C. This indicated that the grafting of PPG is limited to the powder surface. The wettability of the aramid powder surface turned from hydrophobic to hydrophilic by the surface‐grafting of PPG onto the surface.
Surface structures of fluoropolymer, polyolefin and polyester films after modification by graft polymerization
Authors: Kang E. T. , Neoh K. G. , Tan K. L. , Loh F. C. , Liaw D. J. 
Published: April 2003

AbstractPristine and argon plasma pretreated polytetrafluoroethylene (PTFE), polystyrene (PS), high‐density polyethylene (HDPE) and poly(ethylene terrephthalate) (PET) films have been subjected to near‐UV light‐induced graft polymerization with water‐soluble acrylamide (AAm), the sodium salt of styrene sulfonic acid (NaSS), acrylic acid (AAc) and N,N‐dimethylaminoethylmethylacrylate (DMAEMA) monomers. The structure and composition at the substrate surface with grafted polymer were studied by angle‐resolved X‐ray photoelectron spectroscopy (XPS). In most cases, the density of surface grafting is enhanced by plasma pretreatment. For each polymer substrate with a substantial amount of grafting, the hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains. This stratified microstructure is consistent with the static secondary ion mass spectroscopy (SIMS) and Ar+beam depth profiling results. The two latter techniques also suggest that when the grafted polymer has a bulky substituent, there is less efficient penetration of the grafted polymer below the surface.
Advanced polymers for electrooptics
Authors: Dubois Jean‐Claude 
Published: April 2003

AbstractPolymers have been in use for a long time as passive materials for components in electronics and electrooptics. They combine the possibility of easy processing with an infinite potential of functionalization. They can be conductors or semiconductors, ferroelectrics and can exhibit interesting properties such as photoconductivity, piezo, pyroelectricity or nonlinear optical properties. As a consequence they are now used for merging active components in the field of electrooptics such as displays, sensors or modulators for optical signal treatment.This paper describes the properties and applications of some recent polymers in the field of electroptics.In the first part of this paper the properties of amorphous copolymers with a pending group with large hyperpolarizability are described. These amorphous copolymers show high optical nonlinear coefficients after poling under an electric field. We have used these copolymers for the manufacture of an electrooptic modulator working at 1.3 μm at a frequency of 1 GHz.The second part deals with ferroelectric polymers and their pyroelectric properties. The realization and performance of an IR pyroelectric sensor using copolymers of polyvinylidene fluoride–ethylene trifluride are described. Some new results concerning polymersdispersed liquid crystals are also described.
Opto‐electronic polymers for advanced computer and communication technologies
Authors: Mizoguchi Katsuhiro 
Published: April 2003

AbstractThis paper describes reviews about the characterization of optical and electronic (opto‐electronic) organic materials including polymers, and their applications for advanced key devices used for computers and communications technologies. On the basis of the author's recent investigations, discussions are made on organic electroluminescent thin film materials for emissive display devices, polymer‐dispersed liquid crystal materials for passive display devices, organic photo‐conductive materials for electrophotographic printer devices, and highly electroconductive polymers for solid tantalum capacitors. Finally, technical issues and development prospects for the opto‐electronic organic materials in the 21st century are suggested.
Blends of a siloxane/urea/urethane‐segmented copolymer with an IPDI‐based polyetherurethane
Authors: Ho Tai , Wynne Kenneth J. 
Published: April 2003

AbstractA series of copolymer blends have been prepared using a poly(ether urethane) and a poly(siloxane–urea–urethane). The copolymers were prepared by a hardsegment first, two‐step polymerization method. The hard segments of the copolymers were derived from isophorone diisocyanate (IP) and 1,4‐benzenedimethanol (B), and the soft segments were based on polytetrahydrofuran (PTMO, Mw = 2000), and polydimethylsiloxane (PDMS, Mw =27,000), respectively. The siloxanecontaining copolymer, PDMS27K‐IP‐B2 (2 moles diol chain extender/mole PDMS27K), was used as the minor component (1.6, 2.5 and 6.0 wt%) in a series of blends. These blends were found to preserve the mechanical properties of the poly(ether–urethane) as well as the surface properties of the poly(siloxane–urea–urethane).
Morphology and properties of fibers based on polycarbonate/liquid crystalline polymer blends
Authors: Petrović Zoran S. , Farris Richard J. 
Published: April 2003

AbstractPolycarbonate‐triad‐4–co‐polybutylene terephthalate liquid crystalline blends were prepared and spun into fibers. It has been shown that fibrillation of the thermotropic liquid crystalline polymer (TLCP) takes place at the given spinning conditions, forming thus “in situ” reinforcement. Continuous fibrils are formed at concentrations between 2.5 and 5% LCP. A degree of miscibility between two phases was observed. The moduli of both as‐spun and cold drawn fibers increase almost linearly with increasing concentration of TLCP. Tensile strength was found to decrease and elongation at break to increase with increasing TLCP content. The structure of the cold drawn fibers was not stable with time, causing a relaxation in the observed properties.
Multi‐electron transfer processes for molecular conversions
Authors: Tsuchida Eishun 
Published: April 2003

AbstractMulti‐electron transfer plays an important role in many chemical reactions. A collection of examples, both of metal complexes that exhibit one‐step, multi‐electron transfer process, and of chemical reactions based on a multi‐electron transfer system, is presented. Emphasis is placed on the role of multi‐electron transfer process in a sense that some molecular conversion systems such as reduction of O2 and oxidation of H2O become feasible through multi‐electron transfer. As an important example of molecular conversion, oxidative polymerization of sulfur‐containing compounds through two‐electron transfer, is also reviewed.
Electrochemical examples of multiple‐electron transfer
Authors: Anson Fred C. 
Published: April 2003

AbstractVarious electroactive reactants that undergo multipleelectron transfer reactions at electrodes are divided into two broad classes. The first class exhibits a series of single electron steps at different electrode potentials. The second class exhibits multiple‐electron transfer in a single voltammetric step. Examples from each class are offered and the reasons for their electrochemical behavior are described.
Multi‐electron transfer in photoelectrochemical processes
Authors: Honda Kenichi 
Published: April 2003

AbstractSimultaneous bidirectional forward and backward electron transfers take place on a light‐exited semiconductor particle, even at the same geometric site. The potentials of the electron pathways are different, giving rise to two independent molecular conversion reactions. This type of multi‐electron transfer reactions is overviewed and the stepwise unidirectional multi‐electron transfer on the excited semiconductor particle is also described.
Model oxygen‐evolving center composed of polymer membrane and dimer ruthenium complex
Authors: Ramaraj Ramasamy , Kira Akira , Kaneko Masao 
Published: April 2003

AbstractThe in situ spectrocyclic voltammetric investigations of the dimeric ruthenium complex used for water oxidation, [(bpy)2(H2O)Ru–O–Ru(H2O)(bpy)2]4+ (H2O–RuIII–RuIII–OH2), were carried out in a homogeneous aqueous solution and in a Nafion membrane under different pH conditions. The in situ absorption spectra recorded for the dimer show that the dimer H2O–RuIII–RuIII–OH2 complex underwent reactions initially to give the detectable H2O–RuIII–RuIV–OH and H2O–RuIII–RuIV–OH2 complexes, and at higher positive potentials, this oxidized dimer underwent further oxidation to produce a presumably higher oxidation state RuV–RuV complex. Since this RuV–RuV complex is reduced rapidly by water molecules to H2O–RuIII–RuIV–OH2, it could not be detected by absorption spectrum. Independent of the pH conditions and homogeneous solution/Nafion membrane systems, the dimer RuIII–RuIV was detected at higher potentials, suggesting that the dimer complex acts as a three‐electron oxidation catalyst. However, in the Nafion membrane system it was suggested that the dimer complex may act as a four‐electron oxidation catalyst. While the dimer complex was stable under oxidation conditions, the reduction of the dimer RuIII–RuIII to RuII–RuII led to decomposition, yielding the monomeric cis‐[Ru(bpy)2(H2O)2]2+.
Electron transfer mechanism in olefin polymerization
Authors: Ciardelli Francesco , Altomare Angelina , Arribas Guillermo , Conti Giuseppe , Colle Renato 
Published: April 2003

AbstractPolymerization of olefins mediated by transition metal derivatives (Ziegler–Natta polymerization) is one of the most scientifically and industrially important processes of molecular conversion. Electron transfer mechanism could play a significant role in both heterogeneous and homogeneous catalysts. The catalytic activity strongly depends on the presence of two metallocene ligands attached to the transition metal (more commonly zirconium) which grants the valence form of zirconium in complexes of the type Cp2ZrX2(X=Cl or CH3) followed by the formation of the (Cp2ZrX)+ cation under the effect of a Lewis acid. On the other hand, Ti complexes with only one metallocene ligand give the syndiospecific polymerization of styrene, where the phenyl group appears to act as electron donor for the transition metal. The remarkable electronic effect of the metallocene groups in determining catalytic activity is demonstrated by the study of substituted metallocene ligands as well as other ligands around the metal. These effects cannot be, however, completely separated from steric effects which seem to be responsible for the impressive and versatile stereochemical control determined by symmetry properties of the transition metal complex.