bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of unsaturated polyester resins for large sized composites
Authors: Abdel‐Azim A. A. , Mahmoud B. H. , Farhat M. S.
Published: April 2003

A series of unsaturated polyesters based on phthalic anhydride (PHA), maleic anhydride (MA), ethylene glycol (EG), diethylene glycol (DG), triethylene glycol (TG), propylene glycol (PG), styrene (Sty) and acrylonitrile (AN) were prepared. The molecular weights of the prepared polyesters were determined by end‐group analysis. The effect of the structure of the resin on its curing behavior has been investigated. On the basis of the experimental study, the following were concluded: (1) The maximum curing temperature (Tmax) is related to the molecular weight of the glycol incorporated in these castings. In this context the Tmax was found to decrease with increasing the molecular weight. Meanwhile the time to peak temperature tmax was increasing. (2) The higher the percentage of AN in the crosslinking monomer system, the slower a resin cures. (3) The values of Tmax were found to be influenced to a large extent by the percentage of AN.
Thermostable poly(p‐phenylene sulfide sulfonic acid) as ion exchangers
Authors: Song H. Y. , Miyatake Kenji , Yamamoto Kimihisa , Tsuchida Eishun
Published: April 2003

Poly(p‐phenylene sulfide sulfonic acid) was thermally crosslinked for use as a cation exchange polymer with high thermal stability. The decomposition temperature (Td) of the polymer increases with an increase in the crosslinking temperature. The crosslinking reaction at 300°C in air resulted in the formation of a strongly acidic cation exchange polymer with a T = 467°C and having an SO2 bond, whose crosslinked structure was investigated using IR spectroscopy.
Synthesis and characterization of conductive polypyrrole grown on the sulfonated surface of polyethylene films
Authors: Berdjane Z. , Rueda D. R. , Balta‐Calleja F. J.
Published: April 2003

Chemical synthesis of polypyrrole (PPy) was carried out in the presence of FeCl3 aqueous solution. The grown PPy is fixed on the sulfonated surface of polyethylene (SPE) films, where the sulfonic groups act as counteranions to balance the positive charge of PPy, giving the composite material of PPy–SPE.

For reasons of comparison, two types of polyethylene (PE) have been used, low and high densities with different degrees of sulfonation, SD (g/m2), defined as the ratio of weight increase to the area of the two surfaces of the sample. A series of reaction times was used to evaluate the variation of the electrical conductivity, σ (S/cm), of polypyrrole. It was found that σ increases as reaction time increases.

To characterize the samples, Fourier transform infrared (FTIR) spectroscopy and conductivity measurements were performed.
Morphological modification of UHMPE fibers
Authors: Economy J. , Andreopoulos A. G.
Published: April 2003

UHMPE fibers can display several morphological features, including skin‐core, microfibrillar and shish‐kebab structures. In this work, an attempt was made to eliminate these morphologies by treating the UHMPE in a two‐roll mill, at temperatures ranging from ambient to 145°C. Up to 130°C the tensile strength and modulus of the fiber were retained, and thermal analysis and crystallographic data showed that ordering in the fiber remained intact. The shish‐kebab and microfibrillar morphologies were greatly reduced and the fiber cross‐section was altered from circular to a flat ribbon.
The effect of electrochemical surface treatments of carbon fibers using scanning tunneling microscopy
Authors: Donnet Jean‐Baptiste , Park Soo‐Jin , Wang Wei‐Dong
Published: April 2003

Scanning tunneling microscopy (STM) has been applied to the study of the topography of polyacrylonitrile (PAN)‐based carbon fibers before and after electrochemical surface treatments. The results show that the electrical anodic oxidation only changes the surface aspects; at nanometric resolution; the nanostructure and nanotexture such as the step‐like crystallite stacking are decreased with increasing electric current densities.
Conformation and electrochemical reduction of myoglobin in PEO oligomers
Authors: Ohno Hiroyuki , Ohkubo Waki , Yamaguchi Natsue
Published: April 2003

Horse‐heart myoglobin (Mb) was modified with poly(ethylene oxide) (PEO) to solubilize it in PEO oligomers. PEO‐modified Mb (PEO–Mb) showed a quasi‐reversible electrochemical redox reaction in PEO200 (molar mass of 200 g). PEO–Mbs, modified with lower molecular weight of PEO chains, were soluble in PEO oligomers with wider range of molecular weight. A conformation of PEO–Mb was studied with circular dichroism spectroscopy in phosphate buffer solution (PBS) or PEO oligomers. The α‐helix content of PEO–Mb, determined by the molar ellipticity at 222 nm, decreased from 71% to about 58% after PEO modification. However, the degree of PEO modification did not affect the α‐helix content of PEO–Mbs. On the other hand, the α‐helix content of PEO–Mbs was reduced by lowering the molecular weight of the modified PEO chains. Since the α‐helix content of PEO–Mb in PBS and that in the PEO oligomers were almost identical, the conformation of PEO–Mb in PBS was considered to be maintained even in PEO oligomers. Although the reduction rate constant of PEO–Mb in PEO oligomers depended on the total molecular weight of the PEO–Mbs, their relation did not obey the Stokes–Einstein equation. The reduction of the PEO–Mb was probably affected by the interfacial electron transfer process at the electrode surface rather than by diffusion in the PEO oligomer.
Molecular basis of healing and fracture at polymer interfaces
Authors: Sperling Leslie H. , Klein Andrew , Sambasivam Mahesh , Kim Kyung Don
Published: April 2003

The interdiffusion of polymer chains across a polymer–polymer interface, and subsequent fracture to re‐create the interface is reviewed. In particular, films formed via latex coalescence provide a very large surface area. Of course, latex film formation is a very important practical problem. Healing of the interface by interdiffusion is treated using the de Gennes reptation theory and the Wool minor chain reptation model. The self‐diffusion coefficients of polystyrene and the polymethacrylates obtained by small‐angle neutron scattering, SANS, direct non‐radiative energy transfer, DET, and other techniques are compared. Reduced to 150,000 g/mol and 135°C, both polystyrene and poly(methyl methacrylate) have diffusion coefficients of the order of 10−16−10−17 cm2/sec. Variations in the diffusion coefficient values are attributed to the experimental approaches, theoretical treatments and molecular weight distribution differences. An activation energy of 55 kcal/mol was calculated from an Arrhenius plot of all polystyrene data reduced to a number‐average molecular weight of 150,000 g/mol, using an inverse square molecular weight conversion method. Interestingly, this is in between the activation energies for the α and β relaxation processes in polystyrene, 84 and 35 kcal/mol, respectively. Fracture of polystyrene was considered in terms of chain scission and chain pull‐out. A dental burr apparatus was used to fracture the films. For low molecular weights, chain pull‐out dominates, but for high molecular weights, chain scission dominates. At 150,000 g/mol, the energy to fracture is divided approximately equally between the two mechanisms. Above a certain number average molecular weight (about 400,000 g/mol), the number of chain scissions remains constant at about 1024 scissions/m3. Energy balance calculations for film formation and film fracture processes indicate that the two processes are partly reversible, but have important components of irreversibility. From the interdiffusion SANS data, the diffusion rate is calculated to be about 1 Å/min, which is nine orders of magnitude slower than the dental burr pull‐out velocity of about 0.8 cm/sec.
Three‐component photopolymer based on a novel mechanism: acid‐catalyzed polymerization and decoupling of crosslinks
Authors: Kamenosono Koji , Naitoh Kazuhiko , Kondo Syun‐ichi , Umehara Akira , Yamaoka Tsuguo
Published: April 2003

Three‐component photopolymers comprising a photoacid generator, a bifunctional vinyl ether monomer and an aqueous base‐soluble polymer as matrix were developed. These photopolymers exhibit either positive‐ or negative‐working character, depending on the prebake temperature and the concentration of the photoacid generator. When the prebake temperature is high, the photo‐polymer film is made insoluble in aqueous base and organic solvents by the formation of crosslinks. However, on exposure to light, the crosslinks are decoupled by the photogenerated acid and the photopolymer layer becomes again soluble in aqueous base, resulting in a positive‐working character. When the concentration of the photoacid generator is low enough, the photopolymer has a negative‐working character due to the cationic polymerization of vinyl ethers. The mechanism of the photochemical reaction of the photopolymers was investigated to elucidate the complicated behavior.
Thermal behavior of bismaleimide resin
Authors: Regnier N. , Mortaigne B.
Published: April 2003

The cure of a bismaleimide (BMI) neat resin modified with an aromatic diamine and a siloxane elastomer, has been studied by 13C solid state nuclear magnetic resonance. Two chemical reactions occur during the cure cycle; at a low temperature, Michael's reaction predominates, while at a high temperature the polymerization of the double bond maleimide creates the network.

The degradation of this BMI material was characterized with isothermal and dynamic thermogravimetric analyses in air and in nitrogen. The BMI thermal stability is lower in nitrogen than in air. This behavior is an indication of oxygen participating in reactions at high temperatures.

The activation energy (Ea) of thermal degradation was determined from isothermal data using an Arrhenius equation (In V vs. 1/T). The global Ea for the weight loss in air was found to be 91 kJ/mol.

The nature and the evolution of the thermal degradation products were the combined analyzed by techniques of pyrolysis, gas chromatography and mass spectrometry. The major thermal decomposition products obtained in the temperature range of 300–700°C are identified as benzene, methyl formamide, aniline, toluene and isocyanate‐derived products.
The synthesis and properties of adducts between poly(4‐vinyl pyridine) and metal alkyls
Authors: Li Xiaochang , Foster Douglas F. , Cole‐Hamilton David J.
Published: April 2003

Poly(4‐vinyl pyridine) is used as a polymeric ligand to react with metal alkyls, MenM (n = 3, M = Al, Ga or In; n = 2, M = Cd or Zn) to form adducts. The adducts are characterized by solid state 13C NMR, infrared spectroscopy, microanalyses and differential scanning calorimetry (DSC). All the adducts are nonpyrophoric and thermally dissociable, so they may have potential both for use in adduct purification processes or for use as safer metal alkyl sources for Metal–Organic Chemical Vapor Deposition.
Processing of product forms for the large‐scale manufacturing of advanced thermoplastic composites
Authors: Cutolo D. , Savadori A.
Published: April 2003

In 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

The 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

The 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

In 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

An 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

A 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

The 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

Theories 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

A 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

A 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

The 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

The 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

Pristine 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

Polymers 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

This 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

A 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

Polycarbonate‐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

Multi‐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

Various 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

Simultaneous 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

The 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

Polymerization 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.
Mechanism of the molecular hysteresis
Authors: Sano Mitsuru
Published: April 2003

The redox behavior in acetone solution of (1,5‐dithiacyclooctane 1‐oxide)bis(pentaammineruthenium(II)) has been characterized, where the concept of “molecular hysteresis” is presented. Detailed thermodynamics for the complex are studied, in which intramolecular electron transfer rates for Ru3+OS/Ru2+→Ru2+SO/Ru3+ were determined as 0.12 sec−1 and 0.055 sec−1.

The molecular hysteresis consists of two important factors: isomerizations for the sulfoxideruthenium complexes and the slow intramolecular electron transfer in the complex; both are examined. Isomerization rates for Ru3+S→O and Ru2+O→S determined range from 0.4 to 5000 sec−1 and from 0.7 to 16 sec−1, respectively, for [Ru(NH3)5(sulfoxide)]2+/3+. A mechanism for the slow electron transfer in the complex is also presented. Features of molecular hysteresis are discussed.
Electron transfer of heme proteins on the ITO electrode in polymer solvents
Authors: Ohno Hiroyuki , Kawahara Natsue Y.
Published: April 2003

The redox reaction of poly(ethylene oxide) (PEO)‐modified hemoglobin (PEO–Hb) was analyzed in PEO oligomers with cyclic voltammetry. The PEO–Hb was made soluble in PEO with molecular weight of 200 (PEO200) containing 0.5 M KCI. Quasi‐reversible redox signals of PEO–Hb were obtained by using an indium tin oxide (ITO) glass working electrode. PEO–Hb, cast on the ITO electrode, also showed the redox response in PEO with molecular weight of 400 (PEO400). The peak current of PEO–Hb on the ITO electrode gradually increased during potential cycling. The effect of the scan rate on the quantity of electricity (Q) was analyzed after the peak current reached a constant value. The constant Q value was observed at the scan rate ranging from 30 to 500 mV/sec. The number of reactive PEO–Hb molecules was estimated from this constant Q‐value. It was suggested that the electron transfer was carried out at the first layer of the PEO–Hb which was in direct contact with the ITO electrode. The quantity of electricity of PEO–Hb increased when the ITO electrode was first washed in an aqueous medium with ultrasonicator. This strongly suggested that the more effective surface area of the ITO electrode turned to be covered with PEO–Hb when the microporous region of the ITO particles was more hydrated.
Structural effect of redox active sites on electron hopping rate in mixed conducting copolymers
Authors: Nagasaka Hideaki , Watanabe Masayoshi
Published: April 2003

The copolymers consisting of a redox monomer, vinylferrocene or 10‐methyl‐3‐vinylphenothiazine, and an ion‐conducting monomer, ω‐methoxy‐nona(ethylene oxide)‐methacrylate, have been prepared. The copolymers, complexed with lithium perchlorate, exhibit reversible redox activity in the absence of low molecular solvents. The charge transport during the redox reactions is carried out by electron hopping reactions between the redox active centers, indicating that the copolymers can be regarded as intrinsic ion/electron mixed conductors. The electron hopping rates during the redox reactions have been evaluated by using an electrochemical technique under diffusion‐controlled conditions. The electron diffusion coefficients in the vinylferrocene and 10‐methyl‐3‐vinylphenothiazine copolymers are 6.8 × 10−12 cm2 sec−1 and 3.2 × 10−11 cm2 sec−1 at room temperature, respectively, and are larger in the latter copolymer. The electron hopping rate would be influenced by the slow and temperature‐dependent dynamics of the polymer segment, judging from the relatively low electron diffusivity and from its quite large and non‐Arrhenius temperature dependency.
Preparation and photochromic properties of oligomeric poly(dimethylsiloxane) with the spiropyran or spirooxazine moiety in the side chain
Authors: Nakao Ren , Ueda Norikazu , Abe Yasuo , Horii Toyokazu , Inoue Hiroo
Published: April 2003

Spirobenzopyran 1, with the 3‐(diethoxymethylsilyl)‐propyl group at the N atom, was synthesized. The condensation reaction of the spiropyran 1 and diethoxydimethylsilane gave oligomeric poly(dimethylsiloxane) with the spiropyran moiety in the side chain. The oligomer was photochromic; its colour changed from colorless to purple‐red on uv irradiation and the color faded on visible irradiation or on standing in the dark. The half‐decay time of the thermal decoloration was about twice that of monomeric spiropyran dissolved in the dimethylsiloxane oligomer. Photochromic poly(dimethylsiloxane) with the spirooxazine moiety in the side chain was also prepared.
Preparation of poly(1,4‐phenylene)s by electro‐oxidative polymerization
Authors: Oyaizu Kenichi , Yamamoto Kimihisa , Asada Toshio , Nishide Hiroyuki , Tsuchida Eishun
Published: April 2003

The effect of substituents on the electropolymerization of benzene derivatives and the redox properrties of the corresponding polymers were determined using Brown's substituent constants (σ+). Electron‐donating groups lower the oxidation potential by which increase in the current efficiency was observed. However, stabilization of the produced cation radicals by the electron‐donating groups resulted in a decrease in the polymerization efficiency. The appropriate values of σ+ for the efficient polymerization ranged near −1.5.
Mechanical properties of films from polymer latices
Authors: Zosel Albrecht
Published: April 2003

The mechanical behavior of latex films is governed by their macromolecular nature as well as by their origin from particles dispersed in an aqueous medium. When monomers of different polarity are copolymerized in emulsion copolymerization, a heterogeneous distribution of the polar groups in the latex and the film can occur, owing to the different water solubilities of the comonomers. Films from these latices in many cases show a two‐phase morphology, first, consisting of the main polymer within the particles and, second, a phase which is concentrated in the interphase between the original particles and which has a strong influence on the mechanical properties of the films. Films from latices with crosslinked particles behave like homogeneous networks in the linear viscoelastic range, i.e. at small strains. Structured networks are found when latex films are interparticularly crosslinked during or after film formation, e.g. by polar bifunctional monomers or metal salts. Tensile tests of films show that the mechanical strength of latex films develops in the last stage of film formation by interdiffusion and entaglement formation across particle boundaries.
Structure–property relationships of latex films: a special emphasis on viscoelastic behavior and water vapor permeability
Authors: Richard Joël
Published: April 2003

The purpose of this work is to investigate the structure and related properties of polymer films obtained upon latex dehydration and coalescence of the particles. Coalesced latex films can be considered as cellular structures, in which the cell cores consist of the hydrophobic particle cores, while the array of interfacial membranes mainly contains hydrophilic species. The linear viscoelastic behavior of the films and their water vapor permeability properties are investigated using dynamic micromechanical analysis and vapor sorption, respectively. It is shown that both core and membrane have a strong effect on the film properties. The structure and viscoelastic behavior of polymer films obtained from sterically stabilized latexes are also studied and compared with that observed for films obtained from electrostatically stabilized ones.
High strain thermomechanical properties of IBMA‐functionalized poly(butyl acrylate) films
Authors: Hidalgo Manuel , Cavaillé Jean‐Yves , Guillot Jean , Perez Joseph , Zanetto Jean‐Emile
Published: April 2003

Batch emulsion polymerization was used in order to obtain latexes from a mixture of butyl acrylate (ca. 90% mole), and a hydrophobic crosslinkable functional monomer called N‐isobutoxymethyl acrylamide (ca. 10% mole). Films were then cast from these latexes, and their thermomechanical properties were studied before and after a heat treatment intended to provoke crosslinking of the functional groups. The differential thermal analysis and the dynamic mechanical analysis of the film samples proved that the functional monomer copolymerized with butyl acrylate; the dynamic mechanical analysis revealed also that crosslinking took place after the heat treatment. Different kinds of high strain experiments (among which there were stress relaxation tests) were carried out in a tensile testing machine Important differences were thus shown to appear between the “as‐dried” and “annealed” samples. In the case of stress relaxation experiments, simple mechanical models were used in order to fit the experimental data, both during the stretching experiment and the stress relaxation following it. The analysis of the high‐strain experiments and their simulation led to the conclusion that the films contained high molecular weight polymers having a broad molecular weight distribution, and that their crosslinking enhanced the entropic elastic behavior, even though a viscoelastic, large relaxation time contribution was kept; the hypothesis of its coming from a trapped‐entanglement effect was proposed.
Glass transition and film formation of VeoVa/vinyl acetate latices; role of water and co‐solvents
Authors: Heymans Denis M. C. , Daniel Mervyn F.
Published: April 2003

The physical forces causing deformation of latex particles during the film formation process have been witley studied. However, the forces resisting particle deformation are still poorly characterized. It is clear that the extent of particle deformation is dependent on the viscoelastic nature of the polymer. In an emulsion, the latex particles will normally contain water, surfactants and “free” monomers which lead to plasticization of the polymer. Although this effect has been recognized, so far it has been studied only on films that had been dried and then partially or completely swollen by water.

In this work, plasticization of the emulsion polymers by water and co‐solvent has been quantified via differential scanning calorimetry investigation directly on the aqueous latex dispersions. More specifically, the plasticizing effect of water on VeoVa/vinyl acetate copolymer latices and its influence on minimum film‐forming temperature (MFFT) has been studied. A linear correlation has been found between Tg and MFFT for the wet latices. This new direct method should help to improve our understanding of the forces resisting latex film formation.

Additionally, the homogeneous distribution of the hydrophobic and hydrophilic monomers (VeoVa and vinyl acetate respectively) in the latex particles was verified via a 13C‐NMR (nuclear magnetic resonance) study performed directly on the latices. This study confirmed that no significant core/shell type of morphology had influenced latex film formation.
Reactive blends of thermoplastics and latex particles
Authors: Vázquez Flavio , Cartier Hervé , Landfester Katharina , Hu Guo‐Hua , Pith Tha , Lambla Morand
Published: April 2003

Monodisperse homogeneous and core–shell latex particles of various sized between 200 and 600 nm were synthesized by emulsion copolymerization. Some of the core–shell particles were functionalized with epoxy groups at their peripheries upon introduction of glycidyl methacrylate (GMA) during the synthesis. The core consisted of crosslinked polybutylacrylate and the shell polymethylmethacrylate. Synthesis conditions at high and low temperatures were optimized to obtain coreshell particles with a well‐defined morphology. The particles were characterized by quasi‐elastic light scattering, scanning electron microscopy and transmission electron microscopy.

The latex particles functionalized with GMA were then dispersed into a reactive matrix (styrene and maleic anhydride copolymer) using a batch mixer to obtain blends with well‐defined and stabilized morphology. 4 Dimethylaminopyridine was used as a catalyst. The reaction between the epoxy groups at the particle surface and the maleic anhydride or diacid groups of the matrix was evaluated by torque and extraction techniques. A small amount of conversion generates sufficient amounts of grafted species at the matrix and particle interfaces to ensure a good interfacial adhesion.
Impact modification of thermoplastics by methyl methacrylate and styrene‐grafted natural rubber latexes
Authors: Schneider Michael , Pith Tha , Lambla Morand
Published: April 2003

The preparation and characterization of polymer blends with structured natural rubber (NR)‐based latex particles are presented. By a semicontinuous emulsion polymerization process, a natural rubber latex (prevulcanized or not) was coated with a shell of crosslinked polymethylmethacrylate (PMMA) or polystyrene (PS). Furthermore, core–shell latexes based on a natural rubber/crosslinked PS latex semi‐interpenetrating network were synthesized in a batch process. These structured particles were incorporated as impact modifiers into a brittle polymer matrix using a Werner & Pfleiderer twin screw extruder. The mechanical properties of PS and PMMA blends with a series of the prepared latexes were investigated. In the case of PMMA blends, relatively simple core (NR)–shell (crosslinked PMMA) particles improved the mechanical properties of PMMA most effectively. An intermediate PS layer between the core and the shell or a natural rubber core with PS subinclusions allowed the E‐modulus to be adjusted. The situation was different with the PS blends. Only core–shell particles based on NR‐crosslinked PS latex semi‐interpenetrating networks could effectively toughen PS. It appears that microdomains in the rubber phase allowed a modification of the crazing behavior. These inclusions were observed inside the NR particles by transmission electron microscopy. Transmission electron photomicrographs of PS and PMMA blends also revealed intact and well‐dispersed particles. Scanning electron microscopy of fracture surfaces allowed us to distinguish PS blends reinforced with latex semi‐interpenetrating network‐based particles from blends with all other types of particles.