bluuebunny/crossref_metadata_2025 huggingface dataset:
Photochemical reactions of polymers bearing chalcone residues
Authors: Akelah A. , Selim A. , Salah Ei‐Deen N. , Kandil S. H.
Published: April 2007

Photosensitive polymers based on pendent chalcone moieties were prepared directly by radical polymerization of vinyl‐chalcone monomers. The monomers were synthesized by the esterification reactions of the hydroxyl groups of 4‐ and 4′‐hydroxychalcones with methacryloyl chloride. The monomers (4‐ and 4′‐(methacryloyloxy)chalcones) were polymerized to give the corresponding homo‐and co‐polymers containing different ratios of p‐nitrophenyl methacrylate as photosensitizer group.

Investigation of the photosensitivities of the chalcone polymers was carried out through study of the photochemical reactions on exposure to UV light and measuring the changes in UV spectra before and after irradiation. The results obtained from the disappearance rates of the C=C bonds indicate that the photoreactivities of the polymers are largely affected by the position of the attachment of the chalcone to the polymer backbone and by the concentration of the photosensitizer group.
Adhesion of polymers to reinforcing fibres
Authors: Hampe A. , Marotzke C.
Published: April 2007

A single fibre pull out technique is presented which makes it possible to measure the strength in the interface between fibre and polymer with high precision even if the embedded length of the fibre is short. The method allows measurements for all kinds of fibres in thermoplastic or thermosetting polymers.

The effect of fibre surface treatment can be investigated as well as the effect of morphology or internal stresses in the polymer. Examples are given.

The shear strength results are compared with results of tensile shear tests performed on symmetrically notched unidirectional reinforced composite samples. The correlation is good and it is shown that the new single fibre pull out method is able to give a better discrimination between the composites than other methods.

An analysis of mechanical stress induced during the pull out demonstrates the use and limitation of this method.
Electrical properties of Cu(II) and Ni(II): N‐salicylidene polymethacrylic acid hydrazide complexes
Authors: Ramadan T. A. , Kandil S. H. , Salah H. , Iskander M. F.
Published: April 2007

Different types of chelated polymer complexes have been synthesized to obtain improved electrical properties. Compact discs from powders of the chelated polymers were prepared and heated in a specially designed holder. Electrical conductivity and dielectric constant of Cu(II) and Ni(II): N‐salicylidene polymethacrylic acid hydrazide samples were measured at a fixed frequency (1600 Hz) throughout the temperature range 25‐150°C.

The AC conductivity as well as dielectric measurements showed maxima at 85°C. The water molecules which were trapped in the polymer matrix are believed to play the main role in conduction and dielectric behaviour of the polymeric material. From the AC conductance and dielectric constant measurements, the dielectric losses of these polymeric materials were calculated as a function of temperature.
Studies on lignin‐based adhesives for plywood panels
Authors: Mittal Mradula , Sharma Chandra B.
Published: April 2007

Lignin, a naturally occurring polymer, was isolated from sawdust and used as a substitute in phenol formaldehyde resins. Thus lignin‐phenol formaldehyde adhesives for plywood with lignin‐phenol ratios of 50:50, 60:40, 70:30, 80:20 and 90:10 were prepared. Glue shear strength for these adhesives was tested by preparing three‐ply plywood panels. The adhesives showed a dry bond strength varying from 0.57 to 0.82 MPa. The glue shear strength for cold water resistance tests varied from 0.16 to 0.25 MPa, indicating that even 80% replacement of phenol with lignin is capable of producing a bond quality acceptable for cold water resistant grade plywood.
Molecular arrangement and polymerizability of n‐alkyl acrylates in langmuir‐blodgett films
Authors: Shiozawa Toyoshi , Shibasaki Yoshio , Fukuda Kiyoshige
Published: April 2007

Langmuir‐Blodgett (LB) films of n‐alkyl acrylates with different chain lengths have been investigated with respect to the molecular arrangement and their polymerizability. X‐ and Y‐types of depositions were obtained depending on surface pressures and temperatures. In the case of acrylate monomers with even‐numbered carbon chains polarized IR spectra revealed that X‐type LB films prepared at lower pressures gave uniaxial orientation while Y‐type films at higher pressures biaxial, although X‐ray diffraction of LB films indicated non‐alternating head‐to‐tail structure irrespective of the deposition types. The uniaxial films with rotational freedom exhibited high polymerizability, whereas the biaxial films with closely packed arrangement showed low reactivity. With odd‐numbered nonadecyl acrylate both types of LB films exhibited similar molecular arrangement and polymerizability.
Crazing of polycarbonate at cryogenic temperature: Effect of specimen thickness
Authors: Shonaike G. O. , Reed P. E.
Published: April 2007

Polycarbonate sheets of varying thickness were subjected to tensile testing in a nitrogen environment at 77 K. Crazes were detected in the thinnest specimens, but the tendency to craze diminished with increasing specimen thickness. Diffusion of the environment into the skin layer of the specimen, as a proportion of the total thickness of the stressed system, is considered to have a major effect on the probability of crazing. A sandwich model, consisting of plasticized skin layer through diffusion of the environment and unplasticized core, is developed to account for the observations.
In‐source and post‐irradiation polymerization of acenaphthylene in the solid state
Authors: Kücükyavuz Savas , Ülkem Iihan , Göksel Cemile
Published: April 2007

Radiation‐induced solid state polymerization of acenaphthylene was studied by using 60Co γ‐rays. The extent of polymerization at room temperature reached 68% when acenaphthylene was irradiated with a dose of 2–5 MGy. Prolonged exposure to the radiation decreased the molecular weight of the polymers. The post‐polymerization of acenaphthylene was found to occur at relatively high temperatures close to the melting point of acenaphthylene. Absence of an effective termination step allows the enhancement of post‐polymerization at higher temperatures after a limiting conversion is accomplished.
Semi‐batch Processes for Emulsion Polymerisation
Authors: Li B. , Brooks B. W.
Published: April 2007

Essential features and advantages of semi‐batch emulsion polymerisation are described. Variations of polymerisation rate, polymer particle number, particle size, copolymer composition and molecular weight distribution are considered and the use of mathematical models is reviewed. Suggestions for future work, both experimental and modelling, are made.
An explanation of the solubility behaviour of cellulose acetate in various solvents in terms of supermolecular structure formed by introduction of a substituent group into the glucopyranose unit
Authors: Okajima Kunihiko , Kowsaka Keisuke , Kamide Kenji
Published: April 2007

An attempt is made to explain the solubility behaviour of cellulose derivatives with hydrophobic substituent groups towards several solvents in terms of supermolecular structure concepts, such as the degree of breakdown in intramolecular hydrogen bonds and conformational variety in the C1—O—C4 glucoside linkage, which depend on the total degree of substitution 〈〈F〈〈 and the distribution of substituent groups in the anhydroglucose (AHG) unit 〈〈fk〈〈 (k = 2, 3, and 6), and solvation.

For this purpose, cellulose acetate (CA) samples with a wide range of 〈〈F〈〈 values were synthesized and the dependence of supermolecular structural parameters, including Xam(Ck) (k = 3, 6) (degree of breakdown in intramolecular hydrogen bond at Ck position) and Δ1/2(Ck)(k = 1,6) (half value width of Q. carbon NMR peak), on 〈〈F〈〈 or (〈fk〈〈 was investigated. It has been shown that a considerable breakdown in O3—H—O'5 hydrogen bond or allowance of wide variation in chain conformation around the C1—O—C'4 linkage is a minimum condition necessary for CA to dissolve in solvents, irrespective of type of solvent. Water‐solubility of CA is mainly governed by the supermolecular structure induced by the introduction of substituents at the C3 position and number of residual hydroxyl groups at the C6 position. Acetone‐solubility of CA is mainly governed by solvation of the side chain but an intramolecular interaction between acetyl groups and ring oxygen bonds tends to hinder its solubility at high values of 〈〈F〈〈. DMSO behaves as an amphoteric solvent solvating both hydroxyl and O‐acetyl groups in CA molecules.
Synthesis and Characterization of Some Novel Poly(nitroarylates)
Authors: Mansour El‐Sayed M. E. , Kandil Sherif H. , Soliman Mohamed E. M. , Ibrahim Moustafa
Published: April 2007

Various types of poly(nitroarylates) (8–17) were prepared using interfacial polycondensation (IPC) and solution polycondensation (SPC) of 5‐nitroiso‐phthaloyl chloride (la) and 2‐nitroterephthaloyl chloride (2a) with different bisphenols: hydroquinone (3), resorcinol (4), 4.4′‐dihydroxydiphenyl (5), 2,2‐bis(4‐hydroxyphenyl) propane (6) and bis(4‐hydroxyphenyl) sulfone (7). A nitro group was introduced in the polymeric chain in order to improve the properties, solubility and thermal stability of these polymers. Some of the factors affecting the IPC were studied, such as the effect of concentration of the initial components and the role of the solvent. The structures of the poly(nitroarylates) (8–17) were confirmed by elemental analysis, infrared and proton magnetic resonance spectrometry. Thermomechanical analysis (TMA) and thermogravimetric analysis (TGA) of the synthesized polymers were also studied.
Structural analysis of electron beam irradiated ethylene‐vinyl acetate copolymer (EVA) film (II)
Authors: Matsui Toshiro , Shimoda Mitsuya , Osajima Yutaka
Published: April 2007

The crosslinked structure of irradiated ethylene‐vinyl acetate copolymer (EVA) film was examined by means of ESR, IR and pyrolysis‐gas chromatography. The ESR spectrum of 35 Mrad irradiated EVA film with 95g kg−1 vinyl acetate content consisted of a three‐line component with an intensity ratio of 1:2:1, a hyperfine structure coupling of 22.4 G and g factor of 2.0049. Therefore, the spectrum was assigned to the methylene radical with two α protons on the same plane; this radical is formed by loss of a hydrogen atom from the acetoxymethyl group.

In pyrolysing EVA films at 500°C, the yield of acetic acid from 10 Mrad‐150 g kg−1 film significantly decreased compared with that of unirradiated film, and it decreased with increasing crosslinking density.

By measuring the IR spectra of methanolysed EVA films, the following results were obtained: the absorbances at 1740, 1250 and 1050cm−1, attributed to the CO, OCOR and COC groups, respectively, had a marked decrease, whereas the three peaks for 20Mrad film were much stronger than those of unirradiated film. On the basis of these findings, it is suggested that the crosslinking reaction in electron beam irradiated EVA film with lower doses takes place between the acetoxy groups and the main chains.
Rheological and mechanical behaviour of tetraglycidyldiaminodiphenylmethane (TGDDM)/anhydride epoxy systems
Authors: Corcuera M. A. , Andres M. A. , Sarasua R. , Mondragon I.
Published: April 2007

The curing of tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) cured with hexahydrophthalic anhydride, tetrahydrophthalic anhydride and nadic methyl anhydride was studied using static rheological techniques under isothermal conditions in different temperature ranges for each system. 1:1 and 1:0.5 stoichiometric ratios were used in all three TGDDM/anhydride systems analysed. From the gelation times of each system at the different conditions employed activation energies were calculated. Flexural mechanical properties, such as elastic modulus, strength and strain to break, were also investigated for all the three TGDDM/anhydride systems employed for different anhydride weight contents which ranged from 0.5 to 1.34 parts of the anhydride weight corresponding to the stoichiometric composition. Possible reasons to explain the mechanical behaviour shown are discussed.
Anionic copolymers of octanelactam with laurolactam (nylon‐8/12)—IV. Dynamic thermomechanical and mechanical properties
Authors: Arvanitoyannis Ioannis , Kehayoglou Aristides H. , Blanshard John M. V.
Published: April 2007

The thermomechanical and the mechanical properties of a recent series of copolyamides of octanelactam (OL) and laurolactam (LL) (nylon‐8/nylon‐12) were studied. The glass transition temperature (Tg) and melting point (Tm) were determined with dynamic mechanical thermal analyser, and compared to those obtained with differential scanning calorimetry and the activation energy for glass transition was calculated. The copolyamides showed a minimum for tensile strength, yield stress, stress at 100% and modulus and a maximum for elongation at break at the composition 60/40 (OL/LL) which has the lowest crystallinity. Young's modulus against % elongation showed the classification of copolyamides in two groups (rich in OL or LL, respectively).
Miscibility of thermoplastic polyurethane elastomers with chlorine‐containing polymers
Authors: Ann Tae Oan , Han Kyeong Tae , Jeong Han Mo , Lee Sang Won
Published: April 2007

The miscibility behaviours of thermoplastic polyurethane elastomers (TPUs) with chlorine‐containing polymers were studied. Four kinds of TPUs containing 20, 40, 60 and 80wt% of poly(caprolactone) (PCL) diol as a soft segment were used for blending. Poly(vinylidene chloride‐co‐vinyl chloride) (P(VDC‐VC)) with a chlorine content of 70%, poly(vinyl chloride) (PVC) and chlorinated polyethylene (CPE) with a chlorine content of 40% were blended with TPUs to study miscibility. The results of optical clarity observation and thermal characterisation suggest that P(VDC‐VC) was miscible with all the TPUs investigated. PVC was only miscible with TPUs containing 40, 60, 80wt% PCL segment, whereas CPE was immiscible with all the TPUs studied. Tensile measurements showed that all the TPU with 60wt% of PCL segment/chlorine‐containing polymer blends were mechanically compatible.
Polymers based on N‐Aryl methacrylatoethyl carbamate
Authors: Santhana Krishnan P. Gopala , Choudhary Veena , Varma I. K.
Published: April 2007

N‐Aryl methacrylatoethyl carbamate monomers were prepared by reacting phenyl isocyanate/4‐chlorophenyl‐isocyanate and 2‐hydroxyethyl methacrylat, Homopolymerisation and copolymerisation with methyl methacrylate in a tetrahydrofuran solution was carried out using azobisisobutyronitrile/benzoyl peroxide as an initiator at 60°C. Molecular characterisation of polymers was done by intrinsic viscosity determination at 30°C in chloroform and molecular weight determination by gas permeation chromatography using poly(methyl methacrylate) standards. Molecular weight distribution ranged from 1.5 to 2.63. Copolymer composition was determined by using 1H‐NMR. Thermal behaviour of the polymers in a nitrogen atmosphere was evaluated using dynamic thermo‐gravimetry.
The synthesis, characterisation and thermal behaviour of functionalised aryl cyanate ester monomers
Authors: Barton John M. , Hamerton Ian , Jones John R.
Published: April 2007

The syntheses of several functionalised aryl cyanate esters bearing reactive allyl groups are presented. The monomers were purified (to c. 98%) using preparative HPLC and a range of techniques, including heteronuclear nuclear magnetic resonance (NMR) spectroscopy, was employed in their characterisation. A model functionalised aryl cyanate ester was doped with a variety of additives and the resulting thermal behaviour examined using dynamic differential scanning calorimetry (DSC). Furthermore, the postulated co‐reaction of the model functionalised cyanate ester with bis‐maleimides was investigated using heteronuclear NMR and dynamic mechanical techniques.
Phase behavior of poly(ε‐caprolactone)/ poly (vinylidene fluoride) blends
Authors: Jo Won Ho , Park Soon Jong , Kwon Ick Hwan
Published: April 2007

The miscibility of blends of poly (ε‐caprolactone) (PCL)/poly(vinylidene fluoride) (PVDF) was studied by measuring the cloud point, melting point depression and crystallization kinetics. Lower critical solution temperature (LCST) behavior was observed at PCL‐rich compositions, whilst it was not observed at high compositions of PVDF. However it is possible that an LCST could exist below the melting point of PVDF. From analysis of the melting point depression, the Flory interaction parameter x12, was calculated from the Nishi‐Wang equation and the value was found to be‐1.5. The crystallization rate of PCL increased with increasing amount of PVDF in the blend. The spinodal curve for PCL/PVDF blends was simulated by using the lattice‐fluid theory.
Studies on the kinetics of photo‐initiated radical polymerisation of modified epoxy resin
Authors: Chandra R. , Thapliyal B. P. , Sehgal Babita , Soni R. K.
Published: April 2007

The diglycidyl ether of bisphenol‐A (DGEBPA) was modified by acrylic acid. The reaction between the active epoxy groups of DGEBPA and the carboxylic group of acrylic acid was catalysed by triphenyl phosphine to prepare di(vinyl‐2‐hydroxypropanoate) ether of bisphenol‐A (DEBA). The DEBA so formed was co‐polymerised with 2‐ethylhexylacrylate using benzophenone as the photo‐initiator to yield a flexible polymer. The kinetics of the photo‐initiated radical polymerisation was studied by a new technique called differential photo‐calorimetery and the results thus obtained were analysed to determine the Arrhenius activation energy and pre‐exponential factor.
Size exclusion chrormatographic studies on the urethane reaction in hydroxyl‐terminated polymers
Authors: Balagangadharan V. P. , Catherine Korah Bina , Kannan K. G. , Ninan K. N.
Published: April 2007

Size exclusion chromatography (SEC) has been used to study the influence of molecular weight on the reactivity of the hydroxyl group in free radically polymerised hydroxyl‐terminated polybutadiene (HTPB). The HTPB prepolymer was converted into a UV‐absorbing urethane derivative by reaction with phenylisocyanate and the degree of conversion was followed from the UV/DRI (Differential Refractive Index) signal of the derivative using dual detector SEC. Though the overall reaction levelled off at about 70% conversion at room temperature, the time taken by different molecular weight species to attain this level was different. The computed rate constants were larger for the higher molecular weights in a given sample. This is attributed to the polyfunctionality of the higher molecular weight species.
Crystal structure, crystallization kinetics and morphology of a new polyimide
Authors: Cheng Stephen Z. D. , Mittleman Martin L. , Janimak James J. , Shen Dexing , Chalmers Tammy M. , Lien Hsun‐Shen , Tso Chung C. , Gabori Patricia A. , Harris Frank W.
Published: April 2007

A new semicrystalline polyimide has been synthesized from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride and 2,2‐dimethyl‐1,3‐(4‐aminophenoxy)propane. The polymer has a high glass transition temperature of 230°C and a melting temperature of 325°C. Its overall crystallization rate between 240 and 325°C is quite fast (t1/2<10min) and relatively insensitive to the crystallization temperature. Although the degree of crystallinity obtained is dependent on the crystallization conditions, it can be as high as 50%. The polymer's morphology, which was examined with transmission electron microscopy (TEM), has a randomly stacked, ribbon‐like, lamellar texture. Both TEM and polarized light microscopy show that mature spherulites do not develop. The crystal unit cell, which was determined from wide‐angle X‐ray diffraction measurements on highly oriented films, is monoclinic with a = 0.960nm, b = 0.582nm, c = 2.46nm and γ = 81.1°.
Polymerization by phase transfer catalysis. 14. Polyesters from terephthalic acid and related diacids with bisphenol A
Authors: Tagle L. H. , Diaz F. R. , Roncero S.
Published: April 2007

Polyesters were synthesized from the following acid dichlorides: terephthaloyl (I), p‐phenylenediacetyl (II), and p‐phenylenedi(oxyacetyl) (III) and bisphenol A as diphenol under phase transfer conditions. Quaternary ammonium and phosphonium salts were used as phase transfer catalysts in a 1,1,2,2‐tetrachloroethane/NaOH system. Polyesters were characterized by IR and 1H NMR spectroscopy, and elemental analysis. The influence of the catalysts and the reaction time were evaluated by the yields and ηinh values. The influence of the nature of the acid dichloride was higher than that of the catalysts due principally to the aliphatic character of the acid dichlorides II and III.
Polymerization by phase transfer catalysis. 15. Polyesters from tetrachloroterephthalic acid and related diacids with bisphenol A
Authors: Tagle L. H. , Diaz F. R. , De Fuente M. La
Published: April 2007

Chlorinated polyesters were synthesized from the following acid di‐chlorides: 2,3,5,6‐tetrachloro‐1,4‐terephthaloyl (I), 2,3,5,6‐tetrachloro‐1,4‐phenylenediacetyl (II), and 2,3,5,6‐tetrachloro‐1,4‐phenylenedi(oxyacetyl) (III), and bisphenol A, under phase transfer conditions, using several ammonium and phosphonium salts as catalysts and a biphasic CH2Cl2/NaOH system. The influence of the nature of the catalysts and the reaction times were evaluated by the yields and ηinh of the polyesters. The reactivity of the monomers was I<II<III, due to the smaller influence of the tetrachlorinated ring when there is a spacer group between the aromatic ring and the acid chloride group.
Semi‐interpenetrating polymer networks from castor oil‐based polyurethanes and chlorinated rubber
Authors: Parthiban S. , Rajalingam P. , Radhakrishnan Ganga
Published: April 2007

Semi‐interpenetrating polymer networks (semi‐IPNs) were prepared by crosslinking castor oil in the presence of chlorinated rubber. Crosslinking in toluene solution was effected with 2,4‐toluene diisocyanate or hexamethylene diisocyanate at various NCO/OH ratios. The semi‐IPNs were obtained as tough films and were characterized by their mechanical, thermal, morphological and electrical properties.
Preparation and characterization of polymer stabilized polystyrene latex
Authors: Oun Ahmed Mohammed
Published: April 2007

A polystyrene latex was prepared which was stabilized using the most effective stabilizer, i.e. a graft copolymer of polystyrene‐poly(ethylene oxide). The latex and the stabilizer were characterized using infrared, elemental analysis, viscometry, osmometry, electron microscopy and microelectrophoresis techniques. The results show that the polystyrene latex is sterically stabilized and could be used for thermodynamic and kinetic studies.
Abnormalities in electrical and acoustic properties of thermoplastic polyurethane
Authors: Volkova A. V. , Domkin A. N. , Strachov V. V.
Published: April 2007

The temperature dependence of ultrasonic pulse velocity C and specific volume resistance ρv of crystallizing thermoplastic polyurethane (TPUR) was investigated. It was revealed that under certain conditions TPUR acquired abnormally low ρv values and C values uncharacteristic of polymers. An explanation for the observed abnormalities could be based on the assumption of the presence of ‘hot’ electrons in TPUR.
New coordination polymers. III: Oxidation of poly(vinyl alcohol) by permanganate ion in alkaline solutions. Kinetics and mechanism of formation of intermediate complex with a spectrophotometric detection of manganate(vi) transient species
Authors: Hassan Refat M.
Published: April 2007

The kinetics of formation of the [PVA. MnVIO] intermediate complex have been measured by the conventional spectrophotometric technique. The rate of formation of the complex was found to be given by the expression d[Complex]/dt = k1[MnO‐4][PVA−]. The results showed that the rate of formation is dependent on the base concentration. A first‐order reaction in permanganate and fractional order with respect to the poly(vinyl alcohol) (PVA) concentration were observed. The activation parameters have been evaluated and a tentative reaction mechanism has been suggested.
Anionic polymerization of methyl methacrylate initiated by thiophenol
Authors: Takeishi Makoto , Iwasaki Norikazu , Sone Atsushi , Chisaka Yuichi , Sekiya Kenichi , Sato Rikiya
Published: April 2007

Methyl methacrylate (MMA) was polymerized by thiophenol without oxidants. Hydroquinone had no effect on the polymerization, indicating that the polymerization proceeded via a non‐radical process. Since other monomers with an x,β‐unsaturated carbonyl group polymerized similarly, the initiation and propagation were explained by the Michael addition. Radical scavengers such as 1,1‐diphenyl‐2‐picrylhydrazyl(DPPH) and galvinoxyl enhanced the polymerization because of an accompanying radical polymerization initiated by radical species formed by the reaction of them with thiophenol. Aluminium acetylacetonate, which has no effect on radical polymerization, accelerated the thiophenol‐initiated polymerization supporting the postulated mechanism.
Poly(methyl methacrylate) and polyacrylonitrile dispersions stabilized by gelatin
Authors: Stejskal Jaroslav , Kratochvíl Pavel , Urban Josef , Kapur G. S. , Lakshminarayana Y.
Published: April 2007

Methyl methacrylate was polymerized in an aqueous medium in the presence of gelatin using potassium persulfate as initiator. The dispersion mode of polymerization, when the monomer is completely miscible with water, was investigated and compared with an emulsion process, which proceeds at higher monomer concentration. Spherical and relatively uniform polymer particles were formed. Macroscopic precipitation of polymer is prevented by combination of the steric stabilization by grafted gelatin and of repulsive electrostatic interactions from the initiator residues attached to the particle surface. Static and dynamic light scattering have been used to determine the molar mass (molar mass of the whole dispersion particle, MwD ∼ 108‐109 g mol−1) and hydrodynamic radius (RhD ∼ 50‐120 nm) of the particles. The number of particles per unit volume does not depend on overall monomer concentration, and it is higher, and therefore the particle size is smaller, than that observed for the soapless emulsion polymerization. The addition of gelatin may be thus used to modify the particle size.

Acrylonitrile dispersions were prepared under similar conditions. Unlike methyl methacrylate, this monomer does not swell the polymer particles. While poly(methyl methacrylate) particles are spherical and relatively uniform, the polyacrylonitrile dispersions consist of polydisperse aggregates of tiny polymer particles.
Fractional composition of partly hydrolysed polyvinyl acetate and its compatibility with hydroxypropyl methylcellulose in aqueous solutions
Authors: Zilberman E. N. , Lerner F. , Joseph H. M. , Grossman D. , Alon M.
Published: April 2007

Fractionation of partly hydrolysed polyvinyl acetate (PVA) was performed by warming of its aqueous solutions. The following properties of the obtained fractions were determined: viscosity, molecular weight and molecular weight distribution, surface tension, and absorbance in the IR range. The blockiness of the polymer molecules, characterized by their behaviour towards iodine‐containing systems such as I2,‐H3BO3 and I2,‐KI, was estimated. Fractionation of the aqueous solutions of PVA by warming is based mainly on the different internal molecular structure of the separated products, i.e. on the length of the vinyl acetate blocks in the PVA molecules and, to a lesser extent, on the degree of hydrolysis and the degree of polymerization. The more blocklike are the PVA molecules, the less compatible are the polymers in the PVA‐hydroxypropyl methylcellulose (HPMC)‐water system. At phase separation in this sytem the PVA molecules which are not compatible with HPMC are, in the first place, those of the highest blockiness.
Separation characteristics of pervaporation membrane separation processes using modified poly(vinyl alcohol) membranes
Authors: Huang R. Y. M. , Rhim J. W.
Published: April 2007

Modified poly(vinyl alcohol) (PVA) membranes prepared by the ‘solution technique’ were tested for ethanol‐water mixtures by varying the reaction density (Xcr = 0.05, 0.1) at various temperatures. The results are compared with those of PVA membranes (Xcr = 0.05) prepared by the technique of the GFT Company, Germany.
Modification of poly(vinyl alcohol) using maleic acid and its application to the separation of acetic acid‐water mixtures by the pervaporation technique
Authors: Huang R. Y. M. , Rhim J. W.
Published: April 2007

The ‘solution technique’ modification of poly(vinyl alcohol) (PVA) using maleic acid was carried out with the help of triethanolamine/water catalysts. The resulting PVA membranes were characterized by differential scanning calorimetry, infrared spectroscopy, and tensile studies to investigate the reaction between PVA polymer and maleic acid. It was found that the resulting PVA membranes had two portions, branched and crosslinked, and there were no more branched than cross‐linked portions. For the pervaporation separation of the acetic acid‐water system, two reaction densities (Xcr = mole maleic acid per mole monomeric unit of PVA) of 0.05 and 0.1 were studied for the separation of the entire range of mixture compositions at 25° C. The separation factors of the Xcr = 0.05 modified PVA membranes were higher than those of the Xcr 0.1 modified ones and the highest separation factor of 7.80 was obtained at 70wt% water in the feed with the Xcr = 0.05 modified PVA membrane.
Toward reduced bias and increased utility in the assessment of school refusal behavior: The case for diverse samples and evaluations of context
Authors: Lyon Aaron R. , Cotler Sheldon
Published: April 2007

The current article reviews the literature on school refusal behavior. Definitional inconsistencies, the effects of biased assessment processes, and the consequences of the lack of ethnic, racial, and economic diversity in school refusal research samples are highlighted. An increase in the use of low‐income, ethnic minority, community samples in school refusal research is proposed in order to create a more representative and useful literature. Concerns regarding artificial and impractical divisions between the commonly used labels of school refusal and truancy are also discussed. Suggestions are proposed for a new pragmatic framework of school refusal assessment for research and clinical work that utilizes and enhances Kearney's functional approach. The framework has the potential to incorporate the influences of multiple cultural contexts in order to aid professionals from different disciplines in both prevention and early intervention for school refusal in low‐income, ethnic minority populations. Additional suggestions for future direction in school refusal research are also discussed. © 2007 Wiley Periodicals, Inc.
The controlled homogeneous organic solution polymerization of new hydrophilic cationic exo‐7‐oxanorbornenes via ROMP with RuCl2(PCy3)2CHPh in a novel 2,2,2‐trifluoroethanol/methylenechloride solvent mixture
Authors: Rankin David A. , P'Pool Steven J. , Schanz Hans‐Jörg , Lowe Andrew B.
Published: April 2007

The authors detail herein the synthesis and controlled polymerization of a series of new permanently cationic ammonium exo‐7‐oxanorbornene derivatives via ROMP, with the first generation Grubbs' catalyst RuCl2(PCy3)2CHPh, in a novel solvent mixture composed of 1:1 vol/vol 2,2,2‐trifluoroethanol (TFE)/methylene chloride. It is demonstrated that this cosolvent mixture is a convenient reaction medium facilitating the polymerization of hydrophilic substrates by hydrophobic initiators under homogeneous conditions. Homopolymerizations and copolymerizations proceed yielding materials with controlled molecular masses, and narrow molecular mass distributions. It is also demonstrated that this protocol is not limited to the use of TFE as a cosolvent and that additional halogenated alcohols, such as 2,2,2‐trichloroethanol and 1,1,1,3,3,3‐hexafluoroisopropanol are also effective cosolvents for the controlled polymerization of such cationic substrates. Finally, it is demonstrated that the TFE/methylene chloride mixture has no apparent detrimental effect on Grubbs' catalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2113–2128, 2007
Rheological behavior of PET/HDPE in situ microfibrillar blends: Influence of microfibrils' flexibility
Authors: Xu Hong‐Sheng , Li Zhong‐Ming , Wang Song‐Jie , Yang Ming‐Bo
Published: April 2007

Poly(ethylene terephthalate) (PET)/high‐density polyethylene (HDPE) in situ microfibrillar reinforced blends were prepared via a slit die extrusion‐hot stretch‐quenching process. The in situ PET microfibrils contain various contents of a segmented thermoplastic elastomer, Hytrel 5526 (HT), hence having different flexibility as demonstrated by dynamic mechanical analysis. It is interesting that the simple mixing leads to nanoscale particles of the HT phase in PET phase, and the size of the HT particles is almost independent of the HT concentration, as observed from the scanning electron microscope micrographs which show that the microfibrils with different HT concentrations have almost the same diameter and smooth surfaces. The static rheological results by an advanced capillary rheometer show that the entrance pressure drop and the viscosity of the microfibrillar blends both reduced with increasing the microfibrils' flexibility. Furthermore, the data obtained by the temperature scan of the PET/HT/HDPE microfibrillar blends through a dynamic rheometer indicates that the more flexible microfibril leads to lower melt elasticity and slightly decreases the viscosities of blends, presenting a consistent conclusion about influences of the microfibrils' flexibility on the rheological behavior from the static rheometer measurements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1205–1216, 2007
Superantigen natural affinity maturation revealed by the crystal structure of staphylococcal enterotoxin G and its binding to T‐cell receptor Vβ8.2
Authors: Fernández Marisa M. , Bhattacharya Suparna , De Marzi Mauricio C. , Brown Patrick H. , Kerzic Melissa , Schuck Peter , Mariuzza Roy A. , Malchiodi Emilio L.
Published: April 2007

The illnesses associated with bacterial superantigens (SAgs) such as food poisoning and toxic shock syndrome, as well as the emerging threat of purpura fulminans and community‐associated methicillin‐resistant S. aureus producer of SAgs, emphasize the importance of a better characterization of SAg binding to their natural ligands, which would allow the development of drugs or biological reagents able to neutralize their action. SAgs are toxins that bind major histocompatibility complex class II molecules (MHC‐II) and T‐cell receptors (TCR), in a nonconventional manner, inducing T‐cell activation that leads to production of cytokines such as tumor necrosis factor and interleukin‐2, which may result in acute toxic shock. Previously, we cloned and expressed a new natural variant of staphylococcal enterotoxin G (SEG) and evaluated its ability to stimulate in vivo murine T‐cell subpopulations. We found an early, strong, and widespread stimulation of mouse Vβ8.2 T‐cells when compared with other SAgs member of the SEB subfamily. In search for the reason of the strong mitogenic potency, we determined the SEG crystal structure by X‐ray crystallography to 2.2 Å resolution and analyzed SEG binding to mVβ8.2 and MHC‐II. Calorimetry and SPR analysis showed that SEG has an affinity for mVβ8.2 40 to 100‐fold higher than that reported for other members of SEB subfamily, and the highest reported for a wild type SAg‐TCR couple. We also found that mutations introduced in mVβ8.2 to produce a high affinity mutant for other members of the SEB subfamily do not greatly affect binding to SEG. Crystallographic analysis and docking into mVβ8.2 in complex with SEB, SEC3, and SPEA showed that the deletions and substitution of key amino acids remodeled the putative surface of the mVβ8.2 binding site without affecting the binding to MHC‐II. This results in a SAg with improved binding to its natural ligands, which may confer a possible evolutionary advantage for bacterial strains expressing SEG. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Computational proteomics analysis of HIV‐1 protease interactome
Authors: Kontijevskis Aleksejs , Wikberg Jarl E. S. , Komorowski Jan
Published: April 2007

HIV‐1 protease is a small homodimeric enzyme that ensures maturation of HIV virions by cleaving the viral precursor Gag and Gag‐Pol polyproteins into structural and functional elements. The cleavage sites in the viral polyproteins share neither sequence homology nor binding motif and the specificity of the HIV‐1 protease is therefore only partially understood. Using an extensive data set collected from 16 years of HIV proteome research we have here created a general and predictive rule‐based model for HIV‐1 protease specificity based on rough sets. We demonstrate that HIV‐1 protease specificity is much more complex than previously anticipated, which cannot be defined based solely on the amino acids at the substrate's scissile bond or by any other single substrate amino acid position only. Our results show that the combination of at least three particular amino acids is needed in the substrate for a cleavage event to occur. Only by combining and analyzing massive amounts of HIV proteome data it was possible to discover these novel and general patterns of physico‐chemical substrate cleavage determinants. Our study is an example how computational biology methods can advance the understanding of the viral interactomes. Proteins 2007. © 2007 Wiley‐Liss, Inc.
pcaH, a molecular marker for estimating the diversity of the protocatechuate‐degrading bacterial community in the soil environment
Authors: Azhari Najoi El , Chabaud Sylvaine , Percept Anthony , Bru David , Martin‐Laurent Fabrice
Published: April 2007

Microorganisms degrading phenolic compounds play an important role in soil carbon cycling as well as in pesticide degradation. The pcaH gene encoding a key ring‐cleaving enzyme of the β‐ketoadipate pathway was selected as a functional marker. Using a degenerate primer pair, pcaH fragments were cloned from two agricultural soils. Restriction fragment length polymorphism (RFLP) screening of 150 pcaH clones yielded 68 RFLP families. Comparison of 86 deduced amino acid sequences displayed 70% identity to known PcaH sequences. Phylogenetic analysis results in two major groups mainly related to PcaH sequences from Actinobacteria and Proteobacteria phyla. This confirms that the developed primer pair targets a wide diversity of pcaH sequences, thereby constituting a suitable molecular marker to estimate the response of the pca community to agricultural practices. Copyright © 2007 Society of Chemical Industry
Insecticide toxicity and synergism by enzyme inhibitors in 18 species of pest insect and natural enemies in crucifer vegetable crops
Authors: Wu Gang , Miyata Tadashi , Kang Chun Yu , Xie Lian Hui
Published: April 2007

The toxicities of three enzyme inhibitors and their synergistic effects on four insecticides were studied by using the dry film method on field populations of 18 species of insects collected in Jianxin and Shanjie, China, from 2003 to 2005. Meanwhile, the inhibitory effects of these enzyme inhibitors on the activities of acetylcholinesterases (AChE), carboxyesterases (CarE) and glutathione‐S‐transferases (GST), in vivo, were also studied. In general, triphenyl phosphate (TPP) and diethyl maleate (DEM) showed low toxicities to six herbivorous pest insects, four ladybirds and eight parasitoids. Piperonyl butoxide (PB) exhibited low toxicities to the herbivorous pest insects and ladybirds, but high toxicities to the eight parasitoids. The tolerance to the insecticides in 11 pest insects and natural enemies was mainly associated with the tolerance to PB. PB showed the highest synergism on methamidophos, fenvalerate, fipronil and avermectin in nine species of pest insects and natural enemies. In general, TPP and DEM showed significant synergisms to these four insecticides in four parasitoid species. However, in contrast to their effects on the parasitoids, the synergistic effects of TPP and DEM on the four insecticides by TPP and DEM against four pest insects and one ladybird varied depending on the insect species and enzyme inhibitor. Activity of AChE, CarE or GST could be strongly inhibited, in vivo, by PB, TPP or DEM, depending on the insect species and enzyme inhibitors. From the results obtained in this study, mixed‐function oxidase (MFO) was thought to play the most critical role in insect tolerances to the tested insecticides in the field. Low competition existed in the evolution of insecticide resistance in the field populations of parasitoids, as compared with herbivorous pest insects and ladybirds. Possible causes of the high synergistic effects of PB on the four classes of insecticides, based on multiattack on the activity of CarE, GST or AChE in the insect species, are also discussed. Copyright © 2007 Society of Chemical Industry
Effect of Bt cotton expressing Cry1Ac and Cry2Ab, non‐Bt cotton and starvation on survival and development of Trichoplusia ni (Lepidoptera: Noctuidae)
Authors: Li Yuan‐Xi , Greenberg Shoil M , Liu Tong‐Xian
Published: April 2007

Effects of Bollgard II® cotton containing two Bacillus thuringensis var. kurstaki Berliner (Bt) toxin proteins (Cry1Ac and Cry2Ab), non‐Bt cotton (DPL 491) and starvation on survival and development of cabbage looper, Trichoplusia ni (Hübner), were determined in the laboratory. Larvae of the first four larval instars died when they fed on the terminal leaves of Bt cotton plants at 50 days after planting (DAP). However, 51.3% of fifth instars that fed on 50 DAP Bt cotton leaves pupated, and 87.1% of the pupae successfully developed into adults. Of the unfed fifth instars (starved), 55.6% pupated and 88.1% of the pupae emerged. Pupae that developed from larvae fed on Bt cotton leaves and unfed were significantly smaller, being 89.7 and 73.2% of the weight of the pupae that developed from larvae fed on non‐Bt cotton leaves. Leaves of 120 DAP Bt cotton were less toxic to T. ni larvae. When the first instars continuously fed on 120 DAP Bt cotton leaves, 75.9, 60.6, 56.4 and 38.4% of larvae survived to second, third, fourth and fifth instars respectively, and 20.9% pupated and 17.9% successfully became adults. However, it took the surviving first instars 37.1 days to become adults, which was 7.2 and 8.9 days longer than those fed on 50 and 120 DAP non‐Bt cottons respectively. Pupae that developed from larvae that fed on 120 DAP Bt cotton leaves were only 50.9 and 52.6% of the weight of those developed from larvae that fed on 50 and 120 DAP non‐Bt cotton respectively. Non‐Bt cotton, both 50 and 120 DAP, did not exhibit significant effects on larval survival and development, except that the pupae in the 50 DAP non‐Bt cotton treatments developed over a significantly longer time than those in the 120 DAP non‐Bt cotton treatment. Copyright © 2007 Society of Chemical Industry
High temperature electrical conductivity in ZnSe:In and in CdSe:In under selenium vapor pressure
Authors: Lott K. , Shinkarenko S. , Volobujeva O. , Türn L. , Nirk T. , Öpik A. , Nisumaa R. , Kallavus U. , Nõges M. , Mikli V. , Viljus M. , Gorokhova E. , Anan'eva G. , Grebennik A. , Vishnjakov A.
Published: April 2007

High temperature electrical conductivity (HTEC) isotherms and isobars of ZnSe:In and of CdSe:In are compared. There are differencies in In‐doping mechanisms of II–VI compounds. When HTEC isotherms and isobars of ZnSe:In and of CdSe:In, measured under metal component vapour pressure give both n‐type conductivity then differences appear in the results of measurements under the selenium vapor pressure (p). ZnSe:In isotherms in the last case are characterized by the conductivity type conversion but no such drastic change of HTEC type is observed on CdSe:In isotherms. Under the conditions of p, the activation energy of HTEC isobars for ZnSe:In is ΔE ≈ 1.3–1.6 eV and for CdSe:In is ΔE ≈ 1.2 eV. The onefold ionized substitutional In at Zn place is proposed to be compensated by native defects in ZnS:In and in CdSe:In under high p. This native defect may be onefold ionized zinc vacancy for ZnSe:In and twofold ionized cadmium vacancy for CdSe:In. Association of defects occur at lower temperatures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical characterization of He+ irradiated n‐ZnO
Authors: Hayes M. , Auret F. D. , Janse van Rensburg P. J. , Nel J. M. , Wesch W. , Wendler E.
Published: April 2007

ZnO Schottky barrier diodes (SBD's) were fabricated with 20/80/40/80 nm Ti/Al/Pt/Au ohmic contacts on the O face and circular 0.5 mm in diameter 50 nm thick Ru Schottky contacts in the Zn face. The carrier concentration of the ZnO prior to irradiation was approximately 5 × 1016 cm−3. These diodes were irradiated with 1.8 MeV He+ with fluences ranging from 1 × 1012 cm−2 to 2 × 1013 cm−2. Deep level transient spectroscopy (DLTS) was used to study the defects introduced. These measurements revealed that this irradiation introduced a defect with an energy level at 0.55 eV below the conduction band. The introduction rate of this defect for 1.8 MeV He+ ions was calculated to be 220 ± 20 cm−1. This appears to be the same defect that is introduced during proton irradiation of ZnO. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic properties of Fe doped SiC crystals
Authors: Kuryliszyn‐Kudelska I. , Diduszko R. , Tymicki E. , Dobrowolski W. , Grasza K.
Published: April 2007

In this paper we report on the crystal growth and magnetic as well as structural studies of SiC:Fe. SiC crystals were grown by Physical Vapor Transport method. We used Fe enriched source material to dope crystals. The magnetic properties were examined by AC/DC magnetometry. AC magnetic susceptibility as well as DC magnetization measurements revealed ferromagnetic type of magnetic ordering. The structural measurements using powder X‐ray diffraction were performed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evaluation of deep‐impurity governed photoelectrical properties in differently doped CdTe
Authors: Kadys A. , Sudzius M. , Jarasiunas K. , Fochuk P. , Feychuk P. , Hellin M. L. , Verstraeten D.
Published: April 2007

We investigated nonequilibrium carrier generation, transport, and recombination processes in differently doped bulk CdTe crystals by the contactless nonlinear optical technique – the degenerate four‐wave mixing. Doping by Ge, Pb, Sb, Se, Si, or Sn was reached by Bridgman, whereas vanadium doped CdTe ingots were grown by the vertical Bridgman–Stockbarger method. Some crystals of CdTe:Sb as well as CdTe:Ge were cut from the different parts of ingots. At 1064 nm below bandgap excitation by light interference pattern and varying the grating period, we measured the space‐charge field dependent values of effective diffusion coefficient and determined a sign of the photogenerated carriers. In samples, doped with V, Sb, Si, or Ge, the experiments revealed that the majority carriers are electrons, while in Pb, Se, Sb, Ge, or Sn‐doped crystals – the holes. Strong feed‐back effect of the light‐created SC electric field to subnanosecond carrier dynamics was observed in the crystals doped with Ge, Pb, Sb, or Sn. Carrier lifetimes longer than 40 ns together with long living SC field component makes the Ge, Sb, or Sn doped crystals as very promising photorefractive media for real time holographic devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)