bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of carboxylic additives on the polymerization characteristics of nylon‐6 reactors with diffusional water removal
Authors: Ahn Young‐Cheol
Published: August 2002

The effects of carboxylic acid on the polymerization characteristics of nylon‐6 were investigated in reactor models that consist of a continuous‐flow stirred tank reactor (CSTR) and a tubular reactor with a diffusional water‐removal system, which are connected in series. Mathematical models for the CSTR and the tubular reactor were established and solved by numerical methods. In the CSTR, with an increase of the feed acetic acid content, the monomer conversion, and the molecular weights are increased. In the tubular reactor, the acid behaves like a catalyst and a modifier at the same time in the polymerization of nylon 6. The effects of the feed acetic acid content and the diffusional water removal on the zeroth, first, and second moments and the polydispersity index of the polymer were investigated. The polydispersity index is greatly affected by the feed content of carboxylic acid in the CSTR, but it finally approaches to values of ∼ 2 in the tubular reactor. The diffusional water removal is found to have little effect on the polydispersity index of the polymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1226–1237, 2001
Effects of polymer concentration and zone drawing on the physical properties of poly(N‐vinylcarbazole) thick film
Authors: Lyoo Won Seok , Kim Joon Ho , Yoon Won Sik , Kim Dae Heum , Choi Jin Hyun , Ji Byuhg Chul , Lee Chul Joo
Published: August 2002

To check the possibility of zone‐drawn poly(N‐vinylcarbazole) (PVK) thick films as base materials of photorefractive polymers, the effects of the initial polymer concentration and zone drawing on the physical properties of PVK film were investigated. PVK films were prepared from 1,1,2,2‐tetrachloroethane (TCE) solutions with different initial concentrations. To investigate the drawing behavior of the PVK films with different solution concentrations, the films were drawn under various zone‐drawing conditions. Through a series of experiments, it turned out that the initial concentration of the PVK solution in TCE caused significant changes in the draw ratio of the PVK film, that is, the zone draw ratios of the film at an initial concentration of 9.8 g/dL exhibited their maximum values and gradually decreased at higher or lower concentrations. Thus, it was determined that the initial concentration of 9.8 g/dL is the optimum polymer concentration to produce the maximum draw ratio in this work. The lightness (whiteness) of the zone‐drawn PVK film was much higher than that of the hot‐drawn PVK film, resulting from diminishing microcrystallite formation, crystallization, and back‐folding of molecular chains by zone drawing. Moreover, the mechanical properties of the PVK film were dominantly improved by introducing a zone‐drawing technique, maintaining lightness of the zone‐drawn film to a similar degree as that of the undrawn film. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1297–1304, 2001
Poly(styrene‐alt‐maleic acid)–metal complexes with divalent metal ions. synthesis, characterization, and physical properties
Authors: Rivas Bernabé L. , Seguel Gloria V. , Geckeler Kurt E.
Published: August 2002

Polymer–metal complexes of the alternating copolymer styrene and maleic acid with Cu(II), Co(II), Ni(II), and Zn(II) were synthesized and characterized by elemental analysis, infrarred and electronic spectra, and thermogravimetry. In addition, magnetic measurements were performed and the electrical conductivity was studied at different temperatures. Semiempirical calculations at the PM 3 level were carried out to elucidate the geometrical arrangement of the polychelates. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1310–1315, 2001
Synthesis and characterization of novel poly(aryl ether ketone ketone)s containing the o‐dibenzobene moiety
Authors: Xuan Yingnan , Gao Yue , Huang Yong , Jian Xigao
Published: August 2002

The synthesis of a novel chloro monomer containing the 1,2‐dibenzoylbenzene moiety was described. The chloro monomer was reacted with 4‐(4‐hydroxyphenyl)‐1(2H)‐phthalazinone compound in the presence of excess anhydrous potassium carbonate in an aprotic solvent (Sulfolane), and high molecular weight amorphous poly(aryl ether ketone ketone) was synthesized. The polymers with high glass transition temperature were soluble in solvents such as chloroform and nitrobenzene at room temperature and easily cast into flexible, colorless, and transparent films. The 5% weight loss of the polymers was >400 °C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1487–1492, 2001
Dynamic adsorption behaviors between Cu2+ ion and water‐insoluble amphoteric starch in aqueous solutions
Authors: Chan Wu‐Chung , Wu Jun‐Yi
Published: August 2002

Dynamic adsorption behavior between Cu2+ ion and water‐insoluble amphoteric starch was investigated. The sorption process occurs in two stages: external mass transport occurs in the early stage and intraparticle diffusion occurs in the long‐term stage. The diffusion rate of Cu2+ ion in both stages is concentration dependent. In the external mass‐transport process, the diffusion coefficient (D1) increases with increasing initial concentration in the low‐ (1 × 10−3‐4 × 10−3M) and high‐concentration regions (6 × 10−3‐10 × 10−3M). The values of adsorption activation energy (kd1) in the low‐ and high‐concentration regions are 15.46–24.67 and −1.80 to −11.57 kJ/mol, respectively. In the intraparticle diffusion process, the diffusion coefficient (D2) increases with increasing initial concentration in the low‐concentration region (1 × 10−3‐2 × 10−3M) and decreases with increasing initial concentration in the high‐concentration region (4 × 10−3‐10 × 10−3M). The kd2 values in the low‐ and high‐concentration regions are 9.96–15.30 and −15.53 to −10.71 kJ/mol, respectively. These results indicate that the diffusion process is endothermic in the low‐concentration region and is exothermic in the high‐concentration region for both stages. The external mass‐transport process is more concentration dependent than the intraparticle diffusion process in the high‐concentration region, and the dependence of concentration for both processes is about equal in the low‐concentration region. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2849–2855, 2001
Water‐soluble poly(vinyl alcohol) grafted with propylene oxide and epichlorohydrin: Characterization, mechanical properties, and model reactions
Authors: Carlotti Stéphane J. , Giani‐Beaune Olivia , Schué François
Published: August 2002

Poly(vinyl alcohol) (PVA) prepared by full hydrolysis of poly(vinyl acetate) was etherified with propylene oxide and epichlorohydrin. The reaction was done in water with sulfuric acid or sodium hydroxide. Previously, model reactions were carried out on propan‐2‐ol, pentan‐3‐ol, and pentan‐2,4‐diol in order to make the NMR characterization of grafted PVA easier. The new materials were also characterized by DSC and mechanical tests. A determination of their solubility in cold water was done as well. Generally, the prepared polymers showed excellent solubility in water at 10°C and a very low glass‐transition temperature. Consequently, the properties of tension, elongation, elasticity, and resistance were improved. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2868–2874, 2001
Morphological development of impact polypropylene produced in gas phase with a TiCl4/MgCl2 catalyst
Authors: Debling Jon A. , Ray W. Harmon
Published: August 2002

This article reports on a comprehensive study of the reaction kinetics, particle morphology development, and polymer properties of impact polypropylene produced in gas phase with a TiCl4/MgCl2 catalyst. Experiments were conducted over a range of copolymerization times, temperatures, monomer compositions, and hydrogen levels. The catalyst was found to exhibit a decay‐type reaction rate for ethylene and propylene, but the presence of both monomers together caused an activation of the catalyst. Copolymer composition was constant over reaction time. Hydrogen was found to reversibly enhance the rate of propylene polymerization but to have no effect on ethylene. Microscopy provided evidence that the copolymer phase segregates from the homopolymer during polymerization. As copolymer content increased, product bulk density decreased because of the presence of sticky material on the particle surface. However, even at 70 wt % copolymer, enough pores were present in the particle to prevent monomer diffusion limitations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3085–3106, 2001
Effect of tacticity of poly(methyl methacrylate) on the miscibility with poly(vinyl pyrrolidone)
Authors: Hsu Wen‐Ping
Published: August 2002

Isotactic, atactic, and syndiotactic poly(methyl methacrylates) (PMMA) (designated iPMMA, aPMMA, and sPMMA) with approximately the same molecular weight were mixed separately with poly(vinyl pyrrolidone) (PVP) primarily in chloroform to make three polymer blend systems. Differential scanning calorimetry (DSC) was used to study the miscibility of these blends. The results showed that the tacticity of PMMA has a definite impact on its miscibility with PVP. The aPMMA/PVP and sPMMA/PVP blends were found to be miscible because all the prepared films showed composition‐dependent glass‐transition temperatures (Tg). The glass‐transition temperatures of the aPMMA/PVP blends are equal to or lower than weight average and can be qualitatively described by the Gordon–Taylor equation. The glass‐transition temperatures of the other miscible blends (i.e., sPMMA/PVP blends) are mostly higher than weight average and can be approximately fitted by the simplified Kwei equation. The iPMMA/PVP blends were found to be immiscible or partially miscible based on the observation of two glass‐transition temperatures. The immiscibility is probably attributable to a stronger interaction among isotactic MMA segments because its ordination and molecular packing contribute to form a rigid domain. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3190–3197, 2001
Synthesis and characterization of novel hydroxyl‐terminated NN–bonded resins
Authors: Sridhara K. , Jain S. R.
Published: August 2002

Novel resins containing carbonyl or thiocarbonyl moiety; NN bonds; ethereal linkage; and terminal hydroxyl groups, that is, bis(bisvanillincarbonohydrazone‐4′‐oxy)butane 1,4‐diyldiether and bis(bisvanillinthiocarbonohydrazone‐4′‐oxy)butane 1,4‐diyldiether, have been synthesized by condensing bisvanillincarbono‐ and bisvanillinthiocarbono‐hydrazone, respectively, with 1,4‐dibromobutane. The resins were characterized by elemental and hydroxyl equivalent analyses, infrared and 1H– and 13C–NMR spectra, and other properties relevant to their use as propellant binders, such as calorific value, thermal analysis, viscosity, and burning rate measurements. Both these resins have convenient viscosity, indicating their suitability as binders for processing high solid loading, at slightly above room temperature. The resins could be cured easily with toluene diisocyanate and glycerol. The DTA–TG data show that the cured samples start to decompose exothermically at relatively low temperatures, in the range around 160°C. The resins ignite immediately on coming in contact with pure nitric acid, indicating their hypergolic nature. The burning rates of the ammonium perchlorate–based propellant compositions having these resins as binders are much higher than those processed with a conventional butadiene binder. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3204–3211, 2001
CHT and TTT curing diagrams of polyflavonoid tannin resins
Authors: Garnier S. , Pizzi A.
Published: August 2002

TTT and CHT curing diagrams for tannin‐based adhesives were built by thermomechanical analysis (TMA) by following the in situ hardening directly in a wood joint, and the curve trends observed were similar to those previously observed for synthetic polycondensation resins on lignocellulosic substrates. Of the parameters that most influence the relative position of vitrification and gel curves on the diagrams (i.e., where the influence has been quantified), chief among them is the reactivity of the tannin with formaldehyde and any factor influencing it: thus, the inherent higher reactivity of the A‐ring of the tannin (such as in procyanidins versus prorobinetinidins) and the pH of the tannin solution. The percentage formaldehyde hardener has some influence in CHT diagrams, especially for the slower‐reacting tannins, but practically no influence in TTT diagrams within the 4–10% formaldehyde range used. As in the case of synthetic polycondensation adhesive resins, regression equations relating the internal bond strength of a wood particleboard, prepared under controlled conditions, with the inverse of the minimum deflection, obtained by constant heating rate TMA of a wood joint during resin cure, have been obtained for the two types of tannins of lower reactivity (profisetinidins/prorobinetinidins) but not for the faster‐reacting procyanidin and prodelphinidin tannins. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3220–3230, 2001
Synthesis and properties of high‐performance and good water‐soluble melamine–formaldehyde resin
Authors: Su Lihong , Qiao Shengru , Xiao Jun , Tang Xuan , Zhao Guodong , Fu Shengwang
Published: August 2002

In this article, high‐sulfonated melamine–formaldehyde (HSMF) resins were prepared with a sulfite/melamine (S/M1.5) molar ratio. During the sulfonation process, the reaction temperature and the added velocity of sodium bisulfite affecting the properties of the resin were studied. In the condensation stage, where the pH range is 6.0 and the temperature is about 25°C, the condensation time was prolonged above 24 h. The stability and water solubility of the resin was improved greatly. It is an effective superplasticizer at small dosages of admixture. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3268–3271, 2001
Preparation of polyvinyl alcohol hydrogel through the selective complexation of amorphous phase
Authors: Hari P. R. , Sreenivasan K.
Published: August 2002

Several methods for the preparation of polyvinyl alcohol (PVA) hydrogel are being reported in the literature. In this communication a new, simple, and mild complexation reaction using phenyl boronic acid, leading to a highly elastic PVA hydrogel, is addressed. It is found that the inherent crystalline property of the semicrystalline PVA is retained by the complexation reaction, which is confined to the amorphous region. An enhanced mechanical property, particularly in the wet condition, is observed after the modification resulting from the intact crystallinity. Also, the inherent nontoxic characteristic property of PVA is unaffected upon this complexation reaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 143–149, 2001
Water‐soluble polymers. LXXXII. Shear degradation effects on drag reduction behavior of dilute polymer solutions
Authors: Cowan Martin E. , Hester Roger D. , Mccormick Charles L.
Published: August 2002

Drag reduction measurements were conducted on extensively characterized poly(ethylene oxide) and poly(acrylamide) utilizing a fully automated rotating disk rheometer equipped with an optical tachometer, torque transducer, and software allowing real‐time data acquisition. The instrument sensitivity allowed the study of concentrations as low as 0.1 ppm. In addition, previously immeasurable concentration‐ and time‐dependent shear degradation effects were readily observed. A power law equation was shown to adequately correlate the percentage of drag reduction and the volume fraction for each polymer. Furthermore, an empirical shift factor was utilized to superimpose data from all the systems that were studied. By conducting measurements in the proper concentration and time domains, it was possible to extract the minimal concentration for the maximum drag reduction efficiency in the absence of shear degradation. The resulting values were significantly higher than those previously reported by our laboratories for poly(ethylene oxide) and poly(acrylamide). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1211–1221, 2001
Kinetic studies on styrene–divinylbenzene copolymerization by suspension technique
Authors: Kiatkamjornwong Suda , Chientachakul Panomsak , Prasassarakich Pattarapan , Damronglerd Somsak
Published: August 2002

Kinetic studies on styrene and divinylbenzene (DVB) copolymerization by the suspension technique in a toluene diluent initiated by benzoyl peroxide are reported. Evaluation of the important reaction parameters is carried out. The crosslinked styrene–DVB copolymers can absorb toluene to a maximum swelling ratio of 17. The absorption/desorption took place instantaneously and reached the maximum value within 10 min, and it could be repeated many times, yet gave the consistent result. Rate equations evaluated by both integral and differential methods are investigated. High monomer orders of 1.5–2.3 were obtained. The activation energy for the polymerization was about 40 kcal/mol−1. Autoacceleration was found even at low conversions. The acceleration was influenced by both monomer, crosslinker, and initiator concentrations. The integral and differential methods for the rate evaluation were compared, and the relationship between the rate equation and polymerization behavior was elucidated. The kinetic orders determined for this copolymerization show considerable deviation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1521–1540, 2001
Synthesis and characterization of two polytrimellitamideimide series with different segment order by direct polycondensation
Authors: Yang Chin‐Ping , Wei Chi‐Shu
Published: August 2002

Poly(amide–imide) (PAI) could be synthesized in regular segment order from trimellitic anhydride (TMA) and various aromatic diamines. By different processes, PAIh‐h‐t‐t containing alternating (amide–amide)–(imide–imide) sequences and PAIh‐t containing amide–imide sequences could be obtained through direct polycondensation. Comparison of PAIh‐h‐t‐t and PAIh‐t, which had different sequence orders and were prepared from TMA and 12 diamines, showed that the latter had better solubility and needed less quantity of solvent and salt (CaCl2) during polymerization, but both two series PAI using p‐substituted diamines (e.g., p‐phenylenediamine) showed poor solubility. Series PAIh‐h‐t‐t possessed larger initial modulus but smaller elongation at break than series PAIh‐t. For the thermal properties, most of series PAIh‐t had glass transition temperatures higher than corresponding series PAIh‐h‐t‐t, but these two series were similar in the 10% weight loss temperatures and the char yields at 800°C in nitrogen. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1556–1567, 2001
Effect of blending polyethersulfone on the cure kinetics and physical properties of dicyanate resin
Authors: Kim Dae Su , Lee Seok Kyu
Published: August 2002

The curing behavior and thermomechanical properties of dicyanate/polyethersulfone (PES) blends were investigated. Differential scanning calorimetry (DSC) was used to study the curing behavior of the dicyanate/PES blends. A second‐order autocatalytic reaction mechanism was used to describe the cure kinetics of the blends. The reaction kinetic parameters were determined by fitting DSC conversion data to the kinetic equation. The main glass‐transition temperatures of the blends decreased with increasing PES content. Two glass‐transition temperatures indicating phase‐separated morphology of the blends were observed. The thermal decomposition behavior of the blends was measured using thermogravimetric analysis. Mechanical and electrical properties of the blends were investigated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1952–1962, 2001
Sorption of chromium (VI) by spent grain under batch conditions
Authors: Low Kun‐She , Lee Chnoong Kheng , Low Choy Hoong
Published: August 2002

Batch experiments were performed to evaluate the ability of spent grain to remove chromium (VI) from aqueous solution. Parameters investigated include pH, contact time, sorbent dosage, agitation rate, and the presence of other anions. Application of the Langmuir isotherm to the Cr(VI)–spent grain system provided a maximum sorption capacity of 18.94 mg/g. This value compares favorably with other reported values for low‐cost materials. Anions such as phosphate, arsenate, nitrate, and sulfate were antagonistic toward the uptake of Cr(VI) by spent grain. It was successful in removing Cr(VI) from a sample of electroplating waste. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2128–2134, 2001
Synthesis of calcium‐containing methacrylate resin
Authors: Abraham Elizabeth K. , Francis Anju , Ramesh P. , Joseph Roy
Published: August 2002

The calcium salt of p‐aminobenzoic acid [p‐ABA(Ca)] was reacted with epichlorohydrin to yield the multifunctional epoxy resin. The epoxy resin was characterized by IR spectroscopy, epoxy equivalent, calcium estimation, high performance liquid chromatography (HPLC) and refractive index. The epoxy resin was further reacted with methacrylic acid to yield the calcium containing methacrylate resin, which was characterized by IR, hydroxyl value, iodine value, HPLC and refractive index. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2342–2346, 2001
Semicontinuous emulsion polymerization of styrene–butyl acrylate–methacrylic acid with high solid content
Authors: Tang Chuanbing , Chu Fuxiang
Published: August 2002

High‐solid‐content (>60 wt %) lattices of styrene (St), butyl acrylate (BA), methacrylic acid (MMA), and N‐hydroxymethacrylic amide (NMA) were prepared through semicontinuous emulsion polymerization. In order to obtain high‐solid‐content lattices with low viscosity, the intermediate emulsion (IE) of the two‐stage pathway had to have viscosity kept low, and so the amount of surfactant for the second stage was about 5–6 wt %. The relationships between IE viscosity and coagulum formation and between surfactant concentration and viscosity are discussed in this article. Particle size and particle size distribution (PSD) were investigated and are also discussed. Lattices through the two‐stage pathway were found to have a bimodal PSD and good mechanical and chemical stability. However, lattices through the one‐stage pathway had a narrow PSD and low mechanical and chemical stability. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2352–2356, 2001
Characterization of styrene/methacrylic acid copolymers by 2D‐NMR spectroscopy
Authors: Brar A. S. , Hekmatyar S. K.
Published: August 2002

Styrene/methacrylic acid copolymers were prepared by free‐radical photopolymerization using the uranyl nitrate ion as the initiator. The copolymer composition was determined from 1H‐NMR spectroscopy. The comonomer reactivity ratios determined using Kelen Tudos and nonlinear error in variable methods (EVM) are rm = 0.61 ± 0.05 and rs = 0.14± 0.07. The broad and overlapping 1H‐NMR spectrum was assigned using the help of 2D TOCSY and NOESY experiments. These methods were used to ascertain the various geminal, vicinal, and spatial couplings between the protons. The methyl and methine protons also show configurational and compositional sensitivity. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2444–2453, 2001
Study of different types of monomer emulsion feedings to semibatch emulsion polymerization reactors
Authors: Sajjadi S.
Published: August 2002

Semibatch emulsion polymerization processes with a monomer emulsion feed are of great importance in both academia and industry. Monomer emulsion feeds can be applied to semibatch reactors using either a stream of an emulsified monomer or two streams of a neat monomer feed and an aqueous solution of an emulsifier. The effect of the feeding policy on the rate of polymerization and on the secondary particle formation was studied for a seeded semibatch emulsion polymerization of styrene. When a single‐stream monomer emulsion feed is applied to a semibatch process, the monomer‐swollen micelles formed in the feed might become the locus of initiation upon entering the reaction vessel. Under the conditions of this study, the application of monomer emulsion feed in either one stream or two streams did not result in secondary particle formation. The incoming monomer‐swollen micelles were disintegrated to supply emulsifier molecules for the stability of growing particles, before they can capture radicals and become polymer particles. The rate of polymerization was found to be independent of the way that the monomer emulsion feed is added. In the absence of nitrogen, the rate of polymerization decreased more appreciably for the monomer emulsion feed, due to the oxygen dissolved in the emulsified monomer. The number of particles, however, was not affected by the purging policy. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2472–2477, 2001
Rheological and mechanical properties of polycarbonate–liquid‐crystalline polymer blends with controlled chemical reactions
Authors: Bum Seung , Kil  , Ok O , Park  , Yoon Kwan Han
Published: August 2002

Chemical reactions can occur during the melt blending of polymers containing an ester group because ester groups are usually unstable at high temperatures; this instability generally deteriorates the mechanical properties of blends. Here, effects of chemical reactions on the rheological and mechanical properties of polycarbonate (PC)/liquid‐crystalline polymer (LCP) blends are carefully investigated to determine a method for minimizing such undesirable impacts. For comparison, a physical blend, in which chemical reactions were minimized, was prepared at 300 °C in a twin‐screw extruder. Both shear viscosity and complex viscosities of reactive blends were lower than those of physical blends, being almost proportional to [Mw]3.4 as a result of depolymerization and transesterification. Because of the enhanced miscibility, the tensile modulus of reactive blends increased compared with that of physical blend, according to the increase in the degree of incorporation (DI). It was also possible to increase tensile modulus if triester was added to the reactive blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2799–2807, 2001
Kinetic interpretation of influence of sodium chloride concentration and temperature on xanthan gum dispersion flow model
Authors: Dolz M. , Hernández M. J. , Delegido J.
Published: August 2002

The present study derives a fixed‐concentration (0.4%) xanthan gum dispersion flow model for different molar concentrations of sodium chloride (0–0.25M) and different temperatures (20–70°C). The Ostwald–de Waele model is used in all cases. A temperature rise reduces the shear‐thinning characteristics of the systems, although the power law index is much less sensitive to changes in temperature when NaCl is added, even in very small amounts. The lowest consistency values correspond to the dispersions formulated in the absence of salt, the highest values are observed for molar values of ≥0.15, and there are decreases in consistency upon raising the temperature in all cases. The viscous behavior of the dispersions is interpreted using the Eyring equation. The activation energy and the free volume decrease when the shear rate is increased. The addition of NaCl, regardless of the molar concentration involved, provokes an important decrease of the activation energy. The free volume is independent of the molar concentration of NaCl for molar values >0.025. These results are related to the structure of the dispersions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 332–339, 2002
Electrochromism of nickel oxide thin film with polymer gel electrolyte
Authors: Tamai Toshiyuki , Chigane Masaya , Matsukawa Kimihiro , Ishikawa Masami , Inoue Hiroshi
Published: August 2002

Polymer gel electrolytes were investigated for an electrochromic device (ECD) using nickel oxide thin film. Poly(ethylene oxide) (PEO) derivatives were cross‐linked and swelled in KOH–aqueous solution giving a hydrogel electrolyte. The ECD containing the uniformly cross‐linked hydrogel showed good result in electrochromic switching performance. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1305–1308, 2002
Peptides that elicit midgut stem cell differentiation isolated from chymotryptic digests of hemolymph from Lymantria dispar pupae
Authors: Loeb Marcia J. , Jaffe Howard
Published: August 2002

Isolated stem cells of Heliothis virescens, cultured in vitro, were induced to differentiate by Midgut Differentiation Factors 3 and 4. These were peptides identified from a chymotrypsin digest of hemolymph taken from newly pupated Lymantria dispar. Partial purification was obtained by filtration through size exclusion filters. The most active preparation was subsequently subjected to a series of 3 Reverse Phase‐HPLC procedures. Partial sequences of the peptides were identified via automated Edman degradation as the nanomers EEVVKNAIA‐OH (MDF 3) and ITPTSSLAT‐OH (MDF 4). These sequences were commercially synthesized. The synthetic compounds proved active in a dose‐dependent manner. Stem cells responded to synthetic MDF 3 and MDF 4 as they did to previously identified peptides MDF 1 and 2, which have quite different amino acid sequences. All of the 4 MDFs administered singly induced statistically similar differentiation responses at 2 × 10–8, 2 × 10–9, and 2 × 10–10 M. However, pairs of the 4 MDFs produced even more differentiation, the same response as one alone, no response, or were inhibitory, dependent on the MDF pair and its concentration. The data suggests complicated receptor interactions. Arch. Insect Biochem. Physiol. 50:85–96, 2002. Published 2002 Wiley‐Liss, Inc.
Captopril, a specific inhibitor of angiotensin converting enzyme, enhances both trypsin and vitellogenin titers in the grey fleshflyNeobellieria bullata
Authors: Vandingenen A. , Hens K. , Macours N. , Zhu W. , Janssen I. , Breuer M. , De Loof A. , Huybrechts R.
Published: August 2002

A strong and constitutive angiotensin converting enzyme‐ or ACE‐like activity was demonstrated in the hemolymph of the adult grey fleshflyNeobellieria bullata. In a competition assay, theN. bullatatrypsin modulating oostatic factor (Neb‐TMOF) was confirmed to be an in vitro substrate for this circulatingNeb‐ACE. Oral uptake of captopril, a selective and specific inhibitor of ACE, resulted in a complete phenotypic knockout of circulating ACE activity. When compared with control animals, captopril‐fed female flies showed an increase in the liver meal–induced trypsin peak in the midgut and elevated levels of protein meal–induced yolk polypeptides in the hemolymph. The latter effect was not due to a slower vitellogenin uptake by the ovaries, because oocyte growth was not affected by the captopril treatment. The apparent synergism between the demonstrated ACE functionality and the previously reported effects of the oostatic peptideNeb‐TMOF are discussed in the context of our recent finding thatNeb‐TMOF represents a prime candidate for being the first known in vivo substrate for circulating insect ACE. Arch. Insect Biochem. Physiol. 47:161–167, 2001. © 2001 Wiley‐Liss, Inc.
Alluvium and geophysical prospection
Authors: Weston D. G.
Published: August 2002

The use of fluxgate gradiometry to investigate archaeological features under >1 m of alluvium is a known problem. However, the frequent opinion that gradiometry has no role in the alluvial environment is incorrect. It is more accurate to say that the results of geophysical surveys are highly variable, as it is often overlooked that the survey results provide other information, most notably of a palaeoenvironmental nature. Four brief case studies are used to illustrate this point. These examples are drawn from geophysical surveys in the valleys of the River Trent, River Tame and River Great Ouse in the English Midlands. Copyright © 2001 John Wiley & Sons, Ltd.
Using statistical and contextual information to identify two‐ and three‐character words in Chinese text
Authors: Khoo Christopher S.G. , Dai Yubin , Ee Loh Teck
Published: August 2002

New statistical formulas were developed for identifying two‐ and three‐character words in Chinese text. The formulas were constructed by performing stepwise logistic regression using a sample of sentences that had been manually segmented. For identifying two‐character words, the relative frequency of the adjacent characters and the document frequency of the overlapping bigrams were found to be significant factors. These provide information about the immediate neighborhood or context of the character string. Contextual information was also found to be significant in predicting three‐character words. Local information (the number of times the bigram or trigram occurs in the document being segmented) and the position of the bigram/trigram in the sentence were not found to be useful in identifying words. The new formulas, called contextual information formulas, were found to be substantially better than the mutual information formula in identifying two‐ and three‐character words. Using the contextual information formulas for both two‐ and three‐character words gave significantly better results than using the formula for two‐character words alone. The method can also be used for identifying multiword terms in English text.
Brief exposure to a 50 Hz, 100 μT magnetic field: Effects on reaction time, accuracy, and recognition memory
Authors: Podd John , Abbott Jeana , Kazantzis Nikolaos , Rowland Al
Published: August 2002

The present study investigated both the direct and delayed effects of a 50 Hz, 100 μT magnetic field on human performance. Eighty subjects completed a visual duration discrimination task, half being exposed to the field and the other half sham exposed. The delayed effects of this field were also examined in a recognition memory task that followed immediately upon completion of the discrimination task, Unlike our earlier studies, we were unable to find any effects of the field on reaction time and accuracy in the visual discrimination task. However, the field had a delayed effect on memory, producing a decrement in recognition accuracy. We conclude that after many years of experimentation, finding a set of magnetic field parameters and human performance measures that reliably yield magnetic field effects is proving elusive. Yet the large number of significant findings suggests that further research is warranted. Bioelectromagnetics 23:189–195, 2002. © 2002 Wiley‐Liss, Inc.
Regulation of cell size in growth, development and human disease: PI3K, PKB and S6K
Authors: Kozma Sara C. , Thomas George
Published: August 2002

It has generally been observed that cells grow to a certain size before they divide. In the last few years, the PI3K signal transduction pathway has emerged as one of the main signaling routes utilized by cells to control their increase in size. Here we focus on two components of this pathway, PKB and S6K, and briefly review the experiments that initially uncovered their roles in cell size control. In addition, we discuss a number of recent observations suggesting that the generic models used to describe this pathway to date may have been oversimplified. Indeed, recent observations in Drosophila and mouse support a more complex interaction between these signaling components in development. Finally, we have utilized two contemporary studies involving PKB‐ and S6K‐deficient mice as a paradigm to underscore the importance of cell size and to accurately delineate the connections between signaling pathways for human disease, such as diabetes mellitus. BioEssays 24:65–71, 2002. © 2002 John Wiley & Sons, Inc.
Differential interactions of antitumor antibiotics chromomycin A3 and mithramycin with d(TATGCATA)2 in presence of Mg2+
Authors: Chakrabarti Sukanya , Mir Mohd. Ayoub , Dasgupta Dipak
Published: August 2002

The antitumor antibiotics chromomycin A3 (CHR) and mithramycin (MTR) are known to inhibit macromolecular biosynthesis by reversibly binding to double stranded DNA with a GC base specificity via the minor groove in the presence of a divalent cation such as Mg2+. Earlier reports from our laboratory showed that the antibiotics form two types of complexes with Mg2+: complex I with 1:1 stoichiometry and complex II with 2:1 stoichiometry in terms of the antibiotic and Mg2+. The binding potential of an octanucleotide, d(TATGCATA)2, which contains one potential site of association with the above complexes of the two antibiotics, was examined using spectroscopic techniques such as absorption, fluorescence, and circular dichroism. We also evaluated thermodynamic parameters for the interaction. In spite of the presence of two structural moieties of the antibiotic in complex II, a major characteristic feature was the association of a single ligand molecule per molecule of octameric duplex in all cases. This indicated that the modes of association for the two types of complexes with the oligomeric DNA were different. The association was dependent on the nature of the antibiotics. Spectroscopic characterization along with analysis of binding and thermodynamic parameters showed that differences in the mode of recognition by complexes I and II of the antibiotics with polymeric DNA existed at the oligomeric level. Analysis of the thermodynamic parameters led us to propose a partial accommodation of the ligand in the groove without the displacement of bound water molecules and supported earlier results on the DNA structural transition from B → A type geometry as an obligatory requirement for the accommodation of the bulkier complex II of the two drugs. The role of the carbohydrate moieties of the antibiotics in the DNA recognition process was indicated when we compared the DNA binding properties with the same type of Mg2+ complex for the two antibiotics. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 131–140, 2001
Model peptide studies of sequence regions in the elastomeric biomineralization protein, Lustrin A. I. The C‐domain consensus—PG—, —NVNCT—motif
Authors: Zhang Bo , Wustman Brandon A. , Morse Daniel , Evans John Spencer
Published: August 2002

The lustrin superfamily represents a unique group of biomineralization proteins localized between layered aragonite mineral plates (i.e., nacre layer) in mollusk shell. Recent atomic force microscopy (AFM) pulling studies have demonstrated that the lustrin‐containing organic nacre layer in the abalone, Haliotis rufescens, exhibits a typical sawtooth force‐extension curve with hysteretic recovery. This force extension behavior is reminiscent of reversible unfolding and refolding in elastomeric proteins such as titin and tenascin. Since secondary structure plays an important role in force‐induced protein unfolding and refolding, the question is, What secondary structure(s) exist within the major domains of Lustrin A? Using a model peptide (FPGKNVNCTSGE) representing the 12‐residue consensus sequence found near the N‐termini of the first eight cysteine‐rich domains (C‐domains) within the Lustrin A protein, we employed CD, NMR spectroscopy, and simulated annealing/minimization to determine the secondary structure preferences for this sequence. At pH 7.4, we find that the 12‐mer sequence adopts a loop conformation, consisting of a “bend” or “turn” involving residues G3–K4 and N7–C8–T9, with extended conformations arising at F1–G3; K4–V6; T9–S10–G11 in the sequence. Minor pH‐dependent conformational effects were noted for this peptide; however, there is no evidence for a salt‐bridge interaction between the K4 and E12 side chains. The presence of a loop conformation within the highly conserved —PG—, —NVNCT— sequence of C1–C8 domains may have important structural and mechanistic implications for the Lustrin A protein with regard to elastic behavior. © 2002 Wiley Periodicals, Inc. Biopolymers 63: 358–369, 2002
Cation–π interaction in a folded polypeptide
Authors: Burghardt Thomas P. , Juranić Nenad , Macura Slobodan , Ajtai Katalin
Published: August 2002

Cationic and aromatic side chains from protein residues interact to stabilize tertiary structure. The stabilization energy originates in part from electrostatic attraction between the cation, and regions of high electron density in π‐orbitals of the aromatic group, leading to the name cation–π interaction. The lysine and tyrosine containing peptide, N–acetyl–Pro–Pro–Lys–Tyr–Asp–Lys–NH2, has near uv CD characteristic of tyrosine in a structured environment. Nuclear Overhauser effect (NOE), coupling constant, and ring current chemical shift constraints obtained with 1H NMR confirm that the peptide (t6p) folds. Simulated annealing consistent with all NMR constraints produces a 40‐structure ensemble for t6p with potential energies within one standard deviation of the lowest value observed. Calculated binding energies indicate that cation–π and cation–phenolic OH interactions exists between the Lys3 and Tyr4 side chains in most of the structures. The t6p peptide in solution is a model for these interactions in a protein. A perturbing electric field from the cationic ground state charge intermingles the excited states of the aromatic group. This intermingling effect may provide a cation–π signature effect in the tyrosine spectroscopy. The absorption and CD for the lowest energy electronic transitions of the tyrosine phenol were computed for the ensemble. Red‐shifted peak energy and hypochromicity in the absorbance band, and decreasing rotational strength, correlates with increasing binding energy of the complex indicating the cation–π spectroscopic signature. The ensemble average spectroscopic signature effects in t6p are small and in agreement with observation. © 2002 John Wiley & Sons, Inc. Biopolymers 63: 261–272, 2002; DOI 10.1002/bip.10070
Effects of humic substances on the bioavailability and aerobic biodegradation of polychlorinated biphenyls in a model soil
Authors: Fava Fabio , Piccolo Alessandro
Published: August 2002

The very high hydrophobicity of polychlorinated biphenyls (PCBs) strongly reduces their bioavailability in aged contaminated soils, thus limiting their bioremediation. The biodegradability of PCBs in heavily contaminated soils can be significantly enhanced by soil treatment with surface‐active agents. In this work, the effects of naturally occurring surfactants such as humic substances (HS) on the aerobic biodegradation of PCBs in a model soil were studied. The soil was amended with biphenyl (4 g/kg), Fenclor 42 (1,000 mg/kg), the aerobic PCB‐biodegrading bacterial co‐culture ECO3 (inoculum: 108CFU/mL), and treated in aerobic batch slurry‐phase conditions (17.5% w/v) with and without the addition of HS at the rates of 1.5 and 3.0% (w/w). Low PCBs biodegradation and dechlorination yields were observed in the HS‐free microcosms, probably as a result of the rapid disappearance of inoculated bacteria. The presence of HS influenced significantly the activity of the specialized biomass and the biodegradation of PCBs in the microcosms. The microcosms that received HS at the 1.5% rate showed a higher persistence of the specialized bacteria and yields of PCB biodegradation and dechlorination about 150 and 100%, respectively, larger than those found for the HS‐free microcosms. Lower stimulating effects were observed in the microcosms added with the HS at 3.0% rate. These effects were attributed to an increased solubilization of PCBs in the hydrophobic domains of the humic supramolecular associations and to a different accessibility of PCBs by the specialized bacteria at the different rates of HS addition. Although the slurry‐phase treatment generally showed a decrease of the original soil ecotoxicity, the addition of the originally non‐toxic HS decreased soil ecotoxicity for the Collembola animal biomarker and increased that towards the Lepidium sativum vegetal biomarker. © 2002 John Wiley & Sons, Inc. Biotechnol Bioeng 77: 204–211, 2002.
Purification of recombinant cutinase by extraction in an aqueous two‐phase system facilitated by a fatty acid substrate
Authors: Fernandes Sheryl , Johansson Göte , Hatti‐Kaul Rajni
Published: August 2002

Purification of recombinant wild‐type cutinase from the culture supernatant of Saccharomyces cerevisiae by extraction in aqueous two‐phase system was investigated. The partition of the enzyme in a polyethylene glycol (PEG)–potassium phosphate system to the top phase was increased with lower molecular weight PEG. Enzyme partition in a 20% PEG/15% phosphate two‐phase system was studied in the presence of detergents, fatty acids, and alcohols, respectively. Addition of 0.5% (w/w) butyrate increased the partition coefficient from 17 to 135 and the purification factor from 10 to 23. The effect of butyrate was also confirmed by using the countercurrent mode of extraction. Recovery of cutinase from the top phase was achieved by a secondary extraction into a new salt phase at a lower pH or a lower temperature. A specific interaction of butyrate to the active site of the enzyme was demonstrated by fluorescence spectroscopy. Size exclusion chromatography showed the cutinase–butyrate complex to be over two times the size of the free enzyme. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 73: 465–475, 2001.
Multivariable control of alcohol concentrations in the production of polyhydroxyalkanoates (PHAs) by Paracoccus denitrificans
Authors: Chanprateep Suchada , Abe Naoya , Shimizu Hiroshi , Yamane Tsuneo , Shioya Suteaki
Published: August 2002

A novel multivariable control strategy is developed for alcohol (ethanol and n‐pentanol) concentrations in the production of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), P(HB‐co‐HV), a biodegradable polymer by Paracoccus denitrificans ATCC 1774. This controller, which is developed to control the mole fraction of P(HB‐co‐HV), consists of two parts: one is for ethanol concentration control and the other is for mole fraction control, based on the concept of metabolic flux distribution control. A simple metabolic reaction (MR) model is constructed for flux distribution analysis. The relationship between mole ratio of specific consumption rate of the two alcohols (ethanol and n‐pentanol) and the mole fraction of 3HV units in the polymer is linear. This result suggests that the split ratio at a branched point of 3‐ketovaleryl‐CoA in the P(HB‐co‐HV) synthetic pathway is constant for several fermentation conditions. When the mole fraction of 3HV units has a target value, the feed rate of n‐pentanol becomes a function of the feed rate of ethanol and the set value of 3HV, based on the MR model. The mole fraction of 3HV units successfully reached the target value using this strategy. The mole fraction control strategy is combined with an optimal production strategy based on the optimal profile of the specific growth rate. The combined strategy is realized using multivariable controllers and P(3HB‐co‐3HV) production is maximized with a given value of mole fraction of 3HV units at the final step of fermentation. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 74: 116–124, 2001.