bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical characterization of polypropylene–wood flour composites
Authors: Nuñez Adrián J. , Sturm Pablo C. , Kenny José M. , Aranguren M. I. , Marcovich Norma E. , Reboredo María M.
Published: February 2003

The mechanical performance of different wood flour/polypropylene (PP) composites with interface modifications was compared. Wood flour was incorporated into the matrix after esterification with maleic anhydride (MAN) or without any modification but with the addition of a compatibilizing agent [maleic anhydride–polypropylene copolymer (PPMAN)] to modify the polymer–filler interaction. Composites were prepared by injection molding with different concentrations of wood flour. Mechanical properties (except Young's modulus) were not improved either by the wood flour chemical modification or by the use of PPMAN. However, both compatibilization methods were successful in improving the dispersion of the wood flour in the PP matrix. Creep behavior of composite samples was improved by the addition of PPMAN, whereas the composites prepared from MAN‐treated wood flour showed larger deformations than composites made with untreated particles. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1420–1428, 2003
Novel block ionomers. III. Mechanical and rheological properties
Authors: Fang Zheng , Wang Shanfeng , Wang Shi Quing , Kennedy Joseph P.
Published: February 2003

Select rheological (dynamic viscoelastic) and mechanical properties of novel block cationomers and anionomers and their blends have been investigated. The block ionomers were linear di‐ and triblocks, and symmetric three‐arm stars comprising hydrophobic polyisobutylene (PIB) blocks attached to ionized poly(methacrylic acid) (PMAA−X+, where X+ = Na+, Zn2+) and poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA+I−) blocks. The specific structures investigated were the well‐defined diblocks PIB‐b‐PMAA− and PIB‐b‐PDMAEMA+ and their blends, the triblocks PMAA−‐b‐PIB‐b‐PMAA− and PDMAEMA+‐b‐PIB‐b‐PDMAEMA+ and their blends, and the three‐arm star anionomer Φ(PIB‐b‐PMAA−)3. For comparison, the properties of the precursor PIBs and unionized blocks have also been studied. Hydrogen bonding between the carboxyl groups of the PMAA blocks in PIB‐b‐PMAA diblocks leads to inverse micelles. Neutralization of the PMAA by Zn(AcO)2 and quaternization of the PDMAEMA segments by CH3I in the triblock copolymers and star copolymers yielded ionic domains, which self‐assemble and produce physical networks held together by coulumbic interaction. The physical/chemical characteristics of the domains control the viscoelastic behavior and mechanical properties of these block ionomers. The mechanical properties of the various block ionomers were significantly enhanced relative to the precursors, and they were thermally stable below the transition temperature. Further, the thermomechanical properties of these novel materials were satisfactory even above 200°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1516–1525, 2003
Mechanical and rheological properties of the maleated polypropylene–layered silicate nanocomposites with different morphology
Authors: Koo Chong Min , Kim Mi Jung , Choi Min Ho , Kim Sang Ouk , Chung In Jae
Published: February 2003

Three types of maleated polypropylene–layered silicate nanocomposites with different dispersion states of layered silicate (deintercalated, intercalated, and exfoliated states) are prepared from two kinds of polypropylenes with different molecular weights, organically modified layered silicate and pristine montmorillonite to investigate the effect of the final morphology of the nanocomposite on the rheological and mechanical properties. Maleated polypropylene with high molecular weight intercalates slowly and the other with low molecular weight exfoliates fast into the organophilic layered silicates. Rheological properties such as oscillatory storage modulus, nonterminal behavior, and relative viscosity has close relationship with the dispersion state of layered silicates. The exfoliated nanocomposite shows the largest increase and the deintercalated nanocomposite shows almost no change in relative shear and complex viscosities with the clay content. The exfoliated nanocomposite shows the largest drop in complex viscosity due to shear alignment of clay layers in the shear flow. In addition, the final dispersion state of layered silicates intimately relates to the mechanical property. The dynamic storage moduli of nanocomposites show the same behavior as the relative shear and complex viscosities. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1526–1535, 2003
Characterization of graft polymerization of fluoroalkyl methacrylate onto PDMS hollow‐fiber membranes and their permselectivity for volatile organic compounds
Authors: Mishima S. , Nakagawa T.
Published: February 2003

Polydimethylsiloxane (PDMS) hollow‐fiber membranes grafted with 1H,1H,9H‐hexadecafluorononyl methacrylate (HDFNMA), which is a fluoroalkyl methacrylate, using a 60Co irradiation source, were characterized and applied to pervaporation. The PDMS hollow‐fiber membranes were filled with N2 gas and sealed. The membranes and the HDFNMA solution were then irradiated simultaneously. In the HDFNMA solution, graft polymerization was performed. The degree of grafting of the outside surface of the hollow fiber was greater than that in the inside surface of the hollow fiber. In the grafted PDMS hollow‐fiber membranes, the best separation performance was shown due to the introduced hydrophobic polymer, poly(HDFNMA). The grafted membrane had a microphase‐separated structure, that is, a separated structure of PDMS and graft‐polymerized HDFNMA. The permeability of molecules in the poly(HDFNMA) phase was so low that the diffusion of molecules was prevented in the active layer with many poly(HDFNMA) domains, as the feed solution was introduced through the inside of the hollow fibers and the outside was vacuumed. As the feed solution was introduced through the outside of the hollow fibers and the inside was vacuumed, the diffusion of molecules was not prevented in the active layer with few poly(HDFNMA) domains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1573–1580, 2003
Continuous polymerization of lactam–lactone block copolymers in a twin‐screw extruder
Authors: Kim Byong Jun , White James L.
Published: February 2003

Continuous copolymerizations of ϵ‐caprolactone with ϵ‐caprolactam and ω‐lauryl lactam were carried out in a modular intermeshing corotating twin‐screw extruder. Sodium hydride (initiator) and N‐acetyl caprolactam (coinitiator) were used to synthesize lactam–lactone copolymers in a twin‐screw extruder. We consider the variables of feeding order and feed rate of comonomers on the reactive extrusion of lactam–lactone copolymers. It was observed that simultaneous feeding of both monomers with initiator and coinitiator in the first hopper produced a mixture of homopolymers. When we fed the lactam into the first hopper and caprolactone sequentially into the second hopper, we obtained the lactam–caprolactone block copolymers. However, when we fed caprolactone first into the first hopper and the lactam into the second hopper, the extruded product was a mixture of poly(ϵ‐caprolactone) and lactam monomer. We synthesized high molecular weight copolymers of poly(caprolactam‐b‐caprolactone) and poly(lauryl lactam‐b‐caprolactone) with different block lengths by sequential feeding of monomers. The block length of the block copolymer could be adjusted by controlling the feed rate of each monomer during reactive extrusion. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1429–1437, 2003
Model for the viscoelastic and viscoplastic responses of semicrystalline polymers
Authors: Drozdov Aleksey D. , deClaville Christiansen Jesper
Published: February 2003

Constitutive equations are derived for the time‐dependent behavior of semicrystalline polymers at isothermal loading with small strains. A semicrystalline polymer at temperatures above the glass‐transition point for its amorphous phase is thought of as a network of macromolecules bridged by junctions (physical crosslinks, entanglements, and crystalline lamellae) that can slide with respect to their reference positions in the bulk material under straining. The network is assumed to be highly inhomogeneous, and it is modeled as an ensemble of mesoregions (MRs) with various strengths of interchain interaction. Two types of MRs are distinguished: passive, where these interactions prevent detachment of strands from junctions; and active, where active strands separate from junctions and dangling strands merge with the network at random times as they are thermally agitated. The viscoelastic response of a semicrystalline polymer reflects reformation of strands in active MRs, whereas its viscoplastic behavior is associated with sliding of junctions. Stress–strain relations for uniaxial deformation are developed by using the laws of thermodynamics. Adjustable parameters in the constitutive equations are found by fitting experimental data for isotactic polypropylene in a tensile test with a constant strain rate and in tensile relaxation tests at various strains. Fair agreement is demonstrated between the observations and the results of numerical simulation. It is revealed that the viscoplastic flow of junctions strongly affects the rearrangement process in active MRs, whose rate reaches a threshold value in the vicinity of the apparent yield point. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1438–1450, 2003
Crosslinked poly(ethylene oxide) hydrogels
Authors: Emami Shahriar Hojjati , Salovey R.
Published: February 2003

Poly(ethylene oxide) with a molecular weight of 2,000,000 was crosslinked by a difunctional peroxide in the molten state. We determined the molecular weight between crosslinks by swelling the samples with deionized water and by indentation and dynamic mechanical analysis. Results were compared with the calculated optimum molecular weight between crosslinks. Fair agreement was obtained between the experimental methods. However, the efficiency of peroxide‐induced crosslinking was very low. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1451–1455, 2003
Immobilization of horseradish peroxidase on chitosan for use in nonaqueous media
Authors: Bindhu L. V. , Abraham Emilia T.
Published: February 2003

Chitosan, a natural polysaccharide, was used for the covalent immobilization of horseradish peroxidase, an enzyme of high synthetic utility, with the carbodiimide method. Of the enzyme, 62% was immobilized on chitosan when 1‐ethyl‐3‐(3‐dimethylaminopropyl carbodiimide) was used as the peptide coupling agent. The influence of different parameters, such as the enzyme concentration, carbodiimide concentration, and incubation period, on the activity retention of the immobilized enzyme was investigated. Kinetic studies using horseradish peroxidase immobilized on chitosan revealed the effects of several parameters, such as the substrate hydrophilicity and hydrophobicity, the solubility of substrates in the medium, the solvent hydrophobicity, and the support aquaphilicity, on the catalytic activity of the immobilized enzyme in nonaqueous media. General rules for the optimization of solvents for nonaqueous enzymology based on the partitioning of the solvent were not applicable for the immobilized horseradish peroxidase. The catalytic efficiency was greatest when o‐phenylene diamine was used as the substrate and least when guaiacol was used. The aquaphilicity of the support played an important role in the kinetics of the immobilized horseradish peroxidase in water‐miscible solvents. The results were promising for the future development of chitosan‐immobilized enzymes for use in organic media. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1456–1464, 2003
Semiquantitative analysis of the thermal degradation of polypropylene
Authors: Ishikawa Tomoyuki , Ohkawa Tomohiro , Suzuki Masaaki , Tsuchiya Toshiaki , Takeda Kunihiko
Published: February 2003

The pyrolysis product distributions of polypropylene (PP) were observed, and the experimental data were semiquantitatively analyzed by computer simulation with the Molic mouse method. Studies by many researchers on PP decomposition and experimental results achieved in this study were examined. The product distributions were classified into three types of hydrocarbon products: 3n, 3n + 1, and 3n + 2 (n = monomer unit). The ratio showed the characteristic tendency, and the thermal degradation of PP appeared to include very complicated scission paths. The Molic mouse method, which was applied to the analysis of the thermal rearrangement and decomposition of poly(phenylene ether), was used to simulate the experimental results. After several steps by which the proper model was constructed, the scission probabilities to generate 2 × 3n, 3n + 1 and 3n + 2, 3n and 3n + 1, 3n and 3n + 2, C9, and C15 hydrocarbons were successfully calculated to be 0.25, 0.67, 0.47, 0.35, 1.0, and 0.33, respectively. This meant that the scission process of PP was very simple except for the C9 and C15 generation paths, for which the cyclic compounds were stable intermediates. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1465–1472, 2003
Synthesis and crystallization behavior of nylon 12,14. I. Preparation and melting behavior
Authors: Li Yongjin , Zhang Guosheng , Yan Deyue
Published: February 2003

A long‐alkane‐segment semicrystalline polyamide based on 1,12‐diaminododecane and 1,12‐dodecanedicarboxylic acid was synthesized and characterized. The polymer was prepared by melt polycondensation. The molecular weight of the material ranged from 20,000 to 40,000 g/mol, depending on the polymerization conditions. The resulting product was characterized by means of elemental analysis, infrared spectrometry, 1H‐ and 13C‐NMR, intrinsic viscosity, differential scanning calorimetry (DSC), thermogravimetric analysis, dynamic mechanical analysis, and wide‐angle X‐ray diffraction (WAXD). Some mechanical properties were measured. In addition, the thermal behavior of nylon 12,14 was systematically investigated with DSC and variable‐temperature WAXD. Double endotherms were observed during the melting of the polymer, which might have originated from the melt and recrystallization processes of nylon 12,14 on heating. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1581–1589, 2003
Hydrophobic cotton fabric coated by a thin nanoparticulate plasma film
Authors: Zhang Jing , France Paul , Radomyselskiy Arseni , Datta Saswati , Zhao Jiangang , van Ooij William
Published: February 2003

The audio frequency (AC) plasma of some kind of fluorocarbon chemical was applied to deposit a nanoparticulate hydrophobic film onto a cotton fabric surface. The measurement of the video contact angle showed that the superhydrophobicity of the cotton fabric was obtained with a treatment of only 30 s. The softness, water retention, moisture regain, color retention, abrasion, friction, and permeability were thoroughly investigated by a standard method that compared the fabric with a commercial Scotchgard‐protector‐sprayed cotton fabric. The results showed that the textile performances of the plasma‐coated fabric were superior to those of Scotchgard‐sprayed samples, except for the moisture regain, which was almost the same. A post‐treatment at a high temperature was conducive to increasing the hydrophobicity and the recovery of the water repellency of the plasma‐coated fabric after it was washed. Atomic force microscopy images and time‐of‐flight secondary‐ion mass spectra of plasma thin films on silicon wafers indicated that some physical and chemical changes took place during the post‐treatment process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1473–1481, 2003
Flexibility and phase transitions of polymers
Authors: Schneider Hans Adam
Published: February 2003

It is shown, that both the mobility of polymers as well their transition temperatures (glass transition and crystallization) depend on the “flexibility” of simple bonds, i.e., on their ability to promote by energetically stimulated rotations conformational changes to release stresses. The polymer class specific interdependence between melting temperature, Tm and glass temperature, Tg, suggests that the “flexibility” of polymers depends additionally on the probability of interactions between sequences of polymer chains. Interaction between polymer chain sequences controls at the same time the ordering necessary for crystallization. Characteristic of polymers is thus the dependence of both transition temperatures on the “mass/'flexible bond” of the monomeric (repeating) unit, μ/ρ. This experimentally observed polymer class specific behavior is reflecting the similar probabilities of interaction within a given class of polymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1590–1599, 2003
In situ polymerization and nano‐templating phenomenon in nylon fiber/PMMA composite laminates
Authors: Caskey Terrence C. , Lesser Alan J. , McCarthy Thomas J.
Published: February 2003

Supercritical Carbon Dioxide (SC CO2) is used as a reaction/processing medium in the fabrication of fiber‐reinforced composite materials. SC CO2 allows resin (reactive monomer), to penetrate inside the fibers themselves, partitioning into the amorphous regions of the fiber. The crystal structure then templates polymerization of matrix within the fiber. This process produces a composite that exhibits ultralong‐range order from the nanoscale reinforcement of crystals to the macroscale fiber reinforcement of matrix. In addition, SC CO2 lowers resin viscosity and aids in wetting out Nylon 6,6 fiber reinforcement in a process similar to reaction injection molding (RIM) or resin transfer molding (RTM). This article will discuss the fabrication technique in detail, including process parameters and the structure of resulting composites and morphology of modified fibers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1600–1607, 2003
Durable antimicrobial treatment of cotton fabrics using N‐(2‐hydroxy)propyl‐3‐trimethylammonium chitosan chloride and polycarboxylic acids
Authors: Kim Young Ho , Nam Chang Woo , Choi Jae Won , Jang Jinho
Published: February 2003

N‐(2‐hydroxy)propyl‐3‐trimethylammonium chitosan chloride (HTCC), a water‐soluble chitosan quaternary ammonium derivative, was used as an antimicrobial agent for cotton fabrics. HTCC has a lower minimum inhibition concentration (MIC) against Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli compared to that of chitosan; however, the imparted antimicrobial activity is lost on laundering. Thus crosslinking agents were utilized to obtain a durable antimicrobial treatment by immobilizing HTCC. Several crosslinkers such as dimethyloldihydroxyethylene urea (DMDHEU), butanetetracarboxylic acid (BTCA), and citric acid (CA) were used with HTCC to improve the laundering durability of HTCC treatment by covalent bond formation between the crosslinker, HTCC and cellulose. The polycarboxylic acid treatment was superior to the DMDHEU treatment in terms of prolonged antimicrobial activity of the treated cotton after successive laundering. Also, the cotton treated with HTCC and BTCA showed improved durable press properties without excessive deterioration in mechanical strength or whiteness when compared to the citric acid treatment. With the addition of only 0.1% HTCC to BTCA solutions, the treated fabrics showed durable antimicrobial activity up to 20 laundering cycles. The wrinkle recovery angle and strength retention of the treated fabrics were not adversely affected with the addition of HTCC. Therefore, BTCA can be used with HTCC in one bath to impart durability of antimicrobial activity along with durable press properties to cotton fabric. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1567–1572, 2003
Preparation of water‐soluble syndiotacticity‐rich high molecular weight poly(vinyl alcohol) microfibrillar fibers using copolymerization of vinyl pivalate and vinyl acetate and saponification
Authors: Lyoo Won Seok , Yeum Jeong Hyun , Ji Byung Chul , Ghim Han Do , Kim Sam Soo , Kim Joon Ho , Lee Ji Youl , Lee Jinwon
Published: February 2003

Water‐soluble high molecular weight (HMW) syndiotactic poly(vinyl alcohol) (s‐PVA) microfibrillar fibers were prepared by the saponification with various conditions such as amount of alkali solution, saponification temperature, and saponification concentration from copoly(vinyl pivalate (VPi)/vinyl acetate (VAc)) copolymerized using various VPi/VAc feed ratios. To produce s‐PVA microbrillar fibers having various water‐soluble temperatures for many industrial applications, the intrinsic viscosities, syndiotactic diad (S‐diad) contents, and degrees of saponification (DS)s of PVAs were finely controlled to 1.2–3.6 dL/g, 56.3–58.3%, and 91.4–98.3%, respectively. Through a series of experiments, it was found that the amount of alkali may alter the structure of the saponified polymers, primarily the DS, and the structural variation changes viscosity. That is, intrinsic viscosity was sharply decreased as the amount of alkali solution was increased. DS was increased with an increase in the amount of alkali solution. S‐diad content was increased with an increase in the VPi content. HMW s‐PVA microfibrillar fibers having S‐diad content of 56.3–58.3% prepared by the saponification of copoly(VPi/VAc) were completely soluble in water at 100°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1482–1487, 2003
Characterization of semi‐interpenetrating polymer network polystyrene cation‐exchange membranes
Authors: Choi Yong‐Jin , Kang Moon‐Sung , Moon Seung‐Hyeon
Published: February 2003

Polystyrene cation exchange membranes were prepared by a PVC‐based semi‐interpenetrating polymer network (IPN) method. The reaction behaviors during polymerization and sulfonation in the preparation method were investigated. The prepared membranes were characterized in terms of the physical and electrochemical properties. The membranes exhibited reasonable mechanical properties (tensile strength, 13 MPa, and elongation at break, 52%) for an ion‐exchange membrane with the ratio of polystyrene–divinylbenzene (DVB)/poly(vinyl chloride) (PVC) (RSt‐DVB/PVC) of below 0.9. Fourier transform infrared/attenuated total reflectance, differential scanning calorimetry, and scanning electron microscopy studies revealed the formation of a homogeneous membrane. The resulting membrane showed membrane electrical resistance of 2.0 Ω cm2 and ion‐exchange capacity of 3.0 meq/g dry membrane. The current–voltage (I–V) curves of the membrane show that the semi‐IPN polystyrene membranes can be properly used at a high current density, and that the distribution of cation‐exchange sites in the membrane was more homogenous than that in commercial membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1488–1496, 2003
Thermal polymerization of a brominated flame retardant in a glass‐fiber‐reinforced polypropylene—quantitative analysis
Authors: Dvir H. , Gottlieb M. , Daren S.
Published: February 2003

Pentabromobenzylacrylate (PBBA) is a possible candidate for use as a fire retardant (FR) in polypropylene (PP) composites. While PBBA imparts FR properties to the PP composite, it also affects adversely its mechanical properties. The FR may undergo thermal polymerization or grafting to the PP chains during processing. To study the effect of the different forms of FR (monomer, polymerized, or grafted) on composite properties, we have quantified the extent of FR polymerization and extent of grafting onto the PP chains. Fourier transform infrared microscopy was used in this work to determine the extent of polymerization and the spatial distribution of the FR. The latter was found to be homogeneous throughout the composite. Thermal polymerization of the FR during extrusion is varied mainly by the addition of an antioxidant. The grafting process of the FR onto PP depends on the degree of thermal polymerization, and therefore on the addition of antioxidant. The limiting value for grafting achieved at full polymerization is ∼10% w/w. The grafted FR was found to have a significant effect on PP crystallinity, and hence it is expected to affect the mechanical properties as well. Bromine analysis indicates the FR has reacted with filler surfaces as well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1506–1515, 2003
Thermal conductivity of misaligned short‐fiber‐reinforced polymer composites
Authors: Fu Shao‐Yun , Mai Yiu‐Wing
Published: February 2003

A fiber length distribution (FLD) and a fiber orientation distribution (FOD) usually exist in injection‐molded short‐fiber‐reinforced polymer (SFRP) composites. In this article, the thermal conductivity of SFRP composites is studied in detail, taking into account the effects of the FLD and the FOD. The effect of fiber volume fraction on the composite thermal conductivity is also investigated. It is shown that the thermal conductivity of SFRP composites increases almost linearly with fiber volume fraction; it also increases with mean fiber length (or mean aspect ratio) but decreases with mean fiber orientation angle with respect to the measured direction. The latter two effects depend highly on the thermal conductivity of short fibers. The effects of mode fiber length and mode fiber orientation angle on the thermal conductivity of short (carbon) fiber reinforced polymer composites have also been studied. The composite thermal conductivity increases marginally with the increase of mode fiber length but lightly with the increase of mode fiber orientation angle. Moreover, comparison of the present model is made with existing theories in predicting the thermal conductivity of SFRP composites. Finally, the present model is applied to published experimental results and the agreement is found to be satisfactory. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1497–1505, 2003
Thermomechanical and creep properties of poly(ethylene terephthalate) fibers crosslinked with disulfonyl azides
Authors: Baker D. A. , East G. C. , Mukhopadhyay S. K.
Published: February 2003

The thermomechanical and creep properties of poly(ethylene terephthalate) fibers crosslinked with 1,6‐hexanedisulfonyl azide, 1,3‐benzenedisulfonyl azide, and 2,6‐naphthalenedisulfonyl azide were investigated. Significant improvements in these properties were observed between the standard fibers and those produced by crosslinking. Cyclic loading studies highlighted minor differences not detectable by normal thermomechanical analysis. The creep at room temperature could be reduced to about one‐third of the normal values observed in the untreated fiber. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1556–1562, 2003
Synthesis of superabsorbent starch‐graft‐poly(potassium acrylate‐co‐acrylamide) and its properties
Authors: Lu Shaojie , Duan Menglin , Lin Songbai
Published: February 2003

The superabsorbent's ability to resist deformation and to resist deswelling under externally applied pressures is important in practical application. For instance, it is used in infant diapers, in soil for agriculture, and in forestry. In this article, we report on the synthesis of a superabsorbent/starch‐graft‐poly(potassium acrylate‐co‐acrylamide) by inverse suspension polymerization. The effects of reaction conditions, such as monomeric concentration, ratio of water to oil, reaction temperature, and obtaining spherical resin, were investigated. Experiments showed that the superabsorbent has a good compressive strength and keeps the shape of particles after absorbing water. After mixing with soil it does not become sticky, and the loose structure can better retain air. It is fit to retain water in soil. In addition, thermogravimetric analysis revealed the superior thermal stability of the grafted product and its large particle size also reduces risk of air pollution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1536–1542, 2003
Preparation of aqueous polyaniline dispersions by micellar‐aided polymerization
Authors: Yu Lei , Lee Jeong‐II , Shin Kwon‐Woo , Park Chan‐Eon , Holze Rudolf
Published: February 2003

Polyaniline (PAn) dispersed in water was prepared with sodium dodecylsulfonate (SDS) as a surfactant with varying concentrations of aniline and HCl and molar ratios of SDS/aniline. The PAn dispersion was homogeneous and stable, and its pH value could be adjusted. The conductivity of PAn powder, precipitated from this dispersion, was as high as 20 S/cm. The transmission electron microscopy morphology of PAn assembled in the dispersion was particle‐like, fiber‐like, or coil‐like, depending on the initial concentration of SDS and aniline. The polymerization of aniline was accelerated by SDS, which was confirmed by open‐circuit potential measurement during the polymerization process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1550–1555, 2003
Ab initio structure prediction of two α‐helical oligomers with a multiple‐chain united‐residue force field and global search
Authors: Saunders Jeffrey A. , Scheraga Harold A.
Published: February 2003

A hierarchical methodology for ab initio structure prediction is extended to treat oligomeric proteins. Modifications are made to a united‐residue (UNRES) force field and a Conformational Space Annealing (CSA) global search method. The computational cost of including additional chains and the increase in speed from symmetry optimizations are evaluated. The native structures of two oligomeric proteins from the CASP3 exercise, the retro‐GCN4 leucine zipper and the synthetic domain‐swapped dimer, were identified as the lowest‐energy families resulting from the search of the proteins when rotational symmetry was imposed. Additional searches in different symmetries and oligomerization states were carried out, and the results indicate some problems in the thoroughness of the search and in the search of packing arrangements if symmetry constraints are not imposed. © 2003 Wiley Periodicals, Inc. Biopolymers: 300–317, 2003
Challenges in structure prediction of oligomeric proteins at the united‐residue level: Searching the multiple‐chain energy landscape with CSA and CFMC
Authors: Saunders Jeffrey A. , Scheraga Harold A.
Published: February 2003

A revised version of the Conformational Space Annealing (CSA) global optimization method is developed, with three separate measures of structural similarity, in order to overcome the inability of a single distance measure to evaluate multiple‐chain protein structures adequately. A second search method, Conformational Family Monte Carlo (CFMC), involving genetic‐type moves, Monte Carlo‐with‐minimization perturbations, and explicit clustering of the population into conformational families, is adapted to treat multiple‐chain proteins. These two methods are applied to two oligomeric proteins, the retro‐GCN4 leucine zipper and the synthetic domain‐swapped dimer. CFMC proves superior to CSA in its search for low‐energy representatives of its conformational families, but both methods encounter difficulty in finding the native packing arrangements in the absence of native‐like symmetry constraints, even when native monomers are present in the population. © 2003 Wiley Periodicals, Inc. Biopolymers: 318–332, 2003
Computer simulation studies of the fidelity of DNA polymerases
Authors: Florián Jan , Goodman Myron F. , Warshel Arieh
Published: February 2003

Computer simulations can provide in principle quantitative correlation between the structures of DNA polymerases and the replication fidelity. This paper describes our progress in this direction. Using several theoretical approaches, including the free energy perturbation (FEP), linear response approximation (LRA), and the empirical valence bond (EVB) methods, we examined the stability of several mismatched base pairs in DNA duplex in aqueous solution, the contribution of binding energy to the fidelity of DNA polymerases β and T7, and the mechanism and energetics of the polymerization reaction catalyzed by T7 DNA polymerase. © 2003 Wiley Periodicals, Inc. Biopolymers 68: 286–299, 2003
Potential energy functions: From consistent force fields to spectroscopically determined polarizable force fields
Authors: Palmo Kim , Mannfors Berit , Mirkin Noemi G. , Krimm Samuel
Published: February 2003

We review our methodology for producing physically accurate potential energy functions, particularly relevant in the context of Lifson's goal of including frequency agreement as one of the criteria of a self‐consistent force field. Our spectroscopically determined force field (SDFF) procedure guarantees such agreement by imposing it as an initial constraint on parameter optimization, and accomplishes this by an analytical transformation of ab initio “data” into the energy function format. After describing the elements of the SDFF protocol, we indicate its implementation to date and then discuss recent advances in our representation of the force field, in particular those required to produce an SDFF for the peptide group. © 2003 Wiley Periodicals, Inc. Biopolymers: 383–394, 2003
Protein decoy assembly using short fragments under geometric constraints
Authors: Kolodny R. , Levitt M.
Published: February 2003

A small set of protein fragments can represent adequately all known local protein structure. This set of fragments, along with a construction scheme that assembles these fragments into structures, defines a discrete (relatively small) conformation space, which approximates protein structures accurately. We generate protein decoys by sampling geometrically valid structures from this conformation space, biased by the secondary structure prediction for the protein. Unlike other methods, secondary structure prediction is the only protein‐specific information used for generating the decoys. Nevertheless, these decoys are qualitatively similar to those found by others. The method works well for all‐α proteins, and shows promising results for α and β proteins. © 2003 Wiley Periodicals, Inc. Biopolymers 68: 278–285, 2003
Molecular dynamics of biological macromolecules: A brief history and perspective
Authors: Karplus Martin
Published: February 2003

A description of the origin of my interest in and the development of molecular dynamics simulations of biomolecules is presented with a historical overview, including the role of my interactions with Shneior Lifson and his group in Israel. Some early applications of the methodology by members of my group are summarized, followed by a description of examples of recent applications and some discussion of possible future directions. © 2003 Wiley Periodicals, Inc. Biopolymers: 350–358, 2003
Neuronal assemblies: Single cortical neurons are obedient members of a huge orchestra
Authors: Grinvald Amiram , Arieli Amos , Tsodyks Misha , Kenet Tal
Published: February 2003

Spontaneous cortical activity of single neurons is often either dismissed as noise, or is regarded as carrying no functional significance and hence is ignored. Our findings suggest that such concepts should be revised. We explored the coherent population activity of neuronal assemblies in primary sensory area in the absence of a sensory input. Recent advances in real‐time optical imaging based on voltage‐sensitive dyes (VSDI) have facilitated exploration of population activity and its intimate relationship to the activity of individual cortical neurons. It has been shown by in vivo intracellular recordings that the dye signal measures the sum of the membrane potential changes in all the neuronal elements in the imaged area, emphasizing subthreshold synaptic potentials and dendritic action potentials in neuronal arborizations originating from neurons in all cortical layers whose dendrites reach the superficial cortical layers. Thus, the VSDI has allowed us to image the rather illusive activity in neuronal dendrites that cannot be readily explored by single unit recordings. Surprisingly, we found that the amplitude of this type of ongoing subthreshold activity is of the same order of magnitude as evoked activity. We also found that this ongoing activity exhibited high synchronization over many millimeters of cortex. We then investigated the influence of ongoing activity on the evoked response, and showed that the two interact strongly. Furthermore, we found that cortical states that were previously associated only with evoked activity can actually be observed also in the absence of stimulation, for example, the cortical representation of a given orientation may appear without any visual input. This demonstration suggests that ongoing activity may also play a major role in other cortical function by providing a neuronal substrate for the dependence of sensory information processing on context, behavior, memory and other aspects of cognitive function. © 2003 Wiley Periodicals, Inc. Biopolymers: 422–436, 2003
The physics and bioinformatics of binding and folding—an energy landscape perspective
Authors: Papoian Garegin A. , Wolynes Peter G.
Published: February 2003

It has been recognized in the last few years that unstructured proteins play an important role in biological organisms, often participating in signal transduction, transcriptional regulation, and a variety of other regulatory activities. Various hypotheses have been put forward for the ubiquity of the unfolded state; rapid turnover, faster or more specific binding kinetics, multifunctionality may all possibly explain apparent ubiquitousness of unfolded proteins in eukaryotic cells. In this paper we extend the energy landscape theory of protein folding to construct an analytical model of how binding and folding are coupled thermodynamically when the energy landscape is partially rugged. To deduce the parameters that enter the theory, which is based on Generalized Random Energy Model, we have analyzed in a bioinformatic sense a large structural database of more than 500 protein complexes. We find that Miyazawa–Jernigan contact potential shows similar energy gaps for folding for both hydrophobic and hydrophilic proteins, but that for binding contacts hydrophobic interfaces turn out to be funneled while hydrophilic ones are antifunneled. This suggests evolution has found a mechanism for avoiding frustration between folding and binding by making use of indirect water‐mediated interactions. By juxtaposing the monomeric protein folding free energy profile in the protein complex database with another database consisting of only well‐folded monomers, we estimate that at least 15% of monomers in the former database are unfolded in the absence of partner protein interface interactions. When employing the parameters characteristic of these unfolded monomers to construct binding/folding phase diagrams, we find that these monomers would indeed fold if sufficiently stabilizing binding contacts, consistent with that fold, are formed. © 2003 Wiley Periodicals, Inc. Biopolymers: 333–349, 2003
Acetylcholinesterase in motion: Visualizing conformational changes in crystal structures by a morphing procedure
Authors: Zeev‐Ben‐Mordehai T. , Silman I. , Sussman J. L.
Published: February 2003

In order to visualize and appreciate conformational changes between homologous three‐dimensional (3D) protein structures or protein/inhibitor complexes, we have developed a user‐friendly morphing procedure. It enabled us to detect coordinated conformational changes not easily discernible by analytic methods or by comparison of static images. This procedure was applied to comparison of native Torpedo californica acetylcholinesterase and of complexes with reversible inhibitors and conjugates with covalent inhibitors. It was likewise shown to be valuable for the visualization of conformational differences between acetylcholinesterases from different species. The procedure involves generation, in Cartesian space, of 25 interpolated intermediate structures between the initial and final 3D structures, which then serve as the individual frames in a QuickTime movie. © 2003 Wiley Periodicals, Inc. Biopolymers: 395–406, 2003
Application of the empirical force field to macrocyclic ion carriers, siderophores, and biomimetic analogs
Authors: Felder Clifford E. , Shanzer Abraham
Published: February 2003

The empirical force field (EFF), developed by Prof. Lifson, was applied to the study of macrocyclic alkali ion carriers and to di‐ and tripodal and open chain siderophores and synthetic biomimetic molecules binding transition metals. The highly symmetric nature of these structures facilitated a favorable coordination geometry of the ligating groups about the metal, which helped organize the entire molecule into a fairly rigid structure. In our combined experimental‐theoretical approach, EFF calculations were used to help predict likely candidates to synthesize, and provided a wealth of structural data to complement what we learned from the spectroscopic measurements, while feedback from these measurements allowed us to continue improving the EFF itself. The simple, highly modular design of the biomimetic analogs allowed rapid synthesis and systematic examination of a large number of related structures, as well as facilitating an efficient, piecewise conformational scanning for the theoretical calculations. In the early years, we focused on macrocyclic polylactones and lactams binding monovalent alkali ions, particularly the natural products enniatin and valinomycin, including inside a crystal lattice. Later we switched to bi‐ and tridentate siderophores, natural microbial iron carriers, and synthetic biomimetic analogs—in particular, of enterobactin, ferrichrome, and ferrioxamine B. Over the years a large number of biomimetic siderophores have been prepared, some active in a broad range of microorganisms while others are highly species specific. The results of this work have broad applications in many areas, including the design of novel drugs and antimicrobial agents, helical polymeric structures, and polynuclear metal complexes. © 2003 Wiley Periodicals, Inc. Biopolymers: 407–421, 2003
The dominant interaction between peptide and urea is electrostatic in nature: A molecular dynamics simulation study
Authors: Tobi Dror , Elber Ron , Thirumalai Devarajan
Published: February 2003

The conformational equilibrium of a blocked valine peptide in water and aqueous urea solution is studied using molecular dynamics simulations. Pair correlation functions indicate enhanced concentration of urea near the peptide. Stronger hydrogen bonding of urea–peptide compared to water–peptide is observed with preference for helical conformation. The potential of mean force, computed using umbrella sampling, shows only small differences between urea and water solvation that are difficult to quantify. The changes in solvent structure around the peptide are explained by favorable electrostatic interactions (hydrogen bonds) of urea with the peptide backbone. There is no evidence for significant changes in hydrophobic interactions in the two conformations of the peptide in urea solution. Our simulations suggest that urea denatures proteins by preferentially forming hydrogen bonds to the peptide backbone, reducing the barrier for exposing protein residues to the solvent, and reaching the unfolded state. © 2003 Wiley Periodicals, Inc. Biopolymers: 359–369, 2003
Vibrational spectroscopy and the development of new force fields for biological molecules
Authors: Gerber R. B. , Chaban G. M. , Gregurick S. K. , Brauer B.
Published: February 2003

The role of vibrational spectroscopy in the testing of force fields of biological molecules and in the determination of improved force fields is discussed. Analysis shows that quantitative testing of potential energy surfaces by comparison with spectroscopic data generally requires calculations that include anharmonic couplings between different vibrational modes. Applications of the vibrational self‐consistent field (VSCF) method to calculations of spectroscopy of biological molecules are presented, and comparison with experiment is used to determine the merits and flaws of various types of force fields. The main conclusions include the following: (1) Potential surfaces from ab initio methods at the level of MP2 yield very satisfactory agreement with spectroscopic experimental data. (2) By the test of spectroscopy, ab initio force fields are considerably superior to the standard versions of force fields such as AMBER or OPLS. (3) Much of the spectroscopic weakness of AMBER and OPLS is due to incorrect description of anharmonic coupling between different vibrational modes. (4) Potential surfaces of the QM/MM (Quantum Mechanics/Molecular Mechanics) type, and potentials based on improved versions of semi‐empirical electronic structure theory, which are feasible for large biological molecules, yield encouraging results by the test of vibrational spectroscopy. © 2003 Wiley Periodicals, Inc. Biopolymers: 370–382, 2003
Structure–function relationship studies of bovine parathyroid hormone [bPTH(1–34)] analogues containing α‐amino‐iso‐butyric acid (Aib) residues
Authors: Peggion E. , Mammi S. , Schievano E. , Schiebler L. , Corich M. , Rosenblatt M. , Chorev M.
Published: February 2003

The N‐terminal 1–34 fragments of the parathyroid hormone (PTH) and parathyroid hormone‐related protein (PTHrP) elicit the full spectrum of bone‐related biological activities of the intact native sequences. It has been suggested that the structural elements essential for bioactivity are two helical segments located at the N‐terminal and C‐terminal sequences, connected by hinges or flexible points around positions 12 and 19. In order to assess the relevance of the local conformation around Gly12 upon biological function, we synthesized and characterized the following PTH(1–34) analogues containing Aib residues: (I) A‐V‐S‐E‐I‐Q‐F‐nL‐H‐N‐Aib‐G‐K‐H‐L‐S‐S‐nL‐E‐R‐V‐E‐Nal‐L‐R‐K‐K‐L‐Q‐D‐V‐H‐N‐Y‐NH2 {[Nle8,18, Aib11, Nal23,Tyr34]bPTH(1–34)–NH2}; (II) A‐V‐S‐E‐I‐Q‐F‐nL‐H‐N‐L‐Aib‐K‐H‐L‐S‐S‐nL‐E‐R‐V‐E‐Nal‐L‐R‐K‐K‐L‐Q‐D‐V‐H‐N‐Y‐NH2 {[Nle8,18, Aib12,Nal23,Tyr34]bPTH(1–34)–NH2}; (III) A‐V‐S‐E‐I‐Q‐F‐nL‐H‐N‐L‐G‐Aib‐H‐L‐S‐S‐nL‐E‐R‐V‐E‐Nal‐L‐R‐K‐K‐L‐Q‐D‐V‐H‐N‐Y‐NH2 {[Nle8,18, Aib13, Nal23,Tyr34]bPTH(1–34)–NH2}; (IV) A‐V‐S‐E‐I‐Q‐F‐nL‐H‐N‐Aib‐Aib‐K‐H‐L‐S‐S‐nL‐E‐R‐V‐E‐Nal‐L‐R‐K‐K‐L‐Q‐D‐V‐H‐N‐YNH2 {[Nle8,18, Aib11,12, Nal23,Tyr34]bPTH(1–34)–NH2}; (V) A‐V‐S‐E‐I‐Q‐F‐nL‐H‐N‐L‐Aib‐Aib‐H‐L‐S‐S‐nL‐E‐R‐V‐E‐Nal‐L‐R‐K‐K‐L‐Q‐D‐V‐H‐N‐Y‐NH2 {[Nle8,18, Aib12,13,Nal23,Tyr34]bPTH(1–34)–NH2}. (nL= Nle; Nal= L‐(2‐naphthyl)‐alanine; Aib= α‐amino‐isobutyric acid.) The introduction of Aib residues at position 11 in analogue I or at positions 11 and 12 in analogue IV resulted in a 5–20‐fold lower efficacy and a substantial loss of binding affinity compared to the parent compound [Nle8,18, Nal23,Tyr34]bPTH(1–34)–NH2. Both binding affinity and adenylyl cyclase stimulation activity are largely restored when the Aib residues are introduced at position 12 in analogue II, 13 in analogue III, and 12–13 in analogue V. The conformational properties of the analogues in aqueous solution containing dodecylphosphocholine micelles were studied by CD, two‐dimensional (2D) NMR and computer simulations. The results indicated the presence of two helical segments in all analogues, located at the N‐terminal and C‐terminal sequences. Insertion of Aib residues at positions 12 and 13, or of Aib dyads at positions 11–12 and 12–13, enhances the stability of the N‐terminal helix of all analogues. In all analogues the Aib residues are included in the helical segments. These results confirmed the importance of the helical structure in the N‐terminal activation domain, as well as of the presence of the Leu11 hydrophobic side chain in the native sequence, for PTH‐like bioactivity. © 2003 Wiley Periodicals, Inc. Biopolymers: 437–457, 2003