bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flexibility and phase transitions of polymers
Authors: Schneider Hans Adam 
Published: February 2003

AbstractIt 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

AbstractSupercritical 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

AbstractN‐(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

AbstractWater‐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

AbstractPolystyrene 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

AbstractPentabromobenzylacrylate (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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractPolyaniline (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

AbstractA 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

AbstractA 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

AbstractComputer 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

AbstractWe 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

AbstractA 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

AbstractA 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

AbstractSpontaneous 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

AbstractIt 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