bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exclusion chromatography using porous glass. II. Application to hydrophilic polymers
Authors: Spatorico A. L. , Beyer G. L. 
Published: April 2003

AbstractA chromatograph employing five columns packed with porous glass of pore size 1250 Å to 75 Å provided peak retention volumes (VR) that were reproducible and essentially independent of sample size and flow rate when aqueous eluents were used. Calibration was carried out with a series of dextran fractions and polystyrene sulfonate samples, both of moderately narrow molecular weight distribution. The universal calibration method, based on hydrodynamic volume, was tested for four different polymer types. All four types produced a common curve within experimental error, which indicates that absolute molecular weight distributions may be derived from aqueous exclusion chromatography data for at least these polymer types. Additional study using a higher salt concentration produced hydrodynamic‐volume plots that superposed with those above. The use of the same set of porous glass columns with polystyrene standards in three different organic solvents produced calibration curves that agreed well with the aqueous curves after corrections were made for differences in available pore volumes.
Polyimides from diisocyanates, dianhydrides, and tetracarboxylic acids
Authors: Alvino William M. , Edelman Leonard E. 
Published: April 2003

AbstractHigh molecular weight polyimide resins have been prepared by the reaction of diisocyanates and a mixture of dianhydrides and their acids in the presence of a tertiary amine catalyst. The polyimides thus formed can be made into tough flexible films similar to those polyimides prepared by the conventional method of reacting a dianhydride with a diamine. The preparation of high molecular weight polymer is affected by the purity of reagents, the anhydride‐acid ratio, temperature, and moisture. Evidence from model compound studies is presented regarding the nature of the reaction mechanism.
Preparation of composite reverse osmosis membranes by plasma polymerization of organic compounds. III. Plasma polymers of acetylene/CO/H2O
Authors: Yasuda H. , Marsh H. C. 
Published: April 2003

AbstractReverse osmosis characteristics of composite membranes prepared by the plasma polymerization of acetylene/CO/H2O mixtures with various ratios of components are investigated; porous film of cellulose nitrate‐cellulose acetate is used as the substrate. This monomer system seems to have the following advantages: (1) A relatively short deposition time (1–2 min) is enough to produce reasonably good reverse osmosis membranes; and (2) good chemical stability of membranes can be obtained, especially in the case of chlorine resistance.
On the thermal degradation of poly(vinyl chloride). III. Structural changes during degradation in nitrogen
Authors: Abbås K. B. , Sörvik E. M. 
Published: April 2003

AbstractThe structural changes in poly(vinyl chloride) during thermal degradation in nitrogen at 190°C have been investigated. From gel permeation chromatography analyses no chain scission, but only crosslinking reactions were observed. An increase in the molecular weight was measured even at 0.3% conversion. For longer polyene sequences and at higher conversions, a crosslinking reaction competed with the “zipper” propagation. The secondary reactions, were more extensive at longer polyene sequence lengths. The growing polyene sequences can be terminated not only by branching reactions but also at existing pendent chloromethylene groups. A decrease in the amount of short chain branching with conversion also indicated other types of secondary reactions. Such a decrease was also observed during thermomechanical degradation in a Brabender Plastograph. The average polyene sequence length was calculated to be around 10, depending somewhat on the type of analysis used. Although allylic chlorine atoms seem to be the main points of initiation, other sites cannot be excluded as the number of initiation points increases appreciably during the early stages of the degradation. Such an increase is, of course, also consistent with a radical mechanism.
End‐wise degradation of hydrocellulose during hot alkali treatment
Authors: Johansson Mats H. , Samuelson Olof 
Published: April 2003

AbstractDeterminations of reducing and carboxylic acid end groups in hydrocellulose treated with hot alkali showed that the end‐wise degradation proceeded to such an extent that some of the molecules were brought completely into solution. The major carboxylic acid end groups formed in reactions competing with the end‐wise degradation were 3‐deoxyhexonic and 2‐C‐methylglyceric acids; but 2‐deoxypentonic, 2‐C‐methylpentonic, and minor amounts of aldonic acids were also formed. The formation of these stable end groups explains the observed increase in number average degree of polymerization during the treatment. The ratio between the number of lost glucose moieties and the number of carboxylic acid groups formed in the solid phase was about 170 and was only slightly affected by the duration of the hot alkali treatment.
Mechanism of low‐profile behavior in single‐phase unsaturated polyester systems
Authors: Pattison Victor A. , Hindersinn Raymond R. , Schwartz Willis T. 
Published: April 2003

AbstractThe mechanism of the low profile behavior in certain single‐phase polyester systems has been examined. It appears that as polymerization occurs, crosslinked beads (< 1μ) of polymer separate from the bulk solution. As the temperature rises, liquid monomer expands, counteracting polymerization shrinkage. As shrinkage surpasses expansion towards the end of polymerization, stresses are induced in the system. These are relieved internally by a series of micro cracks in the continuous matrix of the polymer rather than, as in ordinary systems, through macroscopic shrinkage of the molded part.
Study of the glass transition of poly(ethylene terephthalate) by gas chromatography
Authors: Hsiung P. L. , Cates David M. 
Published: April 2003

AbstractThe technique of gas chromatography is used to detect the temperature (Tg) at which the solubility of organic solutes in poly(ethylene terephthalate) (PET) becomes detectable, when the temperature is raised from below to above the glass transition temperature. For a given solute, Tg varies with the structure of PET. For a given structure of PET, Tg varies with the nature of the solute.
Craze growth and void coalescence in PMMA round notched bars
Authors: El‐Hakeem H. , Marshall G. P. , Zichy E. L. , Culver L. E. 
Published: April 2003

AbstractA study of the kinetics, failure mechanism, and fracture surfaces of PMMA/methanol crazes has been made on notched circular bar specimens subjected to constant tensile loads. Failures were by void growth and coalescence inside the craze away from the notch tip and near to the specimen center. Two distinct features of void coalescence were observed; the first a cluster of very small voids (each of the order of 3.4 × 103 Å) and the second, separate larger voids which usually caused final failure.An analysis of craze growth, based on fracture mechanics concepts in conjunction with simple flow analysis, suggests that the growth is controlled mainly by the ability of the environment to flow through the voided structure of the craze. Good agreement has been obtained between predicted behavior and experimental data.
Infrared detection of polymers in gel permeation chromatography
Authors: Dawkins John V. , Hemming Malcolm 
Published: April 2003

AbstractA gel permeation chromatograph equipped with an on‐line Grubb‐Parsons infrared spectrometer is described. The versatility, specificity, sensitivity, and limitations of such an infrared detector are discussed with particular reference to spectrometer specification, eluent absorbance, and solute absorbance. A stable baseline is produced when this detector is operated at high temperatures, e.g., for the separation of polyethylene in o‐dichlorobenzene at 135°C. Individual functional groups in a chemically inhomogeneous solute, such as a copolymer, may be monitored by repeated injections of the solute, changing the wavelength setting between separations. This procedure is illustrated with AB poly(styrene‐b‐t‐butyl methacrylate) block copolymer in trichloroethylene at 35°C.
A rheological model of viscose rayon
Authors: Aksan Stanisława , Żurek Witold 
Published: April 2003

AbstractIn viscose rayon samples subjected to cyclic loading the phenomenon of supertension was observed as a variation of the linear elasticity limit in the consecutive cycles. To enable a mathematical description of this phenomenon a rheological model with an inertional‐frictional element was devised. The curves calculated on the basis of the model well approximated the experimental results.
The effect of pressure on carbon black/elastomer powders. IV. Comparison of press‐cured powders containing vulcanizing agents with mill‐mixed compounds
Authors: Angerer G. , Schilling H. 
Published: April 2003

AbstractSBR latex was compounded with six different types of carbon black (SRF, FEF, HAF, SAF, HEB, and HCC‐I) and vulcanization ingredients in aqueous dispersion by means of a dispersing agent. The particle size of the carbon black agglomerates in aqueous dispersion was estimated from turbidity and light scattering measurements. It was found that the size of the aggregates is by far larger than the average particle size of the SBR‐latex used. The latex mixture containing carbon black and vulcanization ingredients was spray‐dried to a fine‐sized powder of an average particle size of 0.25 mm; this powder was subsequently vulcanized without the action of shear forces at a pressure of 200 bar. It was the aim of this study to answer the question whether latex‐stage compounded vulcanizates can be reinforced without applying shear forces, if only the distribution of the carbon black in the compound is sufficiently good. The tensile strength was used for judging reinforcement; the quality of the carbon black dispersion was estimated by means of the Cabot rating method. The carbon black dispersion in the compounded powders proved to be excellent with fine‐sized carbon blacks and was in the order of A 1 and B 2 of the Cabot scale. Scanning electron micrographs of the fracture zones and transmission electron micrographs on ultrathin cuts showed, however, differences in the microdispersion of the carbon blacks between powder‐and mill‐mixed compounds. A comparison of the mechanical properties of powder‐and mill‐mixed compounds yielded partially comparable tensile values for the powder compounds up to 20 MN/m2, but strikingly high hardness, elongation set and a pronounced stress‐softening after repeated deformation (Mullins‐effect).
An investigation of the surface areas of dyed and undyed secondary cellulose acetate by p‐nitrophenol adsorption
Authors: Blair Hal S. , McElroy Mervyn J. 
Published: April 2003

AbstractThe surface areas of dyed and undyed secondary cellulose acetate fibers were estimated using p‐nitrophenol adsorption. When values of specific surface area are plotted against dye concentration, there is a marked change in the region corresponding to a theoretical monolayer adsorption of the dye.
Analysis for vinyl chloride in PVC powders by head‐space gas chromatography
Authors: Berens A. R. , Crider L. B. , Tomanek C. J. , Whitney J. M. 
Published: April 2003

AbstractAt a temperature above the glass transition point of poly(vinyl chloride) (PVC), the solubility of vinyl chloride monomer (VCM) in PVC accurately follows Henry's law behavior for VCM contents up to 4000 ppm. This observation has lead to a rapid, simple gas‐chromatographic method for the determination of VCM in PVC from the analysis of the vapor phase (head‐space) over PVC powder samples in a sealed container. The basic experimental techniques, calculations, and examples of experimental data are given. The method can be used with any commercial gas chromatograph equipped with a flame ionization detector without instrument modification.
Block polymers from isocyanate‐terminated intermediates. IV. Properties of cured butadiene–ε‐caprolactam block polymers
Authors: Hergenrother William L. , Ambrose Richard J. 
Published: April 2003

AbstractButadiene–ε‐caprolactam block polymers containing a high proporation of 1,2 units in the butadiene‐segments were synthesized and physical properties were measured on the cured copolymers. Flexural strength and impact resistance both increase regularly with increasing ε‐caprolactam content in peroxide cured copolymers. This behavior is explained by the higher values of flexural modulus and impact resistance for poly(ε‐caprolactam) compared with peroxide‐cured polybutadiene resins. Copolymers reinforced with silica showed higher heat distortion temperatures but lower impact resistance than corresponding unfilled samples. Arrhenius plots of flexural properties at various test temperatures were linear. Both flexural modulus and strength decreased regularly with increasing test temperature. Flexural properties of filled copolymers were relatively unaffected by heat aging up to 204°C for several weeks, however, dramatic decreases in these properties were noted in a matter of days when heat aging was done at 260–316°C. These results are explained by the rapid degradation of poly(ε‐caprolactam) above its melting point. Block polymers whose butadiene segments contained a high proportion of 1,4 units were also synthesized. These copolymers were elastomeric when cured with either sulfur or peroxide.
Mechanical degradation of dilute solutions of high polymers in capillary tube flow
Authors: Culter John D. , Zakin Jacques L. , Patterson Gary K. 
Published: April 2003

AbstractExperimental results on mechanical degradation in capillary tubes of polyisobutylene polymers in dilute solution are described. In laminar flow, degradation is independent of tube length, indicating that entrance effects are dominant. This shows that capillary experiments do not yield explicit information on the effect of shear stress on mechanical degradation. In turbulent flow, large entrance effects are also observed, but some degradation does take place in the fully developed flow region.
Porous polymer carbons. V. Macroporous carbons from crosslinked α‐chloroacrylonitrile polymers
Authors: Ehigiamusoe R. E. , Howard G. J. 
Published: April 2003

AbstractSuspension copolymerizations of α‐chloroacrylonitrile and divinylbenzene have been carried out both with and without diluents. The polymers are macroporous except for those without diluent and of higher crosslinker content. At a fixed divinylbenzene content, the macroporosity increases with diluent content and is always higher with nonsolvating diluent. The gross morphologic features of the polymers depend on the crosslink density and on both the nature and amount of the diluent; scanning electron micrographs of typical examples are shown. Semicarbons are readily produced by dehydrochlorination. On full carbonization at 900°C, microporous carbons are produced which have some residual nitrogen‐containing groups able to act as specific sites for anionic adsorbates. Homopoly α‐chloroacrylonitrile fuses on heating to 900°C unless it has been previously dehydrochlorinated by treatment with base. All crosslinked polymers give carbons which are pseudomorphs of the original specimens.
Client‐side monitoring for Web mining
Authors: Fenstermacher Kurt D. , Ginsburg Mark 
Published: April 2003

Abstract“Garbage in, garbage out” is a well‐known phrase in computer analysis, and one that comes to mind when mining Web data to draw conclusions about Web users. The challenge is that data analysts wish to infer patterns of client‐side behavior from server‐side data. However, because only a fraction of the user's actions ever reaches the Web server, analysts must rely on incomplete data. In this paper, we propose a client‐side monitoring system that is unobtrusive and supports flexible data collection. Moreover, the proposed framework encompasses client‐side applications beyond the Web browser. Expanding monitoring beyond the browser to incorporate standard office productivity tools enables analysts to derive a much richer and more accurate picture of user behavior on the Web.
DocCube: Multi‐dimensional visualisation and exploration of large document sets
Authors: Mothe Josiane , Chrisment Claude , Dousset Bernard , Alaux Joel 
Published: April 2003

AbstractThis paper presents a novel user interface that provides global visualizations of large document sets in order to help users to formulate the query that corresponds to their information needs and to access the corresponding documents. An important element of the approach we introduce is the use of concept hierarchies (CHs) in order to structure the document collection. Each CH corresponds to a facet of the documents users can be interested in. Users browse these CHs in order to specify and refine their information needs. Additionally the interface is based on OLAP principles and multi‐dimensional analysis operators are provided to users in order to allow them to explore a document collection.
ZstatFlu®‐II test: a chemiluminescent neuraminidase assay for influenza viral diagnostics
Authors: Achyuthan Komandoor E. , Pence Lisa M. , Appleman James R. , Shimasaki Craig D. 
Published: April 2003

AbstractThe ZstatFlu®‐II test is a highly sensitive, specific, rapid, point‐of‐care chemiluminescent diagnostic test for influenza infection. Influenza viral neuraminidase‐specific substrate, spiroadamantyl‐1,2‐dioxetane‐4,7‐dimethoxy‐N‐acetyl‐neuraminic acid, is at the core of the ZstatFlu®‐II Test. The enzymatic reaction was carried out at 25°C and neutral pH, representing the optimum assay conditions for influenza types A and B viral neuraminidases. The results were outputted on a Polaroid™ High Speed Detector Film. Positive results appeared as a ‘+’‐shaped white film image; negative results produced no image. The ‘glow’ kinetics, facilitated by a unique combination of light enhancers, also ‘tuned’ the wavelength of emission to match the spectral properties of the film. The substrate hydrolysed non‐enzymatically at acid pH or at temperatures above 25°C. In order to minimize false positives, the ZstatFlu®‐II Test was formatted with 0.3–0.4 Km substrate and freezing the test kit until use. The pH optimization of the ZstatFlu®‐II test is discussed with reference to model compounds of sialyl‐glycosides. A nucleophilic attack or an electrostatic stabilization of a developing carbonium ion under the influence of the adjacent carboxyl group was probably responsible for non‐enzymatic hydrolysis of the substrate. Intramolecular general acid catalysis is proposed as a mechanism for the lability of the O‐glycosidic linkage of the substrate. Copyright © 2003 John Wiley & Sons, Ltd.
Stimulation of DNA repair as an evolutionary drive for bacterial luminescence
Authors: Czyż Agata , Plata Konrad , Wȩgrzyn Grzegorz 
Published: April 2003

AbstractIt was demonstrated recently that luminescence of a free‐living marine bacterium, Vibrio harveyi, stimulates DNA repair, most probably by activation of the photoreactivation process. Here, we ask whether the stimulation of DNA repair could be an evolutionary drive that ensured maintenance and development of early bacterial luminescent systems. To test this hypothesis, we cultivated V. harveyi lux+ bacteria and luxA mutants in mixed cultures. Initial cultures were mixed to obtain a culture consisting of roughly 50% lux+ cells and 50% luxA mutants. Then bacteria were cultivated for several days and ratio of luminescent to dark bacteria was measured. Under these conditions, luxA mutants became highly predominant within a few days of cultivation. This indicates that, without a selective pressure, the luminescence is a disadvantage for bacteria, perhaps due to consumption of significant portion of cell energy. However, when the same experiments were repeated but cultures were irradiated with low UV doses, luminescent bacteria started to predominate shortly after the irradiation. Therefore, we conclude that stimulation of photoreactivation may be an evolutionary drive for bacterial bioluminescence. Copyright © 2003 John Wiley & Sons, Ltd.
RGD‐grafted poly‐l‐lysine‐graft‐(polyethylene glycol) copolymers block non‐specific protein adsorption while promoting cell adhesion
Authors: VandeVondele Stephanie , Vörös Janos , Hubbell Jeffrey A. 
Published: April 2003

AbstractA novel class of surface‐active copolymers is described, designed to protect surfaces from nonspecific protein adsorption while still inducing specific cell attachment and spreading. A graft copolymer was synthesized, containing poly‐(L‐lysine) (PLL) as the backbone and substrate binding and poly(ethylene glycol) (PEG) as protein adsorption‐resistant pendant side chains. A fraction of the grafted PEG was pendantly functionalized by covalent conjugation to the peptide motif RGD to induce cell binding. The graft copolymer spontaneously adsorbs from dilute aqueous solution onto negatively charged surfaces. The performance of RGD‐modified PLL‐g‐PEG copolymers was analyzed in protein adsorption and cell culture assays. These coatings efficiently blocked the adsorption of serum proteins to Nb2O5 and tissue culture polystyrene while specifically supporting attachment and spreading of human dermal fibroblasts. This surface functionalization technology is expected to be valuable in both the biomaterial and biosensor fields, because different signals can easily be combined, and sterilization and application are straightforward and cost‐effective. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 784–790, 2003.
Salt hydrates for in situ water activity control have acid–base effects on enzymes in nonaqueous media
Authors: Fontes Nuno , Harper Neil , Halling Peter J. , Barreiros Susana 
Published: April 2003

AbstractSalt hydrates very frequently are utilized as in situ water activity buffers in reaction mixtures of enzymes in nonaqueous media. In addition to buffering water activity, there is evidence that salt hydrates also often affect initial rates in other ways. This has been generally overlooked or thought to be related to water transfer effects. Here we show that salt hydrates can have important acid–base effects on enzymes in nonaqueous media. We performed transesterification reactions in n‐hexane and in supercritical ethane catalyzed by cross‐linked crystals of subtilisin, differing in the method used to set aW, and confirmed that the presence of salt hydrate pairs significantly affected the catalytic performance of the enzyme. However, in the presence of a solid‐state acid–base buffer, salt hydrates had no effect on enzymatic activity. Direct evidence for the acid–base effects of salt hydrates was obtained by testing their effect on the protonation state of an organo‐soluble H+/Na+ indicator. The four salt hydrate pairs tested affected the indicator to very different extents. By promoting the exchange of H+ for Na+, salt hydrates will tend to affect the ionization state of acidic residues in the protein and, hence, enzymatic activity. In fact, salt hydrates were able to affect the pH memory of subtilisin lyophilized from different aqueous pHs, bringing about up to 20‐fold enhancements and up to 5‐fold decreases in catalytic activity. The possibility of such acid–base effects need to be considered in all experiments using salt hydrates to control water activity. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 802–808, 2003.