bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and physical properties of polyurethanes
Authors: Tanaka Takehide , Yokoyama Tetsuo 
Published: June 2010

AbstractThe relations between structure and physical properties of polyurethane elastomers, particularly elastic properties, were studied. Polyurethanes with various structures were prepared by a prepolymer technique. Among the conceivable structural factors the substituted urea group, which was introduced by the use of a diamine‐type curing agent, had a remarkable reinforcing effect. This was attributed to the strong hydrogen‐bonding effect between urea groups. In this connection, softening occurred during repeated deformation of diamine‐cured polyurethane elastomers. It was proved that this is due not to the melting of crystallite but to the slip of hydrogen bonding between urea groups. On the other hand, urea groups did not have much influence on equilibrium rubber elasticity. The contribution of the force caused by the internal energy to the total force was independent of curing agents, being determined by the principal segments of network chains.
Rheo‐optical behavior of isotactic and linear atactic poly‐alpha‐olefins in solution
Authors: Philippoff W. , Tornqvist E. G. M. 
Published: June 2010

AbstractThe influence of the stereochemistry of the monomer on the optical properties, namely the stress optical coefficient C of polymer solutions has been investigated by using polymers of α‐olefins in solution. Polymers of α‐olefins up to and including polyoctadecene were used. The experimental results are shown in Figure 1 on the example of a 5% solution of Poly(Decene‐1). The three properties, the degree of birefringence Δn, the extinction angle χ and the viscosity η were measured over a range of rates of shear D. These measurements are then combined to the stress optical coefficient C: C = Δn sin 2x/2τ, which, as is well known, is independent of the molecular weight, concentration, and rate of shear (τ shear stress = η.D). For Poly(Decene‐1) the results are shown in Figure 2. All the results obtained are shown in Figure 3 where C is plotted versus n, the number of carbon atoms in the side chain for two main‐chain C atoms. The result is a linear relationship between C and n giving an isotropic polymer at n = 4. This means that the side chain atoms contribute only 1/2 the value of the main‐chain atoms towards the anisotropy of the molecule. This is believed to be the result of the free rotation of the molecular units against each other and allows a number of polymers including polyisobutylene to be discussed in a uniform manner. Equally the influence of the tacticity was established, that is, a maximum occurs for polypropylene and it becomes nearly negligible for polyhexene‐1 and higher polymers. Having now a well‐established series of poly‐α‐olefins, and corresponding C values, one can use these data to check the stereochemistry of further polymers.
Stable polyradicals
Authors: Braun Dietrich 
Published: June 2010

AbstractMacromolecular chemistry has so far been concerned nearly exclusively with neutral macromolecules and with polyions. Very little is known about macromolecular compounds having radical character. Although polymerizable, stable organic radicals have not been obtained as yet, stable polyradicals have been prepared in the past few years by performing chemical conversions on macromolecules. At first a nitrogen polyradical, which is also stable in the solid state, a polyhydrazyl similar to diphenyl picrylhydrazyl, was prepared; it was obtained from dinitrated poly‐p‐fluorostyrene and N,N‐diphenylhydrazine by subsequent oxidation of the polyhydrazine formed. Similar polymeric hydrazyls can be obtained in an analogous manner from poly(vinyltriarylmethyl chlorides) and N,N‐diphenyl hydrazine; in contrast to their low molecular weight models, these polyhydrazyls can also be isolated as solids. Polymeric carbon radicals were prepared for the first time from poly‐p‐(vinyltriarylcarbinols) by converting the carbinol monomer units into triarylmethyl chloride units, which can subsequently be converted into polymeric trityl radicals by treatment with zinc or alkali metal. Polyradical‐anions constitute a further group of radical‐carrying macromolecules; they are formed, for instance, by addition of alkali metals to polymers having CO or CN bonds.
Synthesis of terminally difunctional polythioethers by polyaddition reactions involving allylic sulfides
Authors: Oswald A. A. , Griesbaum K. , Hall D. N. 
Published: June 2010

AbstractThe terminal functional groups of polythioethers derived in polyaddition reactions were examined, and the reactions were studied systematically for the first time. Free‐radical thiol polyaddition reactions involving allylic sulfides, i.e., polyaddition of dithiols to allene and allylic sulfides and poly‐self‐addition of allylic mercaptans were found to yield terminally difunctional polythioethers of 500 to 5000 molecular weight. If such polyadditions were carried out with an excess of the dithiol reactant, polythioetherdithiols were obtained. The latter in turn could be readily converted to hydroxy‐terminated polymers by reaction with an unsaturated alcohol or an epoxide.
The preparation of graft copolymers of polystyrene with poly‐2‐vinylpyridine
Authors: Gervasi J. A. , Gosnell A. B. , Stannett V. 
Published: June 2010

AbstractGraft copolymers have been prepared with polystyrene backbones and poly‐2‐vinylpyridine side chains. The approach used was to couple together two preformed polymers which were themselves separately characterized. Thus, a knowledge of the overall composition and separate descriptions of the two homopolymers gave reasonably well defined grafts. The living‐polymer technique of Szwarc was found to be well suited to this approach. Polystyrene backbones were prepared by anionic polymerization, with Mw/Mn values of less than 1.1 and then chloromethylated to provide reactive grafting sites. The poly‐2‐vinylpyridine side chains were also prepared by anionic polymerization and, while still active, were allowed to react with the chloromethylated polystyrene. The homopolymers were removed by solvent extractions, leaving the graft copolymer as a residue. The molecular weight of the graft was then determined by osmotic‐pressure measurements. Several features of the synthesis and characterization of the grafts and of the homopolymers are discussed. Within very broad limits this method permitted an unrestricted choice of backbone and of side‐chain length and of the average number of side chains per backbone.
Photolysis in a well‐stirred solution
Authors: Shultz A. R. 
Published: June 2010

AbstractAn equation is derived describing the extent of photolysis of a photosensitive solute in a well‐stirred solution. The solute, solvent, and photolysis products are all assumed to absorb the monochromatic light employed. The optical density of the system is therefore time(conversion)‐dependent, but not position‐dependent. The derived equation has been programmed in FORTRAN language for digital computing. Computed relations for some chosen sets of input data are illustrated graphically. Besides being useful in determining quantum efficiencies in photolytic reactions, the derived relations should assist in the extrapolation of findings in optically thin systems to those to be expected in optically thick geometries.
Polymer reactors and molecular weight distribution. IV. Free‐radical polymerization in a steady‐state stirred‐tank reactor train
Authors: Duerksen John H. , Hamielec Archie E. 
Published: June 2010

AbstractThis paper reports the simulation of steady‐state styrene polymerization in a single, continuous, stirred‐tank reactor (CSTR) at high viscosity, a train of three CSTR's with and without recycle, and a single, imperfectly mixed CSTR. Monomer conversion and polymer molecular weight distribution (MWD), measured experimentally by gel permeation chromatography, were used as criteria of simulation. Earlier results for the single CSTR were used to modify the catalyst efficiency f and termination rate constant kt, to account for the effect of viscosity, μ. The regression equations obtained were log μ = −1.06 −0.522 log (S + 1) −8.34 log (1 − PF) + 0.565 logr̄w, log (f/fi) = 0.022 log (1 + μ) −0.0285 [log (1 + μ)]2, and log (kt/kti) = 0.060 log (1 + μ) −0.0934 [log (1 + μ]2, where μ is reactor viscosity in centipoise, S is solvent concentration in g‐mole/1., PF is polymer weight fraction, r̄W is weight‐average chain length, and fi and kti are values at zero conversion. The theoretical models for the single CSTR and train of CSTR's simulated the behavior of the real, bench‐scale CSTR's over a range of experimental conditions. The model for the CSTR system was applied to a theoretical mixing model made up of perfectly mixed CSTR's.
A simple model for the virtually crosslinked block copolymers
Authors: Fedors R. F. 
Published: June 2010

AbstractA simple model is presented for the virtual crosslink effect in triblocks of the type A–B–A, where A is a segment having a relatively high Tg value and B is a segment having a relatively low Tg value. It is assumed that phase relationships can be estimated by using thermodynamics of polymer mixtures, but certain constraints are imposed on the morphology of phases by the fact that different segments are chemically attached to each other. According to the model, at least two requirements are necessary for a block copolymer to behave as a chemically vulcanized elastomer: (a) the A and B segments must be mutually insoluble, and (b) the A segment must have a higher Tg value than the maximum temperature for which the material will be expected to function. The size of the glassy domains is discussed along with the notion that the glassy domains function both as crosslinks and as filler particles.
Stochastic contributions to latex polydispersity
Authors: O'Toole J. T. 
Published: June 2010

AbstractParticle size distributions are modified during the growth process by means of two classes of mechanisms. Deterministic contributions result from formation during an extended period of time and from dependence of growth on size. Stochastic broadening can be a consequence of the discrete nature of any of the participating steps. This process was suggested to play a role in emulsion polymerizations by Ewart and Carr and by Brodnyan but has not been treated quantitatively. This work employs specific, familiar models to obtain explicit distributions and variances. For moderately large particles the stochastic contribution should be significant if the ratio of propagation to termination rate constants is greater than about 1:10. The predicted and observed distributions are compared for vinyl acetate. The initial development from monodisperse micelles is followed in detail.
Particle size distribution by turbidimetry
Authors: Maxim L. D. , Klein A. , Meyer M. E. , Kuist C. H. 
Published: June 2010

AbstractA turbidimetric method for rapidly estimating particle size distribution parameters for latex systems has received intensive evaluation. This method originally proposed by W. Heller and co‐workers [J. Chem. Phys. 34, 1796 (1961)], and based on Mie theory, involves the generation of theoretical turbidity functions versus wavelength and the comparison of these theoretical curves with ones determined experimentally. A digital computer program involving the use of a lattice search technique by minimization of residual sums of squares over a response surface was developed and used for comparing these curves. It has been found that this curve matching leads to multivalued solutions and, unless prior estimates of the answer from some other technique are available, there are no criteria for choosing between alternative solutions. The response surface is in the form of a “trench” rather than a unimodel “depression.” Consideration of typical experimental errors for this technique yields quite large areas of uncertainty in the final answers further complicating the analysis of results. These findings indicate that this method, though very attractive because of the simplicity of the experimental technique, should not be used alone for particle size analysis and hence cannot be considered a routine or simple procedure.
The effects of various monomer addition methods on the emulsion copolymerization of vinyl acetate and butyl acrylate
Authors: Chujo K. , Harada Y. , Tokuhara S. , Tanaka K. 
Published: June 2010

AbstractVarious monomer addition methods were applied to the emulsion co‐polymerization of vinyl acetate and butyl acrylate of which polymerization reactivities are very different from each other. The grafting efficiency and homogeneity of copolymer were determined by the fractionation and measurement of dynamic viscoelasticity of emulsion polymers. As the content of the second fraction of acetone‐soluble part increased and that of the third fraction decreased, then the homogeneity of the copolymer increased, In this case, only one dynamic loss peak existed near 0°C. The result showed that homogeneous copolymers were obtained by continuous monomer addition methods and heterogeneous copolymers were obtained by initial addition of total monomers or stepwise monomer addition methods. Homogeneity of copolymer had great influence on various properties, e.g., hardness and adhesive properties. Film hardness was the lowest for homogeneous copolymer and it was the highest for heterogeneous copolymer. Homogeneous copolymer was best for adhering plywood and poly(vinyl chloride). It is remarkable that copolymers of vinyl acetate and butyl acrylate with very different properties were obtained by changing only the monomer addition methods.
The stabilization of cellulose to alkaline degradation by novel end unit modifications
Authors: Procter A. R. , Wiekenkamp R. H. 
Published: June 2010

AbstractCellulose may be stabilized to alkaline degradation by treatment with hydrogen sulfide, in the presence of aqueous sodium carbonate, at elevated temperatures and pressures. Under these conditions, the cellulose reducing end groups are converted to 1‐thio‐D‐glucitol functions. The observed alkaline stability of hydrogen sulfide‐stabilized hydrocellulose can be rationalized in terms of the degree of end group modification.
Small‐angle scattering studies on carbonized cellulose fibers
Authors: Ruland W. 
Published: June 2010

AbstractA small‐angle scattering study has been carried out on heat‐treatment series of cellulose fibers. It was found that: the periodic density fluctuations along the fiber axis are enhanced in the first stages of pyrolysis and can persist after the decomposition of the cellulose structure; a memory of the microfibrillar structure of the starting material persists up to high temperatures of heat‐treatment; needle‐like pores with average diameters in the 10–30 Å range and lengths above 200 Å with a preferred orientation parallel to the fiber axis are formed at high temperatures.
Micro void system in pine cellulose
Authors: Jurbergs K. A. 
Published: June 2010

AbstractCellulose, which originates in the plant cells as a porous material, subsequently may undergo different changes. Incrustations and phenomena connected with drying are the most important among these changes. It is impossible to predict what the physical state should be after the cellulose is further isolated and purified. Electron microscopy in the past has been surprisingly ineffective in unequivocally resolving the question of porosity of cellulosic materials. Indirect methods, such as the various density and absorption determinations, usually yield controversial results. In the present work, slash and loblolly pine pulp fibers were preswelled in different swelling media, sectioned, stained with phosphotungstic acid, and investigated with an electron microscope. Some regular patterns of voids became discernible along with numerous distortions and introduced artifacts. Essentially two types of enlarged micro pores were found: round holes and elongated fissures. Both features are believed to represent interstitial spaces among the different structural units of cellulose. The round openings could represent interstices among fibrils and fibrillar bundles. The fissures are openings between the individual lamellae. In the finished pulp some of the micro voids are apparently still filled, either partially or completely, with different foreign materials, such as hemi, lignin, and resin residues.
Diffusive permeabilities and reverse osmosis rejection coefficients for four cellulosic membranes
Authors: Klein E. , Smith J. K. , Wendt R. P. 
Published: June 2010

AbstractDiffusive permeabilities of the solutes D2O, NaCl, creatinine, and bacitracin, and reverse osmosis rejection coefficients of the last three solutes, were measured for four cellulosic membranes chosen for their differences in symmetry, porosity, and degree of acetylation. The capillary‐pore theory of Durbin and the irreversible thermodynamic theory of Spiegler and Kedem were both used to calculate Staverman coefficients, σ, for each membrane with respect to each solute. Values measured for the permeabilities and rejection coefficients and effective pore area‐length ratios calculated using the capillary‐pore theory were generally in agreement with the assumed structural differences between the membranes. However, there were appreciable differences between corresponding values for σ calculated according to the two theories. Although no independent determinations of σ were made in these studies, we estimate the irreversible thermodynamic theory gives the more reliable result for membranes with low or intermediate rejection coefficients, and both theories give reliable results for membranes which are highly rejecting (σ > 0.9).
Fine structure of natural polysaccharide systems
Authors: Mühlethaler Kurt 
Published: June 2010

AbstractThe ultrastructure of cellulose in higher plant cell walls is discussed. The primary and secondary wall is built up of a framework of microfibrils composed of smaller strands which are termed elementary fibrils. In recent years a number of models for the chain‐arrangement of the cellulose molecules have been proposed. According to one view the cellulose chains are in a folded conformation. Based on a new method which allows the determination of the chain‐arrangement in the elementary fibrils it was found that the structural carbohydrate must be aggregated into continuous, extended‐chain filaments of nearly perfect crystallinity. Freezeeten profiles suggest that the mechanism of fibrillar formation is characterized by enzyme particles attached to the plasma membrane and involved in cellulose synthesis.
Effet des proprietes thermodynamiques des melanges de solvants sur les dimensions de Chaines macromoleculaires
Authors: Dondos Anastasios , Rempp Paul , Benoit Henri 
Published: June 2010

AbstractIn a binary solvent mixture, the χ1 2 interaction parameter has a marked influence upon the intrinsic viscosity of a polymer. If χ 1 2 is positive, the [χ] value is higher than the weighted average of the viscosities measured in the pure constituents. When the latter are non‐solvents of the polymer, and the mixture dissolves it, the so‐called cosolvency‐effect requires a positive value of χ1 2. If χ 1 2 is negative, the [χ] value is found lower than the average of the viscosities measured in the pure constituents. Demixtion can even occur when in a given composition range the mixture of two good solvents behave like a precipitant (χ1 2 <0). Athermal mixtures (χ1 2 = 0) exhibit no such effect, and behave like a pure solvent.To determine the unperturbed dimensions of a polymer coil in various binary solvent media, the Stockmayer‐Fixman extrapolation was used. It is known that for a given polymer the same Kχ value is found in any pure solvent. In binary mixtures the Kχ values are found higher or lower than this unique value, depending upon the sign of χ1 2. These qualitative results remains valid as long as selective adsorption of the better solvent on the chain remains low. If this is not the case, account has to be taken of the fact that composition inside the coil is not identical with the average composition of the mixture.A pure solvent in which molecules have a tendency to associate behaves like a solvent mixture in which χ1 2 is negative: the Kθ value is found lower than the unique Kθ value for this polymer in all other pure solvents.
Etude des moments dipolaires et des temps de relaxation du poly‐l‐glutamate de benzyle et de la poly‐dl‐phenylalanine en chaine en solution diluee
Authors: Marchal E. , Dufour C. 
Published: June 2010

AbstractOn détermine le moment électrique permanent μ et le temps de relaxation d'échantillons de poly‐L‐glutamate de benzyle et de poly‐DL‐phénylalanine dans l'acide dichloracétique (ADC) et les mélanges ADC‐heptane ou ADC‐chloroforme, solvants où ces polypeptides sont en chaǐne. L'élèment constitutif de ces polymères a une composante du moment dipolaire le long de la chaǐne et toujours dirigée vers la měme extrémité. Dans les bons solvants, on trouve que μ2 /M augmente avec M, tandis que dans les mélanges de solvants qui se comportent comme un solvant théta, aucune variation de μ2 /M avec M n'a été observée. Les variations du temps de relaxation en fonction de M ont également été déterminées dans de bons et mauvais solvants et comparées aux calculs de Zimm. On montre ensuite comment la transition chaǐne‐hélice du PLGB dans un mélange du solvants peut ětre mise en évidence par l'étude de la variation de la constante diélectrique et du temps de relaxation.
Anomalies des courbes experimentales donnant le gradient d'indice et permettant la determination du coefficient de diffusion de translation
Authors: Soulie L. 
Published: June 2010

AbstractLes courbes expérimentales donnant le gradient d'indice et permettant de déterminer le coefficient de diffusion de translation présentent plusieurs anomalies: dissymétrie des courbes par rapport à la surface de séparation initiale solvant‐solution, déplacement du maximum vers la région solvant et abaissement de ce maximum. Ces effets ne sont pas dus à une influence de la concentration sur le phénomène de diffusion, car ils sont expliqués par une étude de la trajectoire d'un rayon lumineux dans un milieu d'indice variable.
Light scattering of mucins in concentrated solutions
Authors: Bettelheim F. A. , Scheinthal B. M. 
Published: June 2010

AbstractLight scattering studies were performed on solutions of calcium slats of bovine submacillary mucin as a function of temperature and concentration. No critical concentration or critical temperature was found in either pure water or 0.155 M NaCl solutions. A steady aggregation process was observed with increasing concentration, and the solution went over to a soft gel structure without precipitation or phase separation. The relationship of bovine mucin aggregation to the aggregation and precipitation of human submaxillary saliva in patients with cystic fibrosis is discussed.
Determination of the structure of friedel‐crafts polymers
Authors: Grassie N. , Meldrum I. G. 
Published: June 2010

AbstractCondensation of di(chloromethyl) benzene and aromatic substances yields polymers which are infusible and insoluble. These polymerizations have been studied by investigating the initial stages of reaction when products are soluble and may be characterized by chromatographic and spectroscopic techniques. Information derived in this way has elucidated structural features of the polymers.