bluuebunny/crossref_metadata_2025 huggingface dataset:
Stable polyradicals
Authors: Braun Dietrich
Published: June 2010

Macromolecular 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

The 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

Graft 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

An 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

This 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

A 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

Particle 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

A 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

Various 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

Cellulose 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

A 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

Cellulose, 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

Diffusive 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

The 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

In 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

On 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

Les 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

Light 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

Condensation 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.
Etude des proprietes du polystyrene en solution en fonction des conditions de polymerisation
Authors: Ahad Elie , Sicotte Yvon
Published: June 2010

En caractérisant, par diffusion de la lumière en solvant thèta, des fractions fines de polystyrène provenant d'échantillons obtenus sous différentes conditions de polymérisation, radicalaire et anionique, on a mis en évidence que le rapport du carré moyen du rayon de giration sur la masse moléculaire varie avec les conditions de polymérisation. Il s'agit vraisemblablement d'une variation de tacticité en fonction des conditions de polymérisation. Cette variation de tacticité se reflète également dans la loi de viscosité en solution qui varie d'un échantillon à l'autre. Ces effets expliquent, en partie du moins, la dispersion très grande des paramètres structuraux rapportés pour le polystyrène atactique. Ce travail a permis par ailleurs de vérifier que la polydispersiteé des échantillons de polystyrène obtenus par polymérisation radicalaire ne montre pas de variations significatives entre 0°C et 60°C comme température de polymérisation.
Induced changes in the molecular weight of polybutadiene using alkyllithium‐alkyl halide complexes
Authors: Halasa A. F. , Adams H. E.
Published: June 2010

It has been demonstrated that gel permeation chromatography is useful in studying the reaction of aliphatic chloride, such as CCl4 and secondary‐butyl chloride, with polybutadiene. These materials produce an increase in average molecular weight of the polymer and the concomitant change in distribution assists in verification of the proposed mechanism of reaction. Reaction is assumed to proceed through intermediate formation of radicals. If live polymer is used, both allyl and alkyl radicals are produced. Allyl radicals readily dimerize while alkyl radicals attack double bonds in the backbone of the chain to produce crosslinking. Quite different distributions result from these two reactions. Molecular weight distributions of polymers produced by reacting either CCl4 or secondary‐butyl chloride with live polymer indicate the predominant reaction to be dimerization of allyl radicals. On the other hand, the crosslinking reaction occurs exclusively if dead polymer is reacted with secondary butyl chloride. In this case, it is necessary to add a strong base, such as n‐butyllithium, to obtain the molecular weight increase.
Conductivite des polymers: Influence de l'etat hygrometrique et de l'etat acide‐base sur la conductivite de l'ovalbumine et de la polyvinyl 4 pyridine
Authors: Petit Michel , Haas Hubert , Debionne Jean Louis , Jozefowicz Mircel
Published: June 2010

En vue de généraliser les résultats obtenus lors des études de la conductivité des polyamides et des polyanilines, l'étude des propriétés de conductivité de l'ovalbumine, de la polyvinyl 4 pyridine et des perchlorates de polyvinyl 4 pyridinium a été effectueé, ces matériaux étant choisis comme substances modèles. Ces études ont été effectuées sur les Polymères pulvérulents pastillés par compression. Les déterminations de la conductivité ont été faites en utilisant des électrodes de mercure, selon une méthode décrite antérieurement. L'influence de l'état hygrométrique, de l'état acide‐base et de la température sur la conductivité de ces polymères a donné lieu à un examen approfondi. Les résultats obtenus montrent que, en fonction de ces paramètres, les échantillons prèsentent trois régimes de conductivité:

— un régime transitoire de basses températures.

— un régime transitoire de hautes températures qui semble ětre ionique.

— un régime permanent de conductivite. Dans le domaine de températures étudié, et quel que soit l'état acide‐base ou le degré hygrométrique, la variation de la conductivité en fonction de la température obéit à une loi d'Arrhénius. Les lois de variation de la conductivité en fonction de la teneur en eau pour ce qui concerne l'ovalbumine, la polyvinyl 4 pyridine et les différents perchlorates de polyvinyl 4 pyridinium étudiés présentent une grande analogie avec celles qui ont été déterminées dans le cas des polyanilines et des polyamides. L'étude de la variation de la conductivité avec l'état acide‐base a permis d'établir dans le cas de la polyvinyl 4 pyridine, une corrélation entre celle‐ci et la variation du potentiel chimique ou électrochimique des ions H+ dans le polymère. Dans tous ces cas, il a été possible de montrer que les températures critiques de transition entre les différents régimes de conductivité varient de manière simple en fonction des paramètres qui définissent l'état physicochimique des échantillons étudiés.
Morphology and kinetics studies of spherulitization of polyethylene terephthalate
Authors: Baranov V. G. , Kenarov A. V. , Volkov T. I.
Published: June 2010

A modified method of registration of small‐angle scattering of polarized light using the principles of the Fraunhofer diffraction permits the study of fast processes of spherulitization with averaging from a large amount of the scattering elements (several million). With the aid of this method the dependencies on temperature of the growth rate of the spherulites and the lag time have been studied for isothermal crystallization from the melt and from the glassy state. It has been shown that the maximum growth rate of spherulites in the course of the crystallization from the melt is observed at 155°C, and that from the glassy state is observed at 190°C. The thermodynamic parameters of the secondary nucleation determining the spherulite growth have been established. The energies of the formation of the lateral surfaces of cylindrical nucleus in the crystallization from the glassy state, and from the melt were found, to be equal, (σu = 5.75 erg/cm2) and those for the end ones were different (in the first case σe is 5.5 erg/c2 and in the second one σe is 14 erg/cm2). The morphology of spherulites depends strongly on the initial state of the system and the crystallization temperature. Spherulites are observed to have polarizability ellipsoids oriented along the radius and at an angle of 45° to it; in the course of the growth of spherulites changes in ellipsoid orientation are possible.
Orientation of polymer single crystals in an electric field; a kerr effect and light‐scattering study
Authors: Picot C. , Hornick C. , Weill G. , Benoit H.
Published: June 2010

Orientation properties of polymer single‐crystal suspensions in an electric field are studied by Kerr effect and light scattering. It is shown that all the crystals are fully oriented in direction parallel to the electric field for relatively weak field strength (400 V/cm). Kerr‐effect measurements carried out in a.c. electric field indicate the existence of an “electrical” relaxation time (10−2 – 10−3 sec) which is very different from the rotationnal relaxation time (0.1 – 0.5 sec). The orientation property of the polymer crystals is explained by the assumption of the presence of electric charges possessing a certain mobility inside the crystal. The use of Kerr effect measurements is proposed for determination of crystal concentration in suspensions of polymer single crystals.
Structure and thermal properties of crosslinked polymers containing isocyanuric rings
Authors: Alaminov H. , Proynova Z. , Michailov M. , Manjova N.
Published: June 2010

Studies were carried out on crosslinked polymers prepared by radical polymerization of new types of oligoestermaleinates containing isocyanuric rings and allyl groups. It was found by infrared spectroscopy, that during polymerization of oligoestermaleinates a great number of the maleic groupings were isomerized to fumaric. It was also found by electronic microscopy, that cured isocyanuric oligoestermaleinates are microheterogenous and have a globular fibrillar structure. The dependence of the thermostability and other properties of the polymers on their chemical composition was studied by differential and thermogravimetric analysis. They have a better thermostability than the crosslinked polyestermaleinates, which do not contain isocyanuric rings.
Corona induced bonding of synthetic polymers to cellulose
Authors: Kim C. Y. , Suranyi G. , Goring D. A. I.
Published: June 2010

Corona treatment improved bonding between sheets of cellulose and synthetic polymers. The bond strength increased at higher temperatures of pressing. Physical changes in the surface were detected microscopically after corona treatment in air. Sheets treated in pure nitrogen made strong bonds although the surface treated in nitrogen was indistinguishable from the untreated surface.
Method of determining the relative stability of different conformational states of biological macromolecules
Authors: Ptitsyn O. B.
Published: June 2010

A general approach is suggested for the determination of the degree of stability of the native structure of macromolecules and the difference of free energies of different conformations of macromolecules. The idea of the approach is that in case a direct measurement of free energy of transition is impossible, use may be made of the effect of the “transforming agent” for the estimation of the difference of free energies of two conformational states evaluating the derivative from the difference of free energies by the external parameter (such as temperature, solvent constituents). This approach is illustrated by the determination of the degree of stability of the helix state of polypeptide chains in water, water‐organic mixtures and in organic solvents, as well as by the determination of the stability of DNA double helices in aqueous medium at different pH and ionic strength including physiological conditions.
Development in polymer statistics
Authors: Staverman A. J.
Published: June 2010

A short survey is given of recent developments in polymer statistics. Through the many years since the original conception of the entropy derived from the large number of configurations of macromolecules by Mark and Guth the basic idea has never been subjected to doubt but not much progress has been made in the way of confirmation of quantitative theoretical relations.

In quantitative relations quantities appear such as the effective number of chains in a network and also the energy differences between more and less elongated configurations which cannot be determined easily and have to be treated as adaptable parameters.

On the other hand the theory of networks has been further developed so as to establish the exact physical meaning of the effective number of chains in a network. The theory of networks has also been extended to entanglement networks in which the entanglements have a finite life time. Based upon the Rouse‐Zimm treatment of viscoelastic dilute solutions on one hand and upon the generalized network model of Duiser and Chömff on the other hand, van Wiechen and Booy have developed a general theory of time dependent elasticity in concentrated polymer systems. This theory is briefly reviewed.
Recent developments in the statistical mechanics of polymers
Authors: Guth Eugene
Published: June 2010

In a previous paper I discussed the statistical mechanics of polymers, particularly the theory of rubber elasticity. The present continuation of that paper emphasizes that the resolution of the stress into internal energy and entropy contributions at constant volume may alternatively also be done at constant pressure yielding a resolution of the stress into internal energy, entropy and pressure contributions. The network theory of rubber elasticity, as developed by James and Guth starting in 1939, presents a framework comparable to the van der Waals equation for real gases and Weiss' theory of ferromagnetism and is compatible with an internal energy contribution at constant volume due to intramolecular forces and thus independent of extension. Until very recently, experimental data did not exhibit this independence. However in 1969 work in extension by Shen on natural rubber and by Price et al. on butyl rubber and polydimethyl siloxane and by Boyce and Treloar on natural rubber in torsion clearly showed this independence. I also stress that our theory does not imply a universal “front factor.” On the contrary, its value will depend, among other factors, on the degree of both segment dispersion and randomness of crosslinking. The experimental situation with regard to the “front factor” urgently needs further clarification.
Ein Graphisches Verfahren zur Ermittlung der Dehnungen bei Langzeitigen Nicht‐Isothermen Kriechversuchen
Authors: Binder K. , Tschamler H.
Published: June 2010

Results of studies of creep in low‐pressure polyethylene carried out by two procedures, involving a precise (nonisothermal) temperature program and alternatively with outdoor exposures of up to 2 3/4 years, are reported and discussed. On the basis of the results, some generally valid characteristics of nonisothermal creep processes are demonstrated. It is shown that the elongation values equivalent to those obtained by the two nonisothermal methods may be graphically ascertained or calculated from the much more easily obtained isothermal tensile creep data. The laboratory data and the graphically determined elongation values show almost complete agreement, and the results of outdoor exposure studies and the calculated elongation values are in sufficient agreement for most practical purposes.
The role of network orientation and microstructure in fracture initiation
Authors: Kausch H. H.
Published: June 2010

Three approaches towards a fracture theory are discussed, namely the statistical, the continuum‐mechanical, and the micro‐morphological approach. The latter recognizes that (amorphous or semicrystalline) high‐polymer solids are composed of chain molecules which show a close range order and/or a superstructure. Information from morphological and spectroscopic investigations is utilized to characterize the different elementary molecular processes (slip of chains, segment rotation, chain scission, crystal deformation) which may lead to fracture initiation, crack growth, or yielding.

The statistical variability of the elementary processes and the correlation of these processes with each other determine the statistical variability of the cumulative process, e.g., time to failure or fracture strength. Thus, a relation between the results of the micro‐morphological approach and the terms of the statistical approach (underlying distribution) is obtained. A mathematical study of the effect of these processes (network degradation, stress relaxation) on the expectation values of strength or time to failure is carried out for networks of different degrees of orientation.

The results obtained for one‐phase networks are applied to critically stressed regions of heterogeneous polymers (amorphous regions in oriented fibers, plastically deformed zone at tip of growing crack). Thus, a correlation between continuum‐mechanical terms (stress intensity factor, surface energy) and molecular terms (network properties, activation energies) is attempted. A failure criterion is derived.
The yield behavior of polymers
Authors: Ward I. M.
Published: June 2010

Starting from a review of recent research on yield behavior, the author emphasizes the need to extend classical yield criteria in two ways. First, for iso‐tropic polymers, inclusion of a term allowing for the hydrostatic component of stress. Second, for oriented polymers, allowance for differences of behavior in tension and compression. The causes for these differences and progress in defining yield criteria by classical plasticity and by regarding yield behavior as an extension of nonlinear viscoelastic behavior are discussed.
Cleavage fracture of oriented poly(vinyl chloride)
Authors: Miller L. E. , Puttick K. E. , Rider J. G.
Published: June 2010

Poly(vinyl chloride) (Cobex) sheet was oriented by hot drawing. Double cantilever beam cleavage specimens were then cut out parallel to the direction of molecular alignment. The fracture surface energy and fracture surface features were then investigated as a function of the birefringence, a measure of the degree of molecular alignment. Two different modes of crack propagation were observed. The first mode was by local plastic deformation at the crack tip coalescing voids present in the material and giving a dimpled fracture surface. This occurred up to a birefringence of 2.55 × 10−3 and was accompanied by a sharp fall in fracture surface energy with increasing birefringence. The second fracture mode was by smooth cleavage, this occurred above a birefringence of 2.13 × 10−3 and was accompanied by a slight decrease in fracture surface energy with increasing birefringence. There was a transition region at intermediate birefringence values where both modes of fracture were found.
Molecular weight distribution of poly(vinyl chloride)
Authors: Lyngaae‐Jørgensen J.
Published: June 2010

Under the assumption that poly (vinyl chloride) (PVC) contains a negligible amount of long branches, simple kinetic considerations lead to the result that the molecular weight distribution (MWD) function resulting from a heterogeneous polymerization will be in accordance with the functional expression for the most probable distribution (mpd). A comparison between the experimental MWD curves determined by gel permeation chromatography (GPC) and the mpd supports this hypothesis and it is shown that the form of the MWD of PVC is very close to or identical with the mpd. Furthermore, it is found that PVC samples prepared by heterogeneous polymerization in the temperature interval 25–55°C have approximately identical distributions when normalized molecular weights are used. The degree of long chain branching is estimated to be equal to or less than 2 × 10−4 long branches per repetition unit.
Particle size of poly (vinyl chloride) latices and rheology of poly (vinyl chloride) pastes
Authors: Rangnes P. , Palmgren O.
Published: June 2010

An anlytical centrifuge for the determination of particles in the micron and submicron range is described. The sedimentation of particles is visualized on an oscilloscope, where light‐absorption curves give an apparent size distribution. The true size distribution can be calculated from the oscilloscope curve. The centrifuge has been especially applied for analysis of PVC latex particles. Sedimentation time is about 10 min. On a later model, four samples can be compared directly on the oscilloscope. A comparison between the centrifuge and electron microscope is given.

The particle size of PVC latex is strongly dependent on type and concentration of the emulsifier used. Sodium octyl sulphate gives large particles. A short description of some fundamental characteristics of PVC paste rheology is given. Viscosity curves for PVC made from mixtures of latices of four different particle sizes show that the viscosity can be altered by altering the proportions between small and large particles. Examples of high and low viscous PVC pastes are given.
Zur Radikalkinetik im Vakuumbestrahlten Polyvinylchlorid
Authors: Bartl A.
Published: June 2010

In the course of the formation of radicals in vacuum irradiated polyvinyl chloride, a limiting concentration occurs within the temperature range from −196°C to +20°C if a high irradiation dose is applied. The value of the limiting concentration decreases with the increasing temperature. This temperature dependence was investigated in detail by using the electron‐spin resonance method. When the formerly described results referring to the recombination of radicals within the temperature range from 40°C to 90°C are taken into consideration, the occurrence of a temperature‐dependent limiting concentration in the course of the formation of radicals can be explained satisfactorily.
Simulation of degradation processes: Influence of degradation on molecular weight distribution: First approach. I. Random crosslinking and chain scission
Authors: Maláč J.
Published: June 2010

The properties of polymers are changed by the influence of degradation processes. Easy to notice are changes in color caused by the formation of chemical groups absorbing the light spectrum in the visible region. The changes in color can, therefore, be determined and measured by sufficiently sensitive photometers, especially because the changes in the visible region are preceded very often by changes in the UV‐region.

Mechanical properties, as well as rheological properties (and consequently the processa‐bility of polymers), depend on the relaxation spectrum which is sensitive to changes in the molecular weight distribution of the polymers.

The molecular weight distribution is changed by the influence of degradation as a consequence of crosslinking, chain scission, and depolymerization.

The questions concerning the influence of degradation processes on the molecular weight distribution of the polymers have hitherto been given less attention than the question regarding the color changes, although these, too, are of considerable importance.

The determination of the gel content and the limit viscosity numbers which are usually employed as a measure for successive degradation processes is less suitable than the determination of the molecular weight distribution, as it gives less information especially in the initial stage of degradation and its interpretation is often difficult.

The aim of this paper is to create a simple model suitable for a computer which would make possible the simulation of the influence of degradation processes on the molecular weight distribution. The results thus obtained should serve as a basic material for a detailed study of these questions.
Poly(vinyl chloride) compositions in medicine
Authors: Buadze O. P. , Gegeshidze G. A. , Nazin A. N. , Shmyreva T. A.
Published: June 2010

The aim of this work has been to obtain a biologically harmless composition on the basis of suspension polyvinyl chloride resin. The authors were trying to select adequate plastifiers and stabilizers and to determine their optimum quantitative relations. Of various types of plastifiers, esters and polyesters of the selected acids were tested. Metallic soaps and organotin compounds were investigated as stabilizers. The polyvinyl chloride composition was first investigated under laboratory conditions and then tested on living animals. About 20 compositions were subjected to experimental tests on 250 dogs in all. On the basis of the results obtained a polyvinyl chloride composition was selected, the implantation of which causes a minimum reaction of the organism.
Monolayer characteristics of alternating block copolymers of dimethylsiloxane and bisphenol‐a carbonate
Authors: Gaines G. L.
Published: June 2010

Dimethylsiloxane (DMS)‐bisphenol‐A carbonate (BPAC) alternating block copolymers having overall compositions ranging from 25 to 83 wt‐% siloxane have been examined as films spread at the air‐water interface. At low surface pressure, the siloxane blocks appear to spread completely, while the BPAC segments are not located in the interface; the area occupied at low pressure is directly proportional to the siloxane content. At π = 6–8 dynes/cm, a rearrangement substantially identical to that observed with homopoly‐DMS films occurs. At areas of 0.2–0.4 m2/mg, fairly stable films persist (π up to > 12 dynes/cm), and the area requirement for these films depends on the overall composition, but we do not yet know the molecular configurations involved in this region. The mono‐layer properties may provide useful characterization data for copolymers of this type, as well as providing insight into their behavior at other interfaces.
Conformation of polylysine and polyglutamic acid adsorbed on the charged mercury/water interface
Authors: Pavlovic O. , Miller I. R.
Published: June 2010

Information on the structure of adsorbed monolayers of polypeptides is obtained from differential capacitance values measured in the presence of the adsorbing polypeptides and supporting electrolyte. The uncharged polylysine (pH>11) is strongly adsorbed and fails to desorb even from highly polarized mercury surfaces, thus no desorption peaks can be determined. The capacity values decrease with increasing polylysine concentration until a limiting saturation capacity curve is reached at a bulk concentration which decreases with the square root of the age of the mercury drop. The area per lysine residue on a saturated surface, calculated from the diffusion controlled adsorption kinetics, is 38Å2, irrespective of polarization. At lower pH values, when the charge on the polylysine increases gradually, a desorption peak appears at positive polarization, while at negative polarization a hump caused by reorientation of the polypeptide in the surface is observed. The surface confor‐mation reflects also the concentration of the polypeptide in the bulk. The area per lysine residue in the saturated surface layer adsorbed from very dilute solution at pH's 1.3–7 was calculated to be 22Å2.

Polyglutamic acid (PGA) at low degrees of ionization (pH 4.6) produces a region of low capacities around the zero charge potential. It is desorbed from either a positively or a negatively charged mercury surface, giving rise to anodic and cathodic desorption peaks at +0.1 and −1.4 volts, respectively, relative to NCE. Completely ionized polyglutamic acid (pH 10.4) raises the differential capacity around the zero charge region and is expelled from the surface at higher negative polarization. The area per residue of fully ionized PGA was found from the adsorption kinetics to be 45Å2, corresponding to a spread out molecule with the residues in the trans position. At pH 4.6, when PGA is only about 20% ionized, the area per residue is 34Å2 at positively charged surfaces. This area decreases gradually with increasing negative polarization of the surface, to values between 13Å2 (40° C) and 18Å2 (0.9° C). These values are in accord with a helical conformation prevailing in the surface.
Adsorption of polymers at the solution‐solid interface. IV. Styrene‐methyl methacrylate copolymers on silica
Authors: Herd Jacqueline M. , Hopkins A. J. , Howard G. J.
Published: June 2010

A series of random and block copolymers of styrene and methylmethacrylate has been prepared and characterized and the adsorption behavior on silica found from several solvents, in particular, from benzene and trichloroethylene. Specific adsorption measure‐ments have been supplemented by infrared determinations of bound fractions. Relatively few methacrylate groups are necessary to bind the copolymers to the silica surface. Little variation in specific adsorption is found over a wide range of copolymer composition and within this range the fraction of bound groups (of both structures) is approximately constant. Only rather small differences in adsorption behavior are shown by the random and block copolymer structures.
Tracer study of kinetics and mechanism of hydrolytically induced interfacial failure
Authors: Schrader M. E. , Block A.
Published: June 2010

Analysis of the kinetics of hydrolytic desorption of chemisorbed C‐14 labelled polymeric APS (gamma‐aminopropyltriethoxysilane, a coupling agent for glass reinforced epoxy resins) from flat silica or borosilicate surfaces, indicated that the polymer probably consisted of short chains each chemisorbed at one end to the surface with little or no cross‐linking. A method was developed to determine from kinetic data whether or not more than one type of bond is severed during the desorption process. Application of the method to these results indicated that more than one type of linkage was being hydrolyzed in the desorption of APS.

Glass‐epoxy adhesive joints were prepared from glass containing various amounts of APS chemisorbed to the surface. In one set of experiments, the amounts were varied through aqueous extraction of increments of the originally deposited material. In a second set, the amounts were varied by adsorption from very dilute solution. The lifetimes of the adhesive joints were measured under static load in hot water. It was found that the maximum lifetime is not dependent on the thickness of the chemisorbed layer, but that it is dependent on the lateral surface concentration of the chemisorbed polymeric units. Examination of the debonded joints for radioactivity indicated that failure resulted from hydrolysis of siloxane bonds in the coupling agent structure.