bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerisation de polyethylene sur trichlorure de vanadium depose sur support. Morphologie du polymere naissant
Authors: Marchessault R. H. , Chanzy H. D.
Published: June 2010

La facilité avec laquelle VC13 se dépose sur différentes surfaces riches en électrons a été Utilisée pour obtenir des catalyseurs de polymérisation supportés sur différents supports plats. Si I'on polymérise de l'éthylène sur ces supports, des membranes de polyéthylène naissant sont obtenues et examinées au microscope électronique. Leur structure se compose d'agglomérats en forme de pustules reliés entre eux par une texture de rubans. Les pustules correspondent à l'encapsulation des cristaux de catalyseur tandis que les rubans sont engendrés par une action simultanée de polymérisation et de déplacement du catalyseur. Ainsi les donneurs d'électrons qui favorisent la désintégration des cristaux de VC13 ont pour effet de multiplier le nombre des rubans et agissent ainsi sur la morphologie. Par analyse thermique on peut obtenir des informations sur l'organisation cristalline moléculaire et supra‐moléculaire des membranes de polyéthylène naissant. Leur cristallinité varie de 74 à 86% tandis que la forme et le comportement des courbes de fusion confirme que la phase cristalline contient en majorité des cristallites où les chaǐnes sont dépliées. Par analyse thermique, on voit également que des membranes préparées à des températures plus élevées ont des degrés de cristallinité plus bas et un point de fusion plus élevé. Enfin, on remarque que par fusion, une membrane étirée de polyéthylène naissant engendre une phase fondue orientée et il est nécessaire de surchauffer les échantillons fondus au moins 40 degrés plus haut que le point de fusion pour obtenir un état fondu normal.
The realtionship between molecular weight and spherulitic growth rates in trans‐1, 4‐polyisoprene
Authors: Lovering Edward G.
Published: June 2010

The growth rate of high melt form spherulites in trans‐1,4‐polyisoprene was found to be Inversely proportional to the molecular weight up to Mn = 150,000. At higher molecular weights the dependence virtually ceases. The growth is given by:

Where ED is the free energy required to transport a crystallizing segment across the liquid‐crystal interface and ΔF2* is the free energy required to form a stable crystal nucleus. The relationship between molecular weight and spherulitic growth rate was not accounted for by the dependence of Tg on molecular weight, expressing ED by the WLF equation, nor by the dependence of ΔF2* on the molecular weight. The product of the end and lateral interfacial free energies of the crystallites is constant to M̄n = 40,000, above which it Increases with molecular weight. This has been attributed to a change in the crystallization mechanism near M̄n = 40,000, perhaps from a mechanism where most molecules crystallize within a single cyrstallite to one where each molecule is involved in several crystallites and the amorphous regions between them.
Steric stabilization of polymer suspensions in hydrocarbon media by adsorbed layers of graft copolymers
Authors: Osmond D. W. J. , Walbridge D. J.
Published: June 2010

Sterically stabilized dispersions of fine polymer particles in hydrocarbon media have been used for the study of the adsorption of amphipathic graft copolymers at polymer/hydrocarbon interfaces. The amount of graft copolymer adsorbed on the particle surfaces during the dispersion polymerization has been determined for a number of polymer substrates, over a range of particle sizes, and at different stabilizer concentrations. From these results the average surface spacing of the solvated component of the adsorbed graft copolymer has been calculated for solvated groups of low, medium and high molecular weight. In a limited number of cases the hydrodynamic steric barrier thickness has also been measured. These stabilizer spacing and barrier thickness values are compared with the dimensions of the solvated groups in free solution and the nature of the packing of these groups on the particle surface is discussed. Anomalous results obtained in a few cases are shown to be due to the mechanism of particle growth.
Stress softening in styrene‐butadiene block copolymers: Rheo‐optical studies
Authors: Fischer E. , Henderson J. F.
Published: June 2010

The stress‐strain and the optical properties of styrene/butadiene block polymers indicate that at strains below those at which finite extensibility of the polybutadiene chains become Important, the mechanical properties of the polymers are determined by the combined effects of the elastic deformation of the polybutadiene phase and the degree of interaction between the polystyrene regions. The process of stress‐softening in styrene/butadiene block polymers is due to the break‐up of polystyrene regions, rather than to flow and rupture of weak crosslinks. Some additional softening occurs in the polybutadiene phase due to loosening‐up of the polybutadiene network structure. Specimens which were softened to the same degree of internal strain of the polybutadiene phase had similar stress‐strain properties when account was taken of the filler effect of the polystyrene regions. Block polymers which were prestretched to a strain below the finite extensibility of the polybutadiene chains exhibited a stable network structure. At large strains non‐Gaussian behaviour of the polybutadiene chains, probably combined with a recoverable plastic deformation of the polystyrene regions, determined the stress‐strain properties of the block polymers. The stress‐strain and the optical studies of the original and the softened block polymers indicate that under the experimental conditions described here the physical crosslinks formed by the polystyrene regions were stable.
Solutions of diphilic copolymers: A quantitative approach to the analysis of fluctuating networks and antithixotropy
Authors: Frenkel S. Ya , Panov Yu. N.
Published: June 2010

The study of the concentration dependence of the molar apparent activation heat of viscous flow of MMA‐MAAc copolymer solutions in EDC (hydrogen bonded systems) permits to resolve three different concentration ranges. The first of them corresponds to the existence in the system of separate macromolecules and small associations, the second one corresponds to the co‐existence of an incomplete fluctuating network in equilibrium with associations and/or separate macromolecules, and the third one corresponds to the formation of a complete network including all the macromolecules present. The existence of the fluctuating network in the systems studied results in an antithixotropic strengthening of the solution structure in conditions of both shear and complex flow.
Application of differential scanning calorimetry to the identification of crosslinks in cellulose
Authors: Gilbert R. D. , Rhodes J. H.
Published: June 2010

Thermograms of reaction products of cellulose with dimethylolurea (DMU) or dimethylolethyleneurea (DMEU) homopolymers show the peak associated with cellulose decomposition is shifted up by as much as 20°C. Solubility measurements in cupriethylenediamine (Cuene) indicate the homopolymers are present as side groups on the cellulose. Cellulose reacted with DMU or its homopolymer is only insoluble in Cuene when oxymethylene crosslinks are simultaneously formed by CH2O. These crosslinks do not affect the thermal stability of cellulose. Linkages to DMEU or its homopolymer are relatively stable to alkaline hydrolysis and may be distinguished from oxymethylene linkages by comparison of thermograms and solubilities before and after acid hydrolysis. Comparison of thermograms of cellulose with those of the n‐methylol compounds, their homopolymers, physical mixtures of cellulose and the homopolymers, and reaction products of cellulose with DMU, DMEU, and CH2O, demonstrated that, depending upon the reaction conditions, CH2O evolution, in situ homopolymenzation, cellulose crosslinking by CH2O, by the n‐methylol compounds, and reaction with their oligomers may occur. Reaction variables, viz., pH, temperature, nature and concentration of catalyst, the time‐temperature interval between application of the n‐methylol compound and the final reaction, and the type of n‐methylol compound determine which reaction predominates. The modification of cellulose by DMU shows a greater dependence on catalyst type than does DMEU which readily polymerizes to low molecular‐weight products and evolves CH2O which crosslinks the cellulose.
Differences in absorption and emission properties of conalbumin and metal‐saturated conalbumin
Authors: Tan A. T. , Woodworth Robert C.
Published: June 2010

The stabilities of conalbumin and transition metal‐conalbumin complexes toward denaturants were studied by UV absorption and emission spectroscopy. The difference spectra of conalbumin and metal‐conalbumins in buffer, pH 8.0 vs. the same species in buffered 8 M urea were similar in shape with maxima at 286‐ and 292‐mμ and a negative absorption near 260‐mμ. The Δε292 for colored Fe‐, Cr‐, Cu‐, and Mn‐conalbumins was 5 × 103 less than that for conalbumin and colorless Co‐, Zn‐, Cd‐, Ni‐, and Mn‐conalbumins, indicating that two tryptophanyl residues were bound to or protected by metal ions in the former but not the latter cases. The F350 of conalbumin was quenched up to 65% on formation of the colored complexes, but not on formation of colorless complexes. The F350 of conalbumin was strongly quenched by increasing temperature (0 to 70°) or pH (5 to 12.5), whereas that of Fe+3‐conalbumin was essentially independent of these variables. These results indicate the presence of tryptophanyl residues, in addition to the known tyrosyl and histidyl residues, in conalbumin‐metal binding sites, and suggest that charge‐transfer interactions between these tryptophanyl residues and the bound metals is probably responsible, at least in part, for color formation, as well as for the marked increase in stability of these colored complexes.
Deoxyribonucleoprotein from sea urchin sperm: Preparation and thermal denaturation
Authors: Subirana Juan A.
Published: June 2010

Deoxyribonucleohistone from sea urchin sperm has a marked tendency to form a gel upon suspension in distilled water. The gel can be disrupted by shear and soluble nucleoprotein is thus obtained. Soluble proteins from the microtubules of the sperm tail have a tendency to contaminate this preparation. At the same time they show some affinity with the nucleohistone. Histones are obtained from treated sperm and differences are reproducibly found at various stages of the preparation. From these results the factors which determine gel formation are discussed. The melting curves of the nucleoprotein are also studied. At low ionic strength a bimodal curve is obtained, probably due to an irregular distribution of histones on the DNA molecule. At high ionic strength a bimodal curve is also found, but in this case it is due to the turbidity of the nucleprotein solution.
Unfolding of a protein molecule in solution with ageing and thermal denaturation as determined by a reverse dye partition technique
Authors: Mukhopadhyay Sailes , Mitra Bhairab Chandra , Palit Santi R.
Published: June 2010

A chloroform solution of an anionic dye bound to polymethyl methacrylate having an amino endgroup is partitioned with an extremely dilute solution (< 0.001 per cent) of a protein at a suitable pH. The amount of dye which gets transferred to the aqueous layer is a measure of the available excess of carboxyl over amino group of the protein. This value increases considerably with age and also with heat denaturation of the protein and so this gives an insight into conformational change or unfolding of the protein molecule as due to thermal denaturation and ageing characteristics.

The same method has also been applied with success to determine, the carboxyl content of polyacrylamide (partially hydrolysed), carboxymethyl cellulose, gum arabie, copolymers containing acrylic, methacrylic and crotonic acids, and graft polymers containing acrylic acid.
Effect of the continuous medium on the color of discontinuous substrates. I. Empirical relationship between the light reflectance of dry textile samples and samples immersed in water
Authors: Goldfinger G. , Goldfinger Herta S. , Hersh S. P. , Leonard T. M.
Published: June 2010

The light reflectance between 380 nm and 700 nm of one white, one black, six red, and six blue cellulose triacetate fabric samples was measured. Each measurement was carried out once on a dry sample and once on a sample immersed in water. From the data a numerical relationship was derived which permits the prediction of “wet” color from “dry” color.
Optical rotatory properties and conformations of esters and polyesters of trans‐1,2‐cyclohexanedicarboxylic acid
Authors: Overberger C. G. , Montaudo G. , Furuyama Toshiuki , Goodman Murray
Published: June 2010

The conformational preferences of trans‐1,2‐cyclohexanedicarboxylic acid (1,2‐CH) and ester derivatives have been studied. The optical rotatory properties of these compounds are discussed in comparison with those of other cyclic dicarboxylic acids. A stereoregular polymer, poly[ethylene‐(+)‐trans‐1,2‐cyclohexane dicarboxylate] (1,2‐CHPE) has been synthesized, and its properties are compared with those of model compounds.
Volume dependence of the C2 correction in the Mooney‐Rivlin elastic equation of state
Authors: Mark J. E.
Published: June 2010

Stress‐strain isotherms at 25°C are reported for a series of unswollen networks of cis‐1, 4‐polybutadiene which differ both in degree of crosslinking and in the volume at which the crosslinks were introduced. The former quantity was varied by variation of the amount of high energy radiation used to bring about the crosslinking, the latter, by crosslinking the polymer in solution as well as in the bulk, undiluted state. The results are interpreted in terms of the equation f*/(α−α−2) = 2C1 + 2C2α−1 where f* is the force per unit area of the undistorted, unswollen sample, α is the relative length of the sample, and C1 and C2 are empirical constants, the latter serving as a measure of the departure of the dependence of stress on strain from that indicated by the statistical theory of rubber elasticity. At equal values of the “modulus” f*/(α−α−2), the correction C2 is found to be very small for networks prepared in solution and to increase markedly with increase in concentration of polymer in the system undergoing crosslinking. In addition, the networks prepared in solution exhibit considerably smaller nonequilibrium, relaxation effects than those crosslinked in the undiluted state.
Cationic polymerization of exo‐2‐methyl‐7‐oxabicyclo [2, 2, 1] heptane. II. Catalysis by PF5
Authors: Baccaredda M. , Giusti P. , Andruzzi F. , Cerrai P. , di Maina M.
Published: June 2010

The polymerization of exo‐2‐methyl‐7‐oxabicyclo[2, 2, 1] heptane by PF 5 in ethylene dichloride solution was investigated. The reaction was followed in vacuum dilatometers fitted with platinum wire electrodes, which allowed us to measure the variations of conductivity during the polymerization. The ultraviolet and visible spectra of the polymerizing solution have also been determined by a high vacuum technique. The conversion‐time curves showed an acceleration period which was gradually reduced by addition of water. The Rmax first increased with water concentration, reached a maximum at a α = [H2O] /[PF5] = 0.17, then decreased, and became zero at α = 1. The polymerizations gave limited yields at room temperature, which was not due to an equilibrium. At temperatures below O°C, 100% yields were obtained and experiments with a second addition of monomer showed that no termination was present but only transfer, as the second quantity of monomer was completely converted without increase of the molecular weight. The reaction mechanism is discussed.
Electron spin resonance study of trimethylolpropane monoallyl ether in radical polymerization
Authors: Doi Yukio , Ränby Bengt
Published: June 2010

Trimethylolpropane monoallyl ether (TMP) was studied with an x‐band electron spin resonance (ESR) spectrometer by applying a flow method, developed by Dixon and Norman, in which TMP was subjected to hydroxyl radical attack. The observed ESR spectra were assigned to two radicals formed by addition of hydroxyl radical to TMP and one by abstraction of hydrogen from the allylic group of TMP. The ESR spectra from copolymerizing systems of vinyl acetate (VAc) and methyl acrylate (MA) with TMP were also studied. In the system VAc‐TMP, the ESR spectrum showed in addition to VAc radicals the presence of the three TMP radicals. In the system MA‐TMP, the ESR spectrum was mainly due to TMP radicals in which the allylic radicals were dominant. This result is consistent with the observation that polymerization of MA is strongly retarded by the addition of TMP, which is interpreted as due to the high reactivity of MA radicals to TMP monomer.
Donor‐acceptor complexes in copolymerization. VI. A proposed mechanism for the homopolymerization of comonomer complexes to alternating copolymers
Authors: Gaylord Norman G.
Published: June 2010

After a brief review of the characteristics of the copolymerization of donor and acceptor monomers in the presence of metal halides, a mechanism is proposed for the formation of alternating copolymers. The charge‐transfer donor‐acceptor complex resulting from the interaction of a strong electron‐acceptor monomer and a strong electron‐donor monomer undergoes spontaneous or radical initiated homopolymerization to yield an equimolar alternating copolymer, irrespective of the initial monomer ratio. The formation of the [DA] complex is enhanced by complexation of the acceptor monomer with a metal halide or organometal halide. The homopolymerization of the (DA… [MX] occurs at a faster rate than conventional radical copolymerization. The spontaneous polymerization occurs when the equilibrium concentration of the complex is sufficiently high. The latter depends upon the electron‐donating strength of the donor monomer and the electron‐accepting strength of the acceptor monomer and the activator. Complex formation is favored at lower temperatures while polymerization may require thermal or catalytic activation. The complexes may be aligned in an ordered array or matrix, and polymerization proceeds through a rapid initial stage in which the molecular weight increases with conversion, followed by a slower stage in which the molecular weight remains constant at the highest level attained in the first stage, indicative of the first‐stage polymer acting as a template for the second‐stage polymerization. The proposed polymerization mechanism involves initiation by a head‐to‐head reaction of two complexes during which hydrogen abstraction or transfer occurs through a six‐membered cyclic transition state to generate a polymer chain with an attached terminal complex. The propagation reaction is head‐to‐tail and involves the addition of complexes to the chain end through hydrogen abstraction via a six‐membered cyclic transition state to regenerate the complex chain end.
Thermal behavior of elastomers at high rates of tensile straining
Authors: Glaser Z. R. , Eirich F. R.
Published: June 2010

The results of high strain‐rate tensile straining of a variety of elastomers at a number of temperatures are reported. Temperature increases, ΔT, occurring within the sample were measured during the deformation; i.e., the technique of adiabatic stretching was applied. The use of well characterized rubbers of different tendencies to crystallize upon elongation gave information on the changes in molecular packing, of the contribution from entanglements to the effective crosslink density, and of the effect of chemical and structural factors on mechanical behavior during rapid extension. An analysis of the effect of frictional heating, of deformational energy conversion, and of the anticipated enthalpy of crystallization was performed. The experimentally obtained temperature increases, the magnitude of the above three main factors which contribute to ΔT, and the amount of strain‐induced crystallization found are in agreement with theoretical considerations.
Relationship between structure of drawn polymers and molecular motion
Authors: Fischer E. W. , Goddar H. , Piesczek W.
Published: June 2010

In order to study the relationship between structure and molecular motion, drawn polymers are more suitable than isotropic samples since their morphology can be characterized more easily by quantitative methods such as small angle X‐ray scattering (SAXS) and electron microscopy (EM). The effects of changes in morphological structure on molecular motion are demonstrated by comparing the results of the SAXS and EM measurements with the dynamic mechanical behavior of drawn polyethylene. In addition the NMR broad line spectra of these samples were analyzed and the influence of annealing conditions and external stress was investigated.
Crystallization of poly(vinyl chloride) at high temperatures
Authors: Michel Alain , Guyot Alain
Published: June 2010

A sample of poly(vinyl chloride) having a very good thermal stability and a high initial crystallinity was annealed between 80 and 260°C, either as it was or mixed with stabilizers, in sealed ampoules or in KBr pellets, and studied by X‐ray and IR techniques. When the sample is treated in glass ampoules, practically no changes in IR spectra are observed up to 240°C; the X‐ray diagrams, however, show an increase in the size of the crystallites but no increase in the amount of crystalline material. The melting point is observed by X‐ray between 250 and 260°C. If the sample is heated in the KBr pellets, it undergoes some stress which causes an increase of the crystalline IR bands at 604 and 635 cm−1, but no change in the X‐ray diagram. At higher temperatures, dehydrochlorination is enhanced by the KBr and involves chiefly the amorphous regions.
Relation between the compression yield stress of poly(vinyl chloride) and the loss peak in the β‐transition range
Authors: Bauwens J.‐C.
Published: June 2010

Previously we have shown that the study of the tensile yield stress of glassy polymers over a wide range of temperatures and strain rates as well as measurements of mechanical losses is of use in revealing secondary transitions.

We report here the correlation between the shape of the β loss peak of poly(vinyl chloride) (PVC) (loss tangent versus temperature at a given frequency) and the yield stress curve (yield stress in compression versus temperature at a given strain rate), on the assumption that the broadness of the β peak is due to an activation energy spectrum around the classical value (14 kcal/mole) associated with this transition.

Because in tensile tests PVC fractures before yielding in the transition temperature range, we have chosen compression tests to investigate this whole range.

An equation is given relating the transition conditions in tensile or compression tests to the transition conditions in damping tests. The theory predicts that the double integral of the β peak must be proportional to the increase of the yield stress due to the transition; the theoretical curve is calculated and is found to fit the experimental data fairly well.
Rheological studies of chlorinated poly(vinyl chloride)
Authors: Krishnan M. , Gupta V. B. , Thampy R. T. , Kothari A. V.
Published: June 2010

Chlorinated poly(vinyl chloride) (CPVC) is known to have a higher softening temperature than conventional poly(vinyl chloride) (PVC). Its processability characteristics are, however, different; and in the literature, it has been reported that CPVC is more difficult to process. However, no detailed characteristics of its processability appear in the current literature. This paper describes some of the studies we have made on the flow behavior of CPVC.

Investigations on the melt properties of CPVC, made on a capillary rheometer, indicate that above 67% chlorine content the resin shows gross distortion of the extrudate even at low stresses. This “melt fracture” phenomenon might arise from the elastic nature of the melt. The simple treatment of the flow data, based on a modified form of Poiseuille equation for capillary flow, gave no direct evidence for the increased elasticity of the melt. The limitations of the assumptions made in the simplified treatment may be responsible for this.

It is proposed that the elasticity of the melt can arise from the crosslinks produced in the melt due to dehydrochlorination, which is known to increase with increasing chlorine content. It is also suggested that modification of the simple approach to capillary flow might give a better idea of the elastic nature of the melt.
Poly(vinyl chloride) with thrombus‐inhibiting properties
Authors: Buadze O. P. , Gegeshidze G. A. , Lakin K. M. , Nazin A. N. , Zhuravleva E. N.
Published: June 2010

The preparation of a polymer on the basis of suspension polyvinyl chloride resin with various chemical combinations offering anticoagulant effects on the blood is considered. As a result of many experiments, a material has been obtained which during its prolonged contact with blood reduces clotting thus preventing the thrombus formation. This gives us a base for preparing vascular catheters, substitutes for vascular conduits and various tubes for an extracorporal blood‐circulation apparatus as well as test‐tubes and vessels for taking and storing blood without the danger of clotting. A reliable extension of clotting time of blood under a continuous contact with the given polymer has been proved experimentally.
Compatible poly(vinyl chloride) vascular catheters
Authors: Gegeshidze G. A. , Buadze O. P. , Nazin A. N. , Zhuravleva E. N. , Shmyreva T. A.
Published: June 2010

The results of comparative investigations of polyethylene and specially developed polyvinyl chloride vascular catheters during their continuous implantation into the blood vascular system of the experimental animals are presented. An analysis of the experimental data allows to identify a certain regularity in the development of essential complications resulting from various physico‐chemical properties of the above‐mentioned polymeric materials. The prolonged presence of the polyethylene catheters in dog's magistral vessels was succeeded by a mass process of thrombo formation in the early period just after implantation and by an aneurysmal injury of the vessel walls occurring in the remote period that hindered a continual use of the catheters. The application of specially developed polyvinyl chloride compositions for the production of catheters possessing a higher elasticity and an inertness to the physiological tissue allowed the above‐mentioned complications to be suppressed completely and the presence of the catheters in the vascular bed of the experimental animals to be prolonged up to one year, and in the clinical practice up to one month. A continuous application of the polyvinyl chloride catheters enables a complex investigation of the function of the cardiovascular system to be carried out, and the process of specified pharma‐cotherapy and multiple analysis of blood to be simplified.
Thermomechanical degradation of poly(vinyl chloride)
Authors: Andersson Kent B. , Sörvik Erling M.
Published: June 2010

The thermomechanical degradation of stabilized and unstabilized poly (vinyl chloride) (PVC) has been investigated by use of a Brabender Plastogiaph. All degraded samples were analyzed by gel permeation chromatograph (GPC) and some of them were studied by infrared measurements and viscometry. The association of PVC molecules seemed to affect the GPC measurements for weight average molecular weights exceeding about 70,000. The heat treatment of solutions of degraded PVC before fractionating by GPC was very important in order to obtain real values of Mw.

After the degradation point was reached, the Ba‐Cd stabilized samples showed a faster increase in Mw than the Sn stabilized or the unstabilized samples did.

The emulsion polymer had not as good stability as the corresponding suspension polymer, presumably due to its larger content of remaining polymerization additives. No noticeable chain scission occurred for the low molecular weight PVC, PEVIKON R‐150. This polymer also showed a very slow increase in Mw when treated without any stabilizer. The average number of trifunctional branch units per molecule was found to be only 0.3 for PEVIKON R‐150 and 0.5 for PEVIKON R‐341, but increased during the degradation. The agreement between the results from the GPC, viscometry, Brabender tests, and the infrared measurements are excellent.
Theory of polymer adsorption at interfaces
Authors: Hoeve C. A. J.
Published: June 2010

Previous theories valid for polymer chains with large loops protruding into the solvent are developed. Interaction in various layers parallel to the interface is calculated according to the Flory‐Huggins theory. Excluded volume effects are shown to be so small that they can be neglected. The adsorption isotherm is expressed in two parameters: one for the partition function for adsorbed segments and the other one for the stiffness of the chains. For adsorption from good solvents, the fraction of segments in the surface layer is large and the loops are small. For adsorption from theta‐solvents, the fraction of segments in the surface layer is small and the loops are large. The trends are in agreement with those experimentally observed, but the observed layer thickness is larger than the theoretically deduced upper limit.
Calculation of interfacial tension in polymer systems
Authors: Wu Souheng
Published: June 2010

We propose an equation, based on “reciprocal” mean and force additivity, for calculating the interfacial tension between polymers or between a polymer and an ordinary liquid:

where γ12 is the interfacial tension; γi the surface tension; γ and γ the dispersion and polar components of γi, respectively. This equation is shown to predict accurately the interfacial tension between polymers or between a polymer and an ordinary liquid. Fowkes' equation or Fowkes' equation with a geometric‐mean polar term 2(γiPγ2p)1/2 is not applicable to polarlpolar systems. The interfacial tension arises mainly from disparity in the polarities of the two phases. The above equation can also be used to calculate the surface tension and polarity of polymers or organic solids from contact angle data.
Surface tension of mixtures of oligomers
Authors: Legrand D. G. , Gaines G. L.
Published: June 2010

The surface tension of mixtures of poly(dimethylsiloxane) and poly(isobutylene) fluids with their low molecular weight oligomers have been measured. These data, as well as those for n‐alkane mixtures from the literature, are fitted well by lattice‐theory expressions for the surface tension of polymer solutions, and do not show a simple dependence on the average molecular weight in the mixture. We conclude that the molecular weight depend‐ence we have previously observed for the surface tension of polymer fluids is only an approximation. The results also suggest that the lattice‐model theory may have broader applicability than the model from which it was developed would imply.
Studies of synthetic polypeptide‐water interactions using monolayer techniques
Authors: Malcolm Benjamin R.
Published: June 2010

Molecular monolayers of a range of synthetic polypeptides spread at the air‐water interface have been investigated. Measurements of the surface pressure and surface potential are correlated with the chemical composition of the side chains. All the polymers are believed to be in the α‐helical conformation at the air‐water interface and the surface potential is accounted for principally by the interaction of the peptide groups with the underlying water; if however, there are ester groups in the side chains, an additional side chain‐water interaction is evident. The infrared absorption spectrum of water and alcohols adsorbed from the vapor on thick orientated specimens in the α‐helical conformation prepared from collapsed monolayers has also been investigated. The OH absorption of water, methanol and ethanol is dichroic and shows evidence of interactions similar to those required to account for the surface potential.
Monomolecular films of poly [methyl(n‐alkyl)siloxanes] on organic liquids
Authors: Jarvis N. L.
Published: June 2010

A series of poly [methyl(n‐alkyl)siloxanes] were studied as insoluble monomolecular films on the following organic substrates: tricresyl phosphate, propylene carbonate, diethyl phthalate, and a highly chlorinated polyphenyl (Aroclor 1242). The siloxanes were discovered to form stable, insoluble, reproducible monomolecular films at each organic liquid/air interface. Film pressure (F) vs. area/molecule (A) isotherms were determined in each instance and were compared with previously determined F‐vs.‐A isotherms for polydi‐methylsiloxanes on the same organic substrates as well as on water. By combining the film balance data with molecular dimensions calculated from ball models, it was possible to make several tentative conclusions regarding the conformation of the adsorbed siloxane molecules as a function of film pressure, n‐alkyl chain length and substrate composition. The F‐vs.‐A curves for the poly(methylethylsiloxane) and polydimethylsiloxane films were consistent with the assumption that they assume a helical configuration when compressed at organic liquid/air interfaces; however, there is little evidence to indicate whether the polymer chains become fully extended at higher areas/molecule or remain in a somewhat coiled configuration.
Adsorption of lysozyme and some acetyl derivatives at the air‐water interface
Authors: Adams D. J. , Evans M. T. A. , Mitchell J. R. , Phillips M. C. , Rees P. M.
Published: June 2010

An examination was made of adsorbed and spread films of lysozyme and a series of its acetyl derivatives at the air‐water interface. Direct observations of adsorption and desorption were carried out by measuring the surface pressure and surface radioactivity of films of native and heat‐denatured 1‐14 C‐acetyl lysozyme. Acetylation of as little as one residue per molecule significantly alters the surface properties of lysozyme. Films of lysozyme derivatives spread on low ionic strength buffer give pressure‐area isotherms which are less expanded than those obtained on concentrated salt solutions because in the former case protein is lost to the subphase. The isotherms of native and heat‐denatured protein‐films spread on 3.5 M KC1 are independent of the degree of modification and compression rate and no desorption occurs. Pressure‐area isotherms of adsorbed films show that a low subphase concentration gives rise to a film containing extensively unfolded molecules, while higher concentrations lead to the formation of a film of higher surface concentration containing incompletely unfolded molecules. Spread protein films generally contain more completely unfolded molecules than adsorbed films and more expanded interfacial films are obtained when heat‐denatured molecules adsorb than when native molecules adsorb from solutions of the same concentration.
Effect of adsorbent on the adsorbed structure of poly (methyl methacrylate)
Authors: Thies Curt
Published: June 2010

Isotherms and infrared bound fraction values (p) have been obtained for atactic poly‐(methyl methacrylate) (PMMA) adsorbed from trichloroethylene (24°C) on four adsorbents: aluminum oxide (γ‐AI2O3) formed by flame hydrolysis, micro‐fine reprecipi‐tated silica, silica formed by flame hydrolysis, and silica formed by flame hydrolysis and then reacted on the surface with dimethyl dichlorosilane. Differences in PMMA adsorbance values obtained with these adsorbents may be attributed in part to differences in surface area available for adsorption per gram adsorbent. However, variations in surface area do not account for variations in adsorbed structure indicated by the infrared bound fraction data. PMMA adsorbed on silica treated with dimethyl dichlorosilane had a value of p ≈0.10; p increased to 0.32–0.39 when untreated flame hydrolyzed silica was the adsorbent, and ranged from 0.46 to 0.49 for micro‐fine reprecipitated silica. PMMA adsorbed on γ‐AI2O3 had p = 0.32–0.28. This was the only adsorbent where values of p tended to decrease with increasing surface coverage. The variations in bound fraction data found in this study are interpreted in light of known differences in surface structure of the four adsorbents used. Drying the reprecipitated silica and γ‐AI2O3 at 310°C (in vacuo) caused a slight decrease in values of p which can also be explained in terms of known changes in surface structure caused by heat treatments.
Polymer adsorption studies at the solid/liquid interface using gel permeation chromatography. II. Influence of molecular weight on the adsorption of poly(vinyl chloride) from chlorobenzene onto calcium carbonate
Authors: Felter R. E.
Published: June 2010

Adsorption of both high molecular weight (M̄w = 114,000) and low molecular weight (M̄w = 42,800) poly(vinyl chloride) resins were followed from chlorobenzene solution onto CaCO3 at room temperature, and compared with data obtained previously for an inter‐mediate molecular weight resin (M̄w = 80,600). At increase in the adsorption saturation capacity (ASC) was observed for increasing M̄w (31.6 mg‐g−1 to 41.7 mg‐g−1) as was a corresponding decrease in the number of molecules adsorbed (9.0 × 10−7 mol‐g−1 to 6.3 × 10−7 mol‐g−1). Preferential adsorption of high molecular weight polymer was noted for all resins. The average molecular weight of polymer adsorbed at ASC increased with increasing M̄w. Fractionation of the adsorbed polymer was also evident and improved with decreasing M̄w. Within the molecular weight distribution (MWD) of all three resins an increase in the amount of polymer adsorbed (described by an adsorption efficiency factor) with increasing molecular weight occurred up to a molecular weight near 75,000. Above a molecular weight of 75,000 the adsorption efficiency factor continued to increase with the low molecular weight resin but stayed fairly constant for the intermediate and high molecular weight resins. Competition of high molecular weight polymer for surface sites was cited as an ex‐planation. The polymer molecules were thought to adsorb as interpenetrating or compressed coils with relatively few points of surface contact.
Numerical interconversion of viscoelastic functions by linear programming
Authors: Shen Mitchel , Jamieson Ronald T. , Drandell Milton
Published: June 2010

Interconversion of viscoelastic functions are customarily accomplished through the use of distribution of relaxation or retardation times. It will be shown that, by employing the Linear Programming (LP) technique, numerical interconversion may be obtained directly. As an example, starting with stress‐relaxation moduli E(t) of polyisobutylene, values of E′(ω), E″(ω), D″(ω), D(t), Dg, and ω of this polymer are obtained. Agreement with experimental data in the literature is found to be excellent. Calculated values are given in the form of upper and lower bounds of the functions, indicating a probable error margin of the computed values. The calculations are performed by standard LP routines, requiring little computer background of the user. Thus LP is a simple and general technique for calculating any viscoelastic function from any other given set of data.
Chemo‐rheology of curing in structural adhesives. II. Polyimide systems
Authors: Kaelble D. H. , Cirlin E. H.
Published: June 2010

Polyimide adhesives are cured through the cyclization of the linear main chain of the polymer, rather than through the formation of a network structure. It was found that the average activation energy E* for the imidization process of the curing is 30.5 ± 5.4 kcal/mole and is substantially higher than that of the epoxy‐phenolic adhesive system which we have reported in Part I. The effect of metal filler upon the curing kinetics and mechanical properties of cured material is discussed on the basis of TMA and DSC measurements. In addition, the influence of moisture exposure on the tensile modulus E of the polyimide adhesives are also discussed.
Dynamic mechanical behavior of partially hydrolyzed ethylene‐vinyl acetate copolymers
Authors: Macknight William J. , Tetreault Roland J.
Published: June 2010

A dynamic mechanical study has been made of two series of partially hydrolyzed ethylene‐vinyl acetate copolymers. Series A contains 75 mole % ethylene and series B contains 59 mole % ethylene. The frequencies employed were 3.5, 11, and 110 Hz, and the temperature range was from −180° to +120°C. Three relaxation regions are discernable in this range and these are labeled α, β, and γ in order of decreasing temperature. The α relaxation is associated with the glass transition of the copolymers. The β relaxation is absent in the unhydrolyzed copolymers and is dependent on hydroxyl content. It is assigned to local motions of hydrogen bonded groups. The γ relaxation is insensitive to hydroxyl content and is assigned to local motions of methylene sequences. The above assignments are supported by the effect of water added to the polymers. Added water decreases the temperatures of the α and β relaxations but does not affect the γ relaxation significantly. The magnitude of the β relaxation is considerably enhanced by water.
Shear rate dependent relaxation spectrum for polyethylene melts
Authors: Shroff Ramesh N. , Shida Mitsuzo
Published: June 2010

Many of the familiar relations in the theory of linear viscoelasticity which relate the relaxation spectrum H(τ) to the experimentally measured quantities were extended to embrace the concept of shear dependent relaxation spectrum H(τ, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}). The concept is based on the relation H(τ, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}) = H(τ)h(θ)g(θ)3/2, where θ = c \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document} τ and c = 0.5. Here \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document} is the shear rate and τ is the relaxation time. The replacement of H(τ) by H(τ',\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}) in the integral relations of the linear theory produced the corresponding nonlinear parameters, e.g., the shear rate dependent viscosity η(\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}), the shear stress relaxation following cessation of steady‐state flow σ(\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document},t) and the dynamic parameters under parallel superimposed rotation η'(ω) and G'(ω, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}). The concept was used successfully for several high‐density polyethylene melts in interconversion between η(\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}), c(\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document},t) and the dynamic viscosity η'(ω) without involving coordinate shifts or empirical parameters. The failure of this approach for interconversion between η(ω) and η(\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}) for the highly branched polyethylenes was ascribed to the level of long‐chain branching. For the high‐density resins, the agreement between measured η'(ω,\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}) and G'(ω,\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}) and those calculated using H(τ,\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document}) was not quantitative since the parallel superimposed experiments require an additional term in ∂H(τ,\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ $\end{document})/∂ \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ ^2 $\end{document} inside the integral.
Thermal behavior of carbohydrates
Authors: Shafizadeh F.
Published: June 2010

Thermal analysis of a hardwood reflected the pyrolysis of its main components including xylan and cellulose. Thermal properties of these components were investigated with model compounds consisting of α‐D‐xylose, substituted phenyl β‐D‐xylopyranosides, β‐Dglucopyranosides and α‐D‐arabino‐hexopyranosides and 1,6‐anhydro‐β‐D‐glucopyranose.

At the lower temperatures these molecules displayed anomerization, loss of water and phase change, which were studied with a variety of physical methods. Calorimeteric and wide line NMR measurements showed that 1,6‐anhydro‐β‐D‐glucopyranose and related anhydro sugars undergo plastic crystalline transition, involving reorientation of the molecules about their centers of gravity and self‐diffusion before melting.

At more elevated temperatures the above compounds showed cleavage of the glycosidic group, polymerization of the sugar moiety, decomposition and evaporation of the pyrolysis products. This involved some heterolytic reactions, which could be catalyzed by acid or alkaline materials.

Kinetics of the pyrolysis process, including the rates and energies of activation were determined by thermal analysis and ESR spectroscopy. These data indicated that cleavage of the glycosidic bond is directly influenced by variation of its electron density and constitutes the rate determining step in pyrolysis of the carbohydrate compounds.
Ring shake in some hardwood species: The individual tree approach
Authors: McGinnes E. A. , Chang C. I‐J. , Wu K. Y‐T.
Published: June 2010

The formation of ring shake, a tangential separation of xylem tissue, is being studied in selected red oaks, white oaks, and black walnut. Previous studies have indicated that it is frequently necessary to make detailed analyses throughout one tree in order to evaluate correctly possible stages of development of this defect for the sample under investigation. In the present study, anatomical and chemical analyses both along the shake zone and for a normal zone within a black walnut tree are discussed. Anatomical investigations formed the basis for selection of xylem subdivisions for subsequent chemical analyses. The ring shake was tangentially confined to a single annual increment. This increment was radially subdivided into eight consecutive portions from earlywood through latewood. Each portion was used for determinations of specific gravity, extractives (ether, alcohol, hot water), methoxyl, and certain inorganics. Similar analyses were made on a “control” increment. The possible development of ring shake within the sample tree is presented in terms of resultant chemical and anatomical data.
Monomolecular film properties of cellulose and amylose triacetates at the air‐water interface
Authors: Hittmeier M. , Sandell L. S. , Luner P.
Published: June 2010

Surface pressure‐area isotherms of cellulose triacetate and amylose triacetate at the air‐water interface were determined on a vertical and horizontal film balance. Both polymers show anomalous behavior on the vertical balance, including: higher compressibilities than obtained on the horizontal balance, movement of the vertical plate, and atypical hysteresis of the isotherms.

The behavior of the cellulose triacetate film is attributed to heterogeneous gelation of the monolayer at low pressures. A mechanism involving the lateral tilting of pyranose units at the interface and subsequent stabilization of the monolayer by van der Waal's interactions accounts for the properties of this film.

A helical conformation for amylose triacetate at the air‐water interface is proposed to explain the low compressibility of this monolayer.