bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared Absorption Spectra of Alternating Copolymers of Butadiene with Acrylonitrile and Deuterated Analogs
Authors: Furukawa J. , Kobatashi E. , Uratani K. , Iseda Y. , Umemura J. , Takenaka T.
Published: February 2011

Random copolymers consisting of various amounts of butadiene and acrylonitrile have been prepared by conventional radical initiators or Ziegler—Natta catalysts. Recently, a novel alternating copolymer of butadiene with acrylonitrile was successfully prepared by the authors using a system of organoaluminum halide—transition metal compound as a catalyst. The NMR and x-ray analyses of the alternating copolymer indicated a high alternating regularity and trans regularity of the butadiene unit. Studies of mechanical properties of the copolymer suggested that the alternating copolymer was more flexible and stronger than the random copolymers. This report deals with a study of the ir spectra under stretching of the alternating copolymer influenced by the regularity of the molecular structure. The ir spectra of trans-1,4-polybutadiene have been studied by several authors and the assignments of the absorption bands of polyacrylonitrile have been given by Liang and Tadokoro et al. Tentative assignments of the absorption bands of the alternating copolymer were attempted on the basis of ir spectra and ir dichroism of partially deuterated copolymers and correlations with the results obtained on the above-mentioned homopolymers.
Modification of Emulsion Polymerization with Blends of Mercaptans
Authors: Uraneck C. A. , Burleigh J. E.
Published: February 2011

Although blends of modifiers have been used in the manufacture of SBR elastomers and similar polymers in emulsion systems for a long time, no studies of the kinetics of their reaction nor of their effect on molecular weights have been reported. This is such a study. Model equations for blends of modifiers are derived to predict modifier depletion and polymer molecular weight. These equations are used to serve as guides for preparing blends of modifiers in SBR-type polymerizations and for comparisons with experimental results.
Terpolymers of Ethylene, Propylene, and Tricyclo [5.2.1.0]Deca-2,5,8-Triene
Authors: Cesca S. , Arrighetti S. , Priola A. , Duranti P. V. , Bruzzone M.
Published: February 2011

Tricyclo[5.2.1.0]deca-2,5,8-triene (1) or a mixture of its methyl derivatives was used as termonomer to obtain ethylene—propylene—triene terpolymers (EPTM) having unusual properties in the curing process, even at low levels of triene (ca. 1 wt %). Three types of catalyst systems have been investigated, based on VCl4, VO[O(CH2)3CH3]3, or V(acac)3 and (C2H5)2AlCl. Several parameters of the terpolymerization process were studied (e.g. Al/V mole ratio; catalyst and termonomer concentration; polymerization time; presence of a Lewis base or chain transfer agent) and their influence on Mv and EPTM composition were evaluated. Fractionation data and the use of model compounds allow to conclude that 1 enters EPTM chains randomly and by selective opening of the norbornenic double bond, whereas the conjugated diene system is involved in side reactions if the catalyst has some acid character or the concentration of the triene is above some critical value.
Excluded-Volume Effects in Dilute Polymer Solutions. V. Butyl Rubber in Various Solvents
Authors: Tsuji T. , Fujita H.
Published: February 2011

It is a fundamental requirement of the two-parameter theory of linear homopolymers in dilute solution that the expansion factor α, and the interpenetration function Ψ depend only on the excluded-volume parameter z and that these functions are universal in the sense that their forms are independent of the chemical nature of the polymer and solvent as well as of the temperature. It follows immediately from the above requirement that the values of Ψ for different combinations of polymer, solvent, and temperature should form a single composite curve when plotted against αs.
Entanglement Networks of 1,2-Polybutadiene Crosslinked in States of Strain. II. Application of the Mooney-Rivlin Equation to Networks Crosslinked at 0°C
Authors: Kramer Ole , Ferry John D.
Published: February 2011

This paper gives the results of a recalculation of the data in Paper I of this series, with an expression for strain energy which is a special case of the Mooney-Rivlin theory, instead of the ideal theory based on Gaussian networks. It was shown in Paper I that the apparent concentration of elastically effective network strands terminated by entanglements, νN, can be estimated by crosslinking linear polymers in states of strain. The maximum value of νN found by this method was about one-half the value obtained from viscoelastic measurements in the rubbery plateau zone, νc=2.5×10−4 mol cm−3. The low value of νN was primarily attributed to the crosslinking temperature being too far (12°) above the glass-transition temperature, Tg. Crosslinking temperatures closer to Tg give values of νN close to νc, as will be shown in Paper III of this series. In addition, it was found that these networks behave slightly differently from the predictions of the ideal Gaussian composite network theory: ideal Gaussian composite networks are isotropic relative to the state of ease whereas these networks exhibit anisotropy of equilibrium swelling, relative to the state of ease, in n-heptane; and νN, instead of being a constant, was found to decrease with increasing extension ratio during crosslinking, λ0. The latter result is illustrated in Figure 1 for irradiation times from 3 to 5 h; here, νN is plotted against the extension ratio, λs, in the state of ease in which the retractive force of the entanglement network and the compressive force of the crosslink network are equal and opposite in direction. The experimental points can be fitted rather well by a curve (not the one shown) with the functional form of a constant divided by λs, like the C2 term in the Mooney-Rivlin equation.
Estimation of Long-Chain Branching in Ethylene-Propylene Terpolymers from Infinite-Dilution Viscoelastic Properties
Authors: Mitsuda Y. , Schrag J. L. , Ferry J. D.
Published: February 2011

A method is outlined for estimation of small degrees of long-chain branching in polymers with moderately narrow molecular weight distribution (Mw/Mn<1.4). The storage and loss shear moduli, G′ and G″, are measured in dilute solution by the Birnboim-Schrag multiple-lumped resonator and extrapolated to infinite dilution, choosing a suitable solvent viscosity and frequency range such that the data lie in the terminal zone where G′ and G″ are proportional to the second and first powers of frequency, respectively. The intrinsic reduced steady-state shear compliance is determined from these data and corrected for moderate molecular weight heterogeneity (assuming a Gaussian distribution) from knowledge ofMw/Mn and the Mark-Houwink exponent a. The resulting value of S2/S12 (where S1=∑ τp/τ1, S2=∑ (τp/τ1)2, the τp's being the relaxation times and τ1 the longest one) is compared with values calculated by the Zimm-Kilb theory as evaluated by Osaki for comb polymers of regular geometry and different numbers of branch points. The method has been illustrated by measurements on four ethylene-propylene copolymers. One containing no termonomer and one containing a saturated termonomer appeared to be linear; two containing unsaturated termonomers showed small degrees of branching. The method appears to be promising for detecting from one to four branch points per molecule.
Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Polymers. Part V. Monomer Sequence in Styrene-Butadiene Copolymers
Authors: Katritzky A. R. , Weiss D. E.
Published: February 2011

Future studies of styrene-butadiene copolymers will undoubtedly reveal much more information. Better resolution should be available with existing instrumentation, by using higher probe temperatures, smaller sweep widths, and longer accumulation times. More peaks could be resolved in the high-field region than the 17 we have assigned. The advent of higher-field 13C instruments will further improve resolution and, perhaps more important, relaxation-time studies will allow better assessment of peak intensities and reveal those diads of the copolymer which have greater mobility and hence facilitate precise correlation of the new structural information now reported with the mechanical properties of the copolymers.
The Use of Stable Free Radicals to Determine Motion in Polymeric Systems
Authors: Miller Wilmer G. , Veksli Zorica
Published: February 2011

The application of thermally and chemically stable nitroxide free radicals to a variety of motional problems in polymeric systems has been investigated. Solvents do not cause significant motion in glassy polymers until the glass transition is lowered to the temperature of measurement. With nonsolvents the results depend on the nature of the sample preparation as well as on the polymer-solvent pair. Molecular motion at the surface of a polymer immersed in a nonsolvent was investigated by means of surface-labeled latex spheres. The application of nitroxides as spin labels to the measurement of translational diffusion coefficients is explored and discussed. Finally, the application of the technique to adsorption and motion of surfactants and polymers onto surfaces is reported.
Reinforcement Studies—Effect of Silica Structure on Properties and Crosslink Density
Authors: Polmanteer K. E. , Lentz C. W.
Published: February 2011

This work was undertaken to study the effect of silica filler structure on the effective crosslink density and on mechanical properties. Vulcanizates of silicone, SBR, and EPM were included in the work. A compression modulus method was used for crosslink density determination. Samples were swollen prior to measurement in two environments : (a) toluene, (b) toluene in an NH8 atmosphere (designed to cleave polymer-filler linkages if they were present). The results showed that, in peroxide-cured silicone and EPM elastomers, the crosslink density increased with filler structure, but after cleavage of polymer-filler bonds by the NH3-modified swelling environment, there was very little change of crosslink density with filler structure increase. The effect of increasing filler structure on crosslink density in the SBR elastomers was very slight, showing a small increase in progressing from discrete particles to low structure and thereafter no change. The quanitative results of this study are important in that they provide excellent support for Medalia's theory of the role of occluded volume in reinforcement. The results show that polymer-filler bonds are required, in combination with occluded volume, in order to achieve a substantial increase in both 200% modulus and crosslink density.
Theory of Bound Rubber
Authors: Meissner B.
Published: February 2011

A theory of bound rubber formation has been developed which treats the effect as random adsorption of structural units of polymer on reactive sites which are assumed to exist on the surface of filler particles. Equations are derived for the fraction of bound rubber and for the molecular weight distribution of free (unbound) rubber. The theory contains only one adjustable parameter, the filler surface area per reactive site, A0. It is shown for the case of the Schulz distribution that the amount of bound rubber depends but slightly on the dispersion parameter of the polymer and is determined essentially by the adsorption index MwcP/A0NA, where c is the filler concentration, P is its specific surface area, and NA is the Avogadro number. All of the experimentally observed features of the bound rubber effect, including preferential adsorption of large molecules, are correctly predicted, the quantitative agreement of the theoretical equations with available experimental data being satisfactory. This supports the underlying assumption that the processes involved in the polymer-filler interaction may be approximated by a random-process model.
Particulate Reinforcement of Polyacrylate Elastomers. I. Introduction and Preparation of Materials
Authors: Blackley D. C. , Sheikh M. W.
Published: February 2011

The series of papers, of which this is the first, aims to demonstrate the importance of chemical reactions between filler particles and elastomer matrix in determining the physical properties of filled elastomers. A model system comprising small glass beads as the filler and crosslinked poly (ethyl acrylate) as the elastomer has been used. The beads themselves are inert towards the matrix during polymerization, but the reactivity of the surfaces of the beads can be varied by suitable treatments. This paper describes techniques for fractionating the beads to give narrow particle-size distribution, for preparing unfilled and filled elastomer sheets, and for preparing composites in which an elastomer sheet is polymerized in contact with a glass plate which may or may not have been previously subjected to surface treatment.
Recent Chemorheological Studies on Rubber Vulcanizates
Authors: Murakami K.
Published: February 2011

The structural changes of materials caused by chemical reactions are reflected in the viscoelastic behavior of these substances. Such viscoelastic behavior induced by chemical reaction was termed “chemorheology” by Tobolsky. This phenomenon is not readily observed in linear polymers since molecular flow, because of diffusion or chemical reaction, is generally much more rapid than relaxation. It has become possible, however, to establish chemorheology of linear polymers, by taking physical flow into consideration. As there is no mechanism for flow in crosslinked polymers, the rheological behavior at sufficiently high temperatures is almost always determined by chemical reactions. A significant problem in the degradation of crosslinked polymers is the determination of whether the scission of the crosslinked polymer occurs along the main chains or at crosslink sites. Both extreme cases have been studied theoretically and experimentally by A. V. Tobolsky and coworkers, while the case in which both types of scission occur simultaneously was suggested by Horikx. However, because of the difficulty of analysis for the case of simultaneous occurrence of both types of scission, there is as yet nothing in the literature. This paper deals with the theoretical and experimental results of the chemorheological treatment of crosslinked polymers concerning their scission mechanisms.
Accelerated Heat-Aging Studies on Fluorosilicone Rubber
Authors: Kalfayan S. H. , Silver R. H. , Mazzeo A. A.
Published: February 2011

The accelerated aging of a vulcanizate of fluorosilicone rubber was studied by four methods: infrared spectroscopy, GPC, weight loss, and stress relaxation, with the object of gathering information pertinent to understanding the basic mechanism of its aging. No changes were observed in infrared spectra of the rubber aged in air up to 315°C although severe degradation took place, as evidenced by high weight loss and drastic change in the physical condition of the test samples. It was concluded that although the polymer degrades, there is no change detectable within the precision of the analytical methods in the structure of the repeat unit of the elastomer. The gel-permeation chromatogram of unheated rubber showed peaks at MW 450 000 (95%) and 630 (5%). The low-molecular-weight component is very likely the cyclic tetramer of λ,λ′,λ″-trifluoropropylmethylsiloxane, the principal monomer of the FVMQ used. Heat aging increased the concentration of the 630 MW component, but rate studies were prevented by complications resulting from solvent-induced rubber degradation. Rapid decrease in the MW of FVMQ, as found by GPC, indicated random scission in the polymer backbone, as opposed to ordered unzipping of the repeat unit. The same conclusion was reached from the effects of crosslink density on stress relaxation. Activation energies obtained from weight-loss measurements (104 kJ/mol) were lower than those obtained from stress-relaxation measurements, (150–155 kJ/mol), suggesting that the processes being measured in each case may not be the same. Chemical stress relaxation takes place more rapidly in the presence of air than in an inert atmosphere, and intermittent stress-relaxation measurements indicate that crosslinks form during thermal aging in air, their rate first increasing and then decreasing.
Recycling Scrap Crosslinked Urethane Polymers
Authors: Gerkin R. M. , Critchfield F. E. , Miller W. A. , Roberts R. , Seefried C. G.
Published: February 2011

A. Scrap LRM polymers can be ground to powder on the Banbury operating at ambient temperature with cooling of the rotors and jacket. Particle size reduction can be accomplished in 5 min at 180 rpm. B. Powdered LRM polymer can be blended with TPU up to 50 wt.% and the composite compression molded to give the same properties as the TPU. C. Powdered LRM polymer can be blended with nitrile, chloroprene, and EPDM rubbers to give incompatible composites. The powdered LRM polymer acts in a manner similar to typical nonreinforcing fillers. D. It is possible to degrade powdered LRM polymers to a tacky mass at 180°C, which behaves much like a typical extender oil, when blended with nitrile and chloroprene rubbers. It is speculated that the degraded urethane should show a high degree of permanency in such blends. E. Addition of the urethane polymer to the rubber stocks does not interfere with the standard sulfur-curing mechanisms. F. Scrap HR foam can be ground to a powder in the Banbury in a manner similar to LRM scrap. G. A blend of 5 phr of powdered foam with a new HR foam formulation was machine processable. Addition of the powder had only a minor effect on the properties of the new foam.
Elasticity of Uncrosslinked Rubbers
Authors: Djiauw L. K. , Gent A. N.
Published: February 2011

Recovery from a prior deformation has been shown to follow simple general laws, which are readily extrapolated to molding or extrusion temperatures. They are also in principle applicable to more complex deformations and deformation histories.
Structure-Property Relationships of N,N′-Dinitroso-P-Phenylene-Bis (Hydroxylamine) Salts. Vulcanization of Nonhalogenated Elastomers
Authors: Martel Rock F. , Smith David E.
Published: February 2011

In a previous report the vulcanization activity of N,N′-dinitroso-p-phenylene-bis(hydroxylamine) salts in Neoprene WRT was discussed. The vulcanization was catalyzed by addition of stoichiometric amounts of aluminum or zinc powder (based upon percentage of allylic chloride), very possibly via the metal halide formed in situ. Natural rubber could not be vulcanized with these materials, however, differential thermal analysis indicated that amine-treated neoprene undergoes a crosslinking reaction at above normal curing temperatures. This evidence led us to propose that bisalkylation (α and/or β) at the allylic position is responsible for the formation of crosslinks. The mechanistic path is shown in Equations 1 and 2, and the analogy with the SN2′ activity of diamines in neoprene is quite apparent. The crosslinks III and/or IV are shown as the β form and one of the possible a structures. A number of structures for the α form have been proposed. The β structure has been known for some time. Our primary interest at this point was to extend the activity of N,N′-dinitroso-p-phenylene-bis(hydroxylamine) salts to elastomers which do not contain halogen. Any hope of achieving this goal depended, for the most part, upon whether or not certain of these materials would produce p-dinitrosobenzene, a known crosslinking agent, during the vulcanization cycle. The silver salt of phenylnitrosohydroxylamine, the monosubstituted counterpart of the bis(hydroxylamine) structure, decomposes readily to nitrosobenzene, nitric oxide and metallic silver. Accordingly, we prepared the di-silver salt of N,N′-dinitroso-p-phenylene-bis(hydroxylamine). The maximum rate of decomposition of this material was determined by differential thermal analysis, and occurred at 295° F. When 1.0 g of the di-silver salt was heated [see Reaction (3)] at 200° F for 2 hours, 0.3 g of a yellow solid sublimate was collected on a cold finger. The infrared spectrum of the yellow solid was identical with that of an authentic sample of p-dinitrosobenzene. Oxides of nitrogen were also visible in the reaction vapors (brown coloration).
Sorption and Diffusion in Crystalline Elastomers. I. Solubility of Isomeric Hydrocarbons in Stretched Rubber
Authors: Barrie J. A. , Platt B.
Published: February 2011

An important property of a polymer matrix which has a marked effect on the diffusion and sorption of vapors in polymer films is the degree of crystallinity. It is well established that the presence of crystallites leads to a decrease in both vapor solubility and permeability. Even so it is only recently that attempts have been made to relate these properties quantitatively with the degree of crystallinity. Most of this work was conducted with unstrained crystalline material, and relatively few data are available for stretched polymers either crystalline or noncrystalline. It was the main object of this work to investigate in more detail interrelations of vapor solubility, vapor permeability, and degree of crystallinity or orientation. The system hydrocarbon vapor-vulcanized natural rubber has been extensively characterized with respect to vapor permeability and solubility for regions of low penetrant concentration in the temperature range 30–60° C. As such it affords a useful reference state for studying the effect on either of these properties of a given degree of crystallinity or of orientation induced by subjecting the rubber to a simple elongation. Further, compared with unstretched semicrystalline polymers, the morphology of stretched rubber is comparatively straightforward, complex spherulitic growths being absent. In Part I of this paper we present and discuss solubility data obtained for isomeric hydrocarbons in stretched vulcanized natural rubber. The corresponding diffusion data are dealt with in Part II (following article, this issue). Throughout the investigation the degree of crosslinking was maintained constant.
Sorption and Diffusion in Crystalline Elastomers. II. Permeation of Isomeric Hydrocarbons in Stretched Rubber
Authors: Barrie J. A. , Platt B.
Published: February 2011

Part I of this series was concerned with the solubility data for the hydrocarbons n-butane and isobutane in stretched peroxide-cured natural rubber. The corresponding permeation data for these vapors and, in addition, for propane, as obtained by the experimental procedure described in Part I, are now presented and discussed, particularly with reference to the effect of crystallinity or orientation on the diffusion properties of the rubber.
The Mechanics of Ozone Cracking
Authors: Braden M. , Gent A. N.
Published: February 2011

Experimental measurements are described of the growth of a cut in a stretched rubber sheet under the action of an atmosphere containing ozone. A well-defined rate of crack growth is obtained, substantially independent of the applied tensile stress when this exceeds a critical value necessary for growth to occur at all. The rate of growth is found to be similar for a number of polymers and principally determined by the ozone concentration when the mobility of the polymer molecules is sufficiently high. When the molecular mobility is inadequate, crack growth is retarded. The critical condition is found to be similar for all the polymers examined, and largely independent of the conditions of exposure; it appears to reflect an energy requirement for growth of about 40 ergs/cm2 of newly-formed surface. The effect of the degree of vulcanization and the presence of additives, including antiozonants, on these two factors has also been examined. The dialkyl-p-phenylene diamines are found to confer protection by raising the critical energy required for growth to occur, in contrast to other protective agents which affect only the rate of crack propagation.
Temperature Coefficient of Vulcanization for Present-Day Tire Compounds
Authors: Ambelang J. C. , Beach K. C. , O'Sullivan D. F.
Published: February 2011

The temperature coefficient of vulcanization was measured for tread type compounds of present-day polymers, carbon blacks and accelerators. The state of cure was judged by modulus and crosslinking (from swell); the temperature coefficient was measured at 80% of the maximum reached at a standard cure temperature. An expeditious and precise method was developed for calculating the vulcanization coefficient.
Viscoelastic Properties of Rubberlike Composite Propellants and Filled Elastomers
Authors: Landel Robert F. , Smith Thor L.
Published: February 2011

The mechanical properties of rubberlike composite propellants and similar filled elastomers are determined largely by the volume fraction of filler, the visco-elastic properties of the binder, and the interactions between the binder and filler particles. The ratio of the quasi-equilibrium modulus of the composite to that for the unfilled elastomer increases with the volume fraction of the filler, apparently according to an equation of the form proposed by Eilers and Van Dyck. However, the same ratio for the dynamic storage modulus decreases as the frequency is increased or the temperature is decreased. The time-dependent tensile properties can be characterized by stress-strain curves measured at different strain rates and temperatures. Both the small deformation and ultimate properties can be represented by master curves, which are functions only of the experimental time scale, along with a temperature function which is a near-universal function of the glass temperature. Propellants under constant loads initially exhibit creep which is qualitatively similar to that of unfilled elastomers, but subsequently dewetting of the filler particles may begin and this causes the deformation to increase exponentially with time. A discussion is given of the use of Poisson's ratio, defined in terms of Hencky strain and measured as a function of extension, to indicate the initiation of dewetting and the subsequent volume increase.
Adsorption Properties and Infrared Spectra of Oxidized Carbon Blacks
Authors: Lygin V. I. , Kovaleva N. V. , Kavtaradze N. N. , Kiselev A. V.
Published: February 2011

Chemical analysis and adsorption of water indicate that strongly oxidized carbon blacks contain various oxygen compounds which greatly influence adsorption of water. Infrared spectra give indications of the nature of these compounds and of their mutual interaction.
Effect of Elongation on the Electrical Anisotropy of Natural Rubber and SBR Vulcanizates Containing ISAF Carbon Black
Authors: Chasset R. , Thirion P.
Published: February 2011

The electrical resistivity of testpieces under different elongations, both parallel and at right-angles to the axis of elongation, was measured for two vulcanizates, i.e. one of natural rubber and the other of SBR, compounded with 20 volume per cent of ISAF black (Vulcan 6). Within the range of validity of Ohm's law, the main results of this study are as follows: a) the resistivities of both vulcanizates increase considerably with elongation, in both directions. b) on the whole, both vulcanizates are electrically anisotropic, since current flows more easily longitudinally than it does transversely. The anisotropy increases at the start with elongation, then becomes practically constant. However, the latter level is much higher with natural rubber, for which it corresponds to an anisotropy of about 1,000 and an elongation of around 150%. For SBR this level is only 20 to 30 and is reached at only 50% elongation. Owing to the complexity of the problem, no interpretation can yet be given for these differences. It will first be necessary to examine other elastomers and carbon blacks. For the time being, it may merely be stated that the electrical anisotropy of natural rubber and SBR reinforced vulcanizates differs as much as their mechanical properties, especially their tearing behavior.
A Towing Device for Estimating Road Wear
Authors: Gelinas L. P. , Storey E. B.
Published: February 2011

The towing device was designed to provide a rapid screening test that might be applied to measure the wear resistance of small quantities of experimental polymers. The reproducibility of the test has been found to depend to a large degree upon the care was taken to design measuring equipment that would provide a good estimate of this value. The nature of the road surface will produce a change in the rate of wear and, with certain polymers, excessive cutting has been encountered that affected the reproducibility of the measurement. This difficulty may be avoided by selecting a smoother road surface and longer test runs may be employed without increasing the duration of the test beyond 6 hours. A towing device has been developed that allows the wear resistance of a small quantity of polymer to be evaluated by towing a test wheel at a slight angle over the surface of a road at normal tire loads and speeds. Data from road wear tests of tires of various sizes showed that a log-log plot of the volume loss per unit width of tread of the experimental against the control vulcanizate gave a single correlation. The volume loss of the control vulcanizate may be taken as a measure of the severity of the test. Tests using the towing device at various angles of tow gave data that showed a correlation of wear values similar to that found in road tests. The towing device provides an adequate method for screening the wear qualities of small quantities of experimental polymer.
Dynamic Mechanical Properties of Stretched Natural Rubber
Authors: Fitzgerald Edwin R.
Published: February 2011

Dynamic shear compliance measurements on a natural rubber vulcanizate have been carried out from 50 to 5000 cps as a function of static elongation in the range 0–400%. Above 300% elongation several very large resonance dispersions appear in the region 1000–2000 cps, but at lower elongations no such resonances are observed. The appearance of mechanical resonance dispersion thus coincides with the development of oriented crystallinity in the stretched rubber as shown from x-ray diffraction data. On the other hand, the magnitudes of the dispersions decrease with increasing elongation above 300% whereas x-ray measurements indicate the amount or extent of crystallinity increases with stretching above 300% elongation. The resonances thus clearly decrease as the crystallinity becomes more perfect or more extensive and hence appear to reflect the imperfections of the crystalline regions formed by elongation rather than the crystallinity itself. Observed changes in the compliance spectrum with time at each elongation also favor this view. Broad retardation dispersions were observed when the rubber was allowed to contract back to elongations below 300% after long times above 300%. These are tentatively ascribed to an extended amorphous state in which the rubber molecules are kept partially extended by very small randomly oriented crystalline regions which persist for some time after retraction. Another interesting feature of the results is an apparent correlation between the percent crystallinity determined from x-ray diffraction and the reciprocal of the general level of storage compliance 1/J′ at frequencies well below or well above the dispersion region.
The Scorching of Rubber Mixes. II. Effect of Retarders on the Kinetics of Sulfur Combination
Authors: Dogadkin B. A. , Dobromyslova A. V. , Belyatskaya O. N.
Published: February 2011

1. Vulcanization retardera decrease the rate of interaction of sulfur with rubber. 2. N-Nitrosodiphenylamine (NDPA) retards the rate of addition of sulfur in the presence of all the investigated vulcanization accelerators: CBS, MBT, TMTD, DPG, N-oxydiethylene-2-benzothiazylsulfenamide, and the 2,4-dinitrophenyl ester of MBT, as well as in the absence of accelerators. 3. The rate of addition of the elements of accelerators CBS and TMTD increases in the presence of NDPA. 4. The effectiveness of NDPA as a retarder decreases with an increase of the vulcanization temperature. 5. The mechanism of the inhibiting action of NDPA is considered from the point of view of the influence that the products of its dissociation (nitric oxide and diphenylamino radicals) may have on the initial vulcanization processes.
Scorching of Rubber Mixes. I. Structural Changes in Unfilled and Filled Stocks
Authors: Dogadkin B. A. , Dobromyslova A. V. , Belyatskaya O. N. , Gyul'-Nazarova T. A.
Published: February 2011

1. In the process of scorching there takes place a combination of the sulfur with the rubber. The flow of unfilled stocks heated at 120° ceases at the instant of combination of ∼0.5% sulfur reckoned on the stock. 2. In carbon black filled stocks there is an increase in the rate of combination of sulfur with rubber and a decrease in the time for which the stock is in the flow state, as the pH value of the carbon black added to the stock increases. 3. In processing a stock on the mill in the presence of fine-particle carbon black there is formed a rubber-carbon black gel, the amount of which hardly changes in the process of heating the stock in the plastimeter at 120°; only at the instant of cessation of the flow of the stock does its solubility decrease perceptibly. 4. In filled stocks in which a rubber-carbon black gel is formed in the course of treatment on the mill, the limiting amount of bound sulfur combined at the instant of cessation of the flow of the stock is less than in stocks in which no rubber-carbon black gel is formed. 5. Alteration in the amount of oxygen-containing functional groups upon the surface of the carbon black does not cause any important influence upon the amount of rubber-carbon black gel, but significantly alters the rate of combination of sulfur with rubber and the tendency of the stock to premature vulcanization. 6. Thus the phenomenon of premature vulcanization is governed for the most part by the reaction of the rubber with the sulfur and the other vulcanizing agents. In stocks with fine-particle carbon blacks there is also a significant influence from the formation of the rubber-carbon black gel in the processing of the stock on the mill.
Crosslinking of Polymers with Dimaleimides. I.
Authors: Kovacic Peter , Hein Richard W.
Published: February 2011

From gelation and compounding studies, dimaleimides were found to crosslink a wide variety of polymers including unsaturated hydrocarbon types, polyethylene, polymers containing amino groups and a urethan polymer. Except for the amino-containing polymers, the presence of catalytic amounts of peroxide was necessary for effective crosslinking. The chemistry of the crosslinking processes is discussed.
Crosslinking of Unsaturated Polymers with Dimaleimides. II.
Authors: Kovacic Peter , Hein Richard W.
Published: February 2011

A study was made of the crosslinking of unsaturated polymers with dimaleimides representative of both the aliphatic and aromatic series. In the presence of catalytic amounts of dicumyl peroxide, dimaleimides functioned as highly effective cross-linking agents for natural rubber and SBR. Comparatively little crosslinking occurred in the absence of peroxide under thermal conditions. With peroxide as a promoter, monomaleimides and dimaleamic acids also crosslinked natural rubber, but to a lesser extent than did the dimaleimides. The chemistry of the crosslinking process is discussed, and correlations are drawn between the structure of the dimaleimide and vulcanizate properties.
Sulfur-Induced cis-trans Isomerization of Polybutadiene
Authors: Bishop William A.
Published: February 2011

Both high cis-1,4-polybutadiene and high trans-1,4-polybutadiene were found to isomerize when heated in the presence of elemental sulfur. The kinetics of the sulfur induced isomerization of high cis-1,4-polybutadiene were studied over a wide range of temperature and sulfur concentration and found to obey a first-order kinetic expression having an effective rate constant directly proportional to the initial sulfur concentration. The apparent activation energy was found to be 30.1 ± 0.4 kcal/mole. Isomerization was also found to be induced by dicumyl peroxide. A comparison of the mechanisms involved in the sulfur and peroxide induced isomerization indicate a basic difference in the nature of the initial interaction of the double bond with the sensitizing species. The initial interaction of the sulfur and the double bond is pictured as a π-complex that decomposes to a freely rotating radical, whereas the peroxide induced isomerization is presumed to involve direct radical addition to the double bond.
Compounding of cis-1,4 Polybutadiene for Tire Applications
Authors: Brown R. J. , Knill R. B. , Kerscher J. F. , Todd R. V.
Published: February 2011

cis-1,4-Polybutadiene is proving to be one of the most versatile compounding materials available to the tire compounder. It has characteristics as a polymer which make it acceptable as a replacement for either natural or synthetic rubber in tire applications. The successful use of cis-polybutadiene in this dual role, however, is dependent upon discovering its peculiarities and sensitivities and then exploiting them in that area of the tire where they are most applicable. Laboratory studies, confirmed by over three million miles of tire testing, have shown that in either passenger or truck tires the carcass durability can be substantially improved, operating temperature lowered, low temperature performance improved, and treadwear resistance increased when cis-PBD is properly used in the respective tire components.
Reactions of Polymers in Bulk. III. Influence of Specific Surface and of Filler Concentration on Deformation Behavior
Authors: Janacek J.
Published: February 2011

The deformation behavior of carbon black-filled vulcanizates depends—after elimination of the influence of the differences in chemical activity of the carbon black—on the product of the specific surface P of the carbon black and the nth power of its volume concentration c; for the correlation of the modulus M100, the Shore hardness, and the rebound elasticity the value n=2 was found. This statement holds true for carbon blacks of similar structure levels and of small enough specific surface that one can assume that it will not agglomerate to an appreciable extent.
Reactions of Polymers in Bulk. IV. Influence of Structure and Agglomeration of Carbon Black Particles on Deformation Behavior
Authors: Janacek J.
Published: February 2011

The deformation behavior of filled rubber vulcanizates depends on the degree of linkage of the carbon black particles and on their tendency for agglomeration. The significance of these factors is discussed with consideration of the specific surface of the particles, their concentration, the degree of crosslinking, the magnitude of the deformation and the character of the polymer system.
Crystallization Phenomena in Filled, Unstretched, Natural Rubber
Authors: Westlinning H. , Butenuth G. , Leineweber G.
Published: February 2011

In two previous communications it was shown that the “reinforcing effect” of active fillers is associated with the formation of highly resilient sheaths of low swelling capacity, surrounding the filler particles. In order to support this concept and to come closer to understanding the qualitative structure of this sheathing material, initial trials were undertaken in an effort to depict it directly with the microscope.
Tetramethylthiuram Monosulfide and Tetramethylthiuram Disulfide: Heats of Formation and the S—S Thermochemical Bond Energy
Authors: Good W. D. , Lacina J. L. , McCullough J. P.
Published: February 2011

The heats of combustion and formation were determined for tetramethylthiuram monosulfide [bis-(dimethylthiocarbamoyl) sulfide] and tetramethylthiuram disulfide [bis-(dimethylthiocarbamoyl) disulfide]. The S—S thermochemical bond energy in tetramethylthiuram disulfide was shown to be about the same as in normal alkane disulfides and in S8. Rotating-bomb combustion calorimetry was found satisfactory for compounds that contain both sulfur and nitrogen.
Reaction of Mercaptobenzothiazole with Rubber during Mastication
Authors: Chatterjee Pronoy K. , Sircar Anil K.
Published: February 2011

Mercaptobenzothiazole (MBT), determined amperometrically in the acetone extract from an unvulcanized rubber-sulfur-MBT mix shows a loss of about 13 per cent of MBT. The results improve slightly when mixing is carried out at a low temperature (10° C) or in an inert atmosphere. After exploring the various possibilities, e.g., oxidation of MBT to MBTS or reaction with rubber it was concluded that main loss of MBT is due to a side reaction with nonrubber ingredients, extractable with acetone. Total MBT recovered when mixed with acetone extracted pale crepe or with synthetic cis-polyisoprene is about 98 per cent. In the absence of sulfur no appreciable reaction takes place even when MBT is heated with rubber at 145° C for 5 hours.
Titrimetric Determination of N,N′-Disubstituted p-Phenylenediamines
Authors: Lorenz Otto , Parks C. R.
Published: February 2011

Three types of p-phenylenediamine derivatives used extensively as antioxidants and antiozonants in rubber compounds are N,N′-di-sec-alkyl-, N-sec-alkyl-N′-aryl-, and N,N′-diaryl-p-phenylenediamines. Available methods for these compounds are based mainly on a colorimetric determination of their colored oxidation products, the Wurster's salts or the p-quinonediimines. The deep coloration of the Wurster's salts was used as the basis of a spot test for the rapid detection of these diamines in rubber compounds. This test permits one to differentiate the three types of p-phenylenediamines. An investigation of the neutralization of p-phenylenediamines in nonaqueous solvents showed that N,N′-di-sec-alkyl- and N-sec-alkyl-N′-aryl-p-phenylenediamines could be determined readily in this way. The N,N′-diaryl derivatives did not give satisfactory titration curves because of their low basicity. By the addition of chloranil, however, diaryl-p-phenylenediamines were oxidized to the Wurster's salts with the formation of one equivalent of base which could be neutralized by acid. A similar procedure was applicable to the determination of N,N′-diaryl-p-quinonediimines, or mixtures of these diamines and diimines.
Tritium Tracer Study of Antioxidant Action in SBR
Authors: McHenry W. Dennis
Published: February 2011

Development of vulcanizates with good heat resistance has been a part of the program at this Arsenal's Elastomer Unit for some time. Freeman made a comprehensive evaluation of 63 commercial chemicals for use as heat stable inhibitors. A cadmium/barium fatty acid soap-chelator mixture was found to be the best heat stable antioxidant evaluated in the styrene-butadiene series of his investigation. Further work with this stabilizing system, by Testroet, in which its components were tested individually, disclosed this effect to be synergistic, as no significant protection was noted when the materials were used independently. An aid to the understanding of this synergism was sought in a radiometry study of the physical behavior of Cd/Ba salts of stearic and myristic acids (soaps) and pentaerythritol (chelating agent) during heat aging of an SBR vulcanizate.
Oxidation of Butadiene-Acrylonitrile Rubbers
Authors: Devirts E. Ya , Novikov A. S.
Published: February 2011

1. The authors investigate the inhibited oxidation of SKN-18, SKN-26 and SKN-40 butadiene-acrylonitrile rubbers in a micro-oxidation apparatus at various temperatures. 2. It is established that the rate of inhibited oxidation of butadiene-acrylonitrile rubbers is determined by their nitrile group content. On increasing the amount of acrylonitrile in the polymer the rate of oxidation decreases. 3. The energy of activation of inhibited oxidation of butadiene-acrylonitrile rubbers (29 to 30 kcal/mole) is calculated according to the Arrhenius equation. The energy of activation of inhibited oxidation of SKN rubbers is 5 kcal/mole higher than the energy of activation of inhibited oxidation of SKS-30 rubber and 10 kcal/mole higher than that of SKB rubber. 4. The structural changes in SKN rubbers in inhibited oxidation are determined by their nitrile groups. For SKN-26 and SKN-40 the predominant process in all stages of oxidation is the process of crosslinking. In the case of SKN-18 the process of degradation predominates at the beginning, and in the later stages the process of crosslinking. 5. A correlation is demonstrated between the behavior of SKN rubbers in oxidation and in thermal oxidative plasticization.
Faster Curing Butyl Rubber
Authors: Dorko Z. J. , Edwards D. C. , Lumb P. B.
Published: February 2011

For many years there has been need for polymers with the characteristics of butyl rubber but with appreciably greater rates of cure. Until recently, however, the range has been defined by PB-100 and PB-400 at the two extremes so far as our commercial products are concerned. This paper describes some of the products we are introducing to extend this range. First of all, the problems of producing faster curing butyl will be outlined. Butyl rubber is essentially polyisobutylene in which a small portion of isobutylene molecules is replaced by isoprene. These isoprene molecules supply the active sites for vulcanization, hence, in order to produce a faster curing butyl, the obvious approach is to make a polymer still essentially polyisobutylene, and containing a larger amount of copolymerized isoprene. This solution did not seem promising, owing to the serious molecular weight depressant effect of isoprene, and of the trace impurities present in the various feed streams. (It is worth noting that the addition of as little as 1% of isoprene to isobutylene reduces the molecular weight of polyisobutylene by a factor greater than 10.) We did, however, feel that a more complete knowledge of the chemistry of the polymerization system might yield a means whereby this poisoning effect would be overcome. In laboratory scale polymerizations, we therefore began a kinetic study of the copolymerization of diolefins with isobutylene under conditions similar to large scale commercial operations. The aim of this work was first to obtain information on the relative rates of all propagation and termination reactions, then to apply these data with the proviso that the engineering advantages of our present process were not lost. From this we hoped to determine whether conditions existed leading to higher unsaturation polymers with high molecular weight. The results of this study, which we intend to publish elsewhere at a later date in detail, have elucidated the order of the principal termination reactions, and have led to an economic process whereby copolymers of isobutylene with larger amounts of isoprene are now commercially available (in both 40–50 Mooney and 70–80 Mooney grades). The properties of the 40–50 Mooney polymers will now be described in comparison with existing grades, to show what properties are now available, and also the relationship between these properties and polymer unsaturation.
Nitrile Rubbers and Vinyl Polymer Mixtures
Authors: Almond C. Y.
Published: February 2011

The outstanding resistance to abrasion, oil, fire and ozone of vulcanized nitrile rubber/PVC blends has stimulated cable manufacturers throughout the world. In this paper the effect of polymer properties on mixing conditions is discussed and physical properties resulting from different mixing conditions reviewed. The physical (including electrical) properties of vulcanized and unvulcanized nitrile rubber/ PVC blends are related to the use of these blends in covering electric cables. Comparisons are made with other types of sheathing and insulating materials and existing potential uses of nitrile rubber/PVC blends in cable coverings are discussed.