bluuebunny/crossref_metadata_2025 huggingface dataset:
Poly(Butadiene)/Poly(Styrene) Interpenetrating Polymer Networks
Authors: Curtius A. J. , Covitch M. J. , Thomas D. A. , Sperling L. H.
Published: February 2011

Interpenetrating polymer networks (IPN's) of poly (butadiene) (PB) and poly(styrene) (PS) were prepared using both random (containing 36 per cent cis, 55 per cent trans, and 9 per cent 1,2 vinyl) PB and high-cis PB. For both series, a wide range of PB/PS compositions were synthesized. Using samples stained with osmium tetroxide, electron microscopical studies revealed an irregular cellular structure of a few hundred A˚ngstrom diameter with the first component, PB, making up the cell walls. The size of the cells was found to depend on the PB crosslink density for the random materials. Modulus-temperature data revealed two distinct glass transitions, confirming the finding of two phases by microscopy. However, the transition temperature and transition slope varied with composition, and with the microstructure of the poly (butadiene), giving evidence of significant molecular mixing. Stress-strain data on the IPN's showed that materials rich in PB behave like self-reinforced elastomers. Charpy impact resistance experiments on materials rich in PS indicated values of 5 ft-lb/in. of notch, which compares well with graft-type polyblends of similar PB/PS composition. The results were interpreted in the light of the recent theoretical work of Bragaw, who considered the importance of the distances between domain boundaries with respect to crack acceleration mechanics. Although the IPN's considered herein exhibited somewhat less than the predicted optimum phase dimensions, the arrangement of the domains is different from ordinary impact resistant plastics.
Structure and Properties of Vulcanized Rubbers from Oligomers
Authors: Lykin A. S. , Sbytov Yu G. , Tunkel I. M.
Published: February 2011

Structural parameters of the vulcanization network of oligomer rubber compounds depend to a much greater degree on the extent of crosslinking than those for rubber compounds based on conventional rubbers. A condition necessary for obtaining oligomer rubber compounds exhibiting a good balance of properties is the maximum possible extent of crosslinking which is determined by the maximum degree of oligomer and crosslinking agent functionalities and the equimolar ratio of their reactive groups.
Aspects of the Relaxation of the Elastic Deformation of a Polymer at High Temperature in a Mold
Authors: Stepanov Yu N.
Published: February 2011

Upon storage of deformed mixes at controlled temperature the relaxation of elastic deformation in most cases occurs at the same time as crosslinking. The segmental mobility of the chains of the rubber disappears rapidly with the formation of crosslinks. This indicates the possibility of obtaining vulcanizates with different shapes of macromolecules.
Properties of Poly(Dimethylsiloxane) Networks Prepared in Solution, and their Use in Evaluating the Theories of Rubberlike Elasticity
Authors: Johnson R. M. , Mark J. E.
Published: February 2011

Poly(dimethylsiloxane) networks were prepared by γ irradiation of solutions of the polymer in cyclohexane; concentrations employed corresponded to volume fractions ν2,s of polymer ranging from 0.3 to 1.0. The moduli of these networks were obtained by stress—elongation measurements on the extracted, dried networks, and the relative degrees of crosslinking were obtained by swelling equilibrium experiments. These data were used to calculate the dependence of the modulus on the volume at which the crosslinking had been carried out. Comparison of experimental and theoretical values of this quantity lends strong support to the theory of rubberlike elasticity developed by Flory and coworkers. In addition, for samples having equal moduli, deviations from the form of the theoretical stress—elongation relationship decrease with decreasing ν2,s, with the strongest such dependence apparently occurring at small values of this volume fraction. In contrast, non-equilibrium effects exhibited by these networks also decrease with decreasing ν2,s, but the largest change is observed at large values of ν2,s. At constant ν2,s, increase in degree of crosslinking seems to increase the cited deviations from theory but to decrease nonequilibrium behavior. These additional results suggest that such deviations from theory can be, at most, only partially due to nonequilibrium effects.
Thermodynamic Interaction in Poly(Dimethylsiloxane)—Hydrocarbon Systems from Gas—Liquid Chromatography
Authors: Summers W. R. , Tewari Y. B. , Schreiber H. P.
Published: February 2011

Poly(dimethyl siloxane) has been used as the stationary phase in gas—liquid chromatography. Retention volumes have been used to calculate the thermodynamic interaction parameters for a series of linear and branched alkanes and aromatic hydrocarbons interacting with the polymer. Values of the χ parameter have been compared with results for the same systems obtained from equilibrium (static) vapor-absorption experiments, and found to be in excellent agreement. The successful comparison indicates the potential value of the glc route as the source of rapidly obtained thermodynamic data at infinite dilution of the volatile phase. A number of the prerequisites are established for useful application of the glc method to polymer solution thermodynamics.
Thermodynamic Interactions in Polymer Systems by Gas—Liquid Chromatography. II. Rubber—Hydrocarbons
Authors: Tewari Y. B. , Schreiber H. P.
Published: February 2011

The application of gas—liquid chromatography (glc) to the study of thermodynamic interactions in polymeric systems is attractive in its ability to generate data rapidly and to extend these into high polymer concentration ranges which are difficult to study by conventional methods. Several recent publications have shown that glc data can produce thermodynamically meaningful results, our most recent work showing very good agreement in a comparison of thermodynamic interaction parameters calculated from glc and equilibrium sorption data for poly(dimethylsiloxane) (PDMS) interacting with selected hydrocarbons. The demand for accuracy in thermodynamic data is considerable, if, for example, these are to be of use in resolution of varying predictions drawn from theories of solution thermodynamics. It is therefore prudent to extend the test of the rapid method's usefulness by comparing thermodynamic data calculated from conventional equilibrium sorption results and from glc data for additional polymers. The system natural rubber—hydrocarbons lends itself for such a comparison and is the subject matter of this report.
Topologically Interpenetrating Elastometric Networks
Authors: Klempner Daniel , Frisch H. L. , Frisch K. C.
Published: February 2011

Several partially interpenetrating polymeric networks (IPN) were made by combining chemically different linear elastomers. The polymer combinations were deposited as films from aqueous emulsions made by mixing the individual emulsions in equal proportions. The films were crosslinked to form two superimposed networks. In two cases, the networks were cleanly separated by hydrolysis of one of the component networks to demonstrate that there was no chemical interaction between the polymers. Measurement of crosslink density showed that, in most cases, partial interpenetration does occur as evidenced by an effective crosslink density of the IPN's greater than the arithmetic mean of the crosslink densities of the component networks. The swelling ratios, densities, and stress-strain properties were determined. For one of the network combinations, a poly (urethane-urea) and a poly (butadiene-acrylonitrile), a series of IPN's varying in polymer composition was made. The swelling ratios and densities are close to the arithmetic means; however, both the tensile strength and crosslink density exhibit a maximum at about 70% poly (butadiene-acrylonitrile). The maximum tensile strength is actually significantly higher than that of either of the component polymers. The elongations all approach that of the poly (urethane-urea), the more extensible material, except for compositions approaching 100% poly (butadiene-acrylonitrile), which exhibit a very low extensibility.
Vulcanization of Liquid Polydienes with Dithiols and Peroxides
Authors: Strecker R. A. H.
Published: February 2011

The vulcanization of polydienes with dithiols and peroxides was investigated. It has been found that liquid polybutadiene can be cured with aliphatic dithiols at temperatures below 100° C, yielding products which are comparable in mechanical properties with those obtained from carboxyl terminated liquid polybutadienes but with greatly improved stability against hydrolysis and air oxidation. Investigations of the curing mechanisms showed that with excess dithiol in respect to the peroxide the formed thiyl radicals react only with the vinyl groups to form stable products. Thus, under these conditions it is not possible to cure cis-polybutadiene and polyisoprene where only isomerization occurs. Of the two antioxidants investigated, phenyl-#x03B2;-naphthylamine does not inhibit the curing reaction whereas 2,2′ -methylene-bis(4-methyl-6-t-butyl phenol) interferes with it.
An Investigation into the High Temperature Strength and Reinforcement of Natural Rubber
Authors: Harwood J. A. C. , Payne A. R. , Whittaker R. E.
Published: February 2011

The failure criterion for amorphous polymers relating hysteresis at break with energy input to failure in tensile stress-strain tests was found to be obeyed only at very high or very low temperatures in natural rubber. Tensile results between about 80° C and 130° C show a high degree of scatter, and this behavior is attributed to the ability of natural rubber to crystallize at high strains. The modification of tensile properties by the addition of carbon black in natural rubber is also discussed and compared with published results from SBR. The effect of changing the degree of crosslinking on the failure properties in both dicumyl peroxide and sulfur-cured vulcanizates of natural rubber is also considered. It is found that differences in failure properties can be accounted for by the use of a crosslinking parameter from simple rubber elasticity theory in some of the failure equations.
Creep and Stress Relaxation of Natural Rubber Vulcanizates. Part I. Effect of Crosslink Density on the Rate of Creep in Different Vulcanizing Systems
Authors: Fairlie E. D.
Published: February 2011

The physical creep of unfilled natural rubber vulcanizates, prepared with different vulcanizing systems, has been studied. For each of the three vulcanizing systems chosen there is a strong dependence of creep rate on crosslink density, but the rates for accelerated sulfur vulcanizates are two or three times higher than those of peroxide vulcanizates of similar crosslink density. Supplementary experiments, in which the crosslink structure of sulfur vulcanizates is modified either by chemical treatment or by variations in the vulcanizing conditions, show that the nature of the crosslink itself is not a determining factor in the type of vulcanizate. Other features, such as the type and quantity of extranetwork material arising from the vulcanizing process, contribute significantly to the viscoelastic behavior of accelerated sulfur vulcanizates.
Study of Sulfur Vulcanization of Brominated Ethylene-Propylene Rubber
Authors: Dontsov A. A. , Novitskaya S. P. , Dogadkin B. A.
Published: February 2011

(1) It is shown that when BEPR is heated at 130–190 ° with various components of a sulfur vulcanizing system, the latter take part in nucleophilic substitution reactions with the combined bromine, and promote dehydrobromination of the polymer chains and crosslinking of the elastomer. (2) The effect of the components of the vulcanizing system on dehydrobromination is dependent on the acidity of the component, and their effect on vulcanization is dependent on the extent to which they activate the reaction of sulfur with the polymer. (3) Zinc oxide is itself a vulcanizing agent. In reacting with BEPR it forms ether crosslinks. (4) When BEPR is vulcanized by sulfur together with sulfur vulcanization accelerators and activators two types of crosslink are formed, namely strong C-C and C-O-C bonds and weaker sulfur bonds. This combination of bonds gives vulcanizates of increased strength.
Influence of Temperature on the Tensile Strength of Carbon Filled Vulcanizates
Authors: Sambrook R. W.
Published: February 2011

Despite undergoing a substantial reduction with increasing temperature the presence of carbon black added to the strength of both natural and styrenebutadiene rubber at temperatures up to 185° C. The magnitude of reinforcement was primarily dependent upon filler surface area although at the higher temperatures when this dependence is not so marked both high structure and particle activity appear advantageous. No theory of carbon black reinforcement can reasonably ignore the morphological characteristics of the material whose action it is attempting to explain. The concept of within aggregate voids, and occluded rubber envisaged by Medalia and used in this paper to describe the effect of fillers on rubber modulus, provides an interesting molecular meaning to the effects that have hitherto been explained on the basis of “shell” theories. Occluded rubber might reasonably be viewed as a type of shell since it undoubtedly represents a polymer zone in which molecular mobility is restricted. Furthermore the view of rubber being pulled from the interstices of an aggregate, manifestly a stress softening action, provides a source of plastic flow and mechanical hysteresis in the region of the aggregate—an apparent prerequisite for reinforcement.
How Does Rubber Slide?
Authors: Schallamach A.
Published: February 2011

Visual observations of contact areas between soft rubber sliders and hard tracks, and between hard sliders and soft rubber tracks, show that relative motion between the two frictional members is often only due to “waves of detachment” crossing the contact area at high speed from front to rear. Adhesion appears to be complete between these waves which are moving folds in the rubber surface, almost certainly produced by buckling. Buckling is attributed to tangential compressive stresses, predicted by a simple theory and qualitatively confirmed by experiment. The driving force for the waves of detachment is a tangential stress gradient, also theoretically predicted.
Studies on Tire Wear. I. Correlation between Laboratory Abrasion Tests and Road Tests
Authors: Satake K. , Sone T. , Hamada M. , Hayakawa K.
Published: February 2011

The correlation between laboratory abrasion tests and road tests were studied and the following results were obtained for SBR and BR tread compounds. 1. The Akron, the Pico and the Williams abrasion test results correlate well with the road test results, especially the Pico abrasion test results, even when formulations and polymers are varied. 2. In Williams abrasion tests, the differences among compounds are much more magnified than in the case of the road tests and they are less magnified in the order of Akron > Pico. These differences might be ascribed to the different severity of each abrasion machine according to Gelinas??? theory. The severity of each abrasion test decreases in the following order: Williams abrasion ≪ Akron abrasion > Pico abrasion The severity of Pico abrasion most approaches that of road tests. 3. The Akron and the Pico abrasion test results on aged samples are well correlated with the road test results as in case of the test results on samples before aged. The differences among compounds are smaller in case of the laboratory test results on aged samples than in case of the results on samples before aging, and approach those of the road test results.
Truck Tire Groove Cracking Theory and Practice
Authors: Clapson B. E. , Lake G. J.
Published: February 2011

The work described has aimed at clarifying the mechanism of groove cracking in tires. Basic studies of the fracture mechanics of rubber have shown that the rate of growth of a crack is independent of sample shape and type of deformation when it is expressed in terms of the available elastic energy. An empirical method is described which enables the energy to be estimated for a tire groove from measurement of the amount by which a crack opens under stress. The method also enables the strain to be determined and can, in principle, be applied to any stressed article. Using this approach and the crack growth characteristics of the tread rubber, the rate of growth of groove cracks in a tire can be predicted. Satisfactory quantitative agreement is found between observed and predicted behavior suggesting that the mechanism has been correctly identified. The work indicates relevant design factors and material properties and enables an appropriate laboratory test for groove cracking resistance to be defined.
Recent Observations on the Mechanical Properties of Polymer Networks
Authors: Thirion P. , Chasset R.
Published: February 2011

The influence of temperature, elongation, swelling or dilution ratio, crosslink density, nature of the polymers, and crosslinking agents on the dynamic properties, creep and relaxation of polymer networks is surveyed in the terminal region of the spectrum. Whereas the deformation does not change the relaxation kinetics in large ranges of extension, the crosslink density acts as a reduced variable apparently accelerating uniformly the viscoelastic processes beyond the glass transition. The other possible reductions ‘time-temperature’ and ‘time—swelling’ do not necessarily seem related to the variations of free volume. From the viewpoint of the explanation of the relaxation mechanisms in the terminal zone, the fact that the equilibrium of loosely crosslinked elastomers would only virtually be reached after several years at room temperature seem in better agreement with chain entanglement effects, either trapped or not by the permanent network, than with the dissociation of secondary linkages.
NMR Study of Vulcanized Rubber
Authors: Fujiwara Shizuro , Fujimoto Kunihiko
Published: February 2011

It is shown that NMR-linewidth measurements are useful to obtain information about the crosslink density and the average distance between the crosslinks in vulcanized rubber. Inhomogeneous structure of the rubber phase in carbon black-filled rubber is evidence and the thickness of the rubber layer on carbon black is estimated at 50 A˚.
Determination of Polymer Composition of Rubber Vulcanizates
Authors: Carlson D. W. , Ransaw H. C. , Altenau A. G.
Published: February 2011

Various methods exist for the quantitative determination of the polymer composition in vulcanized stocks. These methods consist of dissolving the vulcanizates in boiling o-dichlorobenzene, removal of the carbon black by filtration, and then infrared determination of the polymer. Pyrolysis of the stock followed by infrared analysis of the products has also been used. This technique had the disadvantages of requiring an analysis of products other than the original polymer or polymers. The infrared calibration based on polymers would no longer be valid. There may also be some uncertainty about changes in the relationship between the original microstructure and the pyrolysis products. Other infrared studies have been made but no quantitative measurements were reported. Recently an NMR method was published for vulcanizate analysis. The method consisted of dissolving the vulcanizate in hexachlorobutadiene, recording the NMR spectrum of the solution, and determining the total amount of butadiene, styrene, and natural rubber from the spectrum. Good results were obtained on a variety of vulcanizates. The one disadvantage of the method was that only a limited amount of microstructure data could be obtained. This was due to the lack of resolution of the 60-megacycle NMR. We have now developed a technique which allows enough of the rubber to dissolve in carbon disulfide for infrared analysis. This solution is free of carbon black. Infrared analysis provides microstructure data on the butadiene and/or isoprene portions as well as the total styrene content.
The Effect of Aging on the Reinforcing Properties of Carbon Blacks
Authors: Lezhnev N. N. , Krasilmikova M. K. , Yakuzhina K. A. , Filimonova G. D. , Nikitina O. V.
Published: February 2011

Carbon blacks age more in air than in a vacuum, and mostly within the first three months of exposure. During the aging process, certain changes occur in the adsorption characteristics of the blacks, such changes being brought about by oxidation, and by rearrangement of the functional groups at the surface. The disappearance of highly active adsorption centers at the surface of the blacks leads to a reduction of the tensile strength, the stress at 300% elongation, and the wear resistance of the vulcanized rubbers into which such blacks are incorporated. There is also a change in the relaxation characteristics of the rubbers.
Specific Surface Area Measurements on Carbon Black
Authors: Janzen Jay , Kraus Gerard
Published: February 2011

Various methods for estimating specific areas of carbon blacks are compared. These include the electron microscope count, methods based on adsorption of nitrogen, iodine and surfactants, and optical reflectance tests.
Thermal Expansion, Free Volume, and Molecular Mobility in a Carbon Black-Filled Elastomer
Authors: Kraus Gerard , Gruver J. T.
Published: February 2011

The thermal expansion of a butadiene-styrene copolymer filled with carbon blacks differing tenfold in mean particle size (HAF and MT) was investigated. The glass transition was unaffected by MT and was raised only 0.2° C for every 10 parts per hundred by weight of polymer of HAF black added. The coefficient of expansion of the polymer component of the composite in the rubbery region was substantially unaffected by either carbon black, but decreased markedly with increasing black loading in the glassy state. These results suggest that free volume is not altered appreciably by the presence of the filler in the rubbery state, but expands with decreasing temperature below Tg. The latter effect is explained by dilatation due to stresses set up around filler particles, arising from differences in the expansion coefficients of filler and polymer, which are not relieved in the glassy state. The near invariability of Tg and of the rubbery coefficient of expansion with filler content indicate that segmental motion is little affected by adsorption of polymer segments on the carbon black surface. A conservative rough estimates indicates that restriction of segmental motion is confined to a 30 A layer around the particles in which Tg is elevated by only 10° C.
Overall Kinetics of Natural Rubber Vulcanization at High Temperatures I—review of Investigation Techniques, Methods and Previous Results of Kinetic Analysis
Authors: Redding R. B. , Smith D. A.
Published: February 2011

Analysis of previously published cure data illustrates the importance of correct determination of the ultimate level of network chain density in the absence of reversion, and the correction of each kinetic data point for “reversion contributions”. A graphical procedure is described for the determination of kinetic parameters which takes these precautions into account.
Chemorheological Treatment of Crosslinked EPDM
Authors: Murakami Kenkichi , Tamura Saburo
Published: February 2011

Stress relaxation mechanisms were investigated on three types of (EPDM) ethylene-propylene terpolymers in air at 109° C. These polymers differ only by the structure of the crosslinkage in which there is a carbon-carbon bond, a polysulfide linkage −Sx⁁− or a monosulfide linkage (—S—). All the stress relaxation of peroxide-cured EPDM polymer was not due to the oxygen-induced cleavage of the main chain but to a physical flow. In the case of sulfur-cured EPDM polymer, the relaxation curve is divided into three straight lines when the procedure X is used and log f(t)/f(0( is plotted linearly with time. It was concluded that this graph was in agreement with an interchange reaction of the polysulfide linkage by an oxidative cleavage of the monosulfide linkage. On the other hand, a TT-cured EPDM polymer gave a plot with a straight line. This stress relaxation could be explained by an oxidative cleavage of the monosulfide linkage.
The Thermal and Oxidative Stability of Chlorosulfonated Polyethylene Vulcanizates as Measured by Stress Relaxation
Authors: Haaf F. , Johnson P. R.
Published: February 2011

Stress relaxation measurements of chlorosulfonated polyethylene vulcanizates show that curing with m-phenylene-bis-maleimide gives thermally more stable crosslinks than the conventional metal oxide/sulfur accelerator system. The superior thermal stability of the bis-maleimide cure is based on the covalent nature of the crosslinks. In conventionally cured vulcanizates interchange reactions of the metal sulfonate and polysulfide crosslinks occur at elevated temperatures. The interchange reactions of the crosslinks cause a rapid stress decline at the beginning of the stress relaxation process. Over longer aging periods stress relaxation due to oxidative degradation becomes apparent in vulcanizates of both types. The activation energies of oxidative stress relaxations are very similar for the bis-maleimide and the conventional cure. The similarity of the activation energies indicates that oxidative degradation follows the same path. The site of the oxidative attack is established for bis-maleimide cured vulcanizates. Oxidative degradation is found to occur in the polymer chains rather than in the crosslinks. The effects of fillers and stabilizers are investigated and their mode of action is explained on the basis of the stress relaxation results.
Some New Concepts in Polymer Stabilization
Authors: Scott G.
Published: February 2011

The mechanisms of antioxidant activity are briefly reviewed. Antioxidant systems based on catalase-active compounds, and the use of sulfur-containing metal complexes and transition metal ions as antioxidants are discussed.
Applications of Elastomers in Solid Rocket Powerplants
Authors: Sayles D. C.
Published: February 2011

Application of elastomers in the manufacture of solid-propelled powerplants is discussed. Thermal, ablative, and erosion-resistant properties of elastomeric composite materials are influenced by the composition of the elastomeric binder, the shape and composition of the reinforcing filler, filler loading, and the filler-to-elastomer ratio. The development of high performance motors, operating at higher chamber pressures, higher combustion flame temperatures, and for longer burning durations clearly point to the need for further advances in the insulative motor components for the liner, motor case, slivers, and nozzle if the requirements for improved future rocket designs are to be met.
Thermal Conductivity of Soft Vulcanized Natural Rubber, Selected Values
Authors: Carwile Lois C. K. , Hoge Harold J.
Published: February 2011

Literature on thermal conductivity of natural rubber has been critically evaluated. Best values of thermal conductivity as a function of temperature were selected, and are presented in both graphical and tabular form. An attempt was made to consult all work that could significantly affect the choice of best values. Relevant references in the papers themselves were followed up until a substantially “closed system” had been generated, as shown by the fact that no new references were being turned up.
Tables of Physical Constants of Rubbers
Authors: Wood Lawrence A.
Published: February 2011

Where a range is given, available observations differ. In most cases the differences are thought to be real, arising from differences in the rubber specimens, rather than from errors of observation. Where a single value is given, it is either because no other observations are available or because there seems to be no significant disagreement among values within the errors of observation. Where no value is given, no data have been found. Where dashes are shown, either the physical measurement is impossible or the constant in question is not adequately defined under the given conditions. Values are given, in most instances, in terms of the units used by the respective authors. Where the calorie has been used, it may be defined, with sufficient accuracy for the purposes of these tables, as the thermochemical calorie, which is equal to 4.1840 joules. The kilogram weight is taken as 980.665 dynes (0.00980665 newton). Values are given for 25° C and 1 bar (=106dyne cm2=106newton m−2), equivalent to 0.986923 (= 1/1.01325) normal atmosphere.
Adsorption of Macromolecules from Solution
Authors: Patat F. , Killmann E. , Schliebener C.
Published: February 2011

This publication arranges published papers on adsorption of polymers with special regard to experiment and theory. A summary is given of all investigated systems. Experimental methods are outlined and amounts adsorbed are discussed as a function of the system and experimental parameters (polymer, adsorbent, solvent, molecular weight, concentration, time, and temperature). Calculated and experimental amounts for saturation, number of contact points per molecule adsorbed, thickness of the adsorbed layer, adsorption isotherms, heats of adsorption, and effects of desorption are compared. Assumptions are made and discussed as to the structure of the adsorbed layer and the mechanism of polymer adsorption.
Aging and Stabilization of Raw and Cured Rubbers
Authors: Kuz'minskii A. S.
Published: February 2011

In recent years a number of monographs and survey articles have been published on individual problems of aging, from which we can compile an idea of the modern state of the problem. In this article we shall attempt to generalize certain new results, analysis of which may be of interest for further development of work on aging and stabilization of raw and cured rubbers. The substantial differences in the mechanisms and rates of aging of purified and technical raw and cured rubbers prepared from them have many times been noted in the literature The presence in technical raw rubbers of contaminants, introduced with the monomers, as well as residues of the catalysts, initiators, and regulators of polymerization exert a vital influence on the aging of rubbers and the behavior of inhibitors. It is also known that introduction of a large number of ingredients into raw rubbers (sulfur, vulcanization accelerators, carbon blacks, plasticizers) radically changes the character of the processes of aging of rubber mixtures. Free impurities and ingredients in most cases weaken, and sometimes suppress the action of antioxidants. For example, sulfur substantially reduces the effectiveness of secondary aromatic amine antioxidants. Other cases are also known when the action of antioxidants is intensified by certain ingredients. Thus, both negative and positive synergic effects may appear in rubber mixtures. Impurities contained in the monomers enter the structure of the polymer chains during polymerization, disturb their regularity, and frequently are the weak sites with which their thermal and thermooxidative decomposition begins. Hence the tendency to produce purer polymers from purified monomers, which will promote a substantial increase in their stability to aging, has now been outlined.
Growth Rate of Natural Rubber Crystallites
Authors: Hammett R. E. , Wingard R. E. , Land J. E.
Published: February 2011

The melting range and growth rate curves for natural rubber crystallites have been studied by the differential thermal analysis technique. The results obtained compare favorably with the growth rate curves obtained by dilatometric techniques. The use of differential thermal analysis revealed details of the crystallite melting which were not apparent when the dilatometer was used; however, no quantitative data on heat effects or the degree of crystallinity were calculated.
Low Temperature Expansion of Polysulfide Rubbers
Authors: Hunter B. A. , Kleinfeld M. J.
Published: February 2011

A novel method for producing a cellular cured rubber product at room temperature has been developed. Pourable liquid polysulfide polymers are treated with a conventional oxidizing curative and selected water-sensitive or oxidation-sensitive blowing agents. Standing at ambient temperature the viscous liquid mixture gradually “rises” and cures to form a finely porous cellular rubber product. Conventional curatives employed include oxidizing agents such as lead peroxide and cumene hydroperoxide. These convert terminal or pendant thiol groups in the polysulfide polymer chains to chain-connecting disulfide linkages. Water is a byproduct of the curing reaction. In the presence of water-sensitive blowing agents such as, (1) metal salts of azodicarboxylic acid or, (2) metal hydride compounds the water produced in the cure reacts to form copious amounts of nitrogen or of hydrogen. Alternatively, oxidation-sensitive blowing agents such as p, p′-oxybis-(benzene sulfonyl hydrazide) react directly with the oxidizing curative to form nitrogen gas. The blowing reactions are concurrent with cure and efficient and controllable expansion can be achieved. The unique process offers possible economies and special properties in applications of liquid polysulfide rubbers as potting compounds, joint sealants, solvent resistant forms, and cold casting compounds.
Self-Diffusion Coefficients and Tack of Some Rubbery Polymers
Authors: Skewis John D.
Published: February 2011

Self-diffusion coefficients for natural rubber, styrene butadiene rubber, ethylene propylene rubber and butyl rubber, are reported. Rates were determined by application of a layer of radioactively labeled polymer to the top of an unlabeled polymer base film and following the decay of radioactivity at the surface of the system, which decreased as a result of self-absorption. Macroscopically, diffusion is very slow, in fact difficult to measure, but on a microscopic scale it is rapid enough to cause considerable intermingling of polymer chains across an interface within a few seconds after two layers of polymeric material are brought into close contact. However, there were no major differences of self-diffusion coefficients between several types of polymers of comparable molecular weights. Therefore, the magnitudes of the coefficients suggest that diffusion may well be an important step for development of tacky adhesion, but the results also suggest that variations in observed tackiness among polymers cannot be simply ascribed to variations in diffusion rates.
Ethylene Propylene Copolymers. I. Monomer Reactivity Ratios
Authors: Bushick R. D.
Published: February 2011

Copolymerization of ethylene and propylene with diisobutylaluminum chloride and various vanadium-containing compounds gave a series of reactivity ratio values for ethyleno which decreased in the order: VO(O−n−Bu)3>VOCl(OEt)2>VOCl2OEt>VO(OEt)3≃VOCl3. All of the catalyst systems were extremely sensitive to changes in the ethylene feed concentration. The reactivity ratio product suggested a random arrangement of monomer units with each catalyst system except VOC13.
Oxidation of Two Isomeric Elastomers: Poly(Propylene Oxide) and Poly(Vinyl Methyl Ether)
Authors: Norling Parry M. , Tobolsky Arthur V.
Published: February 2011

Rates of oxygen absorption and chain scission have been measured for benzoyl peroxide initiated oxidation of the two isomeric hydrocarbons, poly(propylene oxide) and poly (vinyl methyl ether) in the temperature range 80–100° C and in the solid phase. Oxygen absorption data show that poly(propylene oxide) forms hydroperoxides 3.5 times as fast as poly (vinyl methyl ether). This may be attributed to steric hindrance in the propagation reaction. Chain scission, measured by stress relaxation of crosslinked samples, demonstrates that each initiating radical produces one scission in the poly(propylene oxide). The process appears to be less efficient in the poly(vinyl methyl ether). Two possible reactions are proposed to explain this observation.
Dynamic Behavior of Rubber During Moderate Extensions
Authors: Schallamach A. , Sellen D. B. , Greensmith H. W.
Published: February 2011

The stresses and energy losses during simple extension cycles to about 130 per cent maximum elongation have been determined for unfilled vulcanizates of natural rubber and acrylontrile-butadiene rubber at various rates of extension and temperatures. The results obey the Ferry transform, with the exception of natural rubber at the larger strains near the high temperature end of the experimental range. The stress-strain curves at increasing strain cannot be described as the product of one strain function and one time function, but the two-term Mooney equation with time dependent coefficients represents the results over a large strain range. Maxima in the strain-increasing stress curves have been observed which are not connected with necking. A suggestion is made as to why the negative slopes in these curves need not necessarily lead to instability.
Effect of Dispersion on Dynamic Properties of Filler-Loaded Rubbers
Authors: Payne A. R.
Published: February 2011

Increased time of mixing carbon black-rubber vulcanizates reduces dynamic modulus and dynamic viscosity as well as phase angle at moderate amplitudes of oscillation. Changes in dynamic properties with mixing time are shown to be associated with dispersion of carbon black.
Thermal Expansion and Viscoelasticity of Rubber in Relation to Crosslinking and Molecular Packing
Authors: Mason P.
Published: February 2011

Effects of crosslinking on specific volume, thermal expansion coefficient, glass transition temperature (Tg) and viscoelasticity of rubber have been studied. Materials were prepared by heating purified natural rubber with varying amounts of cumyl peroxide. This procedure formed networks by intermolecular carbon-to-carbon bonding, and an approximately sixty-fold range of crosslink density was obtained. Crosslink density could be estimated with reasonable confidence up to about 1020/g. At this level the effects observed were, approximately, a one per cent decrease in specific volume; 23 per cent and 6 per cent decreases in the thermal expansion coefficients respectively below and above Tg; 5° C increase in Tg; and a displacement of the viscoelastic response by +5° C. These changes are accounted for in terms of the reduction in free volume consequent on crosslinking. There was also a qualitative change in behavior, the thermal expansion and viscoelastic transitional regions widening as crosslinking increased. The thermal expansion behavior is explained in terms of a linear increase in the variance of monomeric free volume with crosslinking up to 1020/g. At higher densities crosslinks are so close that their packing effects interact and the nature of the phenomenon changes.
Solution Polymerization Initiated with Alkyllithiums
Authors: Hsieh H. L.
Published: February 2011

To summarize, solution polymerization of dienes and styrene with alkyllithiums offers many advantages. Two new elastomers have been developed, based on this system. The random copolymer (Solprene 1204) exhibits advantages over SBR, particularly with regard to hysteresis properties, abrasion resistance, electrical properties and color. The block copolymer (Solprene 1205) is well suited to applications requiring outstanding extrusion characteristics, high hardness and modulus and excellent low temperature properties. The versatility of this polymerization system makes it possible to produce copolymers at will with different molecular weight, molecular weight distribution, microstructure, comonomer ratio, block length, and degree of branching. Each can be “tailor-made” for specific applications.
Use of C14 Tagged Cumyl Peroxide to Study Peroxide Vulcanization of Ethylene Propylene Copolymers
Authors: Ballini G. , Baldi L. , DiGiulio E.
Published: February 2011

Peroxides are used today as crosslinking agents for elastomers in general, and for saturated elastomers in particular. Among peroxides, cumyl peroxide merits special attention because of the small danger in handling since it decomposes appreciably only above 120–130° C. The mechanism of the vulcanization reaction has been considered very simple, leading to the formation of carbon-to-carbon bonds between polymer molecules. The path of the reaction can be followed if one can determine at every instant the amount of crosslinking and of peroxide decomposition products, or the quantity of residual peroxide. From the existing literature, it appears evident that the degree of crosslinking in natural rubber and the recovery of peroxide fragments justify the reactions proposed in the chemical scheme. However, in the case of ethylene propylene rubber these lead to the conclusion that the peroxide is only partly used. This different fate of cumyl peroxide, depending on whether the decomposition occurs in natural rubber or in an ethylene propylene copolymer, demonstrates that other reactions occur, which involve primary peroxide radicals or the secondary polymeric radicals, or both, in a manner different from the proposed scheme.
Photodegradation of Rubber
Authors: Morand Mme J.
Published: February 2011

If we consider a cumyl peroxide vulcanizate, prepared from deproteinized crepe and from which all vulcanization residues have been extracted after cure, the variation of the overall quantum yield for chain scissions ϕ, as a function of wavelength, deduced from relaxation measurements in the air at 30° C, presents several discontinuities. At the beginning of the solar ultraviolet, ϕ equals 5.4×10−2 near 330 m/µ, it then presents a minimum value of 3×10−2, at about 340 mµ, before reaching a very pointed maximum of 5.3×10−2 at 355 mµ. Afterwards, it vanishes at the start of the visible radiation. It should be noted that ϕ in the ultraviolet region is of the same order of magnitude as the corresponding value found in the case of polymethyl methacrylate (1.2×10−2). In investigating the different parts of the spectrum in which the dissociation of chemical bonds present in the isoprene unit is energetically possible two assumptions seem justified: one, the high value of ϕ near 330 mµ may be due to photolysis of the main chain C—C bonds adjacent to the double bond; this will be manifest directly as a random breaking in the polymer chain, and two, the maximum of ϕ at 355 mµ presumably results from the photochemical dissociation of the α-methylenic C—H bonds. The radicals so formed initiate an autoxidation process, producing in the termination step oxidative cleavage of the chain. On the other hand, sulfur vulcanizates prepared from deproteinized crepe, vulcanized with mercaptobenzothiazole and sulfur and extracted after cure, contains some residues of vulcanization, namely zinc oxide and zinc sulfide, which are not extracted by the solvents employed. In this case, a determination of the overall quantum yield for scissions will not be adequate for theoretical purposes. From the practical point of view, an investigation of the influence of free substances present in different vulcanizates shows, once again, that non-rubber constituents display a protective effect. Otherwise, the action of vulcanization residues clearly depends upon their nature. Mercaptobenzothiazole and sulfur considerably slow down degradation by solar ultraviolet; zinc oxide protects only against radiation below 370 mµ, but it presents a sensitizing effect in the near visible. As a result, the most harmful rays for the greatest part of pure gum vulcanizates are found, not at the beginning of the ultraviolet sunlight, but in the region of 400 mµ.
Aging Behavior of Butyl Vulcanizates
Authors: Edwards D. C.
Published: February 2011

Network degradation measurements on gum vulcanizates have shown a large improvement in air aging with increasing unsaturation for sulfur and quinoid cures, and have indicated that the distinction is due to a relative increase in the rate of oxidative crosslinking. Solubility data have provided evidence that crosslink scission occurs in sulfur cures, while quinoid or resin cures produce relatively stable crosslinks. Mechanical tests support this conclusion. Degradation rates of resin cures are not dependent upon polymer unsaturation, a fact which may be ascribed to antioxidant activity on the part of the resin. Water of itself causes no degradation at 177° C, nor does thermal degradation occur to a measurable extent at this temperature. Severe surface damage results when oxygen and water are simultaneously present. Finally, data have been shown for “practical” resin vulcanizates, illustrating the diversity of behavior of these systems with respect to air aging, water absorption and surface degradation.
Strain Energy as a Criterion for Stress Softening in Carbon-Black-Filled Vulcanizates
Authors: Dannenberg E. M. , Brennan J. J.
Published: February 2011

Stress softening of vulcanizates of SBR 1500 containing different blacks possessing the same “structure” but varying in surface activity, and effects of different black loadings, of black structure levels, and of particle size, were investigated. It was concluded: 1. Strain-energy loss can be used as a quantitative measure of stress softening, and initial strain-energy input as a measure of prestress severity. 2. The effects of carbon black and polymer variables can be normalized in a single general relationship by plotting per cent strain-energy loss as a function of initial strain-energy input for filled vulcanizates. 3. With the exception of natural rubber, gum vulcanizates studied showed no stress softening. The stress softening of natural rubber gum vulcanizates is attributed mainly to stress-crystallization. 4. Stress-softening of filled vulcanizates is not a completely reversible process. Rates of stress recovery are reasonably rapid. 5. The degree of stress softening can be predicted from the initial stress—strain curve, the prestress severity desired, and the general correlation based on strain-energy considerations found in this study. 6. Prestressing reduces abrasion resistance as measured in the laboratory.
Sedimentation Analysis of Styrene Butadiene Copolymer Rubber
Authors: Homma Terutake , Fujita Hiroshi
Published: February 2011

Methods are presented by which the limiting viscosity number [η]Θ and the limiting sedimentation coefficient s0 of a monodisperse linear polymer in its theta solvent as functions of the molecular weight M may be deduced from data taken with a series of polydisperse samples of the polymer. The necessary data are the limiting viscosity numbers and the distribution functions of s0 of the chosen samples in the theta solvent, plus their number-average molecular weights. The methods are applied to unfractionated and fractionated samples of a styrene-butadiene co-polymer rubber (SBR) having 24 weight per cent bound styrene in a theta solvent, 2-pentanone, at 21.0° C. The following relations are deduced for monodisperse unbranched SBR in this theta solvent: [η]Θ=1.73×10−3M21 and s0=0.83×10−15M21, where [η]Θ is expressed in deciliters/gram and s0 in seconds. Besides these, the viscosity—molecular weight relations for this cold rubber in toluene and in cyclohexane, both at 30° C, are established. The new relation for the toluene system does not accord with the French-Ewart relation for “hot” rubber in the same solvent. The integral distribution of molecular weight in an unfractionated SBR is calculated from its distribution function of s0 in 2-pentanone at 21.0° C by using the derived s0 versus M relationship, and is found to coincide well with the mass distribution obtained from fractionation data if the new viscosity—molecular weight relation is used for the molecular weight of each fraction.