bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Certain Organic Sulfur Compounds as Preventive Antioxidants. II. Activity as Peroxide Decomposers and Effect of Bases
Authors: Shelton J. R. , Harrington E. R.
Published: February 2011

The results of this study of the activity of certain organic sulfur compounds as peroxide decomposers provides considerable insight to the mechanisms by which they function as preventive antioxidants. First, it is clearly evident that sulfides, disulfides, and their initial oxidation products are not the actual preventive antioxidants but rather the source from which the active materials are obtained. Thus, the sulfoxides and thiolsulfinates, formed in the initial reactions of sulfides and disulfides with hydroperoxides, serve as sources of sulfenic acid and thiosulfoxylic acid, which, together with their reaction products, are the real peroxide decomposers. It has also been demonstrated that sulfenic acid is the most effective peroxide decomposer, and that the acidic product of the initial reaction with hydroperoxide is also an effective peroxide decomposer. This product and the thiosulfoxylic acid from thiolsulfinate react with hydroperoxide by a catalytic mechanism which destroys many moles of hydroperoxide per mole of sulfur compound. The polar acidic character of these reactions was demonstrated by the effect of base. The catalytic decompositions were both effectively stopped by addition of CaCO3, and the thiosulfoxylic-acid-induced peroxide decomposition was stopped by complexing the acid with a sulfoxide.
Radiothermoluminescence and Its Application to the Study of Elastomers Structure
Authors: Zlatkevich L. Y.
Published: February 2011

To summarize, it can be seen that the investigation by the radiothermo-Iuminescence method provides important and varied information on the structure of elastomers. Possible applications of this method are not, however, confined to the examples mentioned here. It is possible to use this method for investigating the microstructure of materials obtained in the process of new organic synthesis, studying the plasticity of elastomers, analyzing super-molecular structure in them, and in whole series of other problems of practical importance.
Physical Constants of Different Rubbers
Authors: Wood L. A.
Published: February 2011

Where a range is given, there are available several observations which differ. In most cases the differences are thought to be real, arising from differences in the rubber 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 values are not given, data have not 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. 50 phr means “50 parts of carbon black by weight per 100 parts of rubber”, corresponding to a volume fraction of about 0.2. The values shown refer to specific vulcanizates cited in the corresponding references. Other vulcanizates may yield a broader range of values. The metric technical unit “kilogram force” or “kilopond” has been taken as 9.80665 newtons (980 665 dynes). Where an undefined calorie has been used by the respective authors, it has been taken as the thermochemical calorie equal to 4.1840 joules. Values are given for constants at a temperature of 25°C and a pressure of 1 normal atmosphere = 1.01325×105 Pa (where 1 Pa = 1 N/m2 = 10 dyn/cm2 = 10−6 bar).
Pressure-Volume-Temperature Measurements for Polyethylene, Polyiso-Butylene, Poly(Vinyl Acetate), and Poly(Dimethylsiloxane) to 1 Kilobar
Authors: Beret S. , Prausnitz J. M.
Published: February 2011

While accurate measurements of volumetric properties of common liquids have been reported over the last 20 years, such measurements are scarce for polymeric liquids at high temperatures and pressures. Quach and Simha measured densities of polystyrene (PS) and poly-(o-methylstyrene) in the region 1–2000 bar and 10–200°C. Goldstein and McKinney measured the density of poly (vinyl acetate) (PVAC) in the region 1–800 bar and −35–100°. Hellwege reported volumetric data for polyethylene (PE), poly(vinyl chloride) (PVC), and poly(methyl methacrylate) (PMMA). Maloney and Prausnitz compared density data for PE from different sources and found appreciable disagreement. Volumetric data for polyisobutylene (PIB) and poly(dimethylsiloxane) (PDMS) are confined to modest pressures (1–40 bar) and those for PVC and PMMA are confined to a small temperature range (120–140°C for PMMA and 90–100°C for PVC). This work presents experimental results at advanced pressures for four polymers (low-density PE, PVAC, PIB, and PDMS) in the temperature region 25–200°C and at pressures from 1 to 1000 bar. All experimental work reported here is confined to the amorphous liquid state.
Derivation of Accurate Glass Transition Temperatures by Differential Scanning Calorimetry
Authors: Richardson M. J. , Savill N. G.
Published: February 2011

Glass transition temperatures, Tg, cannot be directly determined from differential scanning calorimetry (DSC) curves because of kinetic effects which are especially serious for well annealed samples. Using an anionic polystyrene as an example it is shown how DSC data can be transformed to enthalpy curves which give Tg with an accuracy of ±1 K. As the rate of cooling through the glassy region is lowered, Tg is found to decrease by 2.2 K per decade decrease in cooling rate. Quantitative data are given for the specific heat increment at Tg.
Crosslink Density of Elastomers. A New Gas-Chromatographic Method
Authors: Parks C. R. , Brown R. J.
Published: February 2011

Information concerning the state or degree of vulcanization of rubber products is often desired. This is because most products are compounded and cured to a specific hardness or modulus depending on the end use. For example, stocks used in mechanical goods usually have a higher hardness than goods where fatigue resistance is important, such as tires. If the modulus changes, however, during the life of the article, this is usually reflected in a shortened service period. For general-purpose diene rubbers, this change depends on the type of polymer: polyisoprene rubbers such as natural rubber tend to soften slightly on aging or service, whereas rubbers derived from butadiene such as styrene-butadiene copolymer tend to harden considerably. Typical physical test methods are usually out of the question. The determination of crosslink density by equilibrium swelling measurements is the only practical method that is presently available. Moreover, any size or shape of sample may be used, which makes the method adaptable to routine measurements for new or aged products.
Dynamic Stress Relaxometer, a New Processability Instrument
Authors: Moghe S. R.
Published: February 2011

Increasing demands for economical, efficient, and high-production output rates require better control on processing methods in the factory. Good processing depends very much upon the uniformity of materials at each stage of the operation. The use of modern equipment and deliberate efforts to make the best use of the materials have narrowed the range of acceptable variations in material properties. Therefore, an instrument is needed which, in a very short period of time, will accurately detect deviations in uniformity. The dynamic stress relaxometer (DSR) described in this paper is an instrument which fulfills these needs. Another aspect of processability which also causes great concern is the need to change some ingredient in the recipe. Variations in the ingredient properties, which may be within specifications, sometimes result in large variations in the final product because of their complex interactions. Therefore, it is important that variations in the ingredients, as well as the final compounds, be detected quickly and satisfactorily so that necessary modifications in the recipe or procedure can be made without delay. The DSR has proven to be a useful tool allowing production personnel to make discriminating decisions effectively in our hose plant. The DSR has been used successfully over the last four years to determine whether the Banbury mixing and milling of the compounds were acceptable for processing through a cold-feed extruder.
Improved Cocure of EPDM-Polydiene Blends by Conversion of EPDM into Macromolecular Cure Retarder
Authors: Hopper R. J.
Published: February 2011

The 1,2-addition of certain N-chlorothioamides to the olefinic sites of EPDM produces modified polymers which exhibit improved covulcanization in blends with polydiene rubbers. A mechanism is postulated in which the modified EPDM retards the cure of the polydiene phase and at the same time is itself activated toward crosslinking. Model compound data are presented to support these views.
Sulfur-Cure-Compatible Blends of Halogenated Ethylene-Propylene Copolymers and Diene Rubbers
Authors: Morrissey R. T.
Published: February 2011

The chlorination of ethylene-propylene copolymers represents a possible economical method of producing a sulfur-curable EPM polymer. There are many feasible uses for these polymers. However, their incompatibility of cure with the more generally used polymers such as SBR, cis-polybutadiene, and natural rubber has limited their use, particularly in blends. It has been found that this can be overcome by halogenation of the EPM in the presence of certain catalysts. Earlier studies of Crespi and Bruzzone have shown that dehydrochlorina tion must follow chlorination for the polymer to show a high state of cure and good rebound characteristics. It has been discovered that the presence of certain metal halide catalysts and uv light tend to promote not only the halogenation of the EPM but also the dehydrohalogenation process. Further modification of the chlorinated and brominated EPM can be produced by halogenating in two steps. The resulting halogenated EPM shows good cure compatibility with highly unsaturated polymers, such as natural rubber. The halogenated copolymers show good adhesive properties to blends of diene polymers and have been used as adhesives between EPDM and fabric.
Reinforcement of Rubber through Short Individual Filaments
Authors: Foldi A. P.
Published: February 2011

Short, individual filaments of seven organic fibers, along with glass and wire, were mixed into several types of rubber stock, mainly on a rubber mill. Both the glass and the wire filaments broke into fragments. A high degree of orientation was achieved with most organic fibers. The presence of these filaments caused, in the direction of orientation, increased green strength (up to 37×) and exceptionally high stress at low elongations (e.g. 5.8 MPa at 100% with only 5 phr fiber). This was accompanied by moderate reduction in uncured yield elongation and by substantial decrease in cured elongation at break. Hardness, both uncured and cured, increased moderately, while heat buildup rose considerably in the presence of fibers. Penetration resistance, measured by a new laboratory test, increased two- to fourfold. The magnitude of these effects was directly proportional to the amount of well-dispersed and oriented fiber. No adhesive coating or special treatment was needed at the aspect ratios studied (> 180) to achieve tensile reinforcement with the organic fibers. The use of an adhesive dip on nylon actually reduced the level of reinforcement. The effects of staple length were insignificant on cured modulus, elongation at break, heat buildup, or penetration resistance; minor on green strength; moderate on Mooney viscosity. The most promising reinforcing filaments were the aramids, nylon, poly(vinyl alcohol), and polyester with aspect ratios between 180 and 3100.
Kinetics and Mechanism of Emulsion Polymerization
Authors: Ugelstad J. , Hansen F. K.
Published: February 2011

The course of emulsion polymerization may be considered as involving three intervals: Interval I, where particle formation takes place. The end of this interval is not dependent upon the degree of conversion, but on the total amount of polymer formed. With usual recipes, it ends at about 1-5% conversion. Interval II lasts from the end of Interval I until monomer disappears as a separate phase. In this interval, the particle number is usually found to be constant, the particle volume increases proportional to conversion, the monomer concentration in the particles is approximately constant, and therefore the termination is also constant within the particles. Interval III starts when the monomer disappears as a separate phase. The transition from Intervals II to III is determined by the degree of conversion and differs for different monomers. In cases where the solubility of monomer in the water phase is low, the monomer present in the aqueous phase may usually be neglected compared to the monomer present in the polymer particles. This will usually hold with most monomers at ordinary conditions, where the amount of polymer per unit of water is relatively high, and when the concentration of monomer in the particles is much higher than in the aqueous phase. In this case, the particle volume during Interval III will decrease slightly due to the contraction by polymerization. The concentration of monomer in the particles generally decreases during Interval III, which leads to an increased viscosity within the particles and thereby also to a decrease in the value of the termination constant. The present paper deals chiefly with the kinetics of emulsion polymerization in the three intervals and the application of kinetics to the study of the mechanism. Several review articles on emulsion polymerization have recently appeared in the literature. The reason for presenting a new review article is that a vast number of papers on emulsion polymerization have recently been published, which have broadened the theoretical and experimental knowledge of the process. Several experimental and theoretical studies on the mechanisms of particle formation have appeared. New theories for particle formation outside the micelles have appeared. Also the relative effectiveness of micelles and particles in capturing radicals from the aqueous phase has been discussed in several papers.
Molecular Weight Control of Elastomers Prepared by Emulsion Polymerization
Authors: Uraneck C. A.
Published: February 2011

Control of molecular weight is a prerequisite for the production of commercial polymers. This is especially true of elastomers for which satisfactory processing is either an implied or a formal specification. This review covers the theories and their applications for the control of molecular weights for the production of styrene-butadiene rubber (SBR), emulsion butadiene rubber (E-BR), nitrile-butadiene rubber (NBR), chloroprene rubber (CR), acrylic-butadiene rubber (ABR), and acrylic rubber. The complexity of the emulsion polymerization system is reflected in the large number of experimental and theoretical studies. Chronologically the theories and experiments based on the original mechanism proposed by Harkins and on the quantitative hypothesis of Smith and Ewart evolved into numerous publications. These works have been periodically reviewed, and several recent reviews give detailed descriptions of these studies. A review by Alexander and Napper, although subjective in choice of papers examined, presents a critical analysis of the major theories of emulsion polymerization systems. However, none of the reviews just cited cover in a significant way the control of the molecular weight of polymers prepared in the presence of reactive transfer agents. The theoretical and experimental studies of the control of molecular weight of elastomers prepared in emulsion systems came from a series of studies different from those concerned solely with emulsion theory and mechanism. In this review the broad features of the mechanism first proposed by Harkins and the hypothesis of Smith and Ewart are accepted. The derivation of modifier depletion and molecular weight equations and the calculation of the theoretical curves used in emulsion systems for the preparation of elastomers are presented next.
Polychloroprene Rubber
Authors: Johnson P. R.
Published: February 2011

Polychloroprene, or neoprene, has been commercially available since 1932. Through the years the use of these polymers has continued to increase to an annual worldwide consumption of almost 300 000 metric tons (660 million pounds, Table I). This represents about 5% of the world market for elastomer. Polychloroprene must, therefore, be regarded as one of the more important specialty elastomers. The polymer has enjoyed this growth because it has filled much of the need for an oxidation-resistant, oil-resistant, and heat-resistant elastomer. It is the purpose of this paper to summarize the technical knowledge of the preparation and use of polychloroprene. In preparing this paper, we have made extensive use of prior review publications. We have attempted to organize the topics in a logical sequence and have updated the information to 1975. Our objective has been to describe the major lines of technical effort. Our reference list is therefore not necessarily an exhaustive one.
Tire Friction on Wet Roads
Authors: Grosch K. A. , Schallamach A.
Published: February 2011

Evidence accumulates that tire forces on wet roads, particularly when the wheel is locked, are determined by the dry frictional properties of the rubber on the one hand and by hydrodynamic lubrication in the contact area on the other. The probable reason why they are so clearly separable is that water is a poor lubricant, tending to separate into globules and dry areas under relatively small pressures. Road surfaces and tire profiles are, therefore, designed to create easy drainage and high local contact pressures. The influence of road friction on vehicle control well below the critical conditions is becoming more clearly understood; but more Investigations are required here, in particular under dynamic conditions.
Evaluation of 2-R-4,6-Dithiol-s-Triazine for Neoprene Vulcanization
Authors: Nakamura Y. , Mori K. , Nakamura T.
Published: February 2011

The most useful accelerator for neoprene (CR) vulcanization with magnesia and zinc oxide has been 2-mercaptoimidazoline (NA-22). However, an alternative accelerator or crosslinking agent that is almost completely devoid of toxic effects is required since toxicity investigation has indicated the danger of carcinogenicity arising from NA-22. Although thiol-s-triazine compounds have already been patented as accelerators in CR vulcanization, these must be reexamined with regard to the vulcanizing effect, since nontoxic dithiol-s-triazine compounds (Table I) have recently been produced on a commercial scale. Curing systems for poly (vinyl chloride) (PVC) or epichlorohydrin rubber (CO) with 2-R-4,6-dithiol-s-triazine (1, R: NHC6H5 or N(C4H9)2) have been found to give crosslinked products with excellent aging resistance; and thus a similar crosslinking effect might be observed in CR vulcanized with 1. The present studies were undertaken to confirm the crosslinking effect of 1 in CR vulcanization and then to show the antioxidative effects which remain after solvent extraction of CR vulcanized with 1 containing antioxidant substituent R.
Contribution to the Identification and Quantitative Determination of Carbon Black in Vulcanizates by Thermogravimetric Analysis
Authors: Pautrat R. , Metivier B. , Marteau J.
Published: February 2011

It has been verified that, in a number of cases, thermogravimetric analysis permits quantitative determination and identification of carbon blacks in the free state or in vulcanized compounds. The proper operating conditions can give sufficiently good repeatability and adequate precision for most routine analyses. As is the case in other methods for determining the loading, numerous difficulties were encountered with elastomers which graphitize on heating. However, quantitative analysis of black in nitrile rubbers remains possible, but the identification of different types of black is very difficult. The authors propose to continue this study, particularly into the new families of blacks, primarily into the function of the diameter of their elementary particles and their degree of structure.
High-Molecular-Weight, High-Unsaturation Copolymers of Isobutylene and Conjugated Dienes. I. Synthesis
Authors: Thaler W. A. , Buckley D. J.
Published: February 2011

This investigation has provided insight into the critical role of solution properties on the course of cationic polymerization and has led to a technique for reconciling the opposing demands for synthesis of isoolefin-diene copolymers both free from gel and high in molecular weight. By this technique, the synthesis of a broad range of intermediate-unsaturation elastomers of quality has been realized.
The Distribution of Olefinic Linkages in Elastomers
Authors: Anderson J. N.
Published: February 2011

A method for determining the distribution of olefinic bonds in elastomers has been developed using dual-detector gpc analysis of the polymer after derivatization with 2,4-dinitrobenzenesulfenyl chloride. The method is particularly useful for determining the distribution of olefinic bonds in hydrocarbon copolymers having small levels of unsaturation.
Functionality Distribution of Hydroxyl-Terminated Polybutadienes by Gel Permeation Chromatography. I. Method and Calibration Procedure
Authors: Anderson J. N. , Baczek S. K. , Adams H. E. , Vescelius L. E.
Published: February 2011

In recent years, considerable attention has been focused on the structural characterization of functionally terminated hydrocarbon prepolymers used in propellant binders and other applications. The molecular weight averages and molecular weight distributions of hydroxyl-and carboxyl-terminated poly butadienes have been determined by gel permeation chromatography (GPC). The functionality distribution of these prepolymers has also been previously studied by column fractionation and a procedure combining GPC and column fractionation of the polymer by stepwise elution from silica gel. The carboxyl or hydroxyl equivalent weights of the fractions were determined by infrared or near-infrared spectroscopy. The fractionation procedure is quite laborious, and multiple peaks were observed in the elution profile, making it difficult to decide how the fractions were to be grouped for subsequent analysis. Previously, a technique for determining the distribution of unsaturation in copolymers containing a small number of double bonds as a function of GPC elution volume was developed. The technique utilized a GPC equipped with uv photometer and differential refractometer detectors to determine the ratio of the weight fraction of olefinic bonds to the weight fraction of polymer by GPC analysis of the polymer after derivatization of the double bonds with 2,4-dinitrobenzenesulfenyl chloride. It was suggested that the technique should be applicable for the determination of the distribution of other functional groups with the choice of suitable reagents for derivatization. The purpose of this investigation was to attempt to extend our previous study to simultaneously determine the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distribution of hydroxyl-terminated polybutadienes by a GPC technique.
Sequence Distribution of cis-1,4- and trans-1,4-Units in Polyisoprenes
Authors: Tanaka Y. , Sato H.
Published: February 2011

Recently 13C NMR spectroscopy has been successfully applied to investigate the sequence distribution of 1,2- and 1,4-units or cis-1,4- and trans-1,4-units in polybutadienes. As for polyisoprenes, however, few investigations have been made on the sequence distribution of isomeric structures using this technique, although Duch and Grant have assigned the 13C NMR signals of cis-1,4- and trans-l,4-homopolyisoprenes. In previous work we have found new signals attributed to cis-trans linkages in the 13C NMR spectra of cis-trans isomerized polyisoprenes and assigned the signals using diad sequences of cis-1,4- and trans-l,4-units. We have also studied the 13C NMR spectra of hydrogenated polyisoprenes containing various amounts of 1,4- and 3,4-units and the sequence distribution of 1,4- and 3,4-units were discussed for n-BuLi-catalyzed polyisoprenes. In this work we have investigated the sequence distribution of chicle polyisoprene and cis-trans isomerized 1,4-polyisoprenes containing various ratios of cis-1,4- and trans-1,4-units.
Synthesis of Radial Thermoplastic Elastomers
Authors: Hsieh H. L.
Published: February 2011

The combination of anionic polymerization techniques and a subsequent coupling reaction created a versatile process for producing block polymers of not only controlled block length and block sequence but also with a controlled number of branches. This process has been successfully used in commercial production since 1967. Radial styrene-diene block polymers have properties significantly different from linear polymers of the same molecular weight, showing lower melt viscosities as well as lower solution viscosities. This feature is significant in adhesive applications because it allows the use of polymers of higher molecular weights with a corresponding improvement in shear resistance.
Rubber-Thermoplastic Compositions. Part I. EPDM-Polypropylene Thermoplastic Vulcanizates
Authors: Coran A. Y. , Patel R.
Published: February 2011

Thermoplastic elastomers are rubbery materials which can be fabricated by techniques usually associated with thermoplastic resins. Classical elastomers rely upon the crosslinked network, developed during vulcanization, to provide the retractive forces of rubber type elasticity. Thermoplastic elastomers contain rubber domains and resinous thermoplastic domains. The thermoplasticity results from the melting characteristics of the hard thermoplastic phase, while the rubber properties arise from the rubbery domains. Thermoplastic elastomers are, therefore, almost by definition, heterogeneous in their phase morphology. Such materials can be blends or block polymers. In the case of block polymers, the rubbery phase is not crosslinked chemically. However, hard or resinous phase domains occur as the hard segments of the block polymer which separate from the composition by agglomeration during cooling from the molten state. These domains act both as well-bonded reinforcing filler particles and as crosslinks. This is, of course, because the hard blocks are connected to the soft or rubbery segments by primary chemical bonds. In the case of the blend compositions, the hard and soft domains are separate polymeric species. However, there must be some form of interaction between the domains if useful properties are to be realized. Recently, uncured or partially cured EPDM rubber has been blended with polyolefin resin to make thermoplastic elastomer-like compositions. However, these compositions suffer deficiencies in performance as well as in certain aspects of fabricability. Only poor to fair performance at temperatures above 70°C in air or in oil has been achieved with the uncured to partially cured compositions. More recently, it has been found in our laboratories that fully cured EPDM compositions which are fabricable as thermoplastics can be prepared. Such compositions, referred to here as thermoplastic vulcanizates, have superior strength, high-temperature mechanical properties, hot oil and solvent resistance, better compression set, etc. This report outlines critical parameters associated with these unique materials.
Viscoelastic Characterization of Long Branching and Gel in Butadiene-Acrylonitrile Copolymer Elastomers
Authors: Nakajima N. , Harrell E. R.
Published: February 2011

Difficulties in relating long-chain branching to processability may be attributable to two causes: one is the definition, pertinent to processability, of what long branches are and the other is a method of determining long branching which is free from interference by other material variables, such as molecular weight distribution, gel, and “short” branches. Measurements of the dilute solution properties are tedious, time-consuming, and require skill for precision. In addition, the requirement for filtering the solution practically obliterates the result, regardless of how precise the measurement may be, because elastomers, as a general rule, have or are suspected to have an insoluble gel fraction. Recent advances in viscoelastic studies of model polymers show that the branches must be 2–3 times longer than the “entanglement coupling” distance in order to exhibit enhancement of viscosity in the Newtonian flow. Whereas Newtonian flow provides a precise definition of the long branches, it is not accessible for most of the elastomers. In the observed time scale, the linear viscoelastic properties as well as the steady-state viscosities are affected not only by branches but also by gels and molecular weight distribution. When these material variables are changed one at a time in the properly designed model systems, their effects are separately observable. On the other hand with a sample of unknown background, the effect of long branching is usually inseparable from those of other variables.
Enthalpic Analysis of Vulcanization by Calorimetry. Thiuram Monosulfide/Sulfur Vulcanization of NR, BR and SBR
Authors: Brazier D. W. , Nickel G. H. , Szentgyorgyi Z.
Published: February 2011

As demonstrated in the foregoing discussion, the chemical complexity of accelerated sulfur vulcanization reactions prevents detailed interpretation of the enthalpy-temperature and enthalpy-time relationship. Nevertheless, the following conclusions can be reached regarding the origin of the enthalpy terms observed under scanning and isothermal temperature regimes. (1) The total enthalpy observed under scanning conditions is the sum of all reactions occurring. This includes (among others) crosslink formation, formation of non-crosslinking sulfidic products and maturation or subsequent polysulfide reactions. (2) In the isothermal experiment, the major contribution to the observed enthalpy arises from reactions resulting in the formation of sulfidic products (although some maturation must be expected and its extent will depend upon the temperature and time of cure). (3) When a precured sample is scanned, the observation of an enthalpic term depends upon the original cure system used. It is small or unobserved, for example, when the sulfur/TMTM ratio is small or with sulfur donor cure systems. On this basis, the DSC scan of a vulcanizate is potentially useful for characterizing that vulcanizate, and in particular, for the rapid quality control assessment of the state of sulfidic products in the vulcanizate. (4) Evidence has been discussed which suggests that the origin of the enthalpy term obtained with vulcanizates which have been precured can be related to the polysulfidic products in the sample. In laboratory experiments, not reported here, the magnitude of this term is reduced as the vulcanizate is heat aged or over-cured, which again supports the conclusion that we are observing the maturation of polysulfidic products. (5) Finally, comparison of rheometer and calorimeter data indicates that, as expected, we are observing all, reactions accompanying cure in the calorimeter; whereas, the rheometer responds only to crosslinking and chain scission, factors having a large effect on viscosity. DSC does not detect chain scission reactions at normal cure temperatures because the rate of scission is too small.
Wear of Metal by Rubber
Authors: Gent A. N. , Pulford C. T. R.
Published: February 2011

Rates of wear have been determined for steel and bronze scrapers sliding over rubber surfaces. The wear rates were found to depend strongly upon the particular elastomer used, varying by orders of magnitude even though the other ingredients in the compound and the physical properties of the rubber were largely unchanged. In the absence of oxygen the metal scrapers were found to wear away much faster in general; by a factor of 5 to 50 times, depending upon the elastomer. Butyl rubber was anomalous in this respect, however, causing three times greater wear in air than in nitrogen. These diverse observations are attributed to the direct attack upon metals of free radical species generated by mechanical rupture of elastomer molecules during abrasion. The rate of metal wear is closely correlated with the stability of polymeric radicals formed in this way. When the radical is highly reactive it is thought to take part primarily in internal reactions and thus cause little wear of the scraper. On the other hand, relatively stable polymer radicals appear to attack metals vigorously.
Synthesis and Properties of Polyoxazolidone Elastomers from Diepoxides and Diisocyanates
Authors: Kitayama M. , Isda Y. , Odaka F. , Anzai S. , Irako K.
Published: February 2011

Polyoxazolidone elastomers are obtained by reacting at 150°C. bisphenol-A-diglycidylether and polyoxytetramethylene-glycol having terminal isocyanate groups in the presence of new diepoxide-soluble catalysts. Among these catalysts, MgCl2/HMPA2 yields an excellent polyoxazolidone elastomer having low modulus and high tensile strength. The stress-strain data of the elastomers show stress-induced crystallisation. The reaction proceeds selectively and completely in one hour at 150°C. The pot life is long enough to ease the handling before curing. The properties of polyoxazolidone elastomer, especially heat resistant properties, are compared to those of polyetherurethane, also a castable elastomer. This comparison has shown (1) a somewhat higher melting point, (2) appreciably better retention of tensile properties after aging at 170°C (3) lower, high-temperature tensile properties and (4) tear energy, stress-relaxation and the creep behavior about the same or somewhat lower.
The Effect of Biaxial Orientation on the Thermal Conductivity of Vulcanized and Unvulcanized Rubber
Authors: Hands D.
Published: February 2011

Experiments have been carried out to investigate the effect of equibiaxial orientation on the thermal conductivity of a series of natural rubber compounds. The conductivity was measured normal to the direction of stretch. The main effect has been explained quantitatively and an equation obtained which relates the conductivity to the extension ratio. The effect of orientation is not only of intrinsic interest but is also technologically significant, since the conductivity can decrease by a factor of 4 for quite modest extension ratios. The size of the effect indicates that it should be taken into account in mixing and extrusion theories, since in such processes the orientation is comparable to or greater than that of our experiments, but so far all theories have ignored any possible change in the thermal transport properties. We have also observed that crosslinking causes a significant decrease in the thermal conductivity.
Halogen-Containing Aminimide Compounds as Tire Cord Adhesives
Authors: Throckmorton P. E. , Luckman E. R.
Published: February 2011

Aminimides derived from dibasic acids such as sebacic acid have proven to be very good adhesives when used in the first dip of a two-dip tire cord system. These aminimide materials have the advantage of being water soluble for easy application. They give effective adhesion of rubber to polyester tire cord. Although they offer process advantages, their performance is only approximately as good as present commercial art. It would be a further advantage if aminimides for tire cord bonding were improved over the best tire cord adhesive. Consequently, a means to effect bonding improvement was sought. Halogenated aminimides were prepared to effect tire cord bonding improvement to polyester cord. Various compounds derived by synthesis procedures for polyhalo aromatic or norbornene aminimide compounds were prepared. The preparations were designed so that the starting materials were readily available. The aminimide precursors avoided base-displaceable halogen because strong base is needed to make aminimides. Thus, aliphatic halogenated starting materials were not used because they contain base-displaceable halogen. Two of the model aminimides prepared were polyhalo aromatic aminimides and five were polychloronorbornene nuclear or side chain aminimides. In a two-dip system, aminimide compounds derived from hexachlorocyclopentadiene showed adhesion values of up to 164.6 newtons and 100% rubber coverage remaining after extracting the polyester cord from the rubber test specimen. This was equal to the best aminimide dibasic acid polyester tire cord adhesion and coverage. But although the bonding with the halogen-containing aminimides was good, the goal of improved adhesion was not met. Although the chlorinated compounds of this study were promising in bonding rubber to polyester tire cords, the first ones lacked water solubility. Water solubility is considered desirable from the process dip viewpoint. A water soluble version was made where each of two of the chlorine atoms were replaced by a methoxy group. However, tire-cord-to-rubber bonding tests of the water-soluble version of the polyhaloaminimide type was not found to be an improvement over the several oil-soluble versions prepared and tested.
1H NMR Study of Polyisoprenes
Authors: Sato H. , Tanaka Y.
Published: February 2011

1H NMR spectra of polyisoprene were assigned using polymers of isoprene-1,1,4,4-d4, isoprene-1,1,5,5,5-d5, and isoprene-4,4-d2 polymerized with various catalysts. The methylene-proton signal at 2.1 ppm in cis-1,4- and trans-1,4-polyisoprenes was divided into H4- and H1-proton signals; H4 resonated at 2.21 ppm in both cis-1,4 and trans-1,4 units, whereas H1 resonated at 2.05, 2.21, and 2.15 ppm. Splitting due to the dyad sequences of 1,4 and 3,4 units was apparent. The methine-proton (H3) in a 3,4 unit showed a broad peak centered around 1.5 ppm in C6D6. The overlapping of this signal with the methyl-proton signals at 1.73 and 1.63 ppm resulted in some uncertainty in the determination of the microstructure of polyisoprene which contained a considerable amount of 3,4 unit.
An Elastomeric Energy Storage Device for Automotive Engine Restart
Authors: Killgoar P. C. , Pett R. A. , Tabar R. J. , Foote L. R.
Published: February 2011

An elastomeric spring starter using rubber in shear has been designed. Design criteria have been established and used to develop potential compounds for use in the device. Natural rubber proved to be the elastomer of choice primarily because of its excellent fatigue resistance. To reconcile bonding requirements and requirements for low hysteresis, the individual rings were fabricated from two elastomer compounds. Limitations on the thermal stability of the adhesive system were identified which put constraints on the operating conditions for the starter. A prototype starter has been assembled and installed in a vehicle. This prototype starter provides quiet, rapid starting of the test car. Questions of cost effectiveness, reliability, durability or manufacturing feasibility of this device have not been addressed. The starter was built for experimental purposes only and development of such a concept for mass production has not been explored.
Characterization of Aniline-Acetone Condensation Products by Liquid Chromatography and Mass Spectroscopy
Authors: Lattimer Robert P. , Hooser E. Ray , Zakriski Paul M.
Published: February 2011

Liquid chromatography has proven to be an extremely valuable tool for many separations involving polymers and polymer chemicals, especially when used in conjunction with mass spectroscopy for chemical identification. The complex products of the condensation reaction of aniline with acetone have been characterized by liquid chromatography and mass spectroscopy. The LC separation procedure utilized a C18 Micro Bondapak (reverse phase) column with a water/tetrahydrofuran gradient system. Eluted peaks were trapped individually for field desorption mass spectral identification. Syringe deposition was used to transfer the isolated components to the field emitter. The major components found in the reaction mixture were oligomers of 2,2,4-trimethyl-l,2-dihydroquinoline (TMDQ), although several other monomeric and oligomeric side-products were observed and characterized. Forty-two components were identified in the product resin. These can be classified into eight major series of oligomers; all series have oligomers separated by the TMDQ monomer unit (173 amu).
S-N Compounds as Delayed Action Chemicals in Vulcanization
Authors: Morita E.
Published: February 2011

Since the discovery by Goodyear in 1839 that the physical properties of rubber may be improved with sulfur, it has been the most commonly used crosslinking agent. The rubber industry is concerned with the production of homogeneous products with appropriate physical properties, by compounding rubber with ingredients, including crosslinking agents, followed by processing, molding, and introduction of chemical bonds. Economically, it is advantageous to apply high temperature which reduces processing and curing time. However, application of high temperatures frequently causes premature cure. Compounding adjustments are often required in the plants to prevent scorch, especially by the use of compounds with S—N bonds as accelerators, vulcanizing agents, and also as prevulcanization inhibitors or retarders which delay the crosslinking reaction of sulfur and rubber. There are several reviews relating to accelerators, retarders, and vulcanization, which discuss S—N compounds as delayed action curing agents. This review covers the development of S—N compounds as delayed action chemicals for vulcanizing rubber, the various structural types, properties, applications, and the mechanism of their function during vulcanization.
Polyurethane Reaction Injection Molding: Process, Materials, and Properties
Authors: Lee L. J.
Published: February 2011

Reaction injection molding includes aspects of polymerization reactor analysis as well as melt injection molding. Processing can be broken down into several unit operations: metering and machine performance, impingement mixing, mold filling, curing and mold design. Commercial RIM machines have been used successfully for non-filler systems. The results are generally satisfactory. Reactants are usually allowed to circulate through the mixhead, or even through impingement nozzles, such that uniform temperature control and appropriate agitation of reactants can be obtained. Most heads can switch from the recycle to injection mode under high pressure operation, to minimize the lead/lag problem. The mixing chamber is self-cleaned at the end of each shot by a hydraulically driven piston which pushes out all the residue mixture from the mixhead after mold filling. Flow rate/flow area can be adjusted externally by the nozzle size adjuster. Flow rate also can be controlled by the pressure setting. Two or four streams impingement mixing is the common mixing technology used in the present RIM machines. Static or impingement type after-mixers have been used extensively to improve the mixing. Mold filling seems not to be a problem for conventional RIM operation if mold design is appropriate. The typical pressure inside the mold cavity during filling is less than 350 kPa. With the help of slight foaming during curing, RIM polyurethanes usually have excellent, depression-free surfaces. A number of qualitative descriptions of automotive type RIM have appeared, and some basic studies of the process are being carried out. However, as yet there does not appear to be a complete understanding of how the process influences the structure and properties of the polymer formed. The majority of RIM parts have been made in the 140–300 MPa flexural modulus range for fascia applications, where appearance, weight-reduction, and impact resistance are the most important criteria. A representative formulation used to produce automotive fascia by reaction injection molding consists of a polyether/polyester polyol with molecular weight in the range of 1000–3000, a short chain extender like ethylene glycol, 1,4-butane diol or a diamine and a modified derivative of 1,4-diphenylmethane diisocyanate, MDI. The need for further weight reduction to meet government mileage requirements, and for improved corrosion and impact resistance, makes the extension of RIM materials to other external automotive body components increasingly attractive. For these applications, there will be several new requirements: flexural moduli in the 700–4000 MPa range to provide dimensional stability, but still with the desirable impact strength; a low thermal coefficient of linear expansion to allow satisfactory mating with sheet metal surfaces. An increased thermal stability would also be required for parts that would be painted and baked on the car, or for applications such as hoods with higher in-use thermal exposure.
The Rolling Loss of Pneumatic Tires
Authors: Schuring D. J.
Published: February 2011

Tire energy loss has long been neglected as an area of scientific concern, in favor of other performance characteristics such as traction and wear. With the advent of federally mandated fuel economy goals, however, priorities have been shifted, and tire energy loss has now become a prime concern. Tires are responsible for a rather large fraction of the total energy expended by a passenger car or truck. For a typical passenger car driven steadily within the legal speed limit, the energy dissipated by the tires ranges between 3 and 7% of the total energy consumed by the vehicle. For a typical truck (18 wheels), these percentages can be about twice as high (see Section 7). Any reduction in tire rolling loss would therefore yield tangible fuel savings. In the past 5 years or so, the tire industry has reduced rolling loss by more than 25% (Hill and Moore). This is partly due to the rapidly increasing use of radial tires, lower loads, higher inflation pressures and less hysteretic materials. However, it is also partly due to the substantial efforts made by tire researchers to understand the general principles governing the loss of energy in tires. These principles are not intuitively apparent. Energy loss of tires is a very complex phenomenon, and there is little hope that it will ever be fully understood to the extent that energy efficient tires can be designed on the drawing board. But substantial progress has been made, as attested by a recent SAE Conference on Tire Rolling Losses in Boston, the first of its kind, organized to review the state-of-the-art and to stimulate further improvements. These are greatly needed. To meet the fuel economy target of 1980, a reduction of 15% of the present average rolling loss of radial tires is required (Tarpinian, Nybakken, and Mishory), and further improvements are necessary to meet the goals of 1985. Vigorous, and costly, efforts are being made—by industry and academic institutions alike—to come to grips with the rolling loss phenomenon. These efforts include mapping the interacting relations between rolling loss and the many tire parameters, building analytical models that would provide insight into these relations, and developing testing methods that would permit testing them with accuracy. This review is an attempt to organize the present knowledge into these categories and to suggest new avenues for further progress.
Elastomeric Block Polymers
Authors: Dreypuss P. , Fetters L. J. , Hansen D. R.
Published: February 2011

Development of new thermoplastic elastomers is a challenge for future years. It is a difficult challenge because existing thermoplastic elastomers offer a wide variety of prices and properties with good performance price ratios. Most advancements will probably be accomplished by blending or compounding or by slight molecular modifications of existing products. However, a new thermoplastic elastomer can not be ruled out if new technology is developed. With new applications yet to be discovered, and as existing markets mature, the growth of new and existing thermoplastic elastomers should be exciting in the years ahead.