bluuebunny/crossref_metadata_2025 huggingface dataset:
Sulfur Vulcanization of Vinyl-Substituted Polysiloxanes
Authors: Polmanteer K. E. , Koch R. J.
Published: February 2011

The vinyl content of the polysiloxane polymer affects the rate of vulcanization in such a way that the vulcanization time varies inversely with the vinyl concentration raised to a power less than 1. Furthermore, this power appears to be dependent upon the vinyl concentration, so that a stationary value cannot be quoted. Sulfur alone crosslinks only polysiloxane polymers of high vinyl content. A 4 mole per cent vinyl-containing polymer exhibited no vulcanization after 3 hours at 160° C with sulfur alone. Vulcanization times in the same range as those found with sulfur-vulcanizing organic polymers were obtained in this polysiloxane system by the proper choice of accelerators. Starting with the most active, compounds for accelerating or activating this vinyl-containing polysiloxane-sulfur system were: strong organic bases (TEPA), DPG, thiuram disulfides (TMTD), magnesium oxide, bivalent metal dithiocarbamates, thiazoles (MBT), weak organic bases (aniline), calcium oxide. Zinc oxide and litharge are inhibitors in this system to varying extents, depending on the accelerator present. Organic acids such as stearic acid inhibit vulcanization in this system. For recipes void of elemental sulfur, the following conclusions may be made: Accelerators that vulcanize vinyl-containing polysiloxanes without the aid of elemental sulfur follow very closely the list of compounds capable of vulcanizing organic polymers. (D.P.)c data indicated that two vinyl groups are involved in each cross link.
Disulfide Interchange in Polysulfide Polymers
Authors: Bertozzi E. R. , Davis F. O. , Fettes E. M.
Published: February 2011

A study has been made on the effect of thiols and disulfides on lowering the molecular weight of polysulfide polymers. It was shown that in the presence of aqueous sodium disulfide there is an interchange of chain segments. This effect is observable if a simple organic disulfide is present in the system, resulting in a lower molecular weight. Copolymers can be prepared by heating together in the presence of sodium disulfide, aqueous dispersions of two different polysulfide polymers. When thiols are present in the system, interchange of disulfide groups occurs in the absence of sodium disulfide. The results show that disulfide/disulfide redistribution and thiol/disulfide interchange take place in polysulfide polymers. The occurrence of these same reactions has recently been recognized by workers in the biochemical field. A literature survey of thiol/disulfide reactions showed that results formerly attributed to oxidation reduction reactions could be also explained by an interchange mechanism.
An Investigation of the Molecular Weight Distribution of Polymers with the Aid of the Ultracentrifuge
Authors: Bresler S. E. , Frenkel S. Y.
Published: February 2011

In the present paper a method for studying the molecular weight distribution of linear polymers, involving the following stages, is developed: 1. Fractionation of the polymer into a series of sufficiently narrow fractions and investigation of these fractions with the aid of the ultracentrifuge and diffusion. 2. Plotting the distribution functions of sedimentation constants for each fraction and subsequent summation of curves in order to build up the distribution function of the sedimentation constants for the whole polymer. 3. Discovery of a general functional relation between the sedimentation constants and molecular weights for a given series of polymer homologs and construction of the distribution function of molecular weights of the polymer. The basis of the method developed by us (method of equivalent Gaussian distributions) was confirmed by direct experiment. Application of this method of investigation to a number of industrial polymers will be described in the next paper.
The Nature of Self-Adhesion (Tack) of Polymers. I
Authors: Voyutskiĭ S. S. , Margolina Yu L.
Published: February 2011

At the present time, ideas concerning cohesion, adhesion, and self-adhesion (self-sticking) are widely used for explaining the phenomena observed in gluing with polymeric substances. But the investigators, in developing the theory of gluing, pay most attention to cohesion and adhesion. Self-sticking (self-adhesion) has thus far remained unstudied and has no satisfactory explanation. Researches devoted to self-sticking are very few. Mention should be made here of the work of Zhukov and Talmud, who separated self-sticking from the total complex of adhesive properties, proposed the term autohesion, and were the first to study this property experimentally. Furthermore, we must mention the researches of Priklonskaya and of Maslovskii˘ and Popova, who investigated the self-sticking of industrial materials (rubber mixtures). Finally, the question of self-sticking of polymeric substances was touched upon in a very small number of researches of foreign authors. It should be noted however that these researches appeared considerably later than those of the Soviet investigators and are very speculative in nature.
Behavior of Highly-Filled Rubber Vulcanizates
Authors: Bryant K. C. , Bisset D. C.
Published: February 2011

Examination of the stress-strain curves of vuloanizates containing up to 60 per cent by volume of mineral filler of particle size greater than 1 µ has led to the discovery of a plateau at which the elongation increases several hundred-fold at constant stress. This has been demonstrated for a number of fillers with several rubbers, natural and synthetic. The effect of filler content, particle size, and degree of cure on the stress at which the plateau occurs, and its length, have been investigated. An explanation is suggested and the significance of the observations for the experimental verification of equations relating modulus to filler content is pointed out. The volume changes accompanying the elongation of these vulcanizates have also been investigated at varying filler contents, particle sizes, and degrees of cure, and shown to correlate with the stress-strain curves. The possible bearing of these results on the nature of the rubber-filler bonds, and hence on the reinforcing action of fillers, is briefly discussed.
Chemical Reactions of Antioxidants Used in Vulcanized Rubber
Authors: Schneider P.
Published: February 2011

The work of Farmer and other authors has shown that the oxidation of unsaturated polymers proceeds via primary formed hydroperoxides. The addition of antioxidants, including chiefly compounds of the class of the phenols and secondary aromatic amines, makes it possible to delay to a great extent the chemical changes taking place in unsaturated compounds. The mechanism of the action of phenols in the oxidation has been explained by Bolland. It is difficult to separate from the polymer the reaction products which are formed from the antioxidant by the dehydrogenating action of the polymeric hydroperoxide radical. In view of the fact, however, that the kinetics of oxidation in the presence of added peroxide corresponds to the autoxidation of the unsaturated compound, the reaction between phenols or secondary aromatic amines and organic or inorganic oxidation agents has been studied in detail by several workers. Depending on type, position, and number of the substituents, different reaction products are formed from phenols. Diphenylamine reacts with manganese dioxide to form a mixture of N,N′-diphenylbenzidine and the corresponding quinonedianil. N,N,N′-tri-2-naphthyl-1,2-naphthylenediamine is formed from di-2-naphthylamine with potassium permanganate, whereas under similar conditions phenyl-2-naphthylamine forms N,N′-diphenyl-N-2-naphthyl-1,2-naphthylenediamine. Starting from the deduction that the chemical reaction products of the antioxidants accumulate on the surface of the vulcanized rubber due to decreasing solubility, pure gum stocks of cured natural rubber containing diphenylamine, N-phenyl-1- and 2-naphthylamine have been exposed to atmospheric conditions for 8 months. The dark colored reaction products could be removed mechanically from the surface of the cured goods after wetting with methanol. After evaporation, the residue was taken up in ethylidene chloride and the resulting solution evaporated to dryness. Amorphous mixtures of brown colored compounds were isolated from the vulcanizate containing diphenylamine and N-phenyl-2-naphthylamine, the reaction products of the N-phenyl-2-napthylamine being obtained as a dark colored tar. In addition to other compounds, the presence of the N,N′-diphenyl-N-2-naphthyl-1,2-naphthylenediamine was proved by paper partition chromatography of the resulting azodyestuff obtained from the mixture of the reaction products from phenyl-2-naphthylamine by coupling with diazotized 1-aminonaphthalene trisulfonic acid. The presence of this compound had also been shown by the ultraviolet spectra. In the same manner, small quantities of the N,N′-diphenylbenzidine could be recognized from the corresponding azodyestuff formed from the reaction product of diphenylamine. Due to extensive oxidation, the presence of reaction products could not be proved in any appreciable quantity from the reaction mixture of the phenyl-1-naphthylamine.
The Quantitative Determination of Rubber Chemicals. II
Authors: Scheele Walter , Gensch Christa
Published: February 2011

A quantitative method for the determination of thiuram compounds has been reported. It has been found that tetramethylthiuram disulfide is converted quantitatively to thiuram monosulfide if it is treated with an excess of potassium cyanide. The thiocyanate, which is also formed, can be determined by argentometric conductometric titration. The execution of the analysis requires a good deal of experience. The conductometric titration with acid of the dithiocarbamate, which is formed by the reaction of TMTD with dodecyl mercaptan is much simpler. This method permits a double determination of the thiuram disulfide in which the excess dodecyl mercaptan is titrated conductometrically with alcoholic iodine solution. Solutions of dipentamethylene thiuram tetrasulfide behave like mixtures of tetramethylthiuram disulfide and sulfur. Also thiuram monosulfide and thiuram disulfides are cleaved by alkali and for the monosulfide a stoichiometric course of the reaction has been established. During our studies on the vulcanization of rubber with thiuram disulfides we have found conductometric analysis procedures to be very useful for the investigation of vulcanization extracts. We will report on this in the near future.
Aspects of the Physical Basis of Reinforcement
Authors: Mullins L.
Published: February 2011

Recent developments in rational ideas of what “reinforcement” means physically are described. It is shown that probably the most important characteristic of rubber vulcanizates with good tear and abrasion resistance is their ability to form strong hard tear resistant structures at the tips of growing tears. The significance of this conclusion in relation to the assessment of the quality of rubber vulcanizates is discussed.
Determination of the Molecular Size and the Molecular Form of Natural Rubber by the Measurement of Light Scattering. I. Development of the Method and Orienting Measurements
Authors: Schulz G. V. , Altgelt K. , Cantow H. J.
Published: February 2011

An experimental method of preparing and purifying natural rubber solutions in the absence of oxygen with an ultracentrifuge is presented. The solutions are suitable for optical measurements. Light scattering is measured as a function of concentration, angle, wave length and temperature. By determining molecular weight, diameter of the coiled molecule, and thermodynamic quantities (Δμ1, Δh1, Δs1) in this way it is possible to get information on branching of the rubber molecules. The method was used for cyclohexene solutions of a carefully tapped crepe rubber. The molecular weight was 1.3⋅106 and the end to end distance of the coil 1750 A˚. The heat of dilution was positive (endothermic) the B-value being nearly as high as that found in benzene solution by osmotic measurements. Comparing these results with measurements on unbranched polymethacrylate and polyisobutylene one can conclude that these rubber molecules are not or only slightly branched.
An Extensometer Microscope Stage for Photoelastic Studies in Rubber
Authors: Andrews E. H.
Published: February 2011

The instrument described is designed for attachment to the stage of a polarizing microscope in place of the conventional mechanical stage. Its purpose is to permit the use of a special compensator technique to determine stress distribution at the tip of a tear in an extended sheet of rubber. Examples are given of the stress distribution, both in magnitude and direction, at the tip of a tear in prevulcanized latex sheet, and the relative behaviors of the two principal stresses are briefly discussed.
Branched Chain Natural Rubber Derivatives Obtained by Reaction with Azodicarboxylates
Authors: Ivanov S. S. , Yuzefovich N. A. , Sidorovich A. V. , Fedorova E. F.
Published: February 2011

1. Ethyl azodicarboxylate (EAD) and ethylene dis-ethyl azodicarboxylate (DEAD) react quantitatively with natural rubber to form branched and cross-linked derivatives, respectively. 2. The mechanical properties of vulcanizates from natural rubber containing side branches (obtained with the aid of EAD) differ greatly from the properties of unbranched vulcanizates. 3. Analysis of the load-extension diagrams shows that the introduction of EAD side chains into natural rubber results in the formation of vulcanizates with high extensions at low loads. Vulcanizates without EAD have steeper load-extension diagrams and lower extensions at break. 4. As the temperature rises from 20 to 100°, the elastic modulus and mechanical losses (or the logarithmic damping decrement) of vulcanizates cross-linked with DEAD decreases greatly (about 4–7 times). Addition of 10 per cent (g-equiv.) of EAD side chains approximately doubles the mechanical losses in comparison with vulcanizates without EAD.
The Vulcanization of Elastomers. XI. The Vulcanization of Natural Rubber with Sulfur in the Presence of Mercaptobenzothiazole. I
Authors: Lorenz Otto , Echte Elisabeth
Published: February 2011

1. The decrease of free sulfur occurs according to the first order law during the vulcanization of natural rubber accelerated by mercaptobenzothiazole in the presence of zinc oxide. The activating energy for this reaction amounts to 30.5 kcal./mole. 2. If zinc benzothiazolylmercaptide is used as an accelerator, one obtains the same rate constants for the sulfur decrease as in the presence of mercaptobenzothiazole. These seem to be equivalent as regards their effectiveness of acceleration. 3. A kinetic analysis of the reciprocal swelling, which represents a measure of network formation, indicates that the reaction is first order. Sulfur decrease and reciprocal swelling prove to be equal processes as regards rate. This is true where vulcanization is accelerated with mercaptobenzothiazole or with the zinc salt. 4. During vulcanization there occurs a decrease of accelerator concentration. This is dependent upon the temperature and is tied in with the combination sulfur with rubber. 5. If the quantity of the accelerator added is changed, the rate constants for sulfur decrease and for reciprocal swelling do not change, provided that a minimum quantity of accelerator is present. 6. In vulcanization accelerated with zinc benzothiazolylmercaptide, zinc oxide being absent, sulfur decrease again occurs according to the first order law but considerably faster, without thereby changing the activation energy. These investigations are being continued and the results will be discussed in detail in relation to other published contributions in this field.
Degree of Cure in Filler-Reinforced Vulcanizates by the Swelling Method
Authors: Kraus Gerard
Published: February 2011

The Flory-Rehner theory of swelling allows an estimate of the number of crosslinks in gum vulcanizates. In reinforced rubbers the apparent degree of crosslinking is raised by some fillers, particularly carbon blacks. It has been shown experimentally that, for vulcanizates of a given polymer at a fixed filler loading and type, most physical properties are, in the first approximation, simple functions of the apparent number of network chains per unit volume, regardless of the possible origin of the linkages. Aside from controlling the number of apparent linkages, sulfur and accelerator levels as well as cure time have relatively minor, secondary effects on vulcanizate properties. Comparison of swelling data of gum and black stocks shows that the apparent contribution of the carbon black to crosslinking increases with the level of cure. Softeners and extender oils cause a reduction in the number of linkages, presumably by reducing the efficiency of sulfur utilization. It has been demonstrated that the swelling of vulcanizates in solvents gives an accurate measure of the degree of vulcanization even in filler-reinforced stocks. The results are apparently not obscured by adsorptive linkages between filler and polymer. When chemically different polymers are compared, the swelling volumes may be used to calculate the density of effective network chains; thus a nearly absolute measure of the degree of vulcanization is obtained. The swelling method is not difficult to apply, requires no special equipment, and imposes no limitation on the size or shape of the test specimen. For instance, it has been used with excellent success in this laboratory to check the state of cure in test-fleet tires. A small sample is cut from the side of the first rib of a tire and tested in the usual manner. The data presented offer some insight into the question of reinforcement. The evidence points to the fact that “contributions” of fillers to crosslinking derived from subtraction of the number of network chains or crosslinks in the filled and gum vulcanizates do not quantitatively represent the number of filler-to-rubber linkages. This filler “contribution” depends on the degree of cure, the vulcanization system, and the filler particle or aggregate shape. It depends only slightly on the particle size or surface area of the filler. The most plausible explanation of the observed behavior lies in a superposition of the effects of the filler on the course of vulcanization, filler-to-rubber linkages, and particle shape or aggregate structure.
A Study of Vulcanization Accelerators. I. Compounds Which React Analogously to Rubber
Authors: Shimozato J. , Ura K.
Published: February 2011

1. To elucidate the chemical behavior of rubber toward sulfur, a series of experiments was carried out using model compounds : tetralin, toluene, xylene, aniline, phenol, chlorobenzene, dichlorobenzene and naphthalene. Similar reactivities between rubber and the model compounds were observed. 2. The effects of the accelerators in the reactions of the model compounds with sulfur were different according to whether or not zinc oxide was present in the reaction system. 3. A detailed examination of the quantities of zinc sulfide formed in the reaction of tetralin with sulfur in the presence of zinc oxide showed that several vulcanization accelerators have similar activating effects in rubber vulcanization. 4. With tetralin as reactant, the quantity of zinc sulfide decreased suddenly at the reaction temperature 150° C, which was ascribed to the rapid decomposition of tetralin peroxide at this temperature. 5. The accelerating action of CPB, contrary to that of the other accelerators, was promoted by tetralin peroxide. 6. Tetralin peroxide had only a small inhibiting influence upon reactions with the amine accelerators, which is ascribed to the antioxidative nature of the amine derivatives; the inhibiting influence becomes larger in reactions with thiol derivatives or without any added accelerators. 7. Substituent effect on the hydrogen abstraction of the model compounds was primarily determined by the negativity of the relevant carbon atom. The order of the reactivity was found to be in accord with that toward the general “cationoid reagents”. 8. Analytical methods during and after the reactions were simplified for industry use.
The Quantitative Determination of Rubber Chemicals
Authors: Lorenz Otto , Echte Elisabeth
Published: February 2011

1. Both the precipitation of mercaptobenzothiazole as a silver salt and its oxidation with an iodine solution to a disulfide may be utilized for quantitative determination. 2. Zinc benzothiazolyl mercaptide can be determined iodometrically, either directly or indirectly, after being cleaved by acids. 3. Benzothiazolyl disulfide is determined as mercaptobenzothiazole after reduction with acidic stannous chloride solution. 4. A procedure for the determination of a mixture of mercaptobenzothiazole, zinc benzothiazolyl mercaptide, and dibenzothiazolyl disulfide is described. 5. Experimental conditions are indicated, under which the quantitative determination of free sulfur is possible in the presence of mercaptobenzothiazole, its zinc salt, the disulfide, and the zinc salts of fat acids. In all cases the uncombined sulfur is determined after its conversin to thiocyanate by an argentometric conductivity titration of the thiocyanate.
The Stress-Strain Behavior of Natural Rubber
Authors: Müller F. Horst
Published: February 2011

This treatment of the stress-strain behavior of natural rubber is based upon experimental and theoretical data on the cold stretching of high polymers gathered from work being in progress for some time at Marburg. These investigations indicate that deformation processes of matter should not be treated exclusively as purely mechanical phenomena though this is still being done. Especially in the case of natural rubber there exist very thorough analyses of these heat effects caused by deformation. Their theoretical evaluation furnished the basis for the thermodynamic-statistical theory of rubber elasticity. This created the picture of a molecular mechanism which with new additions permitted the description of a host of details including those for stress-strain behavior. However the relationship between the shape of the stress-strain diagrams and any particular deformation condition can only be explained if the actions of the deformational heat effects upon the course of the deformation are considered. In the following an attempt will be made to discuss the actions of the heat effects, in other words to examine the deformation processes as mechanical-thermal ones. Although there are, at present, no experimental results on hand, the expected consequences for the deformational behavior of rubber will be surveyed. Experimental work is in progress.
Behavior of Rubber in Compression under Dynamic Conditions
Authors: McCallion H. , Davies D. M.
Published: February 2011

At first sight, it would appear that previous investigators, have dealt fully with the main variables affecting the behavior of rubber. For instance, many publications have dealt with the effects of such variables as frequency, amplitude of deformation, and temperature. A closer examination of these publications, however, brings out the fact that no attempt has been made to keep the amplitude of deformation constant in any of the previous investigations into the effect of temperature at low temperatures. It is important that the amplitude of deformation should be kept constant, since both the stiffness and hysteresis energy absorbed per cycle depend on its value. It does not appear that work has been published on the frequency dependence of the hysteresis energy absorbed per cycle at low temperatures, nor even on how the hysteresis energy absorbed per cycle varies with temperature. For these reasons alone, the main investigation was initiated, and the results are presented to show the effects of frequency, temperature, and amplitude of deformation on the dynamic properties of rubber.
Cis-Trans Isomerization in Polybutadiene
Authors: Golub M. A.
Published: February 2011

About twenty years ago, in an effort to transform natural rubber into gutta-percha, Meyer and Ferri irradiated a solution of Hevea in cyclohexane with ultraviolet light, but were unable to detect any cis-trans isomerization in polyisoprene. Later, Ferri showed that treatment of both Hevea and Gutta with certain chemicals, such as chlorostannic acid and titanium tetrachloride, gave rise to closely resembling products which were considered at the time to have structures intermediate between the two geometric forms of naturally-occurring polyisoprene. These resulting polymers were, however, crosslinked in the course of chemical treatment and probably also cyclized, so that in the light of present knowledge about the cyclizing tendencies of the materials employed, this change cannot be regarded as a genuine interconversion of cis and trans double bonds. No true instance of cis-trans isomerization unaccompanied by other structural changes has been reported heretofore for a high polymer, except for the polyenes which are conjugated structures of relatively very low molecular weight. This communication reports the successful transformation of the cis-1,4 units in polybutadiene into corresponding trans units by means of ultraviolet irradiation in the presence of a suitable sensitizer, which may be any one of a wide variety of organic bromine or sulfur compounds. Surprisingly, this isomerization could not be induced in natural rubber.
The Mechanism of the Deactivating Effect
Authors: Bras Jeanle , Danjard Jean Claude
Published: February 2011

It was shown by one of us that certain substances, called deactivates, can protect vulcanized rubber against aging by a process which is different from that of antioxidants. The proposed mechanism involved a deactivation of the primary peroxides by transforming them into oxides of rubber without causing any chain scission. This hypothesis, however, did not appear to be completely satisfactory. In fact, deactivators do not protect raw rubber against oxidation, but actually accelerate its degradation in solution, especially in the presence of a peroxide which enhances this deterioration. Moreover, if was shown that the deactivators possess a chemical structure which is very similar to that of certain vulcanization accelerators, and also that they have an effect on the vulcanization. This had led to the suggestion that their effect could be attributed to the initial structure of the vulcanized rubber. We have considered the possibility of obtaining some useful information on this subject by means of stress relaxation measurements which involve the decrease in tensile strength with time of a stretched test piece. The measurements were carried out either by maintaining the test piece at constant elongation (continuous relaxation), or by stretching the relaxed sample to a constant elongation from time to time (discontinuous relaxation). It has been established that the continuous relaxation method accounts solely for the chain scissions which are produced in the vulcanized rubber network, whereas the intermolecular linkages formed during the tests contribute to the discontinuous relaxation picture. The results of some preliminary experiments we have carried out are given in Figure 1. Two rubber compounds, accelerated with diphenylguanidine and mercaptobenzothiazole, respectively, and known to have quite different aging properties, were employed. Vulcanizates containing either an antioxidant A (phenyl-2-naphthylamine) or a deactivator D (zinc mercaptobenzimidazolate) were compared with the control vulcanizates T.
Quantitative Determination of Antioxidants, after a Chromatographic Separation on Completely Acetylated Filter Paper. II. Determination of Some p-Phenylenediamine Derivatives
Authors: Zijp J. W. H.
Published: February 2011

In this paper methods are given for the quantitative determination of three antioxidants, viz., N,N′-diphenyl-p-phenylenediamine, N,N′-di-2-naphthyl-p-phenylenediamine and N-phenyl-N′-cyclohexyl-p-phenylenediamine. According to these methods the antioxidants are extracted from the rubber compound, separated by partition chromatography on completely acetylated filter paper and oxidized to the corresponding p-quinonediimines, after which these oxidation products are determined colorimetrically.
Some Factors Which Determine the Flight of Aerological Sounding Balloons
Authors: Angioletti A. , Felice J.
Published: February 2011

Examination of Equations (8), which connect the external pressure and thus the altitude to the dilation of the balloon, shows that the most important factor with regard to the “limited” bursting height is the elongation at break of the envelope at temperatures of the order of −40° C and −60° C. The elasticity modulus of the material and the thickness of the envelope are therefore of little importance with respect to the bursting height. It must be remembered, however, that the thickness has an indirect influence because it increases the weight of the balloon proportionally, and possible irregularities in the envelope will be all the more harmful as the thickness decreases. As for the lift force, this remains practically constant during the ascent of the balloon. On the basis of experimental determinations, the elevated concentrations of ozone will not have a particularly harmful influence on the rubber envelope, even if it is of natural rubber, due to temperatures at high altitudes of less than −40° C, the high state of tension of the rubber, and the brief duration of the flight.
Dynamic Properties of Elastomers
Authors: Gehman S. D.
Published: February 2011

The large volume uses of rubber involve its cushioning, quieting, vibration-energy absorbing and isolating characteristics. Applications such as tires, belts, and engine mounts employ rubber under conditions of rapidly repeated deformations which are relatively small compared to ultimate breaking values. Although ultimate values and fatigue tests are important as criteria of quality, they are of no assistance to the engineer, designer or technologist for anticipating the response of his product to the forces experienced in service. To fill this need, there has grown up a body of technical and scientific methods, data, and principles usually referred to as the field of dynamic properties. The term dynamic properties as applied to elastomers usually means vibration properties which are displayed in response to sinusoidal forces. But restriction to sinusoidal forces is unduly narrow. In principle, both theory and experiment can be extended to more complex force patterns, such as square or saw tooth waves, if there is occasion to do so. The distinctive feature of the field of dynamic properties lies, perhaps, more in the amplitudes of the deformations, which are relatively small, than in the force diagram or the frequency. Results at quite low frequencies are sometimes included in work regarded to be on dynamic properties but the amplitudes are always rather small. In polymer science, the field of dynamic properties has tended to be restricted to amplitudes so low that the properties are essentially linear. This would provide a convenient definition but it is an unacceptable limitation from a technological standpoint where it is highly desirable to extend the work into the nonlinear region. On the other hand, fatigue and failure phenomena are definitely excluded from consideration here. Ordinary tensile stress-strain tests have a dynamic aspect but such results are not included in the catagory of dynamic properties. The field to be known as the dynamic properties of elastomers logically comprises the properties exhibited in response to periodic or transient forces for all types of deformation small enough not to induce appreciable fatigue or failure during the investigation. There is no good reason for limiting the frequency on either the low or high side. Temperature is, of course, a most important variable.
The Vulcanization of Rubber with Sulfur
Authors: Craig David
Published: February 2011

E. H. Farmer compiled a review of vulcanization which was published in 1946 as an important chapter in Volume II of “Advances in Colloid Science”. About two years later, Normann Bergem published a review under the same title. These authors dealt with the subject from rather fundamental points of view, but, because of more recent work from many laboratories and the increasing importance of elastomers, a fresh survey seems warranted. Accordingly, the present review aims to bring a part of the subject up-to-date. The viewpoint taken differs from those of Farmer and Bergem in some respects which seem rather important. For example, emphasis will be placed on the various rates of reactions including those of the scorch and reversion periods and on the importance of possible intermediates such as hydrogen sulfide and suitably terminated sulfur chains. The kinetic theory of elastomeric behavior constitutes the background against which any current treatment of vulcanization should be developed. Actually, vulcanization is a part of this background. Thus, Busse considered the following conditions necessary for the existence of rubberlike elasticity: (1) the presence of long chain molecules with freely rotating links, (2) the presence of weak secondary forces between molecules, and (3) the crosslinking of molecules into a three dimensional network. The three conditions taken together, at least in present day thinking, imply that long range elasticity results from the kinetic activity of segments which resembles yet differs from the kinetic activity of gas molecules. A segment is composed at most of only a few monomer units and is terminated at either end with another segment, a crosslink or an endgroup. When terminated with an endgroup, its kinetic activity may even detract from network behavior and then it is a defect. When terminated by a crosslink or another segment it is an integral part of the network and as such can contribute to the overall elasticity. It is more or less obvious that segments terminated by crosslinks and the crosslinks themselves should display an activity different from that of segments distant from crosslinks. Crosslinks, though relatively massive, are expected to move in a limited way (microBrownian) as a result of the kinetic activity of nearby segments. Crosslinks are necessary but are thus a sort of network defect. Those of lower functionality probably can contribute beneficially to the overall kinetic activity.
Carboxylic Elastomers
Authors: Brown H. P.
Published: February 2011

The degree to which a polymer is rubbery is influenced by the detailed shape and chemical composition of the macromolecules. Polymers which are rubbery possess relatively weak interchain forces and may lack linear symmetry and orderly arrangement of the molecule. As stronger interchain forces are added and symmetry and regularity are increased, the rubbery characteristics are gradually supplanted by those of fiber forming materials. Copolymerization with hydrocarbon chains may be used to reduce polymer to polymer interaction, destroy regularity and symmetry and favor rubbery characteristics. On the other hand it may be employed to introduce polar groups into hydrocarbon polymers and thereby increase interchain and intrachain forces. With increasing amounts of these polar groups polymer strength increases at the expense of elasticity with respect to both speed and range of extension and recovery. The polar groups also alter the solvent resistance of the polymer. In copolymerizations, carboxylic monomers tend to destroy regularity and symmetry thereby favoring rubbery properties over crystallinity. The strong polar nature of the carboxyl groups however increases interchain and intrachain forces imparting increased strength to the polymer at the expense of elasticity. Carboxyl groups were first introduced into rubbers for the purpose of altering polymer properties. When carboxyl groups are so employed, the resultant carboxylic rubbers are best regarded as polar elastomers. Carboxyl groups have also been introduced into rubbers in order that reactions characteristic of the carboxylic functional group might be employed to crosslink the polymer chains or attach them to other molecules or surfaces. When the carboxyl group is present in order that its functional reactivities may be employed, the carboxylic rubbers are best regarded as functional elastomers. This review is concerned with the preparation, properties and evaluation of carboxylic rubbers both as polar and as functional elastomers.
Rubbers from Basic Monomers. Vinylpyridine Polymers
Authors: Haws J. R.
Published: February 2011

Interest in vinylpyridine and vinylpyridine derivatives as monomers for production of synthetic rubber was evidenced immediately prior to World War II. In 1939 and 1940, European patents were issued on polymerization of vinylpyridines and their copolymerization with other monomers. Research in the United States on vinylpyridines and their derivatives as comonomers began in the early 1940's. Much of the early work was conducted under the Government synthetic rubber program with work carried out by several of the participating universities and rubber companies. At that time, vinylpyridine rubbers created a considerable amount of interest in the rubber industry. Compared to the 122° F butadiene/styrene copolymer then in use, butadiene/vinylpyridine copolymers displayed a superiority in several properties, notably tensile strength, tear resistance and resistance to cut growth. A number of terpolymers containing vinylpyridine type monomers were also investigated and these, with some exceptions, exhibited the same general advantages and disadvantages as the two-component copolymers. Some difficulty was encountered in early polymerization of vinylpyridine copolymers on a large scale, chiefly in preflocculation and lack of proper control over polymer viscosity and conversion rates. These problems were lessened somewhat in the polymerization of three-monomer systems. Processing difficulties were also encountered arising from incompatibility of vinylpyridine copolymers with other rubbers and a high rate of cure resulting in scorching tendencies. Treadwear results of tires made with these rubbers were encouraging but again complications appeared in the form of tread separations and an excessive increase in hardness after use. Because of the above-mentioned problems, together with the introduction of improved 41° F butadiene/styrene rubber, interest in these rubbers waned somewhat after World War II. More recently, however, interest in vinylpyridine rubbers has risen due to commercial availability of new monomers and the possibility of utilizing the reactivity of vinylpyridine polymers through new compounding techniques.
Changes in Elastomers Due to Radiation from Cobalt
Authors: Gehman S. D. , Hobbs L. M.
Published: February 2011

A survey has been made of the effects of intense gamma radiation on the physical properties of elastomers and plastics. Such information is required to determine the types of elastomers which are most resistant to radiation, to estimate the service life of elastomers exposed to radiation, and to show favorable trends in compounding for radiation resistance. Intense radiation may affect the physical properties of elastomers benficially or adversely, depending on the type of elastomer and the exposure dose, although hardening and embrittlement are most commonly observed. The possibility is apparent of developing elastomer compounds with improved radiation resistance, especially by the use of chemical agents which affect free-radical reactions. The nature of the elastomer, however, will probably severely limit what can be accomplished by compounding.
Heat Build-Up and Destruction of Vulcanizates under Dynamic Stress
Authors: Kainradl P. , Händler F.
Published: February 2011

The classification of various mixtures of natural rubber and of synthetic rubber and of synthetic rubbers with respect to heat build-up under dynamic stress depends on the experimental conditions under which the vulcanizates are tested. In many cases a reversal of the order of the mixtures is found when the latter are compared at constant deformation instead of at constant periodic stress. This is true also of flexing to the point of destruction of various types of vulcanizates. The dependence of the dynamic properties on the temperature and on the stress is characteristic of the type of vulcanizate. Hence, any classification of various mixtures depends not only on the character, but also on the magnitude of the stress. These differences were found within the temperature range encountered in practice, as in tires. Consequently, no definite conclusions about the temperature rise in the range of heat build-up extending to the point of destruction can be drawn from measurements of the dynamic properties at room temperature. Changes of the dynamic properties can also take place during dynamic stressing without any considerable rise of temperature. In general, the temperature rise in the static state and the flex life are related in the sense that the higher the temperature, the shorter is the flex life, if the preceding facts are taken into consideration. However, the experiments on the temperatures of destruction show that the flex life of different vulcanizates differs even when the rise of temperature is the same. For a flex life of 100 minutes, natural-rubber vulcanizates containing active carbon blacks were destroyed at higher temperatures (170°–185° C) than was the base mixture containing no filler (about 160° C). The synthetic-rubber mixtures showed greater heat build-up (190°–220° C). These differences are found with different, as well as with equal, mechanical stress on the vulcanizate. The nature of the destruction for a given stress depends to a considerable degree on the structure of the vulcanizate. When flexed to the point of destruction, natural-rubber vulcanizates containing zinc oxide or SRF carbon blacks, and all synthetic-rubber vulcanizates, crack from the core outward, without showing any extensive thermal decomposition. On the other hand, natural-rubber vulcanizates containing active carbon blacks or Aerosil showed definite evidence of heat decomposition in the center, i.e., stickiness and porosity. This distinction in the destruction patterns gives the impression that the cause of destruction in the first case is chiefly a mechanical attack, whereas in the latter, it is chiefly thermal decomposition. It must be concluded from all the experimental results that several chemical reactions of destruction, having different temperature coefficients, proceed simultaneously, and that direct mechanical attack by the external forces is, to a greater or less extent, added to the heat effect.
The Solubility of N-Phenyl-2-Naphthylamine in Elastomers
Authors: Reitlinger S. A. , Kuzminskii˘ A. S.
Published: February 2011

The determination of the solubility of N-phenyl-2-naphthylamine in elastomers is of great importance in determining the correct percentage of this substance to add to an elastomer to protect it from oxidation. Kuzminskii˘ and Lezhnev have shown that the duration of the induction of the oxidation of rubber depends on the concentration of N-phenyl-2-naphthylamine inhibitor in the rubber.
The Cross-Linking of Rubber by Pile Radiation
Authors: Charlesby Arthur
Published: February 2011

The degree of cross-linking produced in a rubber by high-energy radiation is proportional to the radiation dose. Unit radiation, as defined in the text, links 1.1 per cent of the isoprene units. The distribution of molecular weight prior to cross-linking agrees with a Poisson distribution. Gel formation begins for γ=0.5. From the radiation dose required to initiate gel formation, the initial average molecular weight can be deduced. The increase of gel fraction with radiation dose follows the relationship deduced theoretically in the first part of the article. Measurement of gel fraction gives an alternative method of calculating the initial average molecular weight. Where some cross-linking is present in the rubber prior to cross-linking, this may be evaluated. In accordance with the theory presented in the article, the viscosity of the sol fraction rises initially, then decreases as the radiation dose increases. This provides a third method of measuring molecular weight, or of relating viscosity to molecular weight, which can be deduced from measurement of gel fraction. The swelling of very lightly cross-linked gel has been compared with the Flory-Huggins relationship, which is found to hold down to very lightly cross-linked gels for which the cross-linking index is only 0.2. To obtain this agreement, it is necessary to consider the swelling of the dry gel, rather than the whole specimen, and to ignore the cross-links required to form the gel itself.
Reinforced Rubber Stocks under the Electron Microscope
Authors: Chappuis M. M. , Polley M. H. , Schulz R. A.
Published: February 2011

A transfer technique and a microtome technique have been developed for preparing standard rubber stocks for electron-microscope examination. The transfer technique is rapid and simple, and is adequate for the identification of unknown carbon black in an unvulcanized stock. The microtome technique is more satisfactory in that it reveals clearly the discrete particles of a reinforcing pigment as they are dispersed in the rubber matrix.
Kinetics and Mechanism of Hydrochlorination of Synthetic and Natural Polyisoprene Latex
Authors: Crampsey Edward , Gordon Manfred , Taylor James S.
Published: February 2011

The kinetics of hydrochlorination of synthetic polyisoprene emulsions, prepared by new and simple methods, are studied for comparison with the same reaction of natural latex. Nearly identical zero-order rate constants apply to both substrates at 300° K and 1 or 2 atmospheres of hydrogen chloride, despite differences in the detailed structure of the polymers. The conclusion that the substrates are not concerned in the rate control follows, since the rates of chain reactions which might give zero-order constants are very sensitive to the detailed structure of the polymers. Two initial rate abnormalities are observed. The first is shown to be due to a fast surface reaction, the second probably reflects the presence of a basic retarder in natural rubber particles only. Similar abnormalities of the cyclization reaction, reported earlier, are explained similarly. The effects of energetic factors and concentration on the hydrochlorination rate support visualization of the simple rate-determining step as: H+ + Cl− → (H+, Cl−) (ion pair), where the proton is probably solvated as H2C+. The critical transition state must be uncharged, because the reaction rate is unaffected by a change of dielectric constant due to the conversion of rubber hydrocarbon into rubber hydrochloride. Existence of the ion pair as reactive intermediate confirms Gordon and Taylor's recent stereochemical theories on hydrochlorination of natural rubber. The rapid surface reaction is ascribed to the ready formation of ion pairs or similar species in the aqueous phase, and the limited range (about 15 A) or the surface reaction to the slow rate of diffusion of unchanged rubber units to the surface.
Introduction to the Mechanism of the Hydrochlorination of Rubber
Authors: Gordon Manfred , Taylor James S.
Published: February 2011

The mechanism of rubber hydrochlorination is discussed in the light of the known crystal structure of rubber hydrochloride. The coiling of a rubber chain segment into a trans-decalin-shaped transition state is shown to be necessary and sufficient to explain the alternation along the polymer chain of d- and l-asymmetric carbon atoms, each separated from the next by three CH2 groups. As a preliminary to kinetic analysis, techniques are described for precise measurements of the degree of hydrochlorination of latex at various times of reaction. An analytical technique defines the reaction progress to 0.5 per cent, and serves to calibrate a diffusion-gradient method of following the reaction by density change. This method is at least equally sensitive, but more convenient. Despite the complexity of the natural-latex medium, the reaction kinetics are shown to be reproducible and free from uncontrolled effects. The reaction is rate-controlled chemically rather than by transport. The main part of the rate curve consists of two straight-line (zero-order) portions meeting at a kink.