bluuebunny/crossref_metadata_2025_split huggingface dataset:
Raman Spectroscopic Studies of the Vulcanization of Rubbers. III. Studies of Vulcanization Systems Based on 2-Mercaptobenzothiazole
Authors: Coleman M. M. , Shelton J. R. , Koenig J. L. 
Published: February 2011

Abstract
The shoulder observed at approximately 440 cm−1 in Raman spectra of CB vulcanizates prepared from MBT based vulcanizing systems has been shown to consist of two components. There are Raman lines contributing at 440 cm−1 and 424 cm−1. The former is due to ZnO present as an extra-network material while the latter appears to be associated with polysulfidic structures. The Raman line at 505 cm−1 seen in extracted vulcanizates prepared from CB-MBT-Sulfur-ZnO-Lauric acid recipes does not appear to be solely due to disulfidic structures. The major contribution appears to be associated with an unsaturated cyclic sulfide and is most probably due to a structure of the type (I). If the assignment to cyclic sulfidic structures such as (I) is confirmed, it will have major significance with regard to the mechanism of accelerated sulfur vulcanization.
The Radiation Curing of Elastomers. I. Physical Strength
Authors: Pearson D. S. , Böhm G. G. A. 
Published: February 2011

Abstract
Data has been presented which shows that sulfur crosslinks have very little importance in producing maximum tensile strength in amorphous polymers. The results suggest that the distribution of crosslinks, especially in the case of crystalline polymers, is. a factor to be considered. In general, radiation cured elastomer compounds have physical strength properties very similar to sulfur or peroxide cured compounds. This similarity has been noted for a wide number of other elastomers not reported here. The observed strength deficiency is minor in degree and of little industrial importance provided the other properties are not too different. These properties such as fatigue life, abrasion resistance, and hysteresis will be discussed in a later publication.
Solvent Effects in Styrene—Butadiene—Styrene Block Copolymer Cast Films and Evidence for Supermolecular Ordering by X-Ray and Light Scattering
Authors: Pillai P. S. , Livingston D. I. , Strang J. D. 
Published: February 2011

Abstract
It has been found that solution-cast films of an SBS block copolymer (Kraton 1101) have two orders of phase structure. The first is of molecular dimension and consists of elongated polystyrene domains (≈ 200 A˚) dispersed in a polybutadiene matrix. There is also a supermolecular heterogeneous structure of spherical domains of fractional micron size. A somewhat larger nearest neighbor distance is also seen. The domain size and separation are larger for the polymers cast from solvents for polystyrene than those cast from a solvent for polybutadiene alone. Furthermore, SBS films cast from good solvents for polystyrene exhibit additional supermolecular ordering in contrast to the more random arrangement of the others.
The Migration of Extender Oil in Natural and Synthetic Rubber. VI. The Use of Oil Type Molecules as Penetrants to Elucidate Elastomeric Molecular Structure
Authors: Corman B. G. , Deviney M. L. , Whittington L. E. 
Published: February 2011

Abstract
Previous work in diffusion of whole extender oil and extender oil fractions in practical rubber compounds has shown the nature of the rubber matrix to be the major controlling factor. Therefore, a sensitive diffusivity approach, using radiotracer labeled hydrocarbon penetrants of sizes comparable to the size of a rotating segment, was used to study various aspects of the matrix structure on penetrant diffusion for polybutadiene, styrene—butadiene, and Butyl rubbers. These results were compared with fractional free volume measurements made by a thermal expansion technique. Neither fractional free volume nor diffusivity of phenyldodecane, benz-a-anthracene, or n-octadecane was affected by 5-fold variations of crosslink density or by variations in loading of 10 to 80 parts of carbon black (HAF-LS); nor were they affected by changes from FEF to SAF black at a 50 phr level. Glass transition temperature and fractional free volume are both affected by increasing percentages of benzene or phenyldodecane, While diffusivity rises with increasing dilution, states of equal free volume in different elastomers are not states of equal diffusivity; for example, at a fractional free volume of 0.10, corresponding to 20% benzene in both polybutadiene and Butyl at 70° C, the diffusivity of benzene in Butyl is lower by a factor of 15. Comparison of diffusivity of large penetrants with their cross-sectional area gives two basic curves, one for flexible penetrants and another for molecularly rigid species. These results are explained in terms of a distribution of free volumes, wherein only holes above a critical size are effective in diffusion. Swelling the system with aromatic diluent greatly increases the total fractional free volume, but only slightly the number of holes above this critical size. To understand the diffusivity of rigid molecules in elastomers, a probability factor must be applied in estimating their effective cross-sectional area.
Identification of Elastomers by Thermal Analysis
Authors: Sircar A. K. , Lamond T. G. 
Published: February 2011

Abstract
Degradation of polymers by thermal and thermooxidative reactions is associated with either evolution or absorption of heat which can be followed by differential scanning calorimetry. In the present investigation, DSC thermographs of elastomers between 0° C and 500° C in nitrogen (thermal degradation) and oxygen (thermooxidative degradation) were used for identification of the elastomers from their degradation patterns. Based on the nature of the thermographs of the raw polymers in nitrogen, the elastomers studied may be divided into the following three main groups: (a) those which show an exotherm, (b) those which show an endotherm, and (c) those which show multiple peaks of endo- or exotherms. Identification is aided in some cases by the thermographs in oxygen as well as by the physical transitions. The nature (exo- or endo-) and shape of the thermal patterns and the temperature domain at which the reactions take place depend on the molecular structure, configuration, chemical composition, and nature of the substituents as well as on the environment. Consequently, thermal and thermooxidative degradation curves may be used as a “fingerprinting” device which can identify many polymers, difficult to identify by other methods.
Gel Permeation Chromatography of Natural Rubber
Authors: Subramaniam A. 
Published: February 2011

Abstract
The Waters Model 200 Gel Permeation Chromatograph has been used to study the molecular weight distribution of natural rubber. The cumulative weight distribution curve of synthetic cis-polyisoprene from the GPC method showed fair agreement with the distribution obtained by fractional precipitation. For natural rubber the agreement was not so good. Natural rubber samples from six clones of Hevea Brasiliensis were examined with the GPC. Differences were observed in their distributions. Five clones showed a distinct bimodal distribution. The weight and number average molecular weights from the GPC were found to be too low. Some possible reasons for this have been suggested.
Stress Relaxation Mechanisms in Rubbers Reinforced with Carbon Blacks
Authors: Bartenev G. M. , Lyalina N. M. 
Published: February 2011

Abstract
1. In vulcanized rubbers containing blacks a multi-stage mechanism for stress relaxation was observed. It was discovered that the stress relaxation process consists of five fundamental processes: the first three relaxation processes, related to the slow stages of physical relaxation within the bulk of the rubber, have no connection with the fillers (“soft” domains); the fourth process has to do with the relaxation in the black-rubber domain; the fifth process involves the chemical relaxation of vulcanizates. 2. The fundamental mechanisms of the first 3 relaxation processes in the soft domains have the same activation energy values and the same segmental mechanism as the rearranged domains found in supermolecular weight structures, which are also present in unfilled vulcanizates. 3. In the investigated stress range of up to 200% elongation, the activation energy for the first 3 relaxation processes in the soft domains of filled vulcanizates is not a function of the deformation strain, whereas the activation energy of the fourth relaxation process in the black-rubber domains of filled rubbers is a function of the deformation and of the filler content. For these reasons, rubber loaded with carbon blacks, in contrast to unfilled rubbers, possess the typical nonlinearity of viscoelastic materials. 4. The activation energies of the relaxation processes in the black-rubber domains decrease in a linear fashion with the value for the initial tensile stress in filled vulcanizates, and decrease in like manner for vulcanizates containing different proportions of fillers. The kinetic units, determined from the activation energies of these processes, appeared to be segments of chains with activation energies of up to 40% more than the activation energies of the physical relaxation processes in the soft domains. The other kinetic units of the processes proved to be black particles, the dimensions of which were calculated from the values for the coefficients in the formula for relaxation time.
Oxidation of Vulcanized Natural Rubber
Authors: Barnard D. , Cain M. E. , Cunneen J. I. , Houseman T. H. 
Published: February 2011

Abstract
The chemistry of oxidative main chain scission in NR and its vulcanizates has been investigated using radiolabelled 2,4-dinitrophenyl hydrazine and dimedone. In this way the number of scission events has been measured and the initial products of oxidation identified and estimated. Product studies have also been carried out with 2-methylpent-2-ene, 2-methyloct-2-ene, and 2,6-dimethylocta-2,6-diene. From these results a more simple and rational mechanism has been suggested for scission in natural rubber. Studies have also been made using radiochemical techniques, of the effect of sulfur compounds structurally related to the crosslinks in vulcanized NR and of conventional antioxidants, on the efficiency of scission. In general both types of compounds increase scission. The effect of mixtures of conventional antioxidants and sulfur compounds on the rate of oxidation of polyisoprenes has been followed. Usually the sulfur compounds reduce the potency of the other antioxidants and reasons are given for this antagonistic action.
Branching in Polymer Chains
Authors: Grechanovskii V. A. 
Published: February 2011

Abstract
The branching that occurs in molecular chains leads to extensive changes of the physico-mechanical and technological properties of various polymers, as compared with the corresponding linear polymers. For example, branched divinylstyrene rubbers, polybutadienes, and other branched elastomers possess a low elasticity, breaking strength, etc. The decrease of strength properties and the change of the dynamic and mechanical properties with the increase of the degree of branching is characteristic for such thermoplastic polymers as polystyrene, polyethylene, polyvinyl chloride, etc. There also exist considerable differences in the rheological properties of linear and branched polymers. For example, at low loads (shear stresses) linear polymers and their melts flow like newtonian fluids and possess a lower viscosity as compared with branched polymers, whereas at high loads the character of flow deviates from that of a newtonian flow, so that the viscosity of a branched polymer is lower than that of a linear polymer or almost equal. Similar regularities have also been observed for concentrated solutions. Hence, the branching, together with the regularity of the structure of polymer chains, the molecular weight, and the molecular weight distribution, represents one of the most important molecular parameters of polymers. The branching occurs during polymerization and is caused essentially by a transfer of active centers to the polymer chain.
Environmental Health Control for the Rubber Industry, Part II
Authors: McCormick W. E. 
Published: February 2011

Abstract
This is the last of a two-part presentation, the first having appeared a year ago. Part I dealt with the health control relating to polymer manufacturing, processing chemicals, and accelerators. Part II is confined to a discussion of antioxidants and antiozonants. While an attempt has been made to review the known toxicology and handling experience of the commercially-used antioxidants and antiozonants, there undoubtedly have been inadvertent omissions from the list.
Polyolefin Elastomers Based on Ethylene and Propylene
Authors: Baldwin F. P. , Strate G. Ver 
Published: February 2011

Abstract
In 1940, the first all-hydrocarbon elastomer containing limited olefinic functionality, butyl rubber, was announced. Because of its resistance to em-brittlement on aging, cracking on exposure to ozone, its impermeability to gases, and high damping capacity, this elastomer found use in inner tubes, cable insulation and miscellaneous hose, grommet, and gasket applications, generally lumped together as mechanical goods. It was the chemist's desire to prepare elastomers from other simple, inexpensive olefins, varying the structure to meet property requirements and using limited functionality to accommodate vulcanization. But no such preparative scheme was found, and, instead, attention was turned to modifications of known, substantially saturated hydrocarbon polymers to effect elastomeric properties and vulcanizability or to prepare elastomers from other raw materials, typical examples being Hypalon (chlorosulfonated, low density polyethylene) and polymers derived from epoxides and acrylates. However, K. Ziegler and coworkers pursued the matter of dimerization or oligomerization of olefins with metal alkyls until a breakthrough was made, and the catalyst system now known as Ziegler or Mulheim catalysts was discovered. This basic discovery, initially applied to the polymerization of ethylene, was expanded by Natta and his group and others to preparation of entirely new polymer structures. And, while attention was initially devoted to the preparation of miscellaneous stereoregular, crystalline homopolymers from simple olefins, it was virtually axiomatic that it would inevitably turn to the preparation of elastomeric copolymers. So, like the development of butyl rubber from polyisobutylene, ethylene/propylene elastomers (EPM) were followed by their olefin-containing terpolymers (EPDM), all of which are commercially prepared today. The Nobel Prize Award addresses by each of these aforementioned men trace the history of this important step forward in organometallic catalysis and polymer science.
Digital Method of Calculating the flow of Heat through a Tire during Vulcanization
Authors: Ambelang J. C. , Prentice G. A. 
Published: February 2011

Abstract
Calculation of the complete temperature cycle in a tire cure has not been published although the digital method here presented was suggested by Gehman. This general method, attributed to Schmidt, consists in dividing the article into cubical volume elements and calculating the heat flow from contiguous surrounding cubes to obtain the temperature for a given element in the next time interval. Vostroknutov reviewed the classical differential equations in a study of retreading cures but his solutions were specific rather than general and utilized the usual graphical methods.
The Determination of “Head-Head” and “Tail-Tail” Structures in Poly(Isoprene)S
Authors: Hackathorn Marjorie J. , Brock M. J. 
Published: February 2011

Abstract
Pyrolysis-gas chromatography has indicated the presence of head-head structures in free radical initiated poly(isoprene)s. Microozonolysis has confirmed the presence of both head-head (15-20 per cent) and tail-tail (4-7 per cent) structures in these polymers. These structures (which are absent in natural rubber) are present in lesser amounts in Lithium and Ziegler poly(isoprene)s (1-3 per cent). Non-equivalent amounts of head-head and tail-tail structures in particular samples indicate a chain reversal in which neither head nor tail units are involved. It has been postulated that chain reversal may occur at points of 3,4 addition.
Microkinetics of Lamellar Crystallization in a Long Chain Polymer
Authors: Andrews E. H. , Owen P. J. , Singh A. 
Published: February 2011

Abstract
The growth kinetics of single crystal lamellae grown from poly(isoprene) melts have been determined by thin film electron microscopy which also reveals the relevant microstructure. The growth rate of a continuous lamellar crystal is independent of the length of the crystal and (in the absence of crosslinks) depends only upon temperature and the chemical composition of the polymer. The temperature dependence is closely similar to that observed for bulk crystallization and spherulite growth, with a maximum crystallization rate around —24° C. The growth rate at a given temperature is extremely sensitive to the chemical composition of the poly(isoprene), being for a polymer containing 10 per cent trans-poly(isoprene) one thousandth of that for pure cis-poly(isoprene). Between these extremes the logarithm of the growth rate decreases linearly with increasing trans content. A similar effect is produced by the introduction of chemical crosslinks instead of trans units. These effects are attributed to a reduction in the probability of formation of the ‘secondary nucleus’, whose size can be calculated from the experimental data. The secondary nucleus is found to correspond to three molecular folds and this agrees well with an independent estimate obtained, by using thermodynamical theory, from the dependence of lamellar thickness on temperature.
Structural Characterization of Vulcan-Izates. XII. Efficient Vulcanization Using a Sulfenamide-Thiuram Disulfide Accelerator System
Authors: Campbell D. S. 
Published: February 2011

Abstract
Vulcanizates obtained from the sulfur vulcanization of natural rubber using a combination of the accelerators N-cyclohexyl-2-benzothiazole sulfenamide (CBS) and tetramethylthiuram disulfide (TMTD) have been analyzed in terms of the numbers of poly-, di-, and monosulfide crosslinks, network-bound accelerator residues, and cyclic sulfide chain modifications as a function of cure time. The vulcanization system produced mainly monosulfide crosslinks at optimum cure, although there were differences in detail between this mixed system and a previously reported efficient sulfur vulcanization (EV) system using a high ratio of CBS to sulfur.
Low Sulfur-Sulfenamide Accelerator Combinations for Injection Molding of Cis-1,4-Poly(Isoprene)
Authors: O'Mahoney J. F. 
Published: February 2011

Abstract
Earlier work with cis-l,4-poly(isoprene) suggested that low levels of sulfur and high levels of sulfenamide accelerator with high levels of secondary accelerator was an excellent method for curing injection molded stocks. However, subsequent experience showed that despite the benefits of reduced sulfur concentrations on reversion, increased sulfur, increased sulfenamide, and reduced secondary accelerator concentrations were necessary for adequate cure and safety. From that experience we explored further and found that, if the sulfenamide concentration is held constant at a higher level and the secondary accelerator concentration is increased as sulfur concentration is decreased, nearly equivalent hardness and modulus can be maintained throughout most cure conditions with no loss in safety and cure rate and much improvement in reversion resistance. Studies were made in a carbon black filled stock with N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N-oxodiethylene-2-benzothiazole sulfenamide (DBS), and N-morpholinyl-2-benzothiazolyl disulfide (MBD) as primary accelerators and tetramethylthiuram monosulfide (TMTM) and tetramethylthiuram disulfide (TMTD) as secondary accelerators.
Mill Processing Behavior of Ethylene-Propylene-Hexadiene Terpolymers
Authors: Shih Chi-Kai 
Published: February 2011

Abstract
The mill processing behavior of ethylene/propylene/hexadiene terpolymers, one type of EPDM, has been described. In agreement with the general observations of Tokita and White, the milling characteristics of the polymers change from an elastic band (region 2) to a crumbling bag (region 3) and then to a viscoelastic fluid (region 4) as the temperature is increased from 5° C to 175° C. The 2-3 transition can be treated as a failure process which is time and temperature dependent. Hence, a continuous curve relating the transition nip setting; and the temperature exists for each polymer sample. The transition nip setting at a given temperature (or the transition temperature at a given nip width) was found to be wider (or higher) for samples of broader molecular weight distribution.
Poly(Styrene CO Acrylonitrile) Polyols. Modulus Enhancing Polyols for Urethane Polymers
Authors: Critchfield F. E. , Koleske J. V. , Priest D. C. 
Published: February 2011

Abstract
A novel class of polyols for polyurethane production was described in 19661. Their unique feature was the presence of an in situ polymerized vinyl polymer which markedly enchanes the modulus of the resultant polyurethane. The final product is a conventional polyol that contains a dispersion of the vinyl polymer. From among the numerous products investigated, a poly-(acrylonitrile) polyol was selected because of the excellent stability of the dispersion. Poly (acrylonitrile) polyols are opaque, cream-colored liquids with viscosities ranging from 1500 to 4500 cps, depending upon the nature of the polyol precursor. Particle size of the dispersed phase was reported to be between 0.25 and 0.5 micron as determined by electron microscopy. Poly (acrylonitrile) polyols have been used in slab-stock flexible foams as additives to conventional polyether polyols to improve load-bearing properties. More extensive utility has been identified in molding applications. Whitman described their use in producing integral skin urethane foams for uses such as automotive arm rests, horn buttons, mirror covers, etc.. Dunleavy discussed the use of polymer polyols in molded, microcellular urethane elastomers for automotive trim parts, particularly for "cosmetic" bumpers. More recently, Patten and Priest showed their utility in highly resilient automotive seating foam. In all of these applications the modulus enhancing characteristics of these polyols are particularly important.
Alternating Copolymerization of Butadiene and Propylene
Authors: Furukawa Junji 
Published: February 2011

Abstract
An alternating copolymer of propylene and butadiene is prepared with vanadium or titanium compounds and alkylaluminum compounds as the polymerization catalyst. The catalyst should be prepared at extremely low temperature as −70° C and halogen atom is essential to the catalyst activity. Carbonyl compounds such as ketone, acid, ester, acid anhydride, and acid peroxide are very effective additives to the catalyst for enhancement of the molecular weight of the polymer. Potentiometric titration and the ESR studies suggest that a divalent vanadium compound associated to form the dimer through a chloride bridge is a precursor of the active species. An anionic copolymerization mechanism involving the alternating coordination of monomers is proposed. The copolymer is always of a 1:1 composition irrespective of the composition of monomer feed and the alternating structure of trans-1,4-poly (butadiene co propylene) is estimated from IR and NMR data. The copolymer seems to be a new versatile synthetic rubber having excellent low temperature properties, high rebound, good compatibility with conventional rubbers, and high resistance toward aging.