bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scattering of Light in Crystalline Polymers. I. Formation and Melting of the Crystalline Phase in Neoprene
Authors: Trapeznikova O. N. , Smirnova G. E. 
Published: February 2011

Abstract
The process of formation and melting of neoprene crystallites was investigated by the polarized light scattering method. Conclusions about the nonreversibility of the crystallization and melting processes were drawn on the basis of angular distribution measurements of depolarized and polarized components of light scattered from polymer films. The appearance of a relatively small number of large crystallites is characteristic for the initiation of crystallization; further development of crystallization is accompanied by a decrease in the size of the crystallites. All crystallites disappear simultaneously during the melting process. The size of the crystallites determined by microphotography corresponds approximately to the particle size determined by the formula for isotropic, spherical particles. A method for the determination of the melting range of crystalline polymers is proposed.
Compatibility as the Basic Factor in the Adhesion of High Molecular Weight Materials
Authors: Alekseenko V. I. , Bogoslavskaya L. A. , Mishustin I. U. 
Published: February 2011

Abstract
1. Relationships were established between the bond strength of joints made from rubber with fabric, leather, or rubber with physical property data from the films made from the mixtures of the adhesive with the rubber from which the vulcanizates were made. 2. The effect of the chemical structure of the adhesive on the bond strength is established. 3. Nairit-NT, mainly the trans isomer of poly-1,4-chloroprene and chemically closely related to gutta percha (trans polyisoprene) gives a good adhesive cement for bonding rubber to fabric, leather, or rubber. It makes chemical surface treatment unnecessary. This new adhesive gives good bonding to SKS-30. Similar results were obtained with cement made from gutta percha; however, bonding strength to SKN-40 rubber was much higher.
The Structure of Gels. IX. Effects of Plasticizers on the Physical Properties of Styrene Butadiene Rubber
Authors: Zverev M. P. , Zubov P. I. 
Published: February 2011

Abstract
1. The glass and flow temperatures and the strength and relative extension of rubber depend not only on the concentration of the plasticizer but also on its molecular structure. 2. Styrene butadiene rubber plasticized with nonpolar plasticizers has higher glass and flow transition temperatures than rubber plasticized with polar substances. The same relationships are found for the strength and relative extension of vulcanizates of this rubber. 3. Nonpolar plasticizers also weaken intramolecular interaction to a greater extent than polar plasticizers.
The Photovulcanization of Butyl and SKB (Polybutadiene) Rubbers
Authors: Zuev Yu S. 
Published: February 2011

Abstract
It is known that the mechanical properties of raw and vulcanized rubbers change markedly under the action of light in which not only oxidation processes but also photovulcanization processes in which sulfur is involved play an essential part. In view of the wide interest shown lately in questions of radiation vulcanization of polymers, as well as the possibility of reducing the photodegradation effect upon the mechanical properties of some polymers, we made studies of the photovulcanization of butyl rubber (degradation by irradiation) and SKB (polybutadiene) rubber (structure formation by irradiation). The study was made on films 200µ thick of purified butyl rubber with a molecular weight of about 42,000 and an unsaturation of about 1%. Both ordinary (twice crystallized) sulfur and radioactive S35 were used. The films obtained from a solution of rubber plus sulfur on cellophane were irradiated with a PRK-7 lamp through a Pyrex glass light filter and distilled water at a distance of 25 cm. Then determinations were made of the absorption spectrum and the static modulus 30 minutes and 24 hours after applying the load. The amount of free sulfur remaining in samples extracted previously was determined from the intensity of the S35 radiation. SKB not containing PBNA was reprecipitated from a benzene solution. When films of SKB (200µ thick) were irradiated, the light filters UFS-1, ZhS-4 and OS-5 were used. After the irradiation of the SKB films their static modulus was determined 30 minutes after the application of the load. When we irradiated butyl rubber containing 0.25 to 2.5% sulfur, we observed a distinct photovulcanization optimum (see Figure 1) in the modulus as a function of irradiation time like that which occurs in thermal vulcanization, and an optimum of the photovulcanization rate as a function of sulfur concentration.
The Nature of Optimum Vulcanization in Natural Rubber
Authors: Kuzminskiĭ A. S. , Chertkova V. F. 
Published: February 2011

Abstract
The vulcanization of natural rubber is accompanied by a considerable change in mechanical properties as the vulcanizate is formed. With sulfur as the vulcanizing agent an optimum is observed in the change in tensile strength and other physical properties. In many studies the presence of an optimum vulcanization has been considered as the result of the superimposition of two processes: (1) the structure-forming action of sulfur and (2) the degrading action of the oxygen, which causes a reversion of vulcanizates. We have established2 that the oxidative degradation of natural rubber in the vulcanization process proceeds extremely slowly and cannot have any substantial effect on the tensile strength of vulcanizates. To resolve the question as to the true causes of the reversion of vulcanizates in “overvulcanization”, several series of experiments were set up. In the first series the mobility of sulfur bonds was studied in natural rubber vulcanizates containing various accelerators by the use of the sulfur radio-isotope S35 with a method described earlier. The results of these experiments shown in Figure 1 indicate the “concentration” of mobile links in the vulcanizate to change proportionately with the change in tensile strength and the maximum density of mobile polysulfide links thus corresponds to optimum vulcanization according to tensile strength. The modulus likewise changes during the course of vulcanization, proportionately to the density of the intermolecular crosslinks formed. The formation of a complex three-dimensional network proceeds continually through all the various stages of the process up to the optimum. The increase in network density in the vulcanizates being formed, up to the optimum, is accompanied by a steady substantial rise in tensile strength. Further vulcanization, however, causes a decrease in network density and a drop in tensile strength. In a second series of experiments with vulcanizates at various stages of the process the polysulfide bonds were removed by extraction with sodium sulfite. When this occurred a decrease in the tensile strength of the vulcanizates was observed, which was especially marked at optimum vulcanization (Figure 2, Curve 2). In a third series of experiments, vulcanization was achieved with tetramethylthiuram disulfide (TMTD) without added sulfur. It is known that TMTD forms monosulfide bonds in rubber which are stable under the usual vulcanization conditions (a temperature of 143° C). Figure 2 (Curve 3) shows that no reversion is observed in vulcanization with TMTD.
Vulcanization of Elastomers. 21. Vulcanization of Natural Rubber with Thiuram Disulfides. VI
Authors: Scheele Walter , Hummel Klaus 
Published: February 2011

Abstract
Bound sulfur in a pure thiuram vulcanizate increases relatively rapidly at first at all temperatures, reaches a poorly defined maximum at about 27 to 30%, independent of temperature, and then recedes slightly to reach a limiting value of 25% also independent of temperature, based on the original thiuram disulfide. The rise in sulfur content at the start points to a temperature-independent limiting value of 33%. It is shown that the combination of sulfur in this region initially follows a first order reaction, and goes at the same rate as the reduction in concentration of thiuram disulfide. It can be seen from the above that sulfur may be combined in thiuram vulcanization without simultaneous crosslinking. The dithiocarbamate formation increases rapidly in the region of longer vulcanization times, after the maximum in bound sulfur has been reached, without further combination of sulfur with the vulcanizate. The rate constants for thiuram decrease, for dithiocarbamate increase and for sulfur combination were calculated. The temperature dependence of each of these reactions has practically the same activation energy, 23 kcal/mole. The bound sulfur content of the vulcanizates in pure thiuram vulcanizations is no criterion of the state of vulcanization.
The Reactions of Amines and Sulfur with Olefins. IV. The Chemical and Thermal Decompositions of N,N′-Thiobisamines and Their Reactions with Olefins
Authors: Saville R. W. 
Published: February 2011

Abstract
Parts I–III of this series described the use of combinations of secondary amine and sulfur and of N,N′-thiobisdiethylamine Et2N⋅S⋅NEt2 as olefinic sulfurating agents. The introduction of N,N′-thiobisamines, (RR′N)2Sx, as vulcanizing agents for rubber justifies a more detailed study of their properties.
Polybutadienes of Controlled Cis, Trans and Vinyl Structures
Authors: Short J. N. , Kraus G. , Zelinski R. P. , Naylor F. E. 
Published: February 2011

Abstract
The physical properties of polybutadiene vulcanizates have been measured as a function of polymer microstructure. Although the over-all properties of any one polybutadiene are determined by the relative ratio of cis, trans and vinyl units in the polymer chain, marked changes in physical properties do not occur until a relatively pure configuration is approached or unless the raw polymer displays crystallinity. Thus, polybutadienes containing more than 85 per cent cis, trans or vinyl units are characteristically different from each other and the differences are accentuated as the isomeric forms approach 100 per cent of a given configuration. Polybutadiene of 95 per cent cis configuration displays very low heat generation and high resilience (equaling natural rubber in these properties) and excellent abrasion resistance. trans-Polybutadiene (90 per cent), a crystalline plastic in the raw state, becomes rubbery after vulcanization. Gum vulcanizates possess high tensile strength, and tread stocks display high modulus and tensile strength, high hardness and fair hysteresis properties. Vulcanizates of amorphous 94 per cent vinyl polybutadiene are characterized by fair tensile properties, low hysteresis, and poor low temperature properties. Crystalline syndiotactic polybutadiene, 70 per cent vinly, displays much higher gum and tread tensile strengths than its amorphous counterpart. Amorphous polybutadienes containing less than 70–80 per cent of any one configuration are generally similar in most properties, and resemble emulsion polybutadiene in many respects. The wide range of properties of the various polybutadienes makes them suitable for many applications. cis-Polybutadiene is an excellent tire rubber, which has given as much as 40 per cent greater abrasion resistance than natural rubber in passenger tire tests. Heavy duty 10:00 × 20 truck tires fabricated with a 1:1 blend of cis-polybutadiene and natural rubber in the treads have given slightly better abrasion ratings and lower running temperatures than control tires fabricated entirely from natural rubber. Amorphous 80 per cent cis-polybutadiene has been found to possess exceptionally good low temperature properties, far superior to present arctic-type unsaturated elastomers, trans-Polybutadienes by virtue of their high modulus, high tensile strength, and high hardness could be utilized in the preparation of hard rubber goods, floor tiles, and shoe soles. While none of these polybutadienes is yet available commercially, their unusual properties and potential applicability in many areas should lead to their manufacture in the future.
Infrared Spectra of Cured and Uncured Rubbers
Authors: Blokh G. A. , Mal'nev A. F. 
Published: February 2011

Abstract
The newest physical-chemical methods of research enlarge the scope of study of the vulcanization process. There is a possibility of studying the structure changes during vulcanization of rubber by the application of infrared spectroscopy. Infrared rays are selectively absorbed. Therefore the infrared absorption spectrum can be used as a characteristic property of a substance and could be used for analytical purposes. The large spectral range of the infrared rays indicates their importance for the study of the properties and structure of substances; this makes possible the determination of the moments of inertia of atomic nuclei and molecules, isotopic mass, arrangement and strength of atomic bonds in the molecule and the frequencies of their vibrations. By knowing the frequencies for pure substances, molecular analyses of complicated mixtures of various organic rubbers, accelerators and other substances could be performed. The study of linear absorption spectra is the basis of the spectrographic method in the infrared region. Since the frequencies of near infrared radiation correspond to the characteristic frequencies of the atoms in the molecules, this method could be used to obtain interesting information concerning the structure of organic molecules, the chemical structure of high molecular weight compounds, the determination of the presence of specific groups or atoms in the rubber molecule, the character of the bonds between these groups and the order of arrangement of the individual chain links. This is true because the position of the absorption bands, which are specific for a given group of atoms, is practically the same for the different combinations in which the group occurs. The complicated process of polymerization of diene and vinyl compounds and the structure of different types of rubbers can be investigated with the aid of infrared spectroscopy. For example, Table I lists the characteristic absorption frequencies in the infrared region for some important chemical combinations.
Effect of Primary Molecular Weight on the Dynamic Properties of Cured Rubber
Authors: Kuvshinskiĭ E. V. , Fomicheva M. M. 
Published: February 2011

Abstract
1. Studied were the moduli of resilience and rebound elasticity of the vulcanized rubbers made from fractions of butadiene-styrene rubber “SKS-30-A” at temperatures of 20, 60, and 100° C in the region of molecular weights from 45,000 to 620,000 with various degrees of vulcanization (with variation in the pseudoequilibrium modulus from 5 to 70 kg/cm2). 2. The dynamic modulus of resilience is little dependent on the molecular weight of the original rubber both at room temperature and at higher temperatures. 3. At higher temperatures the elasticity of vulcanized rubber is mainly determined by the degree of vulcanization, the measure of which is the pseudo-equilibrium modulus, and is little dependent on the initial molecular weight. At low temperatures (20° C) elasticity increases with the degree of vulcanization, but it increases at different rates for vulcanized rubbers made from fractions with different molecular weights. At 20° C the increase in the degree of vulcanization increases the elasticity of vulcanized rubbers made from low-molecular fractions (45,000) to a lower degree than of those made from high molecular weight fractions (above 133,000). 4. The value of the maximum elasticity of vulcanized rubbers obtained from rubbers of the same molecular weight is not dependent on the type of accelerator used.
The Plastic Flow and Elasticity of Raw Rubber and Raw Rubber Mixes
Authors: Gengrinovich B. I. , Slonimskii G. L. 
Published: February 2011

Abstract
Data have been obtained on the mechanical properties of rubber, two-component rubber-carbon black systems, and loaded raw rubber mixes at various temperatures and under different stresses. The true viscosity and the elasticity modulus of a raw rubber mix depend on the time, temperature, and the magnitude of the applied force ; it is suggested that this is a consequence of the variability of the structure of the mix under stress and on heating.
The Influence of Temperature on The Kinetics of Cut Growth in Vulcanizates
Authors: Gul V. E. , Vilnits S. A. 
Published: February 2011

Abstract
Recently published research has conclusively demonstrated that rupture in vulcanizates represents a process which increases with time. Slow and fast stages of rupture were discerned. Through the use of high speed photography it was found that, in the usual testing of tensile strength, the rate of rupture growth is initially very small but then quickly although intermittently increases. This behavior occurred both in the rupture of specimens which were not cut and in testing specimens that had been previously cut. The effect of a cut has been thoroughly investigated. Studies conducted on the mechanism of rupture in elastomers indicate that the rupture of vulcanizates has much in common with that of brittle solids. Nevertheless there is a significant difference in the mechanism of rupture in elastomeric materials and brittle solids. It was natural, therefore, to expect a significant change in the kinetics of rupture growth in the region of the glass transition temperature. The aim of the present investigation was to follow the change in the kinetics of rupture of vulcanizates through the transition from the rubbery to the glassy state.
Crosslink Density in Polybutadiene
Authors: Howland L. H. , Nisonoff A. , Dannals L. E. , Chambers V. S. 
Published: February 2011

Abstract
1. A method has been developed for the measurement of crosslink density of diene polymers. This method, which involves the use of radioactive chain transfer agents, is applicable to ungelled polymer prepared under a wide variety of conditions so that any polymerization variable can be studied independently. 2. The crosslink density in polybutadiene decreases with decreasing polymerization temperature. At low molecular weight of polymers, the amount of crosslinking varies linearly with the polymerization temperature. 3. The crosslink density of polybutadiene increases with increasing number-average polymer molecular weight. The rate of increase is less for polymer prepared at −18° C than for that polymerized at 5° to 50° C. This means that, in a polymerization, as the average molecular weight increases with conversion the crosslink density increases. However, when the molecular weight is kept constant, by changes in the modifier loading, the crosslink density of polybutadiene appears to be independent of the degree of conversion attained within the range of 0.12–0.48. 4. The crosslink density of a high molecular weight fraction of polybutadiene was not significantly different from that of the whole polymer (from which about 3% of low molecular weight material had been removed). 5. The kind of initiator system does not affect the crosslink density of polybutadiene, providing the initiator loading is not too high. However, if large amounts of initiator are used in the polymerization, 10% or more of the polymer molecules may not contain mercaptan modifier. 6. Tertiary alkyl mercaptans are necessary for the crosslinking studies because they do not appear to give side reactions. Primary dodecylmercaptan and diisopropyl xanthogen disulfide are unsatisfactory for determinations because they appear to add to the double bonds of the polymer molecule in addition to the usual chain transfer reactions. 7. Incomplete emulsification of monomers in some 5° C recipes apparently increased the crosslink density of polybutadiene by retarding the diffusion of monomer into the monomer-polymer particles.
Cis to Trans Isomerization of Polyisoprene
Authors: Golub M. A. 
Published: February 2011

Abstract
Although polybutadiene readily undergoes photochemical or radiation chemical cis to trans isomerization in solution sensitized by bromine atoms or thiyl radicals, no such isomerization has been achieved with polyisoprene. Moreover, although polyisoprene has been isomerized to a variety of resins, no evidence for any cis to trans change in this polymer has been heretofore described. This communication reports the cis to trans isomerization of polyisoprene in solution catalyzed by elemental selenium at temperatures of around 180–200° C. A common structure was obtained having a cis/trans ratio estimated to lie somewhere between 50/50 and 60/40, starting with either the essentially all-cis polyisoprene (Hevea) or all-trans polyisoprene (balata). The mechanism presumably involves π complexing of the polymer double bonds with selenium in the manner depicted for the selenium-catalyzed isomerization of oleic acid and stilbene. A 2–3% solution of Hevea or balata in a suitable high-boiling solvent such as o-dichlorobenzene or tetralin, containing 0.5 g/l powdered selenium, was refluxed under nitrogen for 2–5 hours. Subsequently the solution was cooled, and filtered to remove the selenium which separated out. Methanol was added to the filtered solution to coagulate the polymer, which was washed with alcohol, airdried and its structure analyzed by infrared absorption procedures. The recovered polymers were lower in molecular weight than originally, dropping in a typical case (e.g., Hevea) from a viscosity average molecular weight of about 550,000 to 300,000.
Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates
Authors: Dunn J. R. , Scanlan J. 
Published: February 2011

Abstract
The thermal and photochemical aging of extracted dicumyl peroxide-, TMTD (sulfurless)- and santocure-vulcanized rubber, in presence of a number of metal and alkylammonium dithiocarbamates, has been investigated by measurements of stress relaxation. The dithiocarbamates have a considerable protective action upon the degradation of peroxide- and TMTD-vulcanizates, but they accelerate stress decay in santocure-accelerated vulcanizates. The reasons for this behavior are discussed. It is suggested that the excellent aging properties of unextracted TMTD vulcanizates are due to the presence of zinc dimethyldithiocarbamate formed during vulcanization.
Thermal Degradation of Polyacrylonitrile, Polybutadiene, and Copolymers of Butadiene with Acrylonitrile and Styrene
Authors: Straus Sidney , Madorsky Samuel L. 
Published: February 2011

Abstract
Polybutadiene and a copolymer consisting of 76.5 per cent butadiene and 23.5 per cent of styrene were investigated as to the rate of their thermal degradation. The rates for polybutadiene indicated an activation energy of 62 kilocalories per mole. The copolymer had very high initial rates of degradation followed by a rapid drop, so that it was not possible to obtain a reliable activation energy. Polyacrylonitrile and a copolymer consisting of 31 per cent of acrylonitrile and 69 per cent of butadiene were investigated with regard to the nature and distribution of volatile products, as well as to the rates of their thermal degradation. The rates were very high initially, but dropped rapidly so that it was not possible to determine accurately the activation energy. The acrylo-nitrile-butadiene copolymer showed a decomposition pattern similar to that of polybutadiene. Here, too, the activation energy could not be deduced accurately from the rate curves. Comparative thermal stability in terms of temperature, at which half of the polymer sample is evaporated in 35 minutes of heating, is as follows: 407° C for polybutadiene, 374° C for SBR, 364° C for polystyrene, 360° C for NBR, and 316° C for polyacrylonitrile.
The Swelling Behavior of Natural Rubber Latex
Authors: Allen P. W. 
Published: February 2011

Abstract
The distribution of a swelling agent (methyl methacrylate) among the particles of natural rubber latex has been shown to be nonuniform. Large particles absorb more swelling agent than do small particles. The data are analyzed by means of the thermodynamic treatment of Morton, Kaizerman, and Altier.