bluuebunny/crossref_metadata_2025_split huggingface dataset:
Small-Strain Modulus of Model Trifunctional Polydimethylsiloxane Networks
Authors: Vallés E. M. , Rost E. J. , Macosko C. W. 
Published: February 2011

Abstract
A number of studies to test quantitatively the molecular basis of the theory of rubber elasticity have been performed during the last few years on elastomeric networks of relatively well-known structure. Many of these studies have been done on end-linked networks, for which the number of chains between junctions, their average length, and the functionalities of the junctions could be calculated. Several studies have been with poly(dimethylsiloxane) (PDMS) networks. One of the major controversial points up to now has been the effect of topological interactions between network chains on mechanical properties. Two groups of researchers have come to quite different conclusions about the role of entanglements with respect to their contribution to the elastic modulus. The first group led by Flory considers that the entanglement contribution to the elastic equilibrium modulus is due to the restrictions that topological interactions impose on junction fluctuations among their mean equilibrium position. The second group follows the hypothesis of Langley and Graessley who argue that these interactions are also present along the chain contour. Their support of this thesis is based on the experimental observation of the rubbery plateau modulus GN0 in linear polymers, which is evidence of topological interactions between chains. These interactions would also be present during network formation, and they will be “trapped”, or prevented from relaxing, by the crosslinking process. Thus, these chain-chain interactions can contribute directly to the modulus. Recently, one of us has reviewed most of the results obtained with PDMS networks. This showed that all the experimental data to date are quite consistent and give support to the second approach. In this work, we add to these data some new experiments obtained by crosslinking trifunctional PDMS networks in different states of dilution. The results give additional evidence of the contribution of chain entanglements to the modulus.
The Formation of Crosslink Precursors in the Sulfur Vulcanization of Natural Rubber
Authors: Morrison N. J. 
Published: February 2011

Abstract
With the accelerator MDB and with MBTS-sulfur, the addition of a relatively small amount of the zinc-accelerator complex (1) caused rapid formation of model crosslinks in 2-methyl-2-pentene under conditions in which neither model crosslink precursors nor model crosslinks were formed appreciably in its absence. In the accelerated sulfur vulcanization of natural rubber, zinc complexes promote both the formation and subsequent reactions of crosslink precursors. At 140°C, the reaction of MBTS-sulfur with 2-methyl-2-pentene gives a disulfidic model crosslink precursor derived by substitution entirely at the methylene site. At 150°C, or in the presence of the zinc-accelerator complex (1) at 130–140°C, precursors are derived by substitution at methylene and methyl sites.
The Natural Higher Fatty Acid Soaps in Natural Rubber Latex and Their Effect on the Mechanical Stability of the Latex
Authors: Chen Seong-Fong , Ng Chiew-Sum 
Published: February 2011

Abstract
The natural HFA soaps present in ammoniated NR latex concentrates are derived from the hydrolysis of the saponifiable lipids on the surfaces of the latex particles. A method based on cold extraction of the soaps has been developed for determining the natural HFA soaps in freshly concentrated latices. This method is better than the hot extraction method, which has been shown to cause some hydrolysis of the lipids. The natural HFA soaps in NR latex increase with time and reach a constant value in 3 to 6 weeks. The rate of increase of the soaps is divided into two linear regions and is more rapid in the first 1 to 2 weeks. More than 92% of the natural HFA soaps are adsorbed on the surfaces of the latex particles. This results in an increase in the negative electrical surface charge density of the particles and causes an increase in the mechanical stability of the latex. In fact, the increase in log MST is linearly proportional to the increase in natural HFA soaps in the latex. After the natural HFA soaps become constant, further increase in MST value is likely to be caused partly by the oxygen from the air.
Model Vulcanization of EPDM Compounds—Part I: Structure Determination of Vulcanization Products from Ethylidene Norbornane
Authors: van den Berg J. H. M. , Beulen J. W. , Duynstee E. F. J. , Nelissen H. L. 
Published: February 2011

Abstract
Vulcanization of ENBH (C9H14), a model for ENB containing EPDM rubber, with a system consisting of zinc oxide, stearic acid, sulfur, TMTD, and MBT at 140°C for 1 h yields slightly more than 30 different crosslinked products C9H13-Sn-C9H13 where n=2,3,4, and 5. In all of the products, the original ENBH structure is maintained (no shift of the double bond) and attachment of the sulfur bridge occurs only at the two allylic positions 3 and 9. Monosulfides (n=1) are probably also formed but no structures could be determined. Only small amounts of the MBT-Sn-C9H13 coupling products and noncrosslinked cyclic sulfides are formed.
Halogenation of Butyl Rubber—A Model Compound Approach
Authors: Vukov R. 
Published: February 2011

Abstract
The study of the halogenation behavior of butyl rubber model compounds has brought about a better understanding of the behavior of these systems. It has been established that the presence of methyl groups, in a position B to the reaction site in the butyl rubber model compound, profoundly influences the course of halogenation. Due to the steric hindrance imposed by these groups, both the products of chlorination and bromination deviate from patterns typical of other trisubstituted alkenes. In the case of chlorination, this deviation is demonstrated by the absence of addition products of chlorine across the double bond. In the case of bromination reactions, the change in product distribution is even more dramatic. Thus, substitution products normally not observed in bromination reactions of other trisubstituted alkenes become predominant products found in yields of between 70–90% depending on the precise reaction conditions. The behavior of the butyl model compound appears to be entirely consistent with the behavior of butyl rubber itself; the model compound approach is therefore a valuable tool for use in the basic study of this type of system.
The Postdispersion Coalescence Phenomenon in Polymer-Polymer Blends
Authors: Jang B. Z. , Uhlmann D. R. , Vander Sande J. B. 
Published: February 2011

Abstract
Three novel experimental techniques have been developed to study the phase separation dynamics and morphology of polymer-polymer blends. Samples prepared from different materials by different methods appear to follow the same phase transformation behavior. The minor phase, dispersed as discrete particles, may change its phase morphology by aggregation and coalescence. The aggregation process involves the change in either particle location (small particles may translate) or particle geometry (to reduce interfacial area). Once the interparticle contact is effected, the flattened interface will break and allow for sintering of particles. The particle size distribution is more or less random and tends to broaden with time. The volume fraction of the second phase has a substantial effect on its growth rate. It has been demonstrated that a combination of hot-staged optical microscopy, transmission electron microscopy, high-speed cinematography, and the three novel sample preparation techniques facilitate a detailed study on the late-stage mechanisms of phase separation of polymeric blends.
Pilot-Scale Guayule Processing Using Countercurrent Solvent Extraction Equipment
Authors: Hamerstrand G. E. , Montgomery R. R. 
Published: February 2011

Abstract
Conventional oilseed processing technology and equipment were successfully utilized to extract rubber from guayule shrubs that had been pretreated to render the rubber accessible to solvent action. When the chopped and ground shrubs are subjected to sufficient shear to rupture cell walls and form agglomerates of material, they can be handled readily in the essentially unmodified percolation, solvent extraction equipment. Although some of the parameters associated with the solvent system have not, as yet, been optimized, rubber recoveries in excess of 80% were achieved with both freshly harvested “lush” shrubs and shrubs that had been field-dried and stored several weeks before processing.
The Deresination of Guayule: A Physical Model. Part I: Effect of Water and Temperature on the Diffusion Coefficients
Authors: Budiman S. , McIntyre D. 
Published: February 2011

Abstract
1. The nature of the static deresination of guayule worms is complicated by the presence of moisture. In analogy with hevea latex coagulum, the moisture occurs in pockets and channels between the rubber agglomerates which contain the solubilized resin, and it enhances desorption of the resin into a solvent. At moisture above a critical level (around 10 wt.%), the pockets are likely to be interconnecting, thus providing easy access for the water-miscible solvent to the interior of the worms through an interchange process with the moisture. 2. Assuming minimal resistance at the surface of the worms, the static deresination is thought to take place in four consecutive steps: (a) the penetration of solvent into the pores of the worms made up of moisture pockets and channels, (b) the absorption (swelling) of the solvent into the rubber phase and subsequent transfer of the solubilized resin from the rubber phase to the solvent, (c) diffusion of the resin as a solute in the solvent through the swollen rubber phase to the internal surface in the pores, and (d) diffusion of the resin solute through the pores to the surface of the worms. 3. The deresination performance of acetone is much better than that of 95% ethanol. 4. The diffusion coefficient of acetone in the rubber phase is shown to be almost one order of magnitude greater than the diffusion coefficient for overall desorption of resin into acetone. This indicates that the rate-limiting step is the diffusion of the resin through the rubber phase to the internal surface of rubber agglomerates inside the pores.
Mechanism and Theories of Rubber Adhesion to Steel Tire Cords—An Overview
Authors: van Ooij W. J. 
Published: February 2011

Abstract
An overview is given of the mechanism and theories of adhesion of brass-plated steel cords to rubber. The literature on this topic in the period 1979–1983 is reviewed. Although the actual type of bond between the interfacially formed copper sulfide film and the cured network still has not been identified conclusively, this aspect of rubber-brass adhesion is becoming rather irrelevant since the literature is unanimous that bond failure seldom occurs adhesively, i.e., between CuxS and rubber, but usually cohesively within the sulfide film or adhesively at the interface sulfide-substrate. A model is described in which most of the recent findings are incorporated. In this model, brass develops a high bond strength to NR as a result of the in situ growth of a thin (≤50 nm) copper sulfide film onto the brass during the early stages of the cure before crosslinking sets in. This sulfide film has good adhesive and cohesive properties but is, on the other hand, so porous that rubber molecules become entangled in this film (interlocking model). ZnS or FeS are considered nonbonding because they lack the microporosity required for interlocking. Synchronization of sulfide growth and rubber cure is not required. The major prerequisite is that sulfide film growth has been completed before cross-linking begins. Previous rubber oxidation theories and the effect of CuxS on crosslink density of rubber adjacent to the cord surface are also discarded for lack of experimental evidence. Ultimate bond strength and bond durability are determined by cord and by compound properties. Optimum cord parameters are predicted by the model as a thin brass coating with a high concentration of diffused iron, a low copper content (60–65%) and a thin but very homogeneous ZnO surface layer which is passivating and which contains copper atoms. Copper oxides are undesirable. The homogeneous ZnO film improves the cords' corrosion resistance, the included Cu atoms are required for rapid initial CuxS formation and prevention of non-bonding ZnS formation. The major compound parameter is the sulfur-to-accelerator ratio. There is evidence that brass is sulfidized by intermediates of the type R-S-Sy-NR where R is an accelerator fragment, rather than by free sulfur. The properties of the CuxS film, such as adhesion, cohesion and stability in corrosive environments depend on the type of CuxS formed. High values of y in the intermediate lead to good CuxS films, low values produce poor films, regardless of the quality of the cord.
The Shear and Elongational Flow of Polymer Melts Containing Anisometric Filler Particles; Part I
Authors: Utracki L. A. 
Published: February 2011

Abstract
There is a dichotomy in the information on flow of anisometric particles. Most of the fundamental studies only consider dilute suspensions in Newtonian liquids, although some authors venture into a semiconcentrated (two-body collision) region and others into pseudoplastic liquids. These publications provide a solid base for understanding the behavior of the high-concentration systems of industrial importance, but without the desirable quantification. The description of these systems is experimental or, at best, qualitative, via simplified constitutive models. At high concentration of anisometric particles, one must consider: yield stress, plug flow, shear segregation, and a change of relaxation spectrum. There is no simple method to correlate the steady-state and dynamic test data. The magnitude of the stress overshoot in transient tests increases with concentration and deformation rate. While the normal stress increases with concentration, the die swell decreases. The yield stress in elongation is larger than that in shear, and the maximum strain at break initially increases with addition of filler, goes through a maximum, and falls to very low values at high loading. The orientation of anisometric particles can be accomplished in converging and diverging, i.e., extensional flow. In a simple shear field, the effect depends on the rate, concentration, and matrix viscosity—in general, shearing causes disorientation of aligned particles. All these effects influence melt processing. For extrusion, the plug flow narrows the range of processing variables, increases the solid-conveying zone, and may lead to flow instability. In injection molding, gating, pattern of orientation (modulated by solidification), and the transient effects depend on the specificity of the rheological behavior of the filled pseudoplastic liquids.
Polymer Self-Diffusion in Entangled Systems
Authors: Tirrell Matthew 
Published: February 2011

Abstract
This article has focused on work in the last several years, a period during which theoretical insights and experimental techniques pertaining to polymer self-diffusion in entangled systems have advanced enormously. The point has been to lay out for the reader the means by which this information has been developed and to lay out the available information itself. The objective has been to facilitate comparisons regarding use and applicability of techniques, quality, and interpretations of data and the trends present in the various data. Presentation of the information in this style leads to a few definite conclusions and a larger number of problems which come more sharply than before into focus as ripe for continued study. Specific conclusions which seem reasonable at this point are: The molecular weight dependence of Ds is, in entangled systems, an inverse square law, consistent with the prediction of the reptation model. The self-diffusion coefficient becomes quite insensitive to the matrix molecular weight Mm at sufficiently high Mm. The variation of Ds with concentration in entangled solution is very strong, considerably higher than the c−3 law suggested by scaling arguments with the reptation model. Free volume effects on the monomeric friction coefficient are at the root of this. Outstanding problems include the following areas and questions: It is necessary to ascertain why there is, in melt Ds data, a reproducible discrepancy between NMR data and those data obtained via other methods. Is NMR sensing the slowest translational mode of motion? Is the marking which is necessary for all the other techniques affecting the measurements? In solution data, the origin of the QELS “slow mode” and the marked disparity between these data and those from other methods must be determined. Critical conditions for the onset of entangled or reptation behavior (in terms of M and c) in Ds must be studied and defined more clearly both experimentally and theoretically. Is the observation that Ds∼M−2 down to unexpectedly low molecular weight an indication that diffusion proceeds via a reptation-like mechanism even for molecular weights which show no other manifestation of entanglement, OI is there another set of conditions which produce Ds∼M−2 scaling? Incisively designed experiments to study matrix and molecular architecture effects seem likely to be most fruitful. Stars, combs, rings, and polydisperse samples hold new information on diffusion mechanisms. A comprehensive experimental and theoretical picture of polymer self-diffusion will advance the state of practice of a wide range of technological applications. The current status of available diffusion information is good enough that the time scales of many practical processes can be predicted approximately. More precise predictions of, for example, diffusion-controlled reaction rates, await the availability of more extensive data and of the resolution of some of the remaining questions and discrepancies highlighted here.
Recent Advances in Controlled Grafting of Elastomers
Authors: Quirk Roderic P. 
Published: February 2011

Abstract
This review describes recent results for preparing graft copolymers with controlled structures. In general, the macromonomer approach appears to be the most promising method for preparation of graft polymers with well defined structures. Not only can macromonomers be prepared using radical, cationic, or anionic polymerization procedures, but the resultant macromonomers can be polymerized using these same methods. Obviously, the macromonomer functionality must be high and well defined. In addition, the average chain length and chain length distribution should be well characterized. In principle, the macromonomer approach can provide comb-type graft copolymers with a random distribution of well characterized graft branches. However, the actual copolymerization of the macromonomers with a variety of comonomers requires careful examination under a variety of reaction conditions before that expectation can be realized. These macromonomers provide an excellent opportunity to examine the effects of chain length on the problem of heterogeneity (i.e., phase-separation) which is expected and found in many grafting systems. “Grafting-from” reactions also should provide graft polymers whose structures are more amenable to prediction and analysis. Like the macromonomer method, it should be possible to eliminate the presence of unwanted homopolymer using this method. However, much more research is required before the generality and value of this method can be evaluated. In conclusion, this era appears to be an exciting time for graft polymerization research. The potential exists for the preparation of model graft polymers with precise structural definition using the methods described herein. This development will, at last, provide graft polymers which can be used to define the relationships between the structure, morphology, and properties of these materials.
Elastomeric Ionomers
Authors: MacKnight W. J. , Lundberg R. D. 
Published: February 2011

Abstract
Ionomers are a class of materials which are emerging as important commercial polymers but yet have many intriguing scientific characteristics. Typically, ionomers consist of a low level of inorganic salt groups pendent to a polymer chain. For this article, we will consider ionomers to possess a maximum level of about 10 mol% ionic groups pendent to a hydrocarbon polymer chain. While this definition is somewhat arbitrary, it is one generally accepted in the polymer field. Unlike homogeneous polymer systems, the pendent ionic groups can interact to form ion-rich aggregates contained in the nonpolar polymer matrix. The resulting ionic interactions can have a major influence on polymer properties and applications which have made this area an extremely fertile one for research and development.
Improvement of Sour Gasoline Resistance for Epichlorohydrin Rubber
Authors: Mori Kunio , Nakamura Yoshiro 
Published: February 2011

Abstract
The resistance to sour gasoline of epichlorohydrin-ethylene oxide terpolymers with allyl groups was studied for various curing systems, antioxidants, and allyl contents. A rubber with 5% of allyl content, cured by a triazine trithiol-MgO-CaCO3 system, showed the best resistance, probably due to the presence of thiol groups in the crosslinks.
The Effect of the Structure of Sulfur—Containing Silane Coupling Agents on Their Activity in Silica-Filled SBR
Authors: Vondráček Petr , Hradec Miroslav , Chvalovský Václav , Khanh Hua Dang 
Published: February 2011

Abstract
A comparative study of α- and γ-functiona1 sulfur-containing silane coupling agents in the silica-filled SBR cured by the conventional sulfur system showed that the influence of the silanes on the vulcanization kinetics and their coupling effectiveness depends on the structure and positioning of the rubber-reactive groups. All the tested silanes containing mercapto or sulfide functional groups led to an improvement in tensile properties and affected the cure kinetics of the system employed.