Mechanical properties of clay coating films containing styrene–butadiene copolymers

The mechanical properties of clay-based pigmented coating films bonded with a series of carboxylated styrene–butadiene latex binders have been investigated. The in-plane tensile strength and the elongation at rupture increased with increasing amount of polymeric binder. It is suggested that this is due to an improvement in stress transfer through the structure. The mechanical behavior of the films was furthermore found to be strongly related to the properties of the polymeric binder at the usage temperature. In torsional pendulum experiments an increase in the glass transition temperature of the polymeric binder was observed when it was incorporated in the coating film. This is interpreted as being the result of a decrease in the segmental mobility of the polymer molecules due to the presence of the clay particles, i.e., due to the interaction between the clay pigments and the binder. The interaction was, however, less noticeable in experiments using an NMR (nuclear magnetic resonance) technique. If the clay was replaced by calcium carbonate, a strong interaction, as measured using NMR, was observed between CaCO₃ and the styrene–butadiene polymer, although the in-plane mechanical strength and ductility were reduced. A structural model accounting for some of the observed differences in mechanical behavior between clay-based and CaCO₃-based coating films is suggested.     

Studies of interaction in silica/styrene–butadiene copolymers

Adsorption, bound rubber, mechanical properties, and electron microscopy determinations were carried out in silica/styrene–butadiene copolymers. These studies reveal equivalent trends with varying copolymer composition. Thus, when the copolymer is richer in styrene, adsorbance and bound rubber increase, the stress softening effect becomes more remarkable, and silica is more uniformly dispersed in the elastomeric matrix. These results indicate that polymer–filler interaction becomes stronger when the content of styrene in the elastomer is increased. This interaction does not appear to be explicitly reflected in the other mechanical properties studied.     

Stress–strain optical study of styrene–butadiene and ethylene–propylene rubbery copolymers

Birefringence–temperature behavior at constant stress during cooling and heating of styrene–butadiene and ethylene–propylene copolymers between ?120°C and +60°C was investigated. Copolymer composition, thermal treatment, and stress levels were shown to have a pronounced effect on the photoelastic properties.     

Anisotropy of styrene–butadiene rubber

Anisotropy of styrene–butadiene rubber (SBR) was investigated. The anisotropy of the copolymer varies linearly with the styrene content and the ultimate value coincides with that of polystyrene at elevated temperature. From these facts, the transverse configuration of the pendant phenyl group is estimated irrespective of the styrene content of SBR.     

Short-fiber-reinforced styrene–butadiene rubber composites

Processing characteristics, anistropic swelling, and mechanical properties of short-jute-fiber-and short-glass-fiber-reinforced styrene–butadiene rubber (SBR) composites have been studied both in the presence and absence of carbon black. Tensile and tear fracture surfaces of the composites have been studied using scanning electron microscopy (SEM) in order to assess the failure criteria. The effects of bonding agent. carbon black, jute fiber, and glass fiber on the fracture mode of the composites have also been studied. It has been found that jute fiber offers good reinforcement to SBR as compared to glass fibers. The poor performance of glass fibers as reinforcing agent is found to be mainly due to fiber breakage and poor bonding between fiber and rubber. Tensile strength of the fiber–SBR composites increases with the increase in fiber loading in the absence of carbon black. However, in the presence of carbon black a minimum was observed in the variation of strength against fiber loading. SEM studies indicate that fracture mode depends not on the nature of the fiber but on the adhesion between the fiber and the matrix.     

Improvement of properties of silica‐filled styrene–butadiene rubber compounds using acrylonitrile–butadiene rubber

Since silica has strong filler–filler interactions and adsorbs polar materials, a silica‐filled rubber compound has a poor dispersion of the filler and poor cure characteristics. Improvement of the properties of silica‐filled styrene–butadiene rubber (SBR) compounds was studied using acrylonitrile–butadiene rubber (NBR). Viscosities and bound rubber contents of the compounds became lower by adding NBR to the compound. Cure characteristics of the compounds were improved by adding NBR. Physical properties such as modulus, tensile strength, heat buildup, abrasion, and crack resistance were also improved by adding NBR. Both wet traction and rolling resistance of the vulcanizates containing NBR were better than were those of the vulcanizate without NBR. The NBR effects in the silica‐filled SBR compounds were compared with the carbon black‐filled compounds. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1127–1133, 2001     

Viscoelastic properties and film morphology of heterogeneous styrene–butadiene latexes

Heterogeneous carboxylated styrene–butadiene (S/Bu) latexes were prepared by a twostage emulsion polymerization process, using three PS seeds with different molecular weights. The second-stage polymer was a copolymer with a fixed S/Bu ratio of 1 : 1 and a methacrylic acid (MAA) content of either 1 or 10 wt %. Morphological studies by transmission electron microscopy (TEM) as well as studies of the viscoelastic properties by mechanical spectroscopy have been performed on films prepared from the latexes. The studies showed that the glass transition temperature, T_g, of the second-stage polymer was considerably affected by copolymerization with MAA. An increase in the MAA content in the second-stage polymer increased the T_g of this phase significantly. Addition of DVB as a crosslinking agent in the preparation of the PS seed phase substantially increased the rubbery moduli of the films, whereas the glass transition temperature of the second-stage polymer was unaffected. On the other hand, the presence of a chain transfer agent reduced the glass transition of the second-stage copolymer containing 1 wt % MAA dramatically, whereas the rubbery modulus was unaffected. When the MAA content was increased to 10 wt % the influence of the MAA monomer had a dominating effect on T_g. Latexes containing 10 wt % MAA had T_g values close to each other, regardless of chain transfer agent present in the second-stage polymerization. It was found that the morphology of the latex particles influenced the rubbery modulus of the films. The presence of irregularly shaped seed particles in samples prepared from a crosslinked PS seed had a considerable reinforcing effect on the films, whereas spherical seed particles originating from core–shell particles had a less reinforcing effect. © 1996 John Wiley & Sons, Inc.     

Dichlorocarbene modification of styrene–butadiene rubber

Dichlorocarbene-modified styrene–butadiene rubber (SBR) prepared by the alkaline hydrolysis of chloroform using cetyltrimethylammonium bromide as a phase-transfer agent resulted in a product that showed good mechanical properties, excellent flame resistance, solvent resistance, and good thermal stability. The activation energy for this chemical reaction calculated from the time–temperature data on the chemical reaction by the measurement of the percentage of chlorine indicated that the reaction proceeded according to first-order kinetics. The molecular weight of the polymers, determined by gel permeation chromatography, showed that chemical modification was accompanied by an increase in molecular weight. The chemical modification was characterized by proton NMR, FTIR studies, thermogravimetric analysis, and flammability measurement. Proton NMR and FTIR studies revealed the attachment of chlorine through cyclopropyl rings to the double bond of butadiene. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 153–160, 1998     

Relaxation properties of styrene–butadiene block copolymers. A comparative study of thermally stimulated currents and thermoluminescence

The thermoluminescence (TL) and thermally stimulated current (TSC) curves observed in styrene—butadiene block copolymers, undoped and doped with different dyes, have been compared in order to test to what extent the thermoluminescence phenomenon can be correlated with intrinsic relaxation properties of the macromolecular chains. Generally, good agreement has been found between the two types of curves. However, the observance of a significant shifting of TL peaks as a function of the nature of the added dye shows that strict correspondence between the kinetics of the two phenomena is unlikely. Consequently, it seems actually dangerous to deduce the characteristic relaxation parameters of the polymer from TL curves.     

The influence of styrene–butadiene diblock copolymer on styrene–butadiene–styrene triblock copolymer viscoelastic properties and product performance

The effects of the styrene–butadiene (SB) diblock copolymer on the viscoelastic properties of styrene–butadiene–styrene (SBS) triblock copolymers were examined in both in the the neat state and within specific product applications. The addition of the SB diblock copolymer into a pure SBS triblock copolymer resulted in a significant decrease in the plateau storage modulus and a quantitative linear rise in tan delta. In a pure triblock, in which all endblocks are anchored in polystyrene domains, all entanglements are physically trapped. The SB diblock embodies untrapped polybutadiene endblocks that are able to relax stress by chain reptation through the rubbery polybutadiene matrix. The SB diblock copolymer quantitatively lowered the microphase separation temperature (MST) of the SBS triblock copolymer. These changes in linear viscoelastic behavior manifest themselves into a reduction in the efficiency and performance of the SBS triblock copolymer in asphalt pavement binders and hot-melt adhesive blends. Specifically, the SB diblock diminished the complex shear modulus and elasticity of a polymer-modified asphalt, which translated into lower predicted rutting specification values. The increase in diblock content altered the viscoelastic response of the hot-melt adhesive blend, translating into a reduction in the shear holding power and shear adhesion failure temperature. The lack of network participation, coupled with the relaxation of the polybutadiene endblocks, accounts for the lower strength and greater temperature susceptibility of the diblock-containing systems. © 1995 John Wiley & Sons, Inc.     

Structure of some styrene–divinylbenzene copolymers

Structures of copolymers of styrene and divinylbenzene (50% crosslinking degree) prepared in suspension polymerization in the presence of mixtures of nonsol (heptane or decane) and sol (toluene or tetralin) diluents were investigated. The studies showed that the diluents enriched with nonsol solvents resulted in an increase of pore volumes and posities for the prepared copolymers. The sol diluents affected mainly the gel regions of the polymer matrices. Isotropic swelling of the matrices prepared in the presence of toluene is the opposite of the effect observed for tetralin family copolymers. The virtual difference of both kind of matrices was demonstrated in the sorption of phenol. The tetralin family copolymers were characterized by a prolonged time for column breakthrough. © 1995 John Wiley & Sons, Inc.     

Use of mid‐ and near‐infrared techniques as tools for characterizing blends of copolymers of styrene–butadiene and acrylonitrile–butadiene

There is increased technological interest in using blends of various dissimilar elastomers in applications for which service, material availability, or cost of a single elastomer do not provide the necessary processing, vulcanizate, or economic properties. The properties of these polyblends are sensitive to small variations in the amounts of the individual polymers used. Accurately estimating the elastomer composition of blends is of vital importance to the elastomer industry. This study illustrates the feasibility of using mid-infrared (MIR) and near-infrared (NIR) spectroscopy to estimate the amount of styrene–butadiene and acrylonitrile–butadiene copolymers in blends composed of varying ratios of the two elastomers. Sometimes it is difficult to obtain a film of an elastomer amenable to IR analysis; to address this problem, several techniques were developed in this study [MIR transmission of a film, attenuated total internal reflection (ATR)-FTIR of a chunk, and NIR using a fiber-optic probe]. A plot of the absorbance ratio (absorbance of the characteristic peak for styrene–butadiene rubber or acrylonitrile–butadiene rubber/absorbance of the CC stretching vibration of polybutadiene) versus the amount of each elastomer in the blend was used to predict the blend composition. In addition, the blends were also characterized by ATR-FTIR using a plot of the characteristic peak absorbance versus the polymeric content for a series of standards. A partial least-squares algorithm was used to develop a calibration curve for the NIR region. Finally, the accuracy of the test methods developed in this work is compared to results obtained by pyrolysis-GC/MS and thermogravimetric analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88:1653–1658, 2003     

Correlation between microstructure and physical properties in styrene–ethylene copolymers

The structural organization and the physical properties of a new copolymer styrene–ethylene have been analyzed. The composition was 80% of ethylene units, corresponding to 52% in weight, with a distribution of styrene units in the chain implying the absence of styrene–styrene sequences. The length of the polyethylene chains, limited by the insertion of the phenyl group, is not sufficient to allow good crystallization, and in fact the copolymer shows a very low crystailinity, of the order of 5–10%, and a broad melting range, with a peak centered at 120°C. The small crystalline domains are segregated into an amorphous matrix, producing a thermoplastic elastomer. The mechanical properties at large deformation were analyzed at different temperatures. The copolymer shows good elastic properties, in terms of deformation reversibility as well as of energy dissipation in the hysteresis cycles. Also the stress level and the elastic recovery are very good, if compared with others thermoplastic elastomers. © 1995 John Wiley & Sons, Inc.     

Epoxidation of styrene–butadiene block polymers. II

Epoxidation of styrene–butadiene block polymers considerably improves their resistance to hydrocarbon oils. Use of peroxyformic acid generated in situ appears to be simple and practical. Although no problems exist when the reactions are carried out in toluene, polymer molecular weight and reactant stoichiometry are important in determining the properties of polymers epoxidized in cyclohexane. In fact, epoxidations in cyclohexane of linear and tapered block polymers of molecular weights in excess of 60,000 with peroxyformic acid invariably lead to gelation. Replacing half or more of formic acid with acetic acid, however, alleviates the problem without adversely affecting the tensile or oil resistance of the resulting polymers. This recipe has also been successfully applied to the epoxidation of divinylbenzene-coupled styrene–butadiene radial block polymers.     

Diffusion of radioactively tagged penetrants through random and block styrene–butadiene copolymers and filled cis-polybutadiene

The diffusion of radioactively tagged n-hexadecane in trace amounts has been studied in 22 random styrene–butadiene (SBR) copolymers with different styrene contents and butadiene microstructures; in several SBR block copolymers with different average block lengths (also diffusion of tagged 1,1-diphenyl ethane); in a triblock SBR copolymer cast from different solvents and also molded at elevated temperature; and in cis-polybutadiene filled to different extents with carbon black, calcium carbonate, and microglass spheres. The diffusion coefficient in random SBR copolymers decreased with increasing content of styrene and/or vinyl configuration and could be correlated with fractional free volume on the basis of linear additivity of the cis, trans, vinyl, and styrene moieties. In SBR block copolymers, the diffusion coefficient increased with increasing average block sequence length. For the triblock copolymer, the diffusion coefficient was approximately the same for samples molded or cast from solvents which are good for polybutadiene, but was far smaller for a sample cast from ethyl acetate, in which the polystyrene domains are probably lamellar. The effect of fillers on diffusion in cis-polybutadiene was compared with calculations on the basis of several theoretical models.     

Flammability and degradation characteristics of styrene–butadiene rubbers

Uncured styrene–butadiene gum, a known cured composition, and four SBR beltings used in underground coal mining were subjected to thermal oxidative degradation in static and dynamic systems. The room temperature volatiles produced under the static conditions at 370°C were identified and quantitated. Monomers and their interaction products were liberated by the raw gum; the cured composition formed together with the above products materials traceable to the curing ingredients. The four beltings gave a large spectrum of products; an attempt was made to correlate these with possible components used in belts manufacture. In the dynamic system, the occurrence of glow, the rate of smoke generation, and char yields were determined at 400°C and 500°C. None of the materials glowed at 400°C. At 500°C, the raw gum volatilized completely, and the cured rubber and two beltings glowed. One of the beltings, which failed to glow, liberated the smallest quantity of toxic products.     

Epoxidation of styrene–butadiene block polymers. I

A styrene–butadiene–styrene (20–60–20) linear block polymer was epoxidized in toluene and cyclohexane solutions with peroxyformic acid generated in situ. The epoxidized polymer, containing about 8% oxygen, exhibits greatly improved resistance to ASTM oils. It can be readily compounded with carbon black, and the unvulcanized stock is found to be comparable to vulcanized polychloroprene and nitrile rubber in tensile strength and resistance to ASTM oils and certain chemicals.     

High‐speed photocrosslinking of thermoplastic styrene–butadiene elastomers

Photoinitiated thiol/ene polymerization was used to crosslink a triblock styrene/butadiene/styrene (SBS) polymer of low vinyl content (8%). The crosslinking process was followed by infrared spectroscopy (loss of unsaturation), insolubilization, swelling, and hardness measurements. The photogenerated thiyl radicals react with both the vinyl and the 2‐butene double bonds of the copolymer. Concentrations of less than 1 wt % in the trifunctional thiol crosslinker and in the acylphosphine oxide photoinitiator proved to be sufficient to create, within 0.5 s, a permanent chemical network in the elastomeric phase. This UV‐curing technology was successfully applied to crosslink rapidly commercial SBS–Kraton® thermoplastic elastomers. It proved also effective in the case of the much less reactive triblock styrene/isoprene/styrene (SIS) polymer which contains no vinyl double bonds. The thiol/ene polymerization was shown to be a much more efficient process to crosslink SBS and SIS thermoplastic elastomers than was the copolymerization of the rubber double bonds with a diacrylate monomer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1902–1912, 2000     

Molecular weights of styrene–maleic anhydride copolymers

A dual-calibration method for the determination of molecular weights and molecular weight distribution of styrene–maleic anhydride copolymers (S/MA) by gel permeation chromatography (GPC) is introduced. It might be applicable to copolymers of other type. A linear relationship of intrinsic viscosity [η] and weight-average molecular weight (M?_w) for unfractionated S/MA in tetrahydrofuran (THF) at 25°C can be expressed by the equation The maleic anhydride content of the copolymers ranges from 5 to 50 mole-%, and the M?_w range is from 2 × 10⁴ to 7 × 10⁶. The plot of log [η] M?_w versus GPC elution volume of the S/MA copolymers falls on the same curve as that of the polystyrene standards in THF.