Styrene-isoprene Copolymers Research Articles

The effect of lubricant viscosity model with improver on friction and lubrication of piston skirt-cylinder liner conjunction

PurposeThis paper aims to investigate the effect of lubricant viscosity model with improver on friction and lubrication of piston skirt-cylinder liner conjunction.Design/methodology/approachA dynamic calculation model is established for the piston skirt-cylinder liner conjunction of a heavy-duty commercial diesel engine, to explore the effects of two kinds of lube oil viscosity models named after polyalkyle-metacrylate-1 (PAMA1) and styrene-isoprene-copolymer (SICP) improvers on the maximum oil film viscosity, the minimum oil film thickness, the peak oil film pressure, the maximum shear rate, the friction force and the total friction power loss.FindingsThe variation trends with the crank angle of the above parameters are not changed with the difference of improvers, while obvious numerical differences are found except the maximum oil film pressure. The minimum oil film thickness and maximum shear rate of PAMA1 are larger than that of SICP, the maximum oil film viscosity of SICP is larger than that of PAMA1, which indicates that the shear-thinning effect of PAMA1 is greater, the maximum friction force on the piston of SICP is larger than that of PAMA1, and the total friction power consumption is also larger, the average friction power consumptions of SICP and PAMA1 are 385.4 and 262.8 W, respectively, with the relative difference of 31.8 per cent.Originality/valueThe influence of different lubricating oil additive models on the lubrication and friction of piston skirt-cylinder liner conjunction is simulated and analyzed.

Rheological Properties of Hot Melt Pressure Sensitive Adhesives (HMPSAs) Based on Styrene–Isoprene Copolymers, Part 3: Rheological Behavior of Different Block Copolymers With High Diblock Content

ABSTRACT The processing and application properties of hot-melt pressure-sensitive adhesives (HMPSA) are governed, to a large extent, by their rheological properties. Coating of the HMPSA is performed at high temperatures in the molten state. At room temperature, the adhesive satisfies the Dahlquist criterion and, consequently, has permanent tack. We have particularly studied the full formulations based on triblock and diblock copolymers, and also those based on newly designed molecules, such as tetrablock or radial copolymers. We have demonstrated in the previous articles of this series that, for these systems, the volume fraction of the free polyisoprene is the most important parameter that drives the tack performances by controlling the level of the secondary elastic plateau modulus observed in the low-frequency range. To improve the end-user properties, we have increased the diblock content in the blends. We describe here the dynamic mechanical properties, at room temperature, of the pure copolymer blends (i.e., without addition of a tackifying resin) and the full HMPSA formulations. We focus particularly in this article on blends that contain a high diblock content. The effect of the morphology of the diblock copolymer on the rheological behavior of the adhesive is discussed in detail. Finally, we propose a model, based on molecular dynamics concepts, which describes the rheological behavior in a very wide range of frequencies for all copolymers and full formulations of the study.

Effects of styrene‐isoprene copolymer glass fiber coatings on woven glass cloth epoxy composite performance

AbstractWoven glass‐epoxy composites were prepared from mats that had been treated in a variety of ways. Fibers were coated with a commercial sizing, no sizing, and a surfactant coating. In addition, fibers were coated with styrene‐isoprene copolymers at varying molar ratios using a novel technique termed admicellar polymerization. Dynamic contact angle measurements were used to quantify the effect of the different coating techniques on the fiber, while dynamic mechanical analysis (DMA) and flexural testing were used to characterize the cured composites. Wetting studies conducted with EPON 828 resin revealed no difference in wetting for the polymer‐treated fiber compared to the commercially‐treated fiber. Aqueous wetting results were consistent with a surfactant layer adsorbed on the polymer treated and surfactant treated fiber surface. DMA established that both the polymer and surfactant treatment depressed the alpha transition temperature of the composite and suggested an interpenetrating network existed at the fiber‐matrix interface. Flexural strength testing showed the properties of the composites made from surfactant‐treated and polymer‐treated glass fibers were comparable to composites made from commercially‐sized fibers and exceeded the flexural strength of the composite made from glass fibers without sizing.

Elastomeric sizings for glass fibers and their role in fiber wetting and adhesion in resin transfer molded composites

Mold fill velocities of 0.067 cm3/s and 2.66 cm3/s were used to impregnate glass fiber preforms with different architectures and sizing types in two force-controlled resin transfer molding (RTM) fixtures. The fabrication of disk-shaped parts at high molding speed and high post-cure fill pressure was proven successful in reducing the amount of flow-induced defects for reinforcements with a random nonlayered structure. Investigations on the effect of fiber/matrix interface modification with controlled-thickness elastomeric films obtained by the admicellar polymerization technique were carried out to assess the structural integrity levels attained with these less expensive polymeric sizings. In particular, parts reinforced with fibers coated with a thin film of styrene-isoprene copolymer performed significantly better than the uncoated control samples in the tensile and flexural tests. For the same sizing type, the interlaminar shear strength was more than 30% higher than the desized composite and compared statistically to the adhesion level exhibited by commercially sized reinforcements. Greater data scatter and poorer adhesion performance was observed for those composites containing fibers with a thin polystyrene coat. We infer that beneficial effects of a nanometer-thick elastomer interlayer are more evident when extensive cooperative segmental motions take place, that is, when the surface glass transition temperature of the sizing is far below the room temperature. These results have implications for composite manufacture applications involving tailored interfaces with flexible sizings.

An experimental investigation into the dimension-sensitive viscosity of polymer containing lubricant oils in microchannels

Abstract In many lubrication processes, lubricating oils containing polymer additives are subject to high shear rate through very small clearance channels. While the influence of shear rate on the performance of these lubricants has been well examined, very little is known about the effects of channel size. In this study a specially designed microchannel viscometer has been used to experimentally characterize the influence of channel height on the effective viscosity of oil lubricants with two different polymer additives (a radial hydrogenated styrene–isoprene copolymer and an A–B–A block ethylene–propylene copolymer) commenly used as viscosity index (VI) modifiers. The mass concentration of the polymer solutions ranged from 0.5% to 1.5% in this study. The viscosity was measured over a range of shear rates in steel slit microchannels with heights of 4.5, 7 and 11.5 μm, respectively. For all solutions a significant viscosity dependence on channel size was observed. In the higher shear rate range the smaller channels exhibited a lower viscosity while in the lower shear rate range all solutions exhibited a significant increase in viscosity. Generally, this observed increase in viscosity is more dramatic in the smaller channels. Possible causes of these behaviors were discussed in this paper.

Step-scan FTIR and photoacoustic detection to assess depth profile of photooxidized polymer

The extent of degradation of photooxidized materials must be determined precisely in order to evaluate its lifetime. Generally, an heterogeneous degree of oxidation is recorded through the sample thickness. Because, oxidation can be much more important near the surface, a photoacoustic (PA) detection of the IR spectrum of the material appears particularly well adapted. A PA detector attached to a step-scan (SS) FTIR spectrometer was used to record the IR spectrum of a photooxidized styrene–isoprene copolymer. In order to evaluate the ability of this technique to perform a depth profile of an oxidized material, the sample was also analyzed using transmission micro-FTIR analysis of cross-sectioned layers. These two techniques allow a complete analysis of the material from its surface to its core. Our main finding is that a PA detection is more suitable to determine the superficial extent of degradation, whereas the micro-FTIR appears more adapted to analyze the bulk properties of the material.

Photooxidation mechanism of styrene–isoprene copolymer: evolution of the profile of oxidation according to the composition

The photooxidation of styrene–isoprene copolymers is investigated on the basis of infrared analysis of irradiated films. The results show that the polystyrene segments are stable under irradiation and degradation results only from the photooxidation of the polyisoprene segments. Oxidation of polyisoprene results in chain scissions and generates various carbonylated photoproducts. A three-dimensional structure is formed by cross-linking reactions resulting from additions on the double bonds and formation of ether linkage. In order to determine the influence of the polyisoprene content on the mechanism and the kinetics of oxidation, different compositions have been tested. The extent of degradation is found to be proportional to the polyisoprene content but the rate of photooxidation is constant whatever the composition. The distributions of the oxidation products within the polymer are similar whatever the composition. This behavior can be attributed to the incompatibility between the polyisoprene and the polystyrene segments, which leads to a phase demixion and the formation of nodules. Each nodule can be considered as an independent photochemical reactor.

Depth Profiling of Photooxidized Styrene-Isoprene Copolymers by Photoacoustic and Micro-Fourier Transform Infrared Spectroscopy

Transmission micro-FT-IR (Fourier transform infrared) and photoacoustic (PAS) FT-IR analysis have been combined to determine the oxidation profiles of various photooxidized polyisoprene-polystyrene copolymers. It is shown that only the polyisoprene phase is oxidized. The front photooxidized layers (0–22 μm) are analyzed by PAS, while the bulk (11–150 μm) is characterized by cross-sectional analysis of microtomed layers. A good agreement between the two methods is found in the region where the analyzed layers overlap (11–22 μm). The extent of the oxidation was determined by monitoring the ratio between the intensity of the carbonyl absorbance at 1718 cm−1 and the absorbance at 1600 cm−1. The results given in this article show that PAS FT-IR can be a rapid and nondestructive technique of quantitative characterization of the surface degradation of aged polymers.

Determination of Calcium, Zinc, and Phosphorus in multigrade crankcase oils by XRF, DRES, and ICP‐AES

AbstractThe effect of viscosity index improvers such as styrene‐isoprene copolymer (SICP), styrene‐butadiene copolymer (SBCP), ethylene‐propylene copolymer (OCP) and poly(alkyl) methacrylate (PMA), in multigrade oils on the determination of Ca, Zn and P in fresh and used lubricating oils was studied using XRF, DRES and ICP‐AES techniques. Crankcase lubricating oil blends containing known amounts of Ca (2900 ppm), Zn (1700 ppm) and P (1600 ppm) were further formulated with different concentrations of these VI improvers and analysed for their Ca, Zn, and P contents by XRF, DRES and ICP‐AES. Based on a comparison of the resulting analytical data, it was concluded that the VI improvers had no effect on the analysis results, and that the concentrations of Ca, Zn and P in the oil determined by these techniques correlate well with each other.

Comparison of rubber reinforcement using various surface-modified precipitated silicas

The reinforcement of a natural rubber compound by various surface-modified precipitated silicas was compared. Compound physical properties were determined for two silicas differing in surface area and were used as controls to evaluate these silicas after surface modification by using either a bifunctional organosilane coupling agent (γ-mercaptopropyl–trimethoxysilane) or a new surface modification process. This new process is based on the in situ polymerization of organic monomers solubilized inside surfactant bilayers that are adsorbed onto the silica surface to afford silicas modified with styrene–butadiene and styrene–isoprene copolymers. Both surface modification processes afford materials that dramatically increase the compound cure rate, thereby significantly reducing T90 cure times, while also improving tensile properties, tear strength, abrasion resistance, and compression set of the cured compound. The silane-modified silica gives a higher flex-cracking resistance than do the silicas modified by the in situ polymerization of organic monomers, whereas these latter silicas significantly increase rebound resilience and offer greater overall improvements in rubber compound performance. The rubber compound physical properties obtained using the modified, higher surface area Hi-Sil® 255 silica are generally improved relative to those obtained using the modified Hi-Sil® 233 silica. © 1996 John Wiley & Sons, Inc.

Morphology of polyethylene blends: 3. Blend films of polyethylene with styrene-butadiene or styrene-isoprene copolymers obtained by extrusion-blowing

The morphologies of blends of polyethylene (PE) with a range of copolymers with different basic structure (diblock, triblock, starblock or statistical) have been compared in order to assess the relative importance and interrelation of rheological and molecular parameters. The development of well defined dispersed phases in extruded-blown PE films results from two successive steps. The first is the dispersion step, dominated by shear force fields and shear viscosity in the extruder barrel and die. The second step involves drawing of the melt and freezing of the structures. If the dispersed phase is characterized by a high value of the shear viscosity ratio η d η m and hence by a low deformability, elongation can be performed in neither step. This was observed for diblock styrene-butadiene (SB) in a low viscosity PE matrix, for SBS r2 and for StatSB which all give spheres or ellipsoids. The dimension of the spheres is governed by the viscosity of the matrix and by the value of η d η m according to the Wu equation. If the dispersed phase is highly deformable ( η d η m < 1 ), it is elongated in one or two dimensions at the exit of the die. For a Newtonian melt, these structures break during the elongation time preceding freezing of the structures if the breaking time given by Tomotika's theory is shorter than the elongation time. Broken filaments have indeed been observed for SBS at 240°C and also for styrene-isoprene-styrene (SIS) at 270°C. For a non-Newtonian dispersed phase, stabilization of the structures occurs by different mechanisms involving the elastic contribution of the elongational viscosity. It is related to entanglements and increases with molecular weight. Yielding or tension thickening behaviour can be involved. This is illustrated by the formation of co-continuous elongated structures when the high-molecular-weight diblock SB and triblock SIS are blended with PE, respectively at 240 and 220°C. Two starblock copolymers, SBS r1 and SBS r3, although non-Newtonian and characterized by a rather low value of η d η m , do not give continuous structures. This is attributed to the low molecular weight of the branches which does not allow the formation of a sufficient number of entanglements.

Reactive Extrusion of Styrene Polymers

Abstract Reactive extrusion is the term used to denote a plastics processing method in which an extruder is used as a reactor for the continuous synthesis and modification of polymers. This paper describes the manufacture of polystyrene and styreneisoprene copolymers by a reactive extrusion process: anionic “living” s-butyl lithium initiated bulk polymerization was performed in a co-rotating closely intermeshing twin screw extruder. The results of the process analysis show that living polymerization of styrene can be performed in a screw-type reactor, despite the high reaction temperatures of over 200 °C. The polystyrene melt can be modified in bulk with comonomers or coupling reagents immediately after polymer synthesis. Depending on the raw material, formulation, and process parameters, the process variants developed and analyzed (homopolymerization of styrene, copolymerization of styrene-isoprene mixtures, sequential polymerization of styrene and isoprene) resulted in styrene polymers with widely differing structural characteristics and properties. For example, the copolymerization or styrene-isoprene monomer mixtures produced poly [(isoprene-co-styrene)-b-styrene]. The sequential polymerization of styrene and isoprene led to poly(styrene-b-isoprene) contaminated with partly crosslinked low molecular weight polyisoprene. The polyisoprene content is presumably formed by side reactions due to the high reaction temperatures.

Synthesis of polystyrene and styrene copolymers by reactive extrusion

AbstractDue to the ever growing and more complex demands on the properties of polymer materials, raw material producers and plastic processing industries are more and more interested in the continuous synthesis and modification of polymers. In this article the production of polystyrene and styrene–isoprene copolymers by anionic s‐butylithium initiated bulk polymerization in a co‐rotating close intermeshing twin screw extruder is described. In spite of high reaction temperatures of above 200°C the polystyrene stays “living,” which makes it possible to modify it in the melt by adding more monomers. The following processing methods were developed and analyzed: (1) homopolymerization of styrene; (2) copolymerization of styrene–isoprene monomer mixtures; (3) sequential polymerization of styrene and isoprene. The polymerized material resulting from the above‐mentioned processes differed considerably in structural features and final properties depending on the process parameters. As for homopolymerization of styrene, the influence of the process parameters screw rotation speed and screw geometry on the range of molecular weight distribution was investigated. Products made according to the two copolymerization methods were analyzed with regard to their structure and mechanical properties. The tests revealed that for sequential copolymerization the temperature in the polymerization zone has a decisive influence on the product quality. The influence of the screw rotation speed is less important. © 1993 John Wiley &amp; Sons, Inc.

Studies on photoresists derived from SI cyclized copolymers.

A series of styrene-isoprene copolymers (SI copolymers) have been synthesized from styrene and isoprene. The styrene- isoprene cyclized copolymers (SI cyclized copolymers) have been synthesized by proper cyclization of the obtained copolymers. Through the regulation of ether additives, the copolymers contain different 1, 4-copolymer content and 3, 4-copolymer content. The relative content of 3, 4-copolymer and 1, 4-copolymer in SI copolymers is calculated by data of IR and 1H NMR spectra and the cyclization process is monitored by IR spectra. In this paper, we discuss the influence of various factors on the copolymerization, the cyclization and the products in detail. The minimum quantity of exposure energy required Emin of the phatoresists prepared by SI cyclized copolymers is about 9.7mJ/cm2. The resistance of the photoresist to acids and plasma etching is better than that of cyclized polyisoprene photoresist.

Modification of styrene-isoprene copolymers—2. Chain extension with ethylene oxide

Chain extension of styrene-isoprene hydroxyl-terminated prepolymers was used to obtain polymers having different sequences and lengths of styrene, isoprene, ethylene oxide and 1,3,6-trioxacyclo-octane blocks. The structures and the chemical and composition homogeneities of the copolymers were determined by 1H-NMR and i.r. spectra, GPC analyses (with u.v. and RI detectors), DSC and by data on swelling and surface tension behaviour.

Modification of styrene-isoprene copolymers—1. End-terminated products

Functionalization of various types of mono- and α, ω-bifunctional copolymers was achieved by termination with carbon dioxide, the potassium salt of chloracetic acid, maleic anhydride, carbon disulphide or ethylene oxide. The functionality was determined on the basis of M n (GPC and VPO) and the concentration of the end-groups obtained from 1H-NMR and i.r. spectra. The experimental conditions for quantitative carbonation and hydroxylation without side reactions were established.

Swelling of lamellar diblock copolymer by homopolymer: influences of homopolymer concentration and molecular weight

The lamellar morphology in a lamellar diblock styrene-isoprene copolymer blended with polystyrenes with various molecular weight (2600-36700) was studied. As the PS concentration increased up to 24 wt %, the PS layer thickness increased, the PI layer thickness decreased and the area per junction increased. Increasing the PS molecular weight at a fixed concentration increased the PS and PI layer thicknesses and decreased the area per junction.

Structural Characterization of Diene Block Copolymers by GPC and Ozonolysis—GPC Measurements

Abstract The sequence distribution and block structure of styrene units in commercial styrene—butadiene and styrene-isoprene copolymers were analyzed by GPC measurements on the original copolymers and on ozonolysis products. Tapered-block structures are clearly differentiated by ozonolysis—GPC measurements. The content of large block styrene sequences in S-B-S type block copolymers was found to be 77 to 99% or more. S-B and S sequences in addition to the S-B-S sequence were observed for most of the triblock copolymers. A star-shaped S-B-S copolymer was distinguished from a linear copolymer by comparison of the molecular weight and chemical composition of the main and shoulder peaks by GPC and also by reference to the molecular weight of the block styrene sequence determined by ozonolysis—GPC measurements. A mixture of block copolymers was estimated for a high-styrene thermoplastic elastomer by GPC and ozonolysis—GPC measurements together with the measurement of chemical composition distribution. In a similar way the block structure was analyzed for S-I-S triblock copolymers.

Temperature Effect on the Micelle Behavior of Styrene-Isoprene Block Copolymers in Selective Solvents

Abstract Micelle formation by several styrene-isoprene two-block copolymers in selective solvents, viz., n-heptane, n-dodecane, N,N′-dimethylformamide, and N,N′ -dimethylacetamide, was studied by viscometry and photon correlation spectroscopy (PCS). Aggregation number and micellar weight were deduced by combining viscosity and PCS data. The temperature effect on the viscosity behavior of micellar solutions of block copolymers in different selective solvents is examined and explained. 1H-NMR spectra of the copolymer in n-heptane were recorded at different temperatures to explain the characteristic features of micellar solutions.

Purification of hydrogenated styrene—isoprene copolymer from residual nickel acetylacetonate by chromatography on dextran gels

Purification of hydrogenated styrene—isoprene copolymer from residual nickel acetylacetonate by chromatography on dextran gels