Dynasol Calprene® SBS 500 is a linear styrene-butadiene-styrene block copolymer manufactured by anionic solution polymerization and supplied as porous pellets. The grade is selected for compounding and modification applications in which reduced melt viscosity, rapid wetting, and lower mixing torque are more critical than maximum tensile strength. Its styrene end-blocks associate into glassy domains that act as physical crosslinks; these domains soften at approximately 80–100 °C and permit melt flow at standard SBS processing temperatures. Published typical properties include a nominal bound styrene content of 30 wt%, a specific gravity of 0.94 g/cm³, and a compression-molded hardness of 70 Shore A. These values place Calprene® SBS 500 in the lower-styrene linear SBS class, giving a softer and more flowable product than grades with 40–45 wt% styrene or a radial architecture.

What Are the Published Typical Properties of Calprene® SBS 500?

The following values are manufacturer-typical data and are not specification limits. For incoming raw-material control, the supplier’s current certificate of analysis should be referenced because production-revision values may differ slightly. All mechanical properties in the table are obtained on compression-molded sheets prepared under conditions equivalent to ASTM D3182, unless the datasheet revision states otherwise.

Melt-flow is not a single-valued specification because SBS viscosity is strongly shear-rate and temperature dependent. When a melt mass-flow rate is reported, it is measured at 190 °C/5 kg under ASTM D1238 or ISO 1133-1:2022. The sample should be free of moisture because water vapor produces bubbles that artificially alter the reported melt-flow value. The 30 wt% bound styrene figure is measured by refractive index or NMR-based methods; it controls the volume fraction of the glassy styrene domains and therefore the hardness, modulus, and upper service temperature of the compound. The 0.94 g/cm³ specific gravity is typical for unsaturated styrenic block copolymers and is used to correct volumetric feeders on compounding lines.

Pellet drying is normally unnecessary when packaging has been stored at ≤ 35 °C and ≤ 60% RH. If visible surface moisture is present after storage in an unheated warehouse, a dehumidified-air dryer set at 50–60 °C for 2–4 h prevents steam venting at the die face. On a corotating twin-screw extruder with L/D 32:1–40:1, typical barrel temperatures range from 150 °C near the feed throat to 190 °C at the die, with the die maintained at 180–200 °C. The feed zone is kept at 40–60 °C because the porous pellet surface becomes tacky above 60 °C, leading to bridging in the feed throat. The linear architecture of Calprene® SBS 500 reduces specific energy input and melt pressure compared with radial SBS grades at equivalent screw speed; however, the screw configuration must use sufficiently deep feed channels because the polymer has limited melt strength in the partially melted state. On a production-scale line, head pressure can drift during the first 30 min of a campaign because of molecular weight distribution effects, so throttle valve settings and feed rate are trimmed after startup. Injection molding of Calprene® SBS 500 compounds is performed at barrel temperatures of 160–190 °C, injection pressures of 50–80 MPa, and mold temperatures of 20–40 °C. The styrene domains re-form on cooling, allowing early ejection; ejection problems are more common with thick sections because the low thermal conductivity of the compound delays the recovery of room-temperature modulus.

When Calprene® SBS 500 Is Used in Polymer-Modified Bitumen

Polymer-modified bitumen producers use Calprene® SBS 500 at addition rates between 3 wt% and 7 wt% based on bitumen mass, depending on the required performance grade and the base bitumen’s aromatic oil content. Typical high-shear mixing temperatures are 170–190 °C; mixing times of 30–60 min are common, but the lower melt viscosity of this linear grade can shorten the dispersion phase compared with high-molecular-weight linear SBS. Binder specifications are referenced to EN 14023 for polymer-modified binders in the EU or ASTM D5976 in the US. Softening point is measured with ASTM D36, elastic recovery with ASTM D6084, and storage stability by holding the binder at 163 °C for 72 h and then measuring the softening-point difference between the top and bottom thirds. Many national road agencies require this difference to remain below 2.5 °C. Production-scale inline high-shear mixers show that Calprene® SBS 500 pellets wet and disperse more rapidly than high-molecular-weight linear SBS pellets, reducing visible gel particles in thin-film binder samples. The trade-off is that the lower molecular weight of the grade can reduce the softening-point increment per unit polymer addition and may lower the high-temperature performance grade of the finished binder under ASTM D6373 or EN 12591 testing. For this reason, some formulations combine Calprene® SBS 500 with a radial grade or use sulfur donors to increase elastic recovery. Sulfur or reactive processing aids must be controlled carefully because premature gelation can occur in the bitumen tank if the temperature exceeds 190 °C or if mixing continues beyond the specified reaction window.

For solvent-borne adhesives and sealants, Calprene® SBS 500 is dissolved in toluene or a toluene/hexane blend at solids contents of 20–35 wt%. The linear structure lowers solution viscosity, permitting higher solids before the adhesive becomes too thick for knife-over-roll or comma coating. Viscosity is commonly measured with a Brookfield RV viscometer at 20–25 °C; shear thinning is observed, so spindle speed must be reported with the viscosity value. Tackifier resins are added at 40–100 phr; aliphatic C5 resins associate with the polybutadiene mid-block, while aromatic C9 resins also interact with the styrene domains. Paraffinic oil addition above approximately 30 phr can exude from the butadiene phase and reduce the shear adhesion failure temperature; naphthenic oils are more compatible but can reduce UV stability. Adhesive performance is tested with ASTM D6195 for loop tack and ASTM D3330 for peel adhesion. Hot-melt formulations containing Calprene® SBS 500 should be processed at 180–190 °C with short residence time; a thermosel viscometer at 180–200 °C is used to screen viscosity. Processing above 200 °C accelerates oxidative degradation of the unsaturation in the butadiene block, leading to chain scission, reduced viscosity, and a characteristic rancid odor. Antioxidants and UV stabilizers are required for outdoor or high-temperature adhesive applications; typical antioxidant loading in the compound is 0.5–1.0 phr of a hindered phenolic antioxidant, often combined with a phosphite stabilizer.

In footwear and mechanical goods compounds, Calprene® SBS 500 is compounded with polystyrene, mineral oil, fillers, and optionally sulfur or peroxide cure systems. A typical shoe-sole compound uses 100 phr SBS, 20–40 phr polystyrene, 30–50 phr naphthenic oil, and 10–30 phr calcium carbonate. Mixing is performed in an internal mixer at 140–170 °C; the batch is dropped at 160–180 °C to avoid scorch. The linear grade produces lower compound viscosity and better knit-line flow in injection molding, but the tensile strength of the final sole is lower than that obtained with radial grades. Hardness is usually in the range of 55–75 Shore A depending on oil loading. DIN abrasion loss is measured by ISO 4649; values are formulation-dependent and cannot be predicted from the polymer alone. The addition of sulfur at 0.5–1.5 phr with accelerators can partially crosslink the butadiene phase and improve elastic recovery, but the scorch time at 170 °C must be measured by moving-die rheometer according to ISO 6502 or ASTM D5289. Premature vulcanization in the barrel is a known failure mode when sulfur-bearing masterbatches are processed above 170 °C with long residence time.

Thermal-Oxidative Stability Boundaries and Storage Limits

The polybutadiene mid-block is unsaturated and is the primary site of thermo-oxidative attack. Degradation is negligible under normal storage at ≤ 35 °C, but the rate increases sharply above 200 °C and in the presence of oxygen. Nitrogen-blanketed hoppers and short melt residence times are recommended for extrusion above 190 °C. If the material is stored in direct sunlight or near radiators, pellet surface tack can increase within weeks; storage under 30 °C and away from UV sources is preferred. The product should not be stored near strong oxidizing agents because the unsaturated mid-block can react exothermically. Dust from pellet handling must be controlled; the powder can form combustible dust-air mixtures, and process equipment should be grounded to prevent static discharge. In the EU, polymeric substances are exempt from registration under REACH, but monomer registrations and downstream safety data sheet obligations remain. For the US, users should verify applicable FDA 21 CFR clearances for adhesive or packaging use because no general food-contact clearance should be assumed from the polymer class alone. RoHS compliance for electrical applications typically requires confirmation that the grade contains no intentionally added heavy metals above the threshold levels in the directive.

Compared with radial SBS grades of similar styrene content, Calprene® SBS 500 has a lower melt viscosity and lower tensile strength. A linear SBS molecule contains two chain ends, whereas a radial grade contains three or more arms coupled through a central agent; the radial architecture increases entanglement density, tensile strength, and elastic recovery at equal styrene content. In melt-compounded thermoplastic formulations, the linear product generates lower mixer torque and can be run at higher throughput, but matching the notched Izod impact of a radial grade may require a higher addition rate. The exact offset is formulation-dependent and should be measured with ASTM D256 or ISO 180. Compared with a higher-molecular-weight linear SBS of similar styrene content, Calprene® SBS 500 exhibits lower solution viscosity and faster solvent release, but the tensile strength of a cast film or compression-molded sheet is typically lower by 10–25%. This difference is measured in ASTM D412 tensile testing and is most apparent in adhesive applications where cohesive strength and high-temperature holding power control failure. In bitumen modification, the product disperses more quickly but may require a higher dosage to reach the same elastic recovery and softening point as a radial grade. The choice between linear Calprene® SBS 500 and a radial grade is therefore driven by the dominant constraint: lower torque and faster dispersion versus higher ultimate cohesive strength and elastic recovery. Published data for the exact percentage difference in softening point increment between Calprene® SBS 500 and every competing grade is limited; direct comparative testing in the target binder is required.

Calprene® SBS 500 is unsaturated, unlike hydrogenated SEBS grades, and therefore requires antioxidant and UV stabilization for outdoor service. Compared with SIS grades, it has higher room-temperature tensile strength and a stiffer styrene domain, but lower tackifying compatibility with rosin ester tackifiers. These differences are visible in pressure-sensitive adhesive performance after accelerated aging at 70 °C for 168 h, where loss of tack and cohesive strength depends on the stabilizer package and the aromatic content of the tackifier system.