Calprene® SBS 487 is a linear styrene-butadiene-styrene block copolymer manufactured by Dynasol Elastómeros, S.A. de C.V. under the Calprene® trademark. The product is supplied as a non-oil-extended thermoplastic elastomer with a nominal styrene fraction of approximately 48 wt%, which places it among high-styrene SBS grades used where elevated hardness, high modulus, and reduced low-temperature tack are required. Its CAS registry number is 9003-55-8. The polybutadiene mid-block is unsaturated; therefore Calprene® SBS 487 is not a hydrogenated styrenic block copolymer such as SEBS. The polymer is typically handled in pellet form for melt compounding, bitumen modification, solvent-borne adhesive manufacture, and injection-moulded footwear components.

The high styrene content alters the room-temperature microstructure relative to conventional SBS elastomers containing 30–40 wt% styrene. A larger polystyrene hard-phase fraction increases Shore A hardness, flexural modulus, and upper service temperature, while reducing elongation at break and low-temperature elastic recovery. The polybutadiene phase retains a glass transition temperature in the region of −85°C to −80°C, whereas the polystyrene domains soften near 95–100°C. This phase separation produces reversible physical crosslinking without the use of sulphur or peroxide curatives. Calprene® SBS 487 is therefore processable on thermoplastics equipment but must be protected against oxidative chain scission of the unsaturated mid-block during high-temperature operations above 200°C.

How does the grade differ from oil-extended and lower-styrene SBS elastomers?

Calprene® SBS 487 differs from oil-extended SBS grades in the Dynasol portfolio because it contains no pre-dispersed extender oil. In oil-extended products, naphthenic or paraffinic process oil is incorporated at the manufacturing stage, which lowers apparent hardness and reduces high-shear processing viscosity. The absence of process oil in the 487 grade returns formulation control to the compounder, allowing precise adjustment of oil content in bitumen, adhesive, or footwear formulations. Compared with lower-styrene SBS elastomers in the 30–40 wt% styrene range, the product develops higher polarity in the hard phase, greater resistance to compression set at moderate temperatures, and higher melt viscosity at a given molecular weight. The styrenic endblock fraction also reduces pressure-sensitive tack, which can be compensated by blending with lower-styrene SBS or by selection of compatible tackifying resins. Relative to SEBS, the unsaturated mid-block of Calprene® SBS 487 provides better solubility in aliphatic/aromatic solvent blends and better adhesion to many polar and non-polar substrates, but the polymer requires antioxidant stabilization and is not recommended for continuous service under intense UV exposure without carbon black or stabilizer packages.

The following table lists representative property ranges from the manufacturer’s technical documentation. The values are intended as orientation for incoming quality control and should be read against the batch certificate of analysis.

Processing of Calprene® SBS 487 by twin-screw extrusion is controlled by the shear sensitivity of the styrenic endblock network. In production-scale compounding on co-rotating twin-screw extruders with L/D ratios from 32:1 to 44:1, barrel set-points of 160–190°C and screw speeds of 250–450 rpm are used to achieve homogeneous melt without excessive thermo-oxidative gel formation. Barrel temperatures above 230°C can initiate oxidative chain scission of the polybutadiene mid-block, followed by radical coupling and gel formation. The resulting gels can appear as hard specks in injection-moulded parts or as surface roughness in film and sheet. Single-screw extrusion requires a compression screw with a mixing section and screen packs from 60/120 to 80/150 mesh to reduce unmelted domain particles in the extrudate. Pre-drying is not required for general compounding when pellet surface condensation is avoided; however, if cold pellets are transferred to a humid production hall, a hopper dryer setting of 55–60°C for 1–2 h with a dew point below −20°C prevents surface splay.

Mechanical property data for thermoplastic elastomers are highly dependent on specimen preparation. The values in the table are obtained from compression-moulded plaques prepared according to ASTM D3182-16 and conditioned at 23±2°C and 50±5% RH for at least 24 h. Injection-moulded specimens may show higher tensile strength along the flow direction and lower elongation perpendicular to flow because of orientation of the polystyrene domains. ASTM D638-14 tensile bars should be milled from 2.0 mm plaques rather than from thick moulded plaques. Because the material is viscoelastic, tensile test speed is a critical variable; values generated at 500 mm/min are not directly comparable to those generated at 50 mm/min. Published data for high strain-rate response of this specific grade are limited, and end-use validation should be performed on the final compounded formulation.

Rheological and tensile response of compression-moulded test plaques

Compression-moulded plaques of Calprene® SBS 487 exhibit stress-strain behaviour that reflects the high styrene content. The initial tensile modulus and Shore A hardness exceed those of lower-styrene SBS products, while elongation at break remains sufficient for many durable elastomeric applications. Melt-mass flow rate determined under ISO 1133-1:2022 with a 5 kg load at 200°C is sensitive to moisture, gel content, and thermal history. Values below 1.0 g/10 min may indicate high molecular weight or gel formation, while values above 3.0 g/10 min can indicate contamination or processing-induced chain degradation. For this reason, incoming quality control should compare each lot against the supplier certificate of analysis rather than against absolute generic SBS values. Melt viscosity is pseudoplastic; laboratory capillary rheometry can show substantial viscosity reduction with increasing shear, but published numerical data for this product at defined capillary shear rates are limited.

Bitumen modification with Calprene® SBS 487 typically involves high-shear dispersion of 8–15 wt% polymer into asphalt at 180–190°C using a rotor-stator mixer or an in-line high-shear mill. The high styrene content raises the ring-and-ball softening point and reduces penetration of the modified binder more than an equivalent addition of a 30 wt% styrene SBS would, but the phase-inversion process can be slower because of the higher melt viscosity. The polybutadiene mid-block absorbs maltene fractions and forms a swollen network, while the polystyrene domains act as reversible physical crosslinks. Storage stability of the modified binder must be tested according to EN 13399:2017 or ASTM D7173-20. Because the product is unsaturated, prolonged storage above 180°C with oxygen ingress can cause viscosity drift. The exact formulation window depends on the base bitumen’s asphaltene content and colloidal index; published data for this configuration are limited when highly aromatic or naphthenic base binders are used.

When solvent-borne adhesives require high cohesive strength and controlled endblock association

Solvent-borne adhesive formulations based on Calprene® SBS 487 are usually compounded with tackifying resins and stabilizers in aliphatic/aromatic solvent blends. The high styrene content raises shear holding power at 25–60°C, but lowers initial pressure-sensitive tack. Formulators frequently blend 10–30 parts by weight of the 487 grade with lower-styrene SBS or liquid polybutadiene to restore tack without sacrificing cohesive strength. Open-time behaviour is controlled by solvent evaporation rate and polymer aggregation. Highly polar ester solvents such as ethyl acetate should be avoided where partial polystyrene solvation causes viscosity instability. Peel adhesion can be evaluated according to ASTM D903-98 or ISO 11339:2022, while shear holding power is measured under ASTM D3654/D3654M-24. The unsaturated polybutadiene mid-block provides adequate adhesion to leather, polyurethane foam, and styrenic substrates after light abrasion or primer application, but the formulation must contain sufficient antioxidant to survive adhesive drying temperatures.

Footwear side-panel and shell compounds exploit the high hardness and fast set-up of Calprene® SBS 487. On rotary injection-moulding machines with clamp force from 800–1,600 kN and 12–16 stations, the grade is typically blended with polystyrene and processing oil at 10–30 phr to reduce viscosity and control final Shore A hardness from 65 to 85. The high styrene content accelerates solidification in the mould, which can shorten cycle time by reducing cooling demand, but it also increases anisotropic shrinkage along the flow direction. Shrinkage values of 1.2–1.8% are typical depending on gate size and holding pressure. Mould temperatures from 25°C to 50°C are used to balance surface finish and dimensional stability. Oxidative stabilizers are mandatory because the unsaturated polybutadiene segment is sensitive to shear heating and oxygen at processing temperatures above 210°C. Tear strength can be evaluated according to ASTM D624-00 or ISO 34-1:2022.

Regulatory clearances for the ungrafted base polymer are not equivalent to approvals for finished compounds. REACH registration obligations under Regulation (EC) No 1907/2006 are fulfilled by the producer for the polymer as a monoconstituent substance under the polymer exemption; Annex XIV and Annex XVII restrictions, if applicable to the final article, must be assessed at article level. The polymer may be incorporated into formulations intended for repeated-use rubber articles under 21 CFR 177.2600, but the final compound must be tested for extractives and migration. Compliance with Directive 2011/65/EU (RoHS) Annex II substance ceilings for lead, mercury, cadmium, hexavalent chromium, PBB and PBDE is determined by the complete compound rather than by the base polymer alone.