Dynasol Calprene® SBS 485 is a linear styrene-butadiene-styrene block copolymer produced by sequential anionic polymerization and supplied as dense, dust-suppressed pellets. The polymer consists of two polystyrene terminal blocks and a polybutadiene mid-block; the polybutadiene segment provides elastomeric recovery without vulcanization, while the polystyrene domains form a physical crosslinked network at service temperatures below the glass transition of the styrene phase. Published technical data list a bound styrene content of approximately 31.5–32.5 wt%, a specific gravity of 0.94 under ASTM D792-20, and a melt flow rate of 4.5 g/10 min at 190 °C with a 5 kg load under ISO 1133-1:2022. The grade is supplied without extender oil; this compositional feature differentiates it from oil-extended SBS grades used for soft molded goods and sealants.

Which property differences separate Calprene® SBS 485 from oil-extended and high-styrene SBS copolymers?

The absence of extender oil is the main differentiator. Oil-extended SBS grades can reach Shore A hardness values of 45–50 after melt blending, but the fixed oil content locks formulators into a narrow hardness and viscosity range. Calprene® SBS 485 is a neat polymer; paraffinic or naphthenic process oils are incorporated at 20–40 phr during compounding, allowing the same base polymer to cover Shore A hardness values from approximately 40 to 70. Bound styrene near 31.5 wt% is lower than high-styrene SBS grades containing 40–45 wt% styrene. The lower styrene fraction reduces melt viscosity and broadens compatibility with aliphatic C5 tackifiers, but it also reduces tensile strength and aromatic solvent resistance. Typical tensile strength of the neat polymer is reported at 15.0 MPa with elongation at break of 750% under ASTM D638-14 Type IV specimens. A high-styrene SBS may exceed 20 MPa tensile strength but generally requires higher processing temperatures and higher melt pressure.

Calprene® SBS 485 in polymer-modified bitumen: shear history controls storage stability

In polymer-modified bitumen, Calprene® SBS 485 is dispersed into 70/100 penetration-grade paving bitumen at 3.0–5.0 wt% polymer using a high-shear stator-rotor mill. The melt temperature is held between 175 °C and 190 °C to reduce viscosity while avoiding excessive thermal breakdown. Production mills typically apply rotor tip speeds of 20–25 m/s; lower tip speeds below 15 m/s are associated with coarse polymer domains, uneven binder properties, and polymer-rich surface skin in storage tanks. Under controlled high-shear dispersion, the modified binder commonly shows a ring-and-ball softening point increase of 15–25 °C under EN 1427, a penetration reduction of 20–40 dmm under EN 1426, and elastic recovery above 80% under EN 13398. The actual response is bitumen-source dependent; low-aromatic maltene phases may require compatibilizers or aromatic process oil addition to achieve storage-stable morphology. Standing storage at 180 °C for 72 h under EN 13399 should produce top-bottom softening point differences below 5 °C; values above this threshold indicate phase separation caused by insufficient polymer particle size reduction or poor compatibility.

Unlike SBS latex modifiers, Calprene® SBS 485 is not water-emulsifiable and must be melt-blended into bitumen. Pre-blending in a dedicated PMB plant is preferred because direct dry addition to aggregate mixtures can produce binder-rich and binder-lean zones. In one production configuration, a side-entry high-shear mixer with a rotor tip speed of 22 m/s and a recirculation rate of 8–12 t/h is used to disperse 4 wt% polymer into bitumen at 185 °C; after 45 min of milling, the binder is transferred to a stirred maturation tank for 2–4 h. Samples taken during maturation show that softening point stabilization occurs before elastic recovery stabilization, which means early transfer to storage can produce binders that pass softening point but fail elastic recovery under EN 13398.

When twin-screw compounding must avoid thermal and thermo-oxidative degradation of the polybutadiene block

The polybutadiene mid-block of Calprene® SBS 485 sets the upper thermal limit for compounding. Melt temperatures above 210 °C accelerate chain scission, gel formation, and torque variability; the recommended melt temperature window is 160–200 °C. On corotating twin-screw extruders with 36:1 to 44:1 L/D ratios, barrel zones should progress from 150 °C in the feed section to 190 °C at the die. Screw speed should be limited to 250–350 rpm because viscous heating in mixing elements can raise local melt temperature well above the barrel setpoint. Residence time above 190 °C should not exceed 120 s. In practice, a 40:1 L/D corotating line with barrel setpoints of 180 °C and screw speed 300 rpm can produce a measured melt temperature of 198 °C due to viscous dissipation; this 18 °C rise above the setpoint must be accounted for when setting inspection ports and die thermocouples. Vacuum venting at 200 mbar absolute removes condensation water and volatile oligomers; nitrogen purge in the feed hopper is recommended when regrind or high-surface-area fillers are processed. The grade should not be combined with strong oxidizers or high concentrations of amine-based additives; amine antidegradants can interfere with phenolic stabilizers and reduce oxidative induction time measured under ISO 11357-6:2022. Batch-to-batch torque variability below 8% is typical for controlled feedstock; torque excursions above 15% indicate moisture, filler dispersion failure, or partial gel formation.

Adhesive compounding and ingredient compatibility limits

In hot-melt pressure-sensitive adhesive formulations, Calprene® SBS 485 is combined with aliphatic C5 tackifier resins and naphthenic or paraffinic process oils. A representative starting formulation contains 25–35 wt% polymer, 40–50 wt% tackifier, and 20–30 wt% oil. Mixing is carried out in a sigma-blade mixer or planetary mixer under nitrogen at 160–180 °C. The tackifier and oil are charged first and heated to 160 °C; the polymer is added in portions over 20–30 min with rotor speed 30–60 rpm. After a homogeneous melt is obtained, vacuum is applied at 200 mbar for 15 min to remove entrained air. Brookfield viscosity at 180 °C is monitored under ASTM D3236-15; values for a 30 wt% polymer PSA commonly fall between 10,000 mPa·s and 30,000 mPa·s. Slot-die coating at 50–100 m/min is possible within that viscosity window. Peel adhesion to stainless steel under ASTM D3330/D3330M-04(2018) is commonly 10–25 N/25 mm for removable PSAs. Aromatic process oils with aromatic carbon content above 20% swell the polystyrene domains and reduce shear holding power; the result is room-temperature shear failure before 24 h under ASTM D3654/D3654M-06(2019). Published data for shear adhesion failure temperature with this specific grade is limited; aliphatic C5 tackifiers and fully saturated oils are preferred over rosins or aromatic oils for maintaining the physical network.

In solvent-borne mastics, Calprene® SBS 485 is dissolved at 25–50 wt% solids in aliphatic or aromatic solvent blends. The linear structure yields lower solution viscosity than radial SBS grades of similar styrene content, allowing higher solids loadings in sprayable formulations. Solvent retention after film casting is governed by the aromatic/aliphatic solvent ratio; high-aromatic blends accelerate solvent release but increase dry-film surface tack. Dried films prepared from a 35 wt% solids mastic show tensile strength of 10–15 MPa and elongation of 700–800% under ASTM D412-16, depending on filler and plasticizer loading. High-polarity plasticizers such as phthalate esters above 10 phr can exude and reduce adhesion to concrete and aluminum, so aliphatic process oils are used when substrate bonding is critical.

For injection-molded footwear soles and sheet extrusion, Calprene® SBS 485 is processed on reciprocating-screw injection molding machines with clamp forces of 80–120 t for multicavity sole molds. Barrel temperatures are maintained at 180–200 °C, mold temperatures at 20–50 °C, and injection pressures between 50 MPa and 80 MPa. Blending with 10–30 phr general-purpose polystyrene raises hardness and abrasion resistance, but polystyrene above 10 phr increases stiffness and reduces flex crack growth resistance under ASTM D1052-09(2014). Oil levels above 40 phr can exude from the molded part after 72 h at 70 °C; published data for this specific configuration is limited, so compound validation under the intended production cycle is necessary.