Calprene SBS 401M is a linear styrene-butadiene-styrene block copolymer supplied by Dynasol as a low-diblock thermoplastic elastomer with a nominal bound styrene content of 30.0 wt% and a non-staining phenolic stabiliser package. The CAS Registry Number for the block copolymer is 9003-55-8. The triblock architecture forms a two-phase morphology in which polystyrene end-blocks separate into glassy domains within a continuous polybutadiene-rich matrix; differential scanning calorimetry under ASTM D3418-21 typically resolves a polybutadiene mid-block glass transition near −85°C and a polystyrene domain glass transition near 95°C. The diblock fraction is held below 1.0 wt%, which reduces the population of non-bridging S-B chains and preserves tensile stress transfer through the physical network. Table 1 reports typical values obtained from compression-moulded test specimens.

These values are not specification limits. The property set places Calprene SBS 401M between low-viscosity high-diblock SBS types and higher-styrene styrenic block copolymers. The melt flow rate of 5.0 g/10 min under 5 kg at 190°C per ASTM D1238-20 indicates a medium melt viscosity relative to the broader Calprene portfolio. The solution viscosity of 1200 mPa·s for 25 wt% solids in toluene at 25°C is higher than the 400–700 mPa·s range commonly associated with high-diblock SBS grades, which is a direct consequence of the low content of non-bridging copolymer chains. In applications where maximum tack is required, a high-diblock grade may be preferred; where higher cohesive resistance and tensile integrity are needed, the low diblock content of 401M is the controlling structural variable.

The molecular weight distribution of the block copolymer is controlled to maintain the 1200 mPa·s solution viscosity; this value is used by solvent-borne adhesive formulators to predict final solution viscosity before resin addition. The ratio of styrenic domain glass transition to service temperature establishes the upper use temperature of the physical network; under load, the material loses physical crosslinks gradually above 70°C, which limits continuous load-bearing applications. The low bound styrene content also results in lower equilibrium water absorption than polar thermoplastic elastomers; 24 h immersion at 23°C usually yields less than 0.5% mass uptake when measured by ASTM D570. These attributes make Calprene SBS 401M suitable for applications where a non-polar, low-moisture-regain elastomer is required.

Melt preparation of Calprene SBS 401M is carried out in a single-screw extruder with L/D ratio between 24:1 and 30:1 for unfilled compounds, or in a co-rotating twin-screw extruder with L/D ratio between 32:1 and 40:1 for filled or oil-extended systems. A flat barrel temperature profile from 150°C in the feed zone to 180°C at the die is typical for strand pelletising. For injection moulding, cylinder temperatures of 170°C to 200°C and mould temperatures of 20°C to 40°C are used. The polymer is not hygroscopic in the same manner as polar engineering thermoplastics, but surface condensation at relative humidity above 60% may require pre-drying for 2 h at 60°C in a desiccant-bed or circulating-air drier. Melt residence time above 220°C should be minimised because the unsaturated butadiene mid-block is susceptible to thermo-oxidative chain scission. Production lines should be purged with a low-melt-flow polypropylene or an antioxidant-stabilised SBS purge stock after shutdown. In solvent-borne adhesive manufacture, dissolution in toluene, methylcyclohexane, or a MEK/toluene blend is performed with high-shear dispersion blades; final adhesive viscosity is controlled by solids loading, resin type, and the inherent solution viscosity of the SBS. In twin-screw compounding, screw design with forward-conveying elements in the melting zone and distributive mixing elements in the downstream section reduces viscous heating and limits melt temperature overshoot above 200°C. The specific energy input for a 30 mm co-rotating twin-screw extruder processing a 30 wt% filler compound typically falls between 0.15 kWh/kg and 0.30 kWh/kg; published data for this specific configuration is limited, and the value must be verified on the production line. In injection moulding, injection pressures of 600 bar to 1,200 bar are common for short flow-path moulds, but the melt temperature should remain below the 220°C degradation threshold.

Why does low diblock content govern tensile property retention in Calprene SBS 401M?

The diblock fraction in SBS consists of S-B chains that carry only one polystyrene terminal segment. These chains cannot bridge two styrenic domains; they dilute the rubber matrix and reduce the effectiveness of the physical crosslink network. In Calprene SBS 401M, the diblock content is held below 1.0 wt%, limiting the population of these non-bridging species. Under ASTM D412-16 tensile testing on compression-moulded sheets of 2 mm thickness, the material typically reaches 18 MPa tensile strength and 700% elongation at break. The tensile strength difference between 401M and high-diblock SBS grades is most evident in formulations without hydrocarbon resin; high-diblock grades may show 20% to 40% lower cohesive strength in peel modes because non-bridging chains promote viscous dissipation and premature failure. In contrast, the low diblock fraction raises room-temperature elastic modulus and creep resistance, but also increases melt viscosity and can reduce pressure-sensitive tack. Processors selecting between 401M and a high-diblock grade should base the decision on the required balance between cohesive strength and tack; ASTM D6195 loop tack testing and ASTM D3654 shear adhesion testing are used to quantify the divergence. Tensile set after elongation to 200% is lower for 401M than for high-diblock grades because the bridged network retracts more efficiently after strain. Hysteresis measurements at 100% elongation show that first-cycle energy loss can be significant due to stress softening of the styrenic domains, but subsequent cycles stabilise as the morphology reaches a dynamic equilibrium. The low diblock fraction also reduces extractable material when the compound is exposed to organic solvents; extraction testing under FDA 21 CFR 177.2600 for rubber articles intended for repeated use is commonly referenced, although the final compound, not the neat polymer, must be evaluated for compliance. Table 2 summarises the structural and processing differentiation against adjacent SBS categories.

Bitumen modification and roofing membrane processing windows

In paving-grade polymer-modified bitumen, Calprene SBS 401M is incorporated at concentrations of 3.0 wt% to 6.0 wt% relative to bitumen mass for dense-graded asphalt applications. Mixing is conducted in a heated high-shear mill, typically a rotor-stator mixer operating at 3,000 rpm to 5,000 rpm, with bitumen temperature held between 170°C and 185°C. Under those conditions the SBS phase absorbs maltenes and swells, reaching a digested state in which the polymer network contributes storage-stable binder elasticity. Softening point tests according to ASTM D36 typically show an increase from unmodified bitumen ranges of 45°C to 52°C to modified binder ranges of 60°C to 75°C depending on bitumen source and addition level; the exact increase is influenced by maltene content and aromatic process oils. In waterproofing membranes, higher addition levels of 10.0 wt% to 15.0 wt% are typically employed, often with calcium carbonate fillers and stabilisers, to produce a thermofusible compound for torch-applied or self-adhesive sheets. A critical processing limit is the maximum compound temperature of 200°C; prolonged exposure above this threshold accelerates oxidation of the butadiene segment and causes a drop in low-temperature flexibility. Batch-to-batch variance in bitumen composition requires adjustment of the high-shear mixing time; a rotational paddle viscometer operated at 135°C may be used to monitor blend viscosity, with acceptance ranges defined by the end specification rather than a fixed value. Differences between 401M and lower-viscosity high-diblock SBS in this application are visible in storage stability: 401M tends to require longer digestion to achieve full swelling, but the low diblock fraction supports a more continuous polymer network after cooling, reducing phase separation under static storage at 160°C in sealed tubes. The final binder is often evaluated under EN 14023, ASTM D6084, or ASTM D5976 for softening point, resilience, and elastic recovery; viscosity is measured under ASTM D4402 at 135°C using a Brookfield thermosel. Low-temperature flexibility of the modified binder is often checked by force ductility or bending beam rheometer; a low-diblock SBS network typically improves the elastic recovery component in EN 13589 force ductility testing at 5°C, provided that the polymer is fully digested. In comparison with high-styrene SBS, 401M dissolves more rapidly in bitumen at equivalent shear because the lower styrene content requires less thermal energy to swell the polystyrene domains; however, it develops less high-temperature stiffness after cooling.

When Calprene SBS 401M replaces medium-styrene SBS in compounded footwear and polystyrene modification

When Calprene SBS 401M is substituted into a thermoplastic elastomer compound for footwear, the 30.0 wt% bound styrene content produces a Shore A hardness of 70 and a correspondingly lower modulus than a high-styrene SBS with 40.0 wt% bound styrene. Compounding may be carried out in a co-rotating twin-screw extruder with an L/D ratio of 32:1 to 40:1, using a temperature profile from 160°C in the feed zone to 190°C at the die. Paraffinic or naphthenic oil addition of 20 phr to 60 phr reduces hardness to 40–55 Shore A while preserving elongation above 500% when measured according to ASTM D412-16. The physical crosslink density supplied by the styrenic domains is lower than that of a 40.0 wt% styrene SBS, so the compound exhibits greater flexibility at −20°C but lower abrasion resistance under DIN 53516. In crystal polystyrene modification, 401M may be melt-blended at 5.0 wt% to 15.0 wt% using a twin-screw extruder to improve impact strength; notched Izod impact testing under ASTM D256-10 shows an inverse relationship with melt flow index and a plateau that depends on the dispersion of the SBS phase. In comparison with a high-diblock grade, 401M gives higher tensile set resistance and lower flow-induced phase coalescence, which is beneficial in injection-moulded articles where knit lines are formed at multi-gate tool locations. In solvent-borne contact adhesives, 401M at 15.0 wt% solids in toluene develops peel strength that is controlled by the breakdown of the physical network; a low diblock fraction increases room-temperature peel resistance but may require higher application viscosity and longer open time than high-diblock variants. Producers using 401M in adhesive applications commonly adjust tack with hydrogenated rosin ester or C5/C9 resins; the final adhesive is tested under ASTM D903 for peel and ASTM D3654 for shear. In extrusion of thermoplastic elastomer profiles, 401M compounds can be run with a single-screw extruder having a barrier screw and L/D ratio of 24:1 to 30:1; die swell is lower than with high-molecular-weight branched SBS, which aids dimensional control in complex profiles. The temperature window between adequate melt strength and thermal degradation is approximately 170°C to 200°C, which is narrower than for styrene-rich SBS because the butadiene segment begins thermo-oxidative degradation at lower temperature. The choice of 401M over a medium-styrene high-diblock grade is therefore not universal: it trades application tack for cohesive strength and higher melt viscosity.

Storage and regulatory handling of Calprene SBS 401M should follow the producer's safety data sheet. The product is not classified as a hazardous substance under CLP Regulation (EC) No 1272/2008 in the supplied pellet form; finished compounds must be assessed separately for REACH registration, RoHS Directive 2011/65/EU, and food-contact suitability where applicable. Inventory conditions below 40°C and protection from direct sunlight prevent agglomeration of pellets. Bales and pellets should be kept free from dust, and the product should not be compounded with amine-based additives that can deactivate the phenolic stabiliser system. Because the butadiene segment is unsaturated, prolonged exposure to strong oxidising agents, chlorinated solvents, or ultraviolet light causes surface cracking and loss of elongation; articles requiring UV resistance must incorporate carbon black or hindered amine light stabilisers and be tested under ISO 4892-2 or ASTM D4329 cycles. Handling should include local exhaust ventilation during high-temperature compounding because minor amounts of styrene monomer may be released during extended melt processing above 200°C; the producer's exposure limit for styrene should be observed. Published data for the long-term retention of tensile properties in outdoor exposure of unpigmented 401M is limited; therefore, qualification trials are required for external applications. Calprene SBS 401M is typically supplied in 20 kg bags or 450 kg bulk packaging depending on region; the producer's certificate of analysis includes styrene content, solution viscosity, melt flow rate, and volatile matter. Quality audits of incoming lots should verify that solution viscosity and melt flow rate are within the producer's control bands because these parameters affect downstream batch-to-batch compound viscosity and adhesive coating weight. The product should not be stored adjacent to metal naphthenate driers or cobalt-based accelerators because these materials promote premature oxidation of the polybutadiene mid-block.