Kraton™ D SBS D1191 is a clear, linear styrene-butadiene-styrene triblock copolymer produced by anionic polymerization and supplied in dense pellet form. The specification is built around a bound styrene concentration of 30 % by mass and a diblock content below 1 %, placing it between softer butadiene-rich SBS grades and higher-styrene, more plastic grades. The bulk specific gravity is 0.94 per ISO 1183-1. On compression-moulded plaques, published typical mechanical properties include a tensile strength of approximately 33 MPa and an ultimate elongation of 880 % determined according to ASTM D412, with a Shore A hardness of 70 measured under ISO 868. The melt flow rate reported at 200 °C and 5 kg is approximately 1.0 g/10 min per ASTM D1238, indicating a higher-viscosity material than higher-flow grades such as D1102. The product is selected where high cohesive strength, low non-bridging fraction, and hydrocarbon compatibility are required; it is not a saturated polymer and therefore must be protected from extended thermal-oxidative exposure above 230 °C.

How Does the Sub-1 % Diblock Fraction Affect Network Integrity and Processing Behaviour?

In anionically synthesized SBS, premature termination after the first polystyrene block produces a styrene-butadiene diblock species. A diblock chain carries only one styrene terminal and therefore cannot bridge two polystyrene domains during microphase separation. In D1191, the diblock content is controlled below 1 % by mass, whereas conventional extrusion-grade SBS grades such as D1101 may contain 17 % to 18 % diblock. The practical consequence is a higher proportion of elastically effective triblock chains; at equivalent styrene content, this raises tensile modulus and resistance to creep while reducing the plastic flow that contributes to pressure-sensitive tack. The same low diblock population increases melt viscosity and makes D1191 more difficult to disperse than high-diblock analogues. On a 30:1 L/D single-screw extruder, barrel settings from 150 °C to 190 °C are typical, but screw speeds above 80 rpm can produce die melt temperatures 10 °C to 20 °C above the set point through viscous dissipation. Residence time above 220 °C should be kept below 5 min to limit gel formation from butadiene unsaturation.

Dynamic mechanical analysis of compression-moulded D1191 shows two principal transitions: a low-temperature loss peak associated with the polybutadiene phase at approximately -85 °C and a polystyrene domain glass transition near 95 °C to 100 °C. The rubbery plateau storage modulus between these transitions is maintained by the immiscible polystyrene domains. Because the diblock fraction is below 1 %, the plateau is flatter and extends to higher temperature before terminal flow than for an equivalent SBS containing 18 % diblock. This is why D1191 can provide creep resistance in sealants and adhesives at service temperatures approaching 70 °C while remaining melt-processable at 180 °C to 210 °C. Rheological data obtained on a parallel-plate rotational rheometer at 180 °C show pronounced shear thinning from a low-shear complex viscosity above 10,000 Pa·s to below 100 Pa·s at 1000 s⁻¹. This non-Newtonian response is critical in hot-melt coating and bitumen milling because the high zero-shear viscosity resists creep while the high-shear viscosity remains low enough for pumping and thin-film application.

Bitumen modification accounts for a significant share of D1191 consumption. In a production-scale operation using a 10 t to 20 t vertical mixing vessel equipped with a rotor-stator high-shear head, the base bitumen is heated to 180 °C before D1191 pellets are added at 3.5 wt% to 5.0 wt%. Mixing at a tip speed of 15 m/s to 20 m/s for 45 min to 90 min is necessary to reduce the polymer domain size below 10 µm and to swell the polybutadiene midblock with the maltene fraction of the bitumen. A draw-down plate at 180 °C should show no undispersed polymer particles larger than 50 µm. The ring-and-ball softening point according to EN 1427 typically increases by 15 °C to 25 °C relative to a 70/100 penetration-grade bitumen, and elastic recovery per EN 13398 exceeds 80 % for well-dispersed D1191-modified blends. Storage stability per EN 13399, measured after 3 days at 180 °C, is generally below 2 °C softening-point difference in properly dispersed systems; poor dispersion or polymer contents above 6 wt% can produce separation and surface skin in storage. Below 170 °C, mixing time increases sharply because the bitumen viscosity is too high for efficient particle break-up. Above 200 °C, the unsaturated butadiene segments oxidize and the polymer network degrades, causing a drop in elastic recovery and an increase in dynamic viscosity.

When D1191 Is Melt-Blended into Pressure-Sensitive Adhesives, Tackifier Aromaticity and Oil Level Shift the Peel–Shear Balance

Hot-melt pressure-sensitive adhesive development with D1191 starts from a ternary formulation of SBS, hydrocarbon tackifier, and naphthenic or paraffinic oil. A working envelope is 25 wt% to 35 wt% D1191, 45 wt% to 60 wt% tackifier, and 5 wt% to 20 wt% oil. The high melt viscosity of D1191 relative to D1102 means that slot-die coating systems operating at 160 °C to 180 °C generally require a formulation viscosity below 20 Pa·s at 1000 s⁻¹; this is achieved by selecting a lower softening point tackifier or by raising the oil content. Loop tack measured by ASTM D6195 increases with C9 aromatic tackifier content, while 180° peel per ASTM D903 peaks at a resin-to-polymer ratio near 2:1 for aromatic-modified C5 resins. Shear holding power per ASTM D3654 follows the opposite trend: high tackifier loadings reduce cohesive strength, and the near-zero diblock population of D1191 preserves longer time to failure at 40 °C than D1102 at equal formulation composition. Low-temperature fibre tear on corrugated board becomes marginal when the combined oil and midblock-compatible tackifier fraction falls below 35 wt% of the total adhesive. Pre-drying of D1191 is unnecessary for hot-melt mixing under normal warehouse conditions; however, surface condensation from outdoor storage at relative humidity above 60 % should be removed by purging the feed hopper with dry air to prevent steam popping during melt mixing.

Compounding into polypropylene-rich impact-modified formulations requires staged feeding on a co-rotating twin-screw extruder. A 40:1 L/D machine with a downstream side-stuffer positioned after the primary melt seal is preferred when D1191 is added at 10 wt% to 30 wt%. The barrel profile is set from 170 °C in the feed section to 200 °C at the die, with screw speed selected to maintain specific mechanical energy near 0.20 kWh/kg to 0.30 kWh/kg. If D1191 is fed in the main throat with polypropylene, the longer residence time and high local shear can generate melt temperatures above 230 °C, producing brown specks and a burnt-rubber odour. At 20 wt% D1191 in a polypropylene impact copolymer, instrumented falling-weight impact per ISO 6603-2 at -20 °C generally shifts the ductile-to-brittle transition 5 °C to 15 °C lower than the unmodified matrix, though the exact shift depends on part thickness and cooling rate. The low diblock content of D1191 reduces the fraction of low-molecular-weight species that can act as interfacial tension reducers; if the desired phase morphology is not reached, a maleated polypropylene compatibilizer is incorporated at 1 wt% to 3 wt% rather than increasing processing temperature.

Solvent-Borne Adhesive Viscosity and Dissolution Profiles in Toluene–Hexane Systems

For contact adhesives and solvent-applied laminates, D1191 is dissolved in hydrocarbon blends at solids contents from 20 % to 35 %. The low diblock fraction and high molecular weight produce a more elastic solution than equivalent solutions of D1102; at 25 % solids in toluene, the Brookfield viscosity is high enough that gravure or roller application often requires reduction with hexane to achieve a coating viscosity below 20,000 mPa·s. Production mixing in a high-shear dissolver with a saw-tooth impeller at 800 rpm to 1200 rpm can require 6 h to 12 h for complete optical clarity, with the longest times observed when the solvent is below 20 °C. Heating the solvent to 35 °C to 45 °C accelerates dissolution but also increases solvent evaporation losses and requires explosion-proof equipment with vapour monitoring. The dried film develops physical crosslinks as the solvent evaporates; this network survives intermittent service temperatures approaching 70 °C to 80 °C, above which the polystyrene domains soften and creep accelerates under shear load. For continuous service above 90 °C, the unsaturated D1191 grade is generally replaced by a saturated SEBS block copolymer or a vulcanizable SBS compound with sulfur or phenolic resin cure. Storage viscosity drift is controlled by limiting water ingress and adding 0.1 % to 0.3 % hindered phenolic antioxidant on solution solids.

In clear sealant and soft-gel applications, D1191 is extended with white mineral oil at oil loadings from 50 wt% to 80 wt% to form physically crosslinked thermoplastic elastomer gels. The low diblock content improves gel firmness at equal oil loading because fewer dangling chains act as plasticizers. Oil retention is evaluated by a 50 mm filter-paper migration cell at 60 °C for 72 h; gels based on D1191 typically show oil bleed below 1 % when the oil is predominantly paraffinic. Higher aromatic process oils may swell the polystyrene domains and reduce thermal resistance. Sealants formulated with D1191 require the same thermal stabilization discipline as hot-melt adhesives, with barrel temperatures below 230 °C and injection pressures typically below 80 bar on small moulding machines.

Differences in Melt Flow and Network Architecture Set D1191 Apart from D1101, D1102 and D1155

The most direct architectural distinction between D1191 and D1101 is the diblock content. D1101 combines a similar bound styrene level of approximately 31 % with a diblock population of 17 % to 18 %, which lowers melt viscosity and eases processing but reduces the fraction of elastically effective triblock chains after microphase separation. D1102 has a lower styrene content of roughly 28 % and a higher melt flow rate, making it easier to dissolve and melt-coat, but its softer polybutadiene-rich morphology gives lower hardness and lower shear holding power. D1155 is higher in bound styrene, commonly near 40 %, producing a harder, more plastic SBS used where stiffness and high-temperature softening resistance are more important than low-temperature elastomeric recovery. D1191 therefore occupies a middle-styrene, low-diblock position: it is selected when the end user needs the elastomeric recovery and hydrocarbon compatibility of a 30 %-styrene SBS but cannot accept the network defects introduced by higher-diblock general-purpose grades.

Batch-to-batch variance in anionic SBS production is monitored through solution viscosity at 25 % solids in toluene, melt flow rate, bound styrene, and diblock content. For D1191, a shift in diblock content from 0.5 % to 2 % may reduce tensile strength by several percent and lower cohesive shear holding time in adhesives; production facilities often request certificates of analysis that report diblock content by gel-permeation chromatography. On a 25 kg bag scale, pellet moisture is generally below 0.3 %; if bags are stored in humid environments, a 2 h drying step at 50 °C to 60 °C is adequate to remove surface condensation without fusing pellets.

Regulatory compliance for D1191 is use-specific. The polymer is not automatically approved for direct food contact; users should verify end-use compliance under 21 CFR 177.1810 for styrene block polymer articles or 21 CFR 175.105 for adhesive components, as appropriate. In the European Union, REACH registration is maintained by the supplier and downstream users should obtain the extended safety data sheet for the specific grade; the base hydrocarbon elastomer is not listed on the REACH candidate list. RoHS screening under IEC 62321 is relevant only when the final compound contains additives such as flame retardants, pigments, or metallic stabilizers. Process heat history is the main operational boundary: the polybutadiene midblock contains unsaturation and will oxidize in air at temperatures above 200 °C to 230 °C, leading to gel, odour, and discoloration. Outdoor weathering of unpigmented D1191 compounds results in rapid surface cracking unless carbon black or a hindered amine light stabilizer is added. Contact with strong oxidizing acids, chlorinated solvents at elevated temperature, or prolonged exposure to certain amine-based additives should be avoided because these agents can accelerate chain scission or discoloration of the unsaturated butadiene segments.