Kraton™ D SBS D1189 is a linear styrene-butadiene-styrene block copolymer supplied as porous pellets for use in polymer modification, bitumen modification, and thermoplastic elastomer compounding. The product is based on a two-phase morphology in which the butadiene midblock forms a continuous elastomeric phase at ambient temperature and the styrene end-blocks aggregate into physical crosslink domains. Published supplier documentation lists bound styrene content in the 30–32 wt% range, specific gravity near 0.94 g/cm³, and Shore A hardness in the 70–75 range after compression molding. Melt mass-flow rate is measured at 200°C under 5 kg load according to ISO 1133-1:2022, with typical values in the low- to medium-viscosity linear SBS envelope; tensile properties determined according to ISO 37 fall in the 30–34 MPa tensile strength range and 800–900% elongation at break in unfilled compression-molded sheets. The grade is differentiated by a low gel count and a controlled diblock content, which influence clarity and mechanical properties. The linear architecture does not build the same degree of long-chain branching as radial grades, and that structural difference controls the melt elasticity, die swell, and solvent viscosity observed downstream.

Molecular characterization of D1189 should include Fourier transform infrared spectroscopy and gel permeation chromatography before reactive formulation. The controlled vinyl content in the butadiene midblock affects crosslink efficiency and thermo-oxidative stability; lower vinyl content favors lower midblock glass transition temperatures, while higher vinyl content shifts the midblock toward a more random structure. Published data for D1189-specific vinyl distribution is limited; therefore, direct substitution in reactive systems requires batch-level verification rather than assumption from other linear SBS grades.

Why Does D1189 Differ from Linear SBS Grades in Melt Rheology and Blend Compatibility?

The linear molecular architecture of D1189 produces a narrower terminal relaxation spectrum than radial SBS grades. In capillary rheometry, this appears as lower die swell and reduced pressure correction at shear rates above 100 s⁻¹; the entry pressure drop on a laboratory capillary rheometer with a 1.0 mm diameter, 20:1 length-to-diameter die is generally lower than that of D1155 at equivalent styrene content. The low diblock fraction reduces soft-phase dilution and sharpens the order-disorder transition during melt processing, which allows D1189 to retain higher tensile strength after oil extension than linear grades with higher diblock content. Compared with D1101, D1189 is selected where the compounding line requires lower head pressure and more uniform pellet feed in a 45 mm co-rotating twin-screw extruder. Published data for direct twin-screw torque comparison between D1189 and D1101 at identical melt temperatures is limited; field observations from compounding trials indicate that D1189 tends to produce lower specific mechanical energy in filled systems when the screw speed is kept within 250–500 rpm and the barrel profile is held below 210°C.

The styrene-rich hard domains also provide a higher plateau modulus above the butadiene glass transition; dynamic mechanical analysis of oil-free D1189 typically shows a styrene-domain glass transition near 90–100°C and a butadiene-domain glass transition near -80–-70°C. These values are useful when selecting a co-continuous morphology in blends with polypropylene or polystyrene. Relative to D1152, which is a lower-styrene linear grade, D1189 shifts the hard-phase content upward and therefore increases modulus; however, oil acceptance in D1152 can be higher before tensile strength falls below 15 MPa. Against D1155, the linear structure of D1189 produces less die swell and less melt strength, so blow molding and deep-draw thermoforming operations may require process adjustments.

Twin-Screw Compounding Parameters and Thermal Degradation Boundaries

On a production-scale co-rotating twin-screw extruder with an L/D of 40:1, the recommended temperature profile for D1189 begins at 140–160°C in the feed zone and rises to 170–200°C in the melting and mixing zones; the die is maintained at 180–210°C. The processing window is narrow in the final mixing zone: at melt temperatures above 230°C, measurable thermal degradation of the butadiene midblock produces an increase in gel particles and a shift of melt viscosity. Batch-to-batch variation in pellet porosity can alter feed intake; if the bulk density of the feedstock drops below 0.40 g/cm³, gravimetric feeders may enter starve-feed oscillation, which appears as torque fluctuation and pressure instability at the screen pack. The use of a 40/80/120 mesh breaker-plate pack is common for film and footwear compounds, and the screen pack should be inspected during color-change or grade-change cleanout when switching from D1189 to polar resins because styrene-domain residue can adhere to mixing elements.

Mineral oil, naphthenic oil, or aliphatic process oil is injected downstream after the mid-barrel melt seal; polar paraffin waxes and aromatic oils with high aniline point depression can soften the styrene domains and reduce upper service temperature. Published compounding data specific to D1189 is limited; therefore, the exact oil uptake before phase inversion must be determined by a ladder study rather than assumed from D1101 data. In twin-screw compounding, a screw profile with at least two kneading blocks before the oil injection point and one atmospheric vent after the oil injection point is typically used to avoid oil back-streaming and vacuum fouling; if vent flooding occurs, the screw speed is reduced in 25 rpm increments until the vent clears.

In polymer-modified bitumen, D1189 is milled or dispersed at concentrations commonly between 3 wt% and 8 wt% into base bitumen at 180–200°C using a high-shear mill. The linear SBS swells in the maltene phase, and the styrene end-blocks form a physically crosslinked network that improves softening point, elastic recovery, and low-temperature cracking resistance. Storage stability of the PMB at 180°C is a function of particle size distribution and compatibilization; coarse dispersion above 10 μm leads to phase separation on 48 h hot storage, while fine dispersion below 5 μm is associated with stable viscosity and no skinning. The use of D1189 instead of D1101 in PMB may require adjustment of mill residence time because of the different melt flow and swelling rate; published values for D1189-specific bitumen network strength at low strain are limited. PMB produced with D1189 often displays a softening point increase of 10–20°C compared with unmodified bitumen and an elastic recovery in the 70–90% range when measured by EN 13398; however, these values depend strongly on base bitumen source and milling conditions. The morphology is usually characterized by fluorescence microscopy to confirm that the SBS phase forms a continuous network rather than discrete islands; a continuous network is required for storage-stable PMB.

When D1189 Replaces D1101 in Footwear Compound Formulations

Reformulation with D1189 in microcellular footwear soles must account for its linear architecture and narrow molecular weight distribution. In a typical SBS compound containing 100 phr D1189, 20–40 phr naphthenic oil, 10–30 phr polystyrene, and 1.0–2.0 phr antioxidant, the mixing sequence on a 45 mm co-rotating twin-screw extruder at 180–200°C affects the final foam cell structure. The compound exhibits a lower die swell than D1101 at matched styrene content, which can reduce dimensional variation in extruded sheet but may require a smaller die gap to maintain target thickness. In injection molding with a clamp force of 150 tonnes, mold temperatures of 20–40°C are used; D1189 compounds usually fill at lower injection pressure than radial grades but may show slightly lower melt strength during gas evolution from chemical blowing agents. The hard-phase styrene domains require sufficient cooling below the glass transition temperature of polystyrene, typically 90–100°C, before demolding to avoid part distortion.

Published data for D1189 in microcellular foaming with azodicarbonamide at 0.5–1.5 phr is limited; therefore, cell size distribution must be qualified per production lot using optical microscopy and ASTM D3574-type density measurements. Abrasion resistance of solid D1189 footwear compounds is usually assessed by DIN 53516, with typical values in the 150–250 mm³ loss range after oil extension; this range overlaps that of D1101 compounds but D1189 tends to show lower surface stickiness after demolding. If higher foam density is required, the addition of 5–10 phr calcium carbonate acts as a nucleating agent and reduces cell collapse; beyond 15 phr, tear strength falls below 20 N/mm in many SBS formulations.

Adhesive formulations based on D1189 use solution-blending in toluene, cyclohexane, or methylcyclohexane at solids between 20 wt% and 40 wt%; the linear structure yields lower Brookfield viscosity for a given solids content than radial SBS. A 25 wt% toluene solution of D1189 typically shows lower viscosity than D1155 but higher viscosity than low-viscosity linear grades such as D1152; direct substitution should be validated by ISO 2555 Brookfield measurements at 25°C. Solvent-borne pressure-sensitive adhesives require the addition of tackifying resin at 20–40 phr; aliphatic C5/C9 hydrocarbon resins are preferred over rosin esters because the latter can shift the styrene-domain glass transition and reduce cohesive strength. Hot-melt adhesives produced on a twin-screw extruder at 170–190°C show lower color development and retained melt viscosity when 0.1–0.3 phr hindered phenol/phosphite stabilizer is added. Plastic modification uses D1189 at 5–20 wt% in polypropylene or polystyrene to improve impact resistance and stress whitening resistance; the SBS domains act as a dispersed elastomer phase, and the dominant processing variable is the viscosity ratio between D1189 and the matrix. In polypropylene, the use of a compatibilizing grade or a peroxide-free reactive coupling step may be required because the polar mismatch limits interfacial adhesion; published data for D1189 in long-glass-fiber polypropylene compounds is limited.

Quality assurance for D1189 batches typically includes melt mass-flow rate, bound styrene, and solution viscosity; a certificate of analysis is supplied. The product is manufactured under ISO 9001-registered quality systems and is accompanied by a safety data sheet. For compound developers, incoming inspection should include pellet visual inspection for fines because excessive fines lead to feeding variation at high screw speed. Retained pellet integrity and controlled fines content reduce the tendency for starve-feed oscillation in gravimetric dosing units.

Solvent Contact Dissolves Styrene Domains in D1189 Compounds

Direct contact with aromatic solvents, methyl ethyl ketone, acetone, or methylene chloride is not recommended for D1189 because these solvents dissolve the polystyrene end-blocks and disrupt the physical crosslink network. In immersion for 24 h at 23°C, toluene uptake can exceed 100 phr and gel the compound surface; methyl ethyl ketone leads to selective extraction of low-molecular-weight polystyrene segments. Pre-drying is not generally required because SBS is non-hygroscopic, but long-term storage at relative humidity above 60% can lead to surface moisture on porous pellets and should be addressed by drying at 50–60°C for 2 h before extrusion. The product contains antioxidant stabilizers; addition of amine-based additives is not recommended in hot-melt systems because amine chemistry can react with residual unsaturation and form color bodies. Storage should be in a cool, dry environment below 40°C, and inventory should follow first-in-first-out rotation; under these conditions, retained mechanical properties remain within specification for 24 months from the date of manufacture. Published data for D1189-specific solvent uptake and long-term weathering is limited; outdoor exposure without UV stabilizer is not recommended because the butadiene midblock undergoes photo-oxidative chain scission. Equipment cleaning after D1189 should use a purge compound rather than solvent flushing; solvent flushing tends to swell the residual polymer and form a sticky film inside the barrel.