Kraton™ G1652 MUP SEBS is a linear triblock copolymer of styrene and ethylene/butylene with a bound styrene content of 30 mass %, a specific gravity of 0.91 (ASTM D792), and a solution viscosity of approximately 1800 mPa·s at 25 mass % in toluene. The saturated ethylene/butylene midblock contains no residual aliphatic double bonds, which distinguishes the product from unhydrogenated SBS and reduces oxidative degradation during prolonged heat aging. Manufacturer-published compression-moulded physical properties include a Shore A hardness of 65 (ASTM D2240), tensile strength of 31 MPa (ASTM D412), elongation at break of 880% (ASTM D412), and a 300% modulus of 5.5 MPa (ASTM D412). Specification limits for total extractables and volatile matter are ≤1.0 mass % each. The polymer is pelletised for adhesive, sealant, coating, and elastomer-modification processes in which controlled melt and solution viscosity is required.

The ethylene/butylene midblock is produced by hydrogenation of a 1,4-rich polybutadiene precursor. Residual aliphatic unsaturation in the hydrogenated midblock is very low, which limits attack by ozone and peroxy radicals. The exact residual double-bond content is not disclosed in the public data sheet. The triblock architecture is supplied with a low diblock fraction. Low diblock content is process-relevant because diblock chains can migrate to surfaces and alter peel adhesion; customers requiring low surface tack should specify diblock content or total extractables in addition to the standard volatile-matter limit.

Polystyrene end-blocks form glassy domains that soften near 95–100 °C, whereas the ethylene/butylene midblock remains elastomeric below -40 °C. Dynamic mechanical analysis of hydrogenated styrenic block copolymers typically places the polystyrene domain glass transition near 95 °C (ISO 6721-1) and the midblock glass transition below -40 °C. These transitions determine service behaviour and melt-processing boundaries. In the melt, the styrene domains require temperature and shear sufficient to disrupt physical junctions; the resulting two-phase melt contributes to melt tension and strand stability but makes localized shear heating a critical variable in twin-screw compounding.

What Processing Boundaries Are Encountered in Twin-Screw Melt Compounding?

Moisture uptake in bulk SEBS is generally low, but surface moisture from high-humidity storage can generate splay. Drying in a desiccant dryer at 70–80 °C for 2–4 h is applied when storage relative humidity has exceeded 60%. On co-rotating twin-screw extruders with L/D ratios from 30:1 to 44:1, G1652 MUP is compounded with polyolefins, oils, and fillers by feeding the polymer in the first barrel and applying sufficient specific energy to reduce domain size. Melt temperature at the die must remain below 240 °C to prevent styrenic block scission; barrel setpoints are therefore maintained below 220 °C in the rear zones, with melt-temperature probes in the transfer pipe. A production-scale failure mode associated with this product is strand break from excessive die pressure when dispersive kneading blocks are placed too early; the high melt viscosity of the styrene domains is better managed with distributive mixing elements followed by vacuum devolatilisation. Published typical melt mass-flow rate at 230 °C/5 kg is 5 g/10 min (ASTM D1238). This is higher than G1650 MUP but remains low relative to polypropylene; therefore, predispersed masterbatches or oil extension are used when the target matrix is a low-melt-index polyolefin.

Lot-to-lot variability in pellet surface dusting can bridge in loss-in-weight feed hoppers. Hopper agitation and vent-port cleaning are routine production controls. When oil extension is used, paraffinic oil is added at 30–50 parts per 100 parts of polymer. Hardness decreases from the neat-polymer value with increasing oil content; tensile strength and 300% modulus decline simultaneously. Oil is preferentially absorbed into the ethylene/butylene midblock, leaving the polystyrene domains solid. The oil absorption step is conducted before filler addition because free oil near the feed throat reduces pellet friction and causes feed instability.

In cast-film and sheet extrusion, die temperatures are kept below 240 °C and the melt is quenched rapidly to preserve a fine polystyrene domain structure. Slow cooling or annealing above 120 °C permits polystyrene domain growth, increasing stiffness but reducing toughness. The processing window is narrower than for polyolefin homopolymers because the physical crosslinks disappear gradually rather than at a single thermodynamic melting point.

In solvent-based contact adhesive operations, G1652 MUP is dissolved at 20–25 mass % solids in toluene, cyclohexane, or MEK/toluene blends. A Brookfield viscosity of approximately 1800 mPa·s for a 25 mass % solution permits roller-coat application and supports sufficient chain entanglement after solvent flash to generate green strength in footwear and upholstery bonding. Because the ethylene/butylene midblock is saturated, adhesive films display lower UV yellowing than SBS-based contact adhesives under the same irradiance; comparative testing in accelerated weathering chambers using ASTM G154 UVA-340 lamps is recommended for quantitative colour-shift data. Hot-melt adhesives based on G1652 MUP require tackifying hydrocarbon resins and paraffinic or naphthenic oils; aromatic process oils are not required to achieve compatibility.

For solvent-free hot-melt systems, the melt viscosity at application temperatures of 180–200 °C requires slot-die or wide-nozzle applicators. Continuous roll lamination can be conducted on equipment with heated nip rolls. If the melt temperature drops below 160 °C, the polystyrene domains begin to reform and the adhesive loses tack.

When G1652 MUP Replaces G1650 MUP in Elastomer Modification

Substitution of G1650 MUP with G1652 MUP reduces the molecular weight of the styrene-ethylene/butylene-styrene triblock, which lowers melt viscosity, solution viscosity, and compounding torque. The trade-off is a reduction in tensile strength and cohesive strength at equal processing-oil content. In polypropylene compounds at addition levels of 20–30 mass %, the lower-viscosity grade disperses more readily and can improve low-temperature impact-crack resistance; however, if the compound must survive repeated elongation above 300% without rupture, G1650 MUP provides greater molecular chain entanglement. The selection is therefore governed by the balance between processability and end-use tensile requirements, not by styrene content, because both grades carry a nominal 30 mass % bound styrene. In comparison with unhydrogenated styrenic block copolymers of similar molecular weight, G1652 MUP requires higher compounding temperatures due to the polystyrene domain glass transition but offers improved heat and UV aging resistance as measured by retention of tensile strength after ASTM D573 aging; published data for the specific aging differential at 100 °C in air for this grade is limited.

The low diblock fraction of G1652 MUP also reduces the formation of low-molecular-weight extractable chains. This is a differentiating factor in adhesive and medical-facing applications where surface migration of diblock species can alter tack, haze, or extraction profiles. Users that require a defined extractables profile should request lot-specific certificate-of-analysis data because the neat-polymer specification is not sufficient to establish compliance in a formulated article.

Comparative Processing Properties and Regulatory Boundaries

The following table compares G1652 MUP with G1650 MUP on parameters that govern solvent and melt processing. The values are manufacturer-published typicals. The lower solution viscosity of G1652 MUP reduces solvent demand and mixing torque, while the higher melt mass-flow rate shortens cycle time in injection-moulded compounds.

Compression-moulded mechanical properties for G1652 MUP include Shore A hardness of 65 (ASTM D2240), tensile strength of 31 MPa (ASTM D412), elongation at break of 880% (ASTM D412), and 300% modulus of 5.5 MPa (ASTM D412). The lower molecular weight of G1652 MUP relative to G1650 MUP reduces tensile strength and cohesive strength but improves melt flow and solution processability.

For formulated articles, regulatory status cannot be established from the neat polymer alone. The following matrix lists assessments that are commonly performed on finished compounds containing G1652 MUP.

In halogen-free flame-retardant cable-sheathing compounds, G1652 MUP is oil-extended and filled with magnesium hydroxide or aluminium trihydroxide. The saturated midblock contributes lower smoke density and reduced acid-gas evolution compared with PVC; smoke-density and acid-gas release are assessed according to IEC 61034-2 and IEC 60754-1, respectively. Filler loadings above 60 mass % raise melt viscosity and require preheated filler side-feeding and a vacuum port.

In polyolefin modification, G1652 MUP is added at 15–30 mass % via twin-screw compounding; the phase-separated rubber domains increase impact-crack resistance without requiring a separate grafted compatibilizer for polyethylene or polypropylene matrices. For polar engineering thermoplastics, maleic anhydride–grafted polymers are used as interfacial coupling agents. Published domain-size distribution data for this specific configuration is limited because the rubber phase size depends on screw design, melt temperature, and cooling history.