Kraton™ G1702 H is a hydrogenated styrenic block copolymer supplied as a clear, linear diblock of styrene and an ethylene/propylene midblock. The grade is a pelletized, non-oil-extended diblock with nominal bound styrene of 28% by mass, specific gravity of 0.91 g/cm³ per ASTM D792, and Shore A hardness near 35 after 10 s per ASTM D2240. The saturated midblock separates this product from unhydrogenated SBS and SIS block copolymers: removal of olefinic unsaturation reduces ozone-induced chain scission, thermo-oxidative embrittlement and ultraviolet discoloration in clear films. The diblock architecture lacks the central polystyrene endblock of triblock SEBS grades. This structure lowers plateau modulus and cohesive strength in unformulated films but increases tack, substrate wetting and compatibility with low-polarity surfaces. These trade-offs define the grade selection window in pressure-sensitive adhesives, sealants and polyolefin modification.

Specification values and test method alignment

Representative values from the current technical data package are summarized below. Lot-specific acceptance must be confirmed against the certificate of analysis for the individual production batch.

Property	Test method	Representative nominal value
Bound styrene content	Supplier method, current CoA	28% by mass
Specific gravity	ASTM D792	0.91 g/cm³
Melt flow rate	ASTM D1238, 230 °C/2.16 kg	1.0 g/10 min
Hardness	ASTM D2240, 10 s	35 Shore A
Tensile strength at break	ISO 37	2.1 MPa
Elongation at break	ISO 37	500%
Total extractables	Supplier method	<1.0% by mass
Volatile matter	Supplier method	<0.5% by mass
Ash	Supplier method	<0.1% by mass

Processing temperature is the strictest boundary condition. Melt temperature should be maintained below 230 °C; above this threshold, styrenic endblock scission generates free polystyrene segments that lower tensile strength and increase gel formation in solvent-borne coatings. Corotating twin-screw compounding of G1702 H is normally carried out with a 30:1 to 40:1 L/D ratio and barrel temperatures from 150 °C to 200 °C from feed to die. High-shear dispersion is required to generate modifier domain sizes below 2 µm in polyolefin compounds, but screw speeds exceeding 400 min⁻¹ on a 25 mm extruder may create local viscous heating beyond the degradation limit. Pellets stored above 60% relative humidity should be dried at 60 °C for 2 h in a dehumidified hopper dryer to reduce absorbed moisture below 0.1% before melt processing. In adhesive compounding, the polymer is fed downstream after tackifier and oil are molten; simultaneous cold feeding can cause motor overload and melt-pressure spikes on small laboratory extruders. Published data for this exact configuration is limited, so extruder temperature profiles should be confirmed by melt-pressure and post-extrusion gel-index measurements.

What Limits the Service Temperature of This Diblock in Unformulated Films?

Differential scanning calorimetry of the neat diblock indicates a midblock glass transition below -50 °C and a styrenic endblock glass transition near 100 °C. In unfilled films, upper service temperature under sustained load is approximately 60–70 °C; beyond this range, creep deformation occurs because no central polystyrene anchor connects the rubber midblocks into a continuous elastic network. Replacing 10–20 wt% of the diblock with a triblock SEBS such as Kraton™ G1652 H, or adding a high-softening-point aromatic tackifier, raises physical crosslink density and extends the upper service temperature. The same limitation appears in compression set: the neat diblock shows higher set at 70 °C than a triblock SEBS compound of equivalent Shore A hardness. For elastic recovery above 80 °C, peroxide or electron-beam crosslinking is normally required.

Hot-melt pressure-sensitive adhesive formulations using G1702 H typically contain 30–40 wt% polymer, 50–60 wt% hydrogenated tackifier and 5–10 wt% naphthenic or paraffinic oil. At 180 °C, Brookfield viscosity falls between 2,000 mPa·s and 8,000 mPa·s depending on tackifier softening point and oil aromaticity. For solvent-borne pressure-sensitive adhesives, the diblock permits high-solids solutions at 35–45% solids in toluene or methylcyclohexane without excessive stringiness. The hydrogenated midblock is compatible with aliphatic hydrocarbons but not with ketones, esters, or aromatic solvents; a balanced solvent such as toluene or a toluene/methyl ethyl ketone mixture at 80:20 by volume produces clear solutions at high solids. Peel and tack performance on low-energy substrates is enhanced when the formulation includes a high-softening-point hydrogenated rosin ester at 40–50 wt% of total tackifier.

Solution rheology also influences coatability. A 40% solids toluene solution at 25 °C typically shows Brookfield LVT viscosity between 1,500 mPa·s and 4,000 mPa·s at 12 min⁻¹; at 60 min⁻¹, measured viscosity may fall to 40–60% of the low-shear value. This shear-thinning behaviour permits high-solids coating without severe orange peel. However, quiescent storage beyond 48 h can produce a clear gel-like layer at the bottom of unagitated tanks; gentle recirculation at 5–10 rpm prevents phase separation.

In polyolefin modification, the diblock functions as a clarity-retaining impact modifier. Addition levels of 5–15 wt% to polypropylene homopolymer reduce low-temperature brittleness at 0 °C and increase notched Izod impact at -20 °C without large reductions in melt flow. Because the bound styrene content is only 28%, the diblock disperses as sub-micron to micron rubber domains when compounded at 200 °C in a corotating twin-screw extruder with 30:1 L/D. When the modifier exceeds 30 wt%, co-continuous morphology emerges, producing flexible transparent compounds with Shore A hardness below 70. Field data from injection molding with 80–120 t clamp force indicate reduced gate blush and flow marks when a 50% masterbatch in a compatibilized polypropylene carrier is used. Edge-gated parts with wall thickness below 2 mm may still require process adjustments because the diblock increases melt elasticity and can cause jetting if the melt temperature is below 210 °C.

Recycled polypropylene streams containing mixed ethylene-propylene rubber often show unpredictable flow marks. Addition of 3–7 wt% G1702 H stabilizes melt elasticity by reducing interfacial tension between recycled rubber particles and the polypropylene matrix. Capillary rheometry at 230 °C shows that the compound’s power-law index rises by 0.05–0.10 relative to the unmodified recycled stream, indicating more Newtonian flow and less visible weld-line distortion in injection molded parts.

When higher tack is required, how does G1702 H compare with triblock SEBS grades?

Triblock SEBS grades such as Kraton™ G1652 H form a continuous elastomeric network above the order-disorder transition because each chain has two polystyrene endblocks. Kraton™ G1702 H, as a diblock, has only one polystyrene endblock per chain, so melt viscosity, tensile strength and creep resistance are lower. The practical result is that G1702 H wets low-energy substrates and builds tack more rapidly, but cohesive strength is typically one-third to one-half that of a triblock of equivalent hardness. The diblock is therefore selected when adhesion, tack and optical clarity dominate; triblock grades are selected when cohesive strength and heat resistance are primary. Within the Kraton™ G1700 series, a higher-styrene diblock such as G1701 H shifts the balance toward higher hardness and tensile but lower tack and low-temperature flexibility. G1702 H therefore sits at the low-styrene end for maximum clarity, tack and impact modification efficiency in polypropylene.

Long-term thermal aging of the neat polymer at 120 °C for 168 h shows retention of elongation above 80% only when a hindered phenolic antioxidant is present at 0.1–0.3 wt%. Without antioxidant, the hydrogenated midblock still oxidizes slowly, but the failure mode shifts from chain scission to surface tack loss. Amine-based antioxidants are less effective in this system because they can form chromophores; phosphite/phenolic blends are preferred. Accelerated weathering in a QUV apparatus at 340 nm for 1,000 h shows higher elongation retention for G1702 H than for a comparable unhydrogenated SBS film, although yellowing may still occur if an unhydrogenated tackifier is used. The lower melt viscosity of G1702 H allows hot-melt application temperatures 10–20 °C lower than comparable triblock compounds.

Regulatory acceptability must be verified against current supplier documentation for the specific formulation and end-use. The grade is manufactured under quality systems aligned with ISO 9001; compliance with REACH and RoHS Directive 2011/65/EU should be confirmed on the current certificate. Food-contact clearances under FDA 21 CFR 175.105 or 177.2600 depend on the compounded article’s extraction profile and are not automatically inherited by formulations containing low-molecular-weight oils or non-hydrogenated tackifiers. Medical applications requiring USP Class VI or ISO 10993 testing are outside the standard scope and require validation on the finished device.

If slot-die stringing occurs during continuous coating, what adjustment is required?

Continuous hot-melt coating with G1702 H is normally performed at slot-die temperatures of 165–175 °C and coat weights of 15–25 g/m². Slot-die pressure at typical production speeds remains below 80 bar. A specific production failure mode observed on rotary die and slot-die systems is stringing at the die exit when polymer concentration exceeds 40 wt% and line speed exceeds 150 m/min. The stringing mechanism is elastic recovery of the diblock-rich phase at the die lip. The corrective action is to reduce polymer concentration by 2–5 wt%, raise melt temperature by 5 °C, or increase the tackifier’s softening point by 10 °C to dampen filament elasticity. If the melt temperature is already at 175 °C, further temperature increase is not recommended because the degradation margin to 230 °C narrows and adhesive colour may shift. In this situation, the preferred adjustment is a formulation change rather than a machine condition change. Batch-to-batch variance in melt flow rate of the diblock is low, but changes in tackifier lot can alter die-exit rheology more than the polymer variation.