Calprene® CH6120 is a linear styrene-ethylene/butylene-styrene triblock copolymer supplied by Dynasol as a low-diblock pellet. The product contains a nominal styrene content of 30 wt% and a diblock content of 0%. The poly(ethylene-co-butylene) midblock is fully hydrogenated, which removes the allylic unsaturation present in conventional SBS and shifts the thermal degradation onset upward. The polymer is used in thermoplastic elastomer compounds, polyolefin impact modification, hot-melt adhesives, sealants, bituminous membranes, and other applications requiring a combination of rubbery recovery, thermo-oxidative stability, and melt processability. Table 1 lists typical property values from manufacturer data.

The phase-separated morphology of CH6120 results from the incompatibility between the styrene end blocks and the ethylene/butylene midblock. The polystyrene domains have a glass transition temperature near 95 °C, while the midblock exhibits a glass transition below -50 °C. This structure forms a physically crosslinked elastomeric network without requiring sulfur or peroxide cure. The upper service temperature of unmodified CH6120 is therefore limited by the softening of the polystyrene domains, not by midblock oxidation. In continuous use, formulations that require retention above 70 °C should include polypropylene or another higher-T_g phase to reinforce the network.

What Limits the Melt Processing Window for CH6120?

Because the polymer has a high entanglement molecular weight and a saturated midblock, melt processing requires controlled energy input. The neat polymer should not be run above 230 °C for prolonged periods; at 240 °C and above, gel formation and viscosity rise can occur, particularly in hot spots at the die or in screw mixing elements. On a corotating twin-screw extruder with an L/D ratio of 40:1 to 52:1, the recommended barrel temperature profile starts at 150–170 °C in the feed section and increases to 200–220 °C at the discharge. Process oil injection is normally placed after the polymer is fully melted, typically after the first third of the screw. Screw speeds of 250–350 rpm and specific energy input of 0.18–0.25 kWh/kg are representative for polypropylene/oil-based soft compounds. In injection molding of ready-to-mold SEBS compounds, barrel temperatures of 190–230 °C, mold temperatures of 20–50 °C, and injection pressures of 60–120 MPa are used; excessive injection speed can cause shear heating that raises melt temperature above the safe ceiling.

In polypropylene modification, CH6120 is typically introduced at the feed throat with a polypropylene homopolymer or random copolymer. The block copolymer contributes impact strength and reduces modulus; in TPE compounds with paraffinic oil, hardness can be adjusted from below 20 Shore A to 70 Shore A by changing the PP/SEBS/oil ratio. The high molecular weight of CH6120 provides adequate oil retention, but the oil must be added incrementally; at oil loadings above 50 wt%, surface oil migration may occur depending on the viscosity and aromatic content of the oil. Published data for this specific configuration is limited for exact migration rates, so extraction testing per ASTM D1566 or ISO 1407 should be applied to validate the formulation.

Structural Differences Among CH6120, High-Styrene Grades, and Unhydrogenated Block Copolymers

The principal structural distinction is the styrene fraction. CH6120 at 30 wt% styrene forms fewer and smaller polystyrene domains than a high-styrene SEBS such as H6170, yielding lower hardness and modulus at equivalent plasticizer content but higher elongation and softer tactile response. The 0% diblock specification differentiates CH6120 from SEBS grades that deliberately retain diblock to increase tack or lower viscosity; those grades typically show lower tensile strength, higher compression set, and reduced elastic recovery. Relative to an unhydrogenated SBS, CH6120 exhibits substantially improved thermo-oxidative and UV resistance because the saturated midblock lacks the reactive allylic hydrogen sites that initiate hydroperoxide formation in butadiene-containing block copolymers. The trade-off is lower affinity for sulfur curatives and some aromatic oils; the saturated midblock is not crosslinkable by sulfur systems and must be formulated as a thermoplastic or modified through coagent-assisted peroxide chemistry if covalent crosslinking is required.

Hot-melt adhesive formulations based on CH6120 are processed in high-shear mixers or Z-blade mixers at 170–190 °C. The saturated midblock requires hydrocarbon tackifying resins with compatible solubility parameters; rosin ester resins are generally less compatible with the EB midblock and can produce haze or phase separation. Pressure-sensitive adhesive formulations often use tackifier loadings in the range of 100–150 phr alongside a low-volatility paraffinic oil. The absence of diblock improves cohesive strength but may reduce tack relative to SEBS grades containing controlled diblock. Formulators should evaluate loop tack and peel adhesion per ASTM D6195 and ASTM D3330; published data for this specific adhesive configuration is limited, so laboratory screening is required before line trial.

Bituminous modification with CH6120 is performed in high-shear rotor-stator mixers at 170–190 °C; the polymer is typically added at 3–7 wt% of the bitumen. The hydrogenated midblock extends high-temperature storage stability relative to SBS-modified bitumen, but the absence of double bonds reduces reactivity with sulfur crosslinking systems used in some bituminous formulations. In waterproofing membranes, compounds containing CH6120 and polypropylene copolymers may be formulated for heat resistance above 100 °C depending on thickness and filler content. Softening point and penetration are tested under ASTM D36 and ASTM D5 respectively.

When CH6120 Is Specified for Outdoor or Long-Term Thermal Exposure

Accelerated weathering of SEBS compounds is commonly assessed under ASTM G154 or ISO 4892-2, with tensile retention and color change measured per ASTM D638 and ASTM D2244. CH6120-based formulations do not undergo the rapid chain scission observed in SBS because the EB midblock is saturated. However, the polystyrene end blocks remain vulnerable to ultraviolet photo-oxidation, so outdoor compounds require a hindered amine light stabilizer and a UV absorber. Heat aging per ASTM D573 at 100 °C or 125 °C should be used to validate antioxidant packages; antioxidant selection must avoid species that volatilize above 180 °C during melt compounding. In continuous thermal exposure, the practical upper service limit is governed by polystyrene domain softening near 95 °C and by the thermal stability of the selected process oil; low-volatility paraffinic or white mineral oils are preferred over aromatic oils.

Operational boundaries include avoiding long residence times above 230 °C, avoiding sulfur cure systems as the primary crosslinking mechanism, and avoiding high-loading aromatic oils that plasticize the polystyrene domains. If the compound contains hygroscopic fillers such as flame retardants or talc, predrying at 70–80 °C for 2–4 h is required to prevent surface splay and hydrolysis-induced viscosity drift. The base polymer should not be considered food-contact or medical-compliant until the specific finished formulation has been tested against the relevant end-use standard. Table 2 summarizes regulatory verification points applicable to finished articles containing CH6120.

In medical device grips and tubing components, SEBS compounds are often selected for latex-free, silicone-free, and DEHP-free formulations. The base polymer is characterized for low extractables, but the finished formulation must undergo extractables and leachables testing under ISO 10993-12 and ISO 10993-18. Sterilization compatibility is not inherent: gamma irradiation at typical doses of 25–50 kGy may produce crosslinking or chain scission depending on stabilizer package, while ethylene oxide and electron beam processing require residual testing and dose optimization on the molded or extruded part.

For adhesive and sealant applications, application viscosity can be controlled by adjusting tackifying resin type, oil content, and processing temperature. The linear architecture of CH6120 yields lower zero-shear viscosity than a comparable molecular weight radial SEBS, which improves pumpability in hot-melt lines but may require higher addition of endblock-reinforcing resins to achieve high-temperature holding power. Shear adhesion failure temperature is evaluated per ASTM D4498; holding power and 180° peel are evaluated per ASTM D3654 and ASTM D3330. These tests should be conducted on the final formulation because tackifier and wax selection shift the effective service temperature more than the base SEBS grade alone.