SIS Block Copolymer for Hot-Melt and Pressure-Sensitive Adhesives: A Buyer's Guide

SIS (styrene-isoprene-styrene) is the styrenic block copolymer of choice when fast, aggressive initial tack matters. In hot-melt pressure-sensitive adhesives (HMPSA) and hot-melt adhesives, SIS delivers the "quick stick" that label converters, tape manufacturers, and hygiene-product producers depend on — and keeps that tack at low temperatures where many alternatives stiffen. This guide explains what SIS is, how its grades differ, where it fits best, and what to check before ordering.

1. What Is SIS?

SIS is a triblock copolymer with the structure polystyrene–polyisoprene–polystyrene. The two hard polystyrene end-blocks aggregate into rigid "domains" that act as physical cross-links, while the soft polyisoprene mid-block provides tack and elasticity. Because the cross-links are physical, not chemical, SIS can be melted, coated, and re-processed — the defining feature of a thermoplastic elastomer (TPE).

Because the polyisoprene mid-block is softer and tackier than SBS's polybutadiene mid-block, SIS compounds show excellent initial tack and quick stick, with good low-temperature flexibility. The trade-off is cohesion: at equal styrene level, SIS holds less load, so structural applications usually call for SBS, SEBS, or an SIS/SBS blend. Related product pages: SIS, SBS and SEBS.

2. Key Properties

3. Main Applications

3.1 Hot-Melt Pressure-Sensitive Adhesives (HMPSA)

The single largest use of SIS. As the HMPSA base polymer, it delivers the instant tack required by labels, tapes, protective films, graphics, and POS displays. Formulators blend SIS with tackifying resins (C5 hydrocarbons, rosin esters, terpene-phenolics) and plasticizers to dial in tack, peel strength, and open time; a typical HMPSA runs 30–50% SIS.

3.2 Hygiene Hot Melts

SIS is the classic base for disposable hygiene construction adhesives — diaper assembly, feminine care, and similar elastic-film bonding. Softness, low-temperature flexibility, and clean flow suit high-speed lines; it is often blended with metallocene polyolefins for sprayable, low-odor positions.

3.3 Packaging and Bookbinding Hot Melts

For case and carton sealing, paper conversion, and bookbinding (spine and side gluing), SIS-based hot melts balance set speed, flexibility, and low-temperature crack resistance — valuable for cold-chain logistics.

3.4 Other Uses

• Tapes and assembly adhesives — double-sided and mounting tapes where immediate grab on vertical surfaces matters more than load-holding
• Solvent-based adhesives — SIS solutions for contact and construction adhesives
• Footwear and soft-touch compounds — where tack and low-temperature performance count

4. Grades and Specifications

"SIS" alone is not a specification — grade selection separates a tacky PSA from a cohesive structural adhesive:

5. SIS vs. SBS: Choosing the Right Base Polymer

Where both tack and cohesion matter, formulators run SIS/SBS blends or move up to hydrogenated SEPS; for long-term UV and heat exposure, SEBS remains the safer choice.

6. How to Source SIS: A Procurement Checklist

• Specify the grade, not just "SIS". Ask for styrene content, architecture (linear/radial), approximate diblock level, and MFI — these four parameters define performance.
• Request the documents. A serious supplier provides TDS, batch-specific COA, and MSDS/SDS.
• Trial on your real formulation. Test with your own tackifier and oil system — tack, peel, cohesion, and color vary more between grades than datasheets suggest.
• Check compatibility with your resins. SIS pairs naturally with C5, rosin ester, and terpene-phenolic tackifiers; confirm before scaling.
• Confirm packaging and storage. SIS ships in bags or big bags; protect from heat, moisture, and compression; rotate stock first-in-first-out.
• Clarify logistics and documentation. For SME-scale orders (typically 1–200 tonnes), confirm lead time and that commercial invoice, packing list, COA, and MSDS accompany the shipment.
• Verify regional export experience. A partner shipping regularly to Vietnam, Thailand, and neighboring markets knows the packaging, labeling, and documentation requirements.

7. Frequently Asked Questions

What is the difference between SIS and SBS?

Both are styrenic triblock copolymers, but SIS has a polyisoprene mid-block and SBS a polybutadiene mid-block. SIS is softer and much quicker-tacking; SBS is stronger and more cohesive. In practice SIS leads in pressure-sensitive and hygiene adhesives; SBS in asphalt modification, footwear, and structural compounds.

How much SIS is used in a typical hot-melt PSA formulation?

A common starting range is 30–50% SIS as the base polymer, balanced with tackifying resin, plasticizer oil, and a little antioxidant. The exact recipe depends on substrate, application temperature, and the required adhesion–cohesion balance.

Can SIS be used in solvent-based adhesives?

Yes. SIS dissolves readily in toluene, cyclohexane, and similar solvents; SIS solutions serve contact and construction adhesives. Confirm viscosity and solids against your coating equipment.

Is SIS suitable for permanent or removable labels?

Both are achievable. Permanent labels lean on higher-styrene, higher-cohesion grades with matched tackifiers; removable labels on lower-cohesion, higher-tack grades. Grade and tackifier ratio, not the polymer alone, decide the outcome.

What is the smallest order quantity, and how is SIS packaged?

HY Chem focuses on SME-scale supply, typically single orders of 1–200 tonnes. SIS is normally supplied in 20–25 kg bags or 500–750 kg big bags; sampling quantities are usually available before bulk commitment.

Column: Industry Information | Product: SIS (Styrene-Isoprene-Styrene) | Related: SBS / SEBS / SEPS thermoplastic elastomers