styreneisoprenestyrene

Styreneisoprenestyrene, often abbreviated as SIS, is a synthetic elastomer belonging to the thermoplastic elastomer family. It is a block copolymer, meaning it is composed of repeating segments of different monomers. In the case of SIS, these monomers are styrene and isoprene. Specifically, SIS has a structure where polystyrene blocks are at the ends of a polyisoprene block. This arrangement is often described as a triblock copolymer (S-I-S).

The unique properties of SIS arise from its molecular structure. The styrene blocks are hard and glassy at room temperature, while the polyisoprene block is soft and rubbery. When SIS is processed, the styrene blocks tend to aggregate into distinct domains, forming physical crosslinks within the rubbery polyisoprene matrix. Upon cooling, these polystyrene domains solidify, providing strength and elasticity. When heated above the glass transition temperature of polystyrene, these domains soften, allowing the material to flow and be molded like a thermoplastic. This reversible nature is characteristic of all thermoplastic elastomers.

SIS exhibits a combination of properties that make it useful in a variety of applications. It is known for its good tensile strength, elasticity, tackiness, and flexibility, even at low temperatures. It is also relatively easy to process using standard thermoplastic processing techniques. Common applications for SIS include adhesives, particularly pressure-sensitive adhesives used in tapes and labels, as well as sealants, coatings, and asphalt modification. It can also be blended with other polymers to improve their properties.