Hot-melt pressure-sensitive adhesives (HMPSAs) have become important in the manufacture of pressure-sensitive labels. Several types of styrenic block copolymers (SBCs) are used to formulate HMPSA adhesives. Styrenic block copolymers are synthetic elastomers made by polymerizing styrene and isoprene or styrene and butadiene. The polymerization is controlled so that the finished elastomer consists of discrete blocks of styrene and isoprene or styrene and butadiene.
The overall macromolecular structure of the elastomer consists of a triblock structure (e.g., styrene-isoprene-styrene) or a diblock structure (e.g., styrene-isoprene). If butadiene is used instead of isoprene, the block copolymer will consist of a styrene-butadiene-styrene tri-block and a styrene-butadiene diblock. The bulk properties of the polymer are a function of the percent styrene, diene chemistry, percent triblock, percent diblock and molecular architecture. The molecular architecture for most SBCs is either linear (most common) or radial.