Synthesis and structure–property relationships of SIS-g-PB copolymers and their application in hot-melt pressure-sensitive adhesives†
A “graft onto” method was combined with an epoxidation reaction and living anionic polymerization to successfully synthesize a series of SIS-g-PB copolymers with defined branch numbers and branch lengths. These copolymers were utilized to formulate various hot-melt pressure-sensitive adhesives (HMPSAs). Their molecular structure and bulk properties were characterized by 1H-nuclear magnetic resonance (1H-NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and rheometry. The adhesion performances were characterized in terms of holding power and 180° peel strength. The epoxidation reaction alone would negatively influence the rheological properties of the parent SIS copolymers, particularly for low-temperature applications. Controlled addition of the low-Tg PB blocks can significantly improve the low-temperature properties of the SIS copolymers. Both η* and G′ increased in the lower shear frequency regime (<101 rad s−1) but decreased in the higher shear frequency regime (>101 rad s−1) with branch number and branch length, in which branch length had a greater effect than the branch number. As a result, the 180° peel strength of the SIS-g-PB based HMPSAs displayed reached 0.23 kN m−1, which is more than twice the value for SIS-based HMPSAs.