Synthesis Of Polarity SIB Based Hot Melt Pressure Sensitive Adhesives

The hot melt pressure sensitive adhesives (HMPSAs) include reinforcing materials, tackifying resins, plasticizers, antioxidants and so on. The main performance of HMPSAs depends on the structure and physicochemical properties of reinforcing materials. Currently, styrene-isoprene-styrene (SIS) thermoplastic elastomer has been one of the most widely used reinforcing material for HMPSAs. However, since SIS is very hydrophobic, SIS-based HMPSAs can only be applied for lipophilic drugs, which greatly restrict their application for transdermal drug delivery systems. Although the introduction of epoxidation groups can increase the polarity of the SIS, it increases the glass transition temperature of the SIS isoprene phase, which reduces the low-temperature performance of SIS-based HMPSAs. In this article, in situ epoxidation, living anionic polymerization and graft-onto coupling reaction were utilized to prepare the long-branched SIS-g-PB graft copolymer, which not only mixed SIS and SBS uniformly at molecular level, but increased compatibility between reinforcing materials and the tackifying resins of SIS-g-PB based HMPSAs. The main work was carried out as follow:Firstly, formic acid and hydrogen peroxide were utilized to in situ epoxidize the SIS. The relationship between and epoxidation degree and reaction time shows that the epoxidation degrees increased with the extension of reaction time. Polybutadienyllithium macroanions, synthesized by anionic polymerization, were grafted onto the epoxidized SIS copolymers to obtain SIS-g-PB which has different branch length and branch number by adjusting the ratio of epoxidation group and polybutadienyllithium macroanions. The branch number of SIS-g-PB reduced as the ratio of epoxidation group and polybutadienyllithium macroanions increases.Secondly, the micro-structures and property of SIS, ESIS and SIS-g-PB were studied by the atomic force microscope (AFM), DSC, rheometer and contact angle tests. The phase structures and polarity were changed. With the increase of branch length and branch number, the Tg of SIS-g-PB copolymer decreased. The Tg of long branched SIS-g-PB could be predicted by the Fox equation to provide guidance for the design of polymer structure. Viscosity and storage modulus in the low frequency region of the graft polymer increased with the increase of the branch length or branch number.Finally, the compatibility, adhesion properties and drug release properties of SIS-g-PB based HMPSAs were studied. The introduction of polymer branch improved the compatibility between the skeleton and C5 resin,180° peeling strength. Meanwhile, hydrophilic drugs could achieve their good release in the SIS-g-PB based HMPSAs. Thus, the obtained SIS-g-PB based HMPSAs have polar structures.