INVESTIGATIONS OF AGING OF PRESSURE SENSITIVE ADHESIVES BASED ON STYRENE-ISOPRENE-STYRENE BLOCK COPOLYMERS

The aging of pressure sensitive adhesives (PSA\u27s) based on styrene-isoprene-styrene (SIS) block copolymers has been explored. The aging of these PSA\u27s has been attributed to the oxidative instability of the SIS polyisoprene midblock. Initial studies concentrated on the aging of SIS films coated on PET backings. Several analytical techniques were used and/or developed to study this aging. These techniques include dual detector size exclusion chromatography (SEC), multiple internal reflectance infrared spectroscopy (MIR-IR), surface tension estimations (STE\u27s), and electron spectroscopy for chemical analysis (ESCA). It was found that antioxidants adequately protected the bulk film. However, the surface of the film was quickly oxidized. Further studies on PSA\u27s found that this surface oxidation lead to a decrease in adhesive performance. As aging progressed the cohesive strength of the oxidized surface was insufficient to transfer a force between the adherend and the adhesive backing. Thus, cohesive failure of the PSA was observed.