Singlet Oxygen Generation and Adhesive Loss in Stimuli-Responsive, Fullerene-Polymer Blends, Containing Polystyrene-Block-Polyutadiene-Block-Polystyrene and Polystyrene-Block-Polyisoprene-Block-Polystyrene Rubber-Based Adhesives
The adhesive properties, as measured by bulk tack and peel strength analysis, were found to decrease in polystyrene-block-polybutadiene-block-polystyrene (SBS) and polystyrene-block-polyisoprene-block-polystyrene (SIS) PSA films containing common singlet oxygen generators, acridine, rose bengal, and C-60 fullerene, when irradiated with a tungsten halogen light in air. The addition of the singlet oxygen quencher, beta-carotene, to the C-60 fullerene samples was found to significantly deter the rate of adhesive loss in the fullerene-SBS and -SIS PSA nanocomposites. The presence of oxygen was essential to the mechanism of adhesive loss and, in combination with the effects of singlet oxygen generators and a singlet oxygen scavenger, strongly supports a singlet-oxygen mediated process. FTIR investigations of fullerene-SBS and -SIS systems suggest the initial formation of peroxides which, upon further irradiation, lead to the generation of carbonyl-containing compounds of a ketonic type after crosslinking. Rates of SBS and SIS C-H abstraction were comparable and found to decrease when the high-pressure, mercury xenon irradiation source was filtered to allow only light of lambda > 390 nm. (C) 2008 Wiley Periodicals, Inc.