SURFACE MODIFICATION OF POLYMERS .2. PHOTOOXIDATION OF SBS CONTAINING ANTHRACENE AND GRAFTING INITIATED BY PHOTO-GENERATED HYDROPEROXIDES

Diffusion of anthracene at room temperature from a methanolic solution into a styrene-butadiene-styrene block copolymer (SBS) follows Fick's law with a diffusion coefficient of 3.4 x 10(-12) m2 sec-1. The equilibrium concentration of anthracene in SBS is 2.8 times the solution concentration. Irradiation around 350 nm of SBS films containing anthracene results in the sensitized production of singlet oxygen that competitively reacts with anthracene to give the 9, 10-endoperoxide and with double bonds of SBS to form polymeric hydroperoxides. Quantum yields of both processes have been measured: they depend on anthracene concentration and are of the order of 10(-2) and 1 respectively. Their ratio increases linearly with anthracene concentration. Thermal decomposition of polymeric hydroperoxides in the presence of an aqueous solution of methacrylic acid initiates the grafting. This actually occurs in the film and not at the surface because diffusion of the monomer in SBS is faster than the grafting. Nevertheless contact angle measurements reveal surface modifications due to hydroperoxidation and subsequent grafting.