Photochemical Crosslinking and Isolation of Block Copolymers in Selective Solvent

Three block copolymer, poly (styrene/butadiene/styrene) micellized in selective solvents is photochemically crosslinked, using benzoyl peroxide as a photochemical initiator. It is found that the ultimate molecular weight of crosslinked micelles increases with the increase in concentration of copolymer and volume percent of precipitant, whereas it decreases with temperature. For isolation purposes of these crosslinked micelles, the nitrobenzene was mixed to the reaction mixture and nitrogen gas was bubbled through the system during precipitation. The micelles were precipitated by dropwise addition of methanol alongwith rigorous stirring. These precipitated micelles were dried at lower than 15°C under vacuum and the molecular weight of so precipitated micelles was found to be the same as before precipitation.