Amphiphilic multi-arm star-block copolymers for encapsulation of fragrance molecules

Novel amphiphilic multi-arm star-block copolymers with a hyperbranched core, a hydrophobic inner shell, and a hydrophilic outer shell have been prepared from a commercial hyperbranched polyester macroinitiator by ring-opening polymerization of -caprolactone, followed by atom transfer radical polymerization of tert-butyl acrylate (tBuA). Hydrolysis of the tert-butyl groups was then used to convert the poly(tBuA) blocks to poly(acrylic acid), resulting in stable amphiphilic core-shell structures with significantly higher degrees of functionality than reported so far in the literature. A strong correlation between the maximum concentration of selected hydrophobic guest molecules and the concentration of amphiphilic star-block copolymer in aqueous solution was observed by 1H NMR, demonstrating the capacity of these copolymers to encapsulate and disperse significant loadings (up to about 27 wt.-%) of volatile hydrophobic molecules such as fragrances in water.