Heterofunctionalized Multiarm Star Polymers via Sequential Thiol-para-Fluoro and Thiol-Ene Double "click" Reactions

The successful postfunctionalization of multiarm star polystyrene (PS) with pentafluorophenyl and allyl moieties at the periphery is demonstrated employing modular thiol-para-fluoro and photoinduced radical thiol-ene double "click" reactions, respectively. α-Fluoro and α-allyl functionalized PS (α-fluoro-PS and α-allyl-PS) are in situ prepared by atom transfer radical polymerization of styrene and their mixture is used as macroinitiator in a crosslinking reaction with divinyl benzene (DVB) yielding (fluoro-PS)_m-polyDVB-(allyl-PS)_m multiarm star polymer. It is found that the multiarm star polymer includes nearly identical number of arms possessing pentafluorophenyl and allyl moieties at the periphery. The obtained multiarm star polymer is then reacted with 1-propanethiol through thiol-para-fluoro "click" reaction to give (propyl-PS)_m-polyDVB-(allyl-PS)_m multiarm star polymer, which is subsequently reacted with N-acetyl-l-cysteine methyl ester via radical thiol-ene "click" reaction in order to give well-defined heterofunctionalized (propyl-PS)_m-polyDVB-(cysteine-PS)_m multiarm star polymer, with higher molecular weight and narrow molecular weight distribution. Multiarm star polymers are characterized by using viscotek triple detection gel permeation chromatography, ¹H, and ¹⁹F NMR.