Synthesis of ABC type miktoarm star copolymers by triple click chemistry

An ABC type miktoarm star copolymer possessing polystyrene (PS), poly(ε-caprolactone) (PCL) and poly(ethylene glycol) (PEG) arms was synthesized by combining existing triple click chemistries, namely thiol-ene, copper catalyzed azide-alkyne cycloaddition (CuAAC) and Diels-Alder (DA) reactions. For this purpose, a core (1-(allyloxy)-3-azidopropan-2-yl (anthracen-9-ylmethyl) succinate) with allyl, azide and anthracene functionalities was synthesized in two steps with high yields. Then, polymers with corresponding clickable sites, namely ω-thiol polystyrene (PS-SH), α-alkyne poly(ε-caprolactone) (alkyne-PCL) and ω-maleimide poly(ethylene glycol) (Me-PEG-MI), were independently prepared. As the first step of the grafting onto process, PS-SH was thiol-ene clicked onto the core to yield PS-N₃-Ant. Finally, alkyne-PCL and Me-PEG-MI were bonded to PS-N₃-Ant either in a sequential or a one-pot in situ manner using CuAAC and DA click reactions. All intermediates, related polymers at different stages and final PS-PCL-PEG miktoarm star copolymer were characterized by ¹H NMR, FT-IR, and GPC analyses.