Synthesis of tadpole polymers via triple click reactions: Copper-catalyzed azide-alkyne cycloaddition, diels-alder, and nitroxide radical coupling reactions

We designed a trifunctional initiator (3) containing anthracene, bromide, and OH functionalities and subsequently used as an initiator in atom transfer radical Polymerization (ATRP) of styrene to yield linear polystyrene (PS) with α-anthracene, OH, and ω-bromide terminal groups, of which bromide is later transformed into azide to result in the linear anthracene-, OH-, and azide-terminated PS (l-α-anthracene-OH-ω-azide-PS). The copper-catalyzed azide-alkyne cycloaddition reaction between l-α-anthracene-OH-ω-azide-PS and α-furan-protected-maleimide- ω-alkyne linkage, 4 afforded the linear anthracene-, OH-, and maleimide-terminated PS. The cyclization via intramolecular Diels-Alder click reaction of this linear PS and the subsequent conversion of the hydroxyl into bromide resulted in the cyclic PS with one bromide located on the ring, (c-PS)-Br. Finally, the c-PS-Br was clicked with either well-defined tetramethylpiperidine-1-oxyl-terminated poly(ethylene glycol) (PEG) or poly(ε-caprolactone) (PCL) yielding the tadpole polymer, (c-PS)-b-PEG or (c-PS)-b-PCL.