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 a-anthracene, OH, and ?-bromide terminal groups, of which bromide is later transformed into azide to result in the linear anthracene-, OH-, and azide-terminated PS (l-a-anthracene-OH-?-azide-PS). The copper-catalyzed azidealkyne cycloaddition reaction between l-a-anthracene-OH-?-azide-PS and a-furan-protected-maleimide-?-alkyne linkage, 4 afforded the linear anthracene-, OH-, and maleimide-terminated PS. The cyclization via intramolecular DielsAlder 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(e-caprolactone) (PCL) yielding the tadpole polymer, (c-PS)-b-PEG or (c-PS)-b-PCL. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012