Cyclic polymers based on UV-induced strain promoted azide–alkyne cycloaddition reaction

A unique method was developed for the preparation of cyclic polymers based on the combination of atom transfer radical polymerization (ATRP) and UV-induced strain promoted azide–alkyne cycloaddition (SPAAC) reaction. By virtue of a cyclopropenone-masked dibenzocyclooctyne functionalized ATRP initiator (I-1), well-defined telechelic polystyrene (PS) was synthesized to have a cyclopropenone-masked dibenzocyclooctyne at one polymer chain end and a bromo group at the other. The single electron transfer-nitroxide radical coupling reaction was then used to modify the bromo end group to azide, resulting in the corresponding linear PS precursor. Under UV irradiation on its highly diluted solution, the dibenzocyclooctyne end group was quantitatively released from cyclopropenone-masked dibenzocyclooctyne, which intramolecularly reacted with the azide end group in situ to ring-close the linear PS precursor and produce the corresponding cyclic PS based on the SPAAC click reaction.