Catalyst-free click cascade functionalization of unsaturated-bond-containing polymers using masked-ketene-tethering nitrile N-oxide

We developed a facile protocol for grafting-onto and cross-linking unsaturated-bond-containing common polymers via the formation of masked-ketene-functionalized polymers. The protocol utilizes a cascade functionalization agent 1 that has nitrile N-oxide and masked ketene functionalities. Through the model ligation reactions using 1, it turned out that the 1 facilitates the catalyst-free click introduction of masked ketene moieties to the unsaturated bonds such as CN and CC bonds, capable of undergoing catalyst-free ligation with not only a nucleophilic amine but also a neutral alcohol with low nucleophilicity. On the basis of these results, the catalyst-free grafting reactions of PEG onto EPDM and PAN using 1 were performed to afford the corresponding graft copolymers in excellent conversion yields. In addition, it was also revealed that heating of both PAN and NR with masked ketene moieties at 250 °C for 1 h without catalyst enables the efficient conversion to give the respective cross-linked polymers.