Ring-expansion cationic polymerization of vinyl ethers

Cyclic polymers have unique topologies that are free from terminal groups and thus have attracted attention among polymer physicists. In sharp contrast to the conventional macrocyclization approach where telechelic linear polymers depend on highly diluted conditions, “ring-expansion polymerization” is expected to become a useful methodology to construct cyclic polymers efficiently and reliably. However, synthesis of tailor-made cyclic polymers with conventional living polymerization methods are still a challenging subject, especially for addition polymerization of acyclic vinyl monomers. We have recently realized ring-expansion cationic polymerization of vinyl ethers by using a hemiacetal ester embedded cyclic initiator that is easily synthesized. Herein, the unique polymerization is reviewed along with the history of ring-expansion polymerization.