Ring-Expansion Cationic Cyclopolymerization for Construction of Cyclic Cyclopolymers
“Cyclic cyclopolymer” was successiblly synthesized via ring-expansion cationic cyclopolymerization with a cycic initiator by using a divinyl ether carrying a gem-dimethyl group on the spacer. The unprecedented polymerization was achived through design of the monomer on the basis of Thorpe-Ingold effect as well as optimization of the condition for living cationic cyclopolymerization with the model “acyclic” initiator. The obtained cyclic cyclopolymer exhibited an unusual trend on glass transition temperature (Tg): Tg was decreased as the molecular weight was increased; it was lower than that of the linear cyclopolymer analogue. The unique feature is presumably derived from the conflicting influence, i.e., lowering Tg by larger free volume due to the cyclic topology and heightening Tg by the semiflexible chain.