A Study on Physical Properties of Cyclic Poly(vinyl ether)s Synthesized via Ring-Expansion Cationic Polymerization

Ring-driven physical properties of cyclic poly (vinyl ether)s were studied, such as thermal sensitivity in solution and glass transition temperature (T-g). The samples were precisely synthesized via ring-expansion cationic polymerization with a hemiacetal ester (HAE)-based cyclic compound as the initiator. To clarify the topology effects, linear polymers with similar molecular weights were also prepared via a conventional living cationic polymerization with the HAE-based acyclic initiator (i.e., an adduct of vinyl ether with acetic acid) for comparison. Cyclic poly(vinyl ether)s carrying bulky tricyclic alkane pendant exhibited higher T(g)s than the linear counterparts of similar molecular weights. Interestingly, the T-g was not so decreased even as the molecular weight was lower, which was clearly different from linear polymers. The thermosensitivity of cyclic polymer was also studied with ethyl acetate solution of poly(dodecyl vinyl ether) showing upper critical solution temperature (UCST) at around 45 degrees C. The UCST behavior on cooling process was clearly different from for the linear counterpart, and the cyclic polymer showed duller sensitivity to temperature than the linear. These unique properties of cyclic polymers are likely attributed to the endless structures free from the terminal groups.