Fluorine-containing vinyl ether polymers: Living cationic polymerization in fluorinated solvents as new media and unique solubility characteristics in organic solvents

Living cationic polymerization of fluorine-containing vinyl ethers [CH₂CHOC₂H₄OC₃H₆CnF₂n₊₁: 5FVE (n = 2), 13FVE (n = 6)] was investigated in various solvents with a CH₃CH(OiBu)OCOCH₃/Et₁.₅AlCl₁.₅ initiating system in the presence of an added base. 5FVE was polymerized quantitatively in toluene at 0 °C, and the obtained polymers had predetermined molecular weights with narrow molecular weight distributions (Mw/Mn < 1.1). On the other hand, for the polymerization of 13FVE, the product polymers precipitated due to their extremely poor solubility in nonfluorinated organic solvents. Therefore, fluorinated solvents such as hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroethers, or α,α,α-trifluorotoluene, as-yet uninvestigated for cationic polymerization, were employed. In these solvents, living polymerization was achieved even with 13FVE, yielding well-defined polymers (Mw/Mn < 1.1, by size exclusion chromatography using a fluorinated solvent as an eluent). The solvents were also shown to be good for living polymerization of isobutyl vinyl ether. The obtained fluorine-containing polymers underwent temperature-responsive solubility transitions in organic solvents. Poly(5FVE) showed sensitive upper critical solution temperature (UCST)-type phase separation behavior in toluene. Copolymers of 13FVE and isobutyl vinyl ether showed UCST-type phase separation in common organic solvents with different polarities depending on their composition, while a homopolymer of 13FVE was insoluble in all nonfluorinated organic solvents.