Methods to prepare quaternary ammonium groups-containing alternating poly(chlorotrifluoroethylene-alt-vinyl ether) copolymers
Résumé
The radical copolymerisation of electron-acceptor chlorotrifluoroethylene (CTFE) with electron-donor
vinyl ethers (VEs) produced poly(CTFE-alt-VE) alternating fluorinated copolymers with a high content of
functional groups. This article describes methods to synthesise poly(CTFE-alt-VE) copolymers that bear
ammonium-groups insensitive to Hofmann degradation. Direct preparation and post-polymerisation
functionalisation methods are presented. First, the radical copolymerisation of CTFE with a tertiary
amine-carrying vinyl ether led to low molecular weight-copolymers with an imperfect structure. That
copolymerisation and the quaternisation of the amino groups using methyl iodide were however
accompanied by side reactions, including transfer reactions and significant loss of functionality. In
contrast, the second strategy dealt with the post functionalisation of an alternated poly(CTFE-alt-2-
chloroethyl vinyl ether) copolymer. Halogen exchange of poly(CTFE-alt-CEVE) copolymers was carried
out using the efficient Finkelstein reaction. Then, the nucleophilic substitution of the iodine atoms on the
obtained poly(CTFE-alt-IEVE) copolymer led to a poor yield of functionalisation and was accompanied
by a substantial amount of side reactions. Then, the iodine atoms in poly(CTFE-alt-IEVE) copolymers
were chemically changed quantitatively into azides (especially from microwave activation) and the
resulting azido-containing copolymer was reacted with 1-dimethylamino-2-propyne. An optimisation of
this Huisgen's or thermal cycloaddition showed that (i) a copper catalyst led to cross-linked copolymers,
(ii) whereas in the absence of the copper catalyst, the cycloaddition was slow and only converted ca.
60% of the azides; (iii) then, microwave activation led to high yield in a few minutes. Dimethylamino
groups were inserted onto the copolymeric backbone and subsequently quaternised using iodomethane
efficiently. Such copolymers, potentially resistant to alkaline media and able to promote hydroxide anion
conduction, may exhibit interesting properties as a component of solid alkaline fuel cell membranes.