Synthesis and reactions of poly-tetrahydrofuran with azetidinium salt end-groups

The bulk polymerization of tetrahydrofuran (THF) intiated by methyl trillate or triflic anhydride leads to poly-THF's of polydispersity < 1.2 and possessing one or two oxonium chain ends, if the conversion is kept below 15%. Reaction of these “living” polymers with an N-substituted azetidine leads to the corresponding poly-THF's with one or two quaternary azetidinium chain ends. These polymers can be isolated in pure form by precipitation in water without affecting the azetidinium functions. At increased temperature, these functions undergo ring-opening reactions with nucleophiles. This process has been used to prepare block-copolymers and polymer networks containing poly-THF segments and to synthesize mono or bifunctional ester-terminated poly-THF's. The last reaction is achieved by simple precipitation of the azetidinium-terminated poly-THF into an aqueous solution of the sodium carboxylate at room temperature.