Efficient Polymer Cyclization by Electrostatic Self-Assembly and Covalent Fixation with Telechelic Poly(tetrahydrofuran) Having Cyclic Ammonium Salt Groups

Uniform-size poly(tetrahydrofuran)s (poly(THF)s) having N -phenyl or N -methylpyrrolidinium salt end groups ( 1 p and 1 m, respectively) carrying a dicarboxylate counteranion have been prepared as ionic polymer precursors for an intramolecular cyclization reaction. Thus, 4,4‘-biphenyldicarboxylate ( 2a ) was first introduced quantitatively as a counteranion by repeated precipitation of the polymer precursor 1 p into an aqueous solution containing dicarboxylate sodium salt. The efficient cyclization was confirmed with the ion-exchange product I p a having the molecular weight ranging from 4 to 12 kg/mol in diluted THF. The polymer cyclization proceeded effectively also with I m a having N -methylpyrrolidinium salt end groups. There was a pronounced effect upon changing the reaction solvent from THF to chloroform, acetone, toluene, and ethanol. A series of dicarboxylate salts, that is, terephthalate ( 2b ), o -phthalate ( 2c ), succinate ( 2d ), adipate ( 2e ), and trans -2-butene-1,4-dicarboxylate ( 2f ), was then employed for the ion-exchange reaction. The ion-exchange reaction was quantitative with 2b and 2c, while the carboxylate content reached at most around 80% with 2d, 2e, and 2f even after five precipitations. Nevertheless, the corresponding cyclic poly(THF)s II were obtained in high yields by the subsequent heat treatment of the precursors I p d − f and I p a − c . A partially ion-exchanged polymer precursor carrying mixed counteranions I p ( f /triflate = 42/58) (42% trans -2-butene-1,4-dicarboxylate and 58% triflate) was then subjected to the reaction under dilution. Besides the unreacted I p (triflate), the cyclic polymer product II p f was effectively produced through the exclusive formation of electrostatic self-assemblies by a single polymer precursor unit, in which cations and anions balance the charges.