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.