Programmed Polymer Folding with Periodically Positioned Tetrafunctional Telechelic Precursors by Cyclic Ammonium Salt Units as Nodal Points.

A programmed polymer folding process has been demonstrated by employing a pair of periodically positioned tetrafunctional, linear telechelic poly(THF)s having 5-membered cyclic ammonium salt groups, i.e., N-ethyl or N-phenylpyrrolidinium groups at both chain ends, and N, N-dialkylpyrrolidinium groups at the two interior positions, accompanying two units of a dicarboxylate counteranion to balance the charges, Ia and Ib, respectively. The electrostatic self-assembly and covalent fixation process has subsequently been applied, to cause the ring-opening reaction of the pyrrolidinium units by carboxylate counteranions under dilution. The obtained doubly cyclized polymer products, IIa from Ia and IIb from Ib, were characterized by H NMR and by a MALDI-TOF mass technique, to indicate the formation of polymeric constitutional isomers of either manacle-, 8-, or θ-form. The SEC peak deconvolution analysis of IIa showed the preferential formation of the manacle-form isomer over the 8- and the θ-form counterparts, to accord with the polymer folding of Ia, having the equivalent chemical reactivity of the linking groups, directed by the spatial distance between the folding points. On the other hand, the relevant SEC analysis of IIb showed the predominant formation of the 8-form isomer, consistent with the polymer folding of Ib promoted by the enhanced chemical reactivity of the N-phenylpyrrolidinium end groups over the interior N, N-dialkylpyrrolidinium groups.