Synthesis and Unimolecular ESA-CF Polymer Cyclization of Zwitterionic Telechelic Precursors

A series of zwitterionic polystyrene (PS) and poly(THF) telechelics having a pair of a cyclic ammonium and a carboxylate end groups have been prepared by making use of a living anionic and cationic polymerization technique, respectively, and have been applied for effective polymer cyclization through the unimolecular ESA-CF (electrostatic self-assembly and covalent fixation) protocol. Thus, a telechelic polystyrene (PS) having a hydroxyl and a methyl ester group (PS-1) was prepared by a living anionic polymerization technique, and the subsequent triflate esterification of the hydroxyl group and the quaternization either by quinuclidine or N-phenylpyrrolidine were conducted to give two types of telechelic precursors, PS-2a and PS-2b, having a respective cyclic ammonium unit and a methyl ester unit. The methyl ester end group in PS-2a and PS-2b was then converted into a carboxylic acid group by the treatment with boron tribromide to afford PS-3a and PS-3b, respectively. On the other hand, the relevant telechelic poly(THF)s having a pair of cyclic ammonium and carboxylic acid groups, PTHF-1a and PTHF-1b, were obtained conveniently through a living cationic ring-opening polymerization of THF with a triflate ester derivative having a carboxylic acid unit, followed by the end-capping by moderately strained cyclic amines. The effective unimolecular ESA-CF polymer cyclization was performed under various dilutions by employing zwitterionic telechelic PS and poly(THF) precursors, PS-Ia and -Ib as well as PTHF-Ia and -Ib, obtained in situ by the deprotonation of the carboxylic acid unit in PS-3 or PTHF-1 with a strong base like DBU or with an excess of quinuclidine to produce cyclic PS and poly(THF) products of different linking units, PS-IIa and -IIb as well as PTHF-IIa and -IIb, in satisfactory yields.