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

Abstract

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.

Click chemistry strategies for the accelerated synthesis of functional macromolecules

“…This approach is based on the electrostatic attraction between cationic end groups (strained N ‐phenylpyrrolidinium cation) of poly(tetrahydrofuran) and dianionic (dicarboxylate) derivative. By preassembly into the cyclic form, subsequent covalent bond formation can specifically occur upon heating in dilute solution 755,756 thus allows cyclic polymer building blocks to be constructed via ESA‐CF with a controlled number of clickable groups on the ring backbone for cross‐clipping between these cyclic building blocks. Using this approach, spiro and bridged tricyclic and tetracyclic polymer topologies have been achieved by CuAAC between single cyclic and dicyclic polymer precursors 757,758 .…”