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A Twisting Ring Polymer: Synthesis and Thermally Induced Chiroptical Responses of a Cyclic Poly(tetrahydrofuran) Having Axially Chiral Units

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journal contribution
posted on 2017-07-13, 12:35 authored by Satoshi Honda, Kaoru Adachi, Takuya Yamamoto, Yasuyuki Tezuka
A series of cyclic poly­(tetrahydrofuran)­s, poly­(THF)­s, having a pair of stereoisomeric forms of axially chiral, 2,2′-disubstituted-1,1′-binaphthyl (BiNap) unit at the opposite positions, CR‑R, CR‑S, and CR‑R/S, have been newly synthesized through an electrostatic self-assembly and covalent fixation (ESA-CF) process by using a center-functionalized (kentro-telechelic) poly­(THF) having an axially chiral BiNap unit and N-phenyl­pyrrolidinium salt end groups, carrying a dicarboxylate counteranion having a BiNap unit. The relevant cyclic and linear analogues, having one axially chiral unit, CR (CR‑1 and CR‑2) and LR, respectively, have also been prepared according to the ESA-CF protocol. The subsequent CD measurements of these cyclic and linear polymers having axially chiral units by lowering the temperature toward −10 °C in hexane revealed the noticeable reduction of the dihedral angle of the binaphthyl units exclusively for the cyclic CR‑R as well as for the CR‑1 and CR‑R/S. The observed thermally induced cyclic topology effect on this chiroptical response is reasoned by the solvophobic interaction promoted for the topologically constrained, looped poly­(THF) segments in the vicinity of the BiNap units.