A Twisting Ring Polymer: Synthesis and Thermally Induced Chiroptical

Article pubs.acs.org/Macromolecules

A Twisting Ring Polymer: Synthesis and Thermally Induced Chiroptical Responses of a Cyclic Poly(tetrahydrofuran) Having Axially Chiral Units Satoshi Honda,† Kaoru Adachi,‡ Takuya Yamamoto,§ and Yasuyuki Tezuka*,∥ †

Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan ‡ Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan § Division of Applied Chemistry, Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan ∥ Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan S Supporting Information *

ABSTRACT: 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.

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INTRODUCTION

Remarkable developments have been observed during the recent decades in the precision syntheses of cyclic polymers, either by the ring-closure of polymer precursors6,7 or by the ring-expansion polymerization,8−10 to provide a scalable amount of tailored cyclic polymers with rigorous structural characterization.3 A new range of topology effects by cyclic polymers has subsequently been uncovered with prescribed cyclic polymers having specific functional groups or having controlled, i.e., block or graft, segment structures.11 And, in particular, a significant topology effect by amphiphilic cyclic block copolymers has been demonstrated upon their self-

Single cyclic (ring) polymers have pertinently attracted a broad range of theoretical and experimental studies since the early period of polymer science.1 A cyclic topology of randomly coiled polymer molecules, free of chain ends in contrast to their linear and branched counterparts, uniquely determines their fundamental physical properties, such as the hydrodynamic volume as well as the viscoelastic and diffusion behaviors.2,3 Moreover, cyclic forms are frequently encountered in such important biopolymers, as DNAs, polypeptides, and polysaccharides, and are dictating their diverse biofunctions, including the chemical, thermal, and enzymatic stabilities as well as the specific physiological activities, covering from insecticidal and antimicrobial competency to preventing cellular infection by HIV.4,5 © XXXX American Chemical Society

Received: April 23, 2017 Revised: June 14, 2017

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DOI: 10.1021/acs.macromol.7b00839 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 1. Synthesis of Cyclic Poly(THF)s Having One or Two Axially Chiral Units by an ESA-CF Process

electrostatic self-assembly and covalent fixation (ESA-CF) process (Scheme 1).3 The ESA-CF process has widely been applied for the precision synthesis of single cyclic polymers having functional groups at the prescribed positions (kyklotelechelics)32 as well as muticyclic polymers up to a tetracyclic K3,3 graph33 and a pentacyclic Shippo-form34 topology. A unique topology effect has been revealed exclusively for the cyclic polymers having the twisting units in contrast to their linear analogue, upon the chiroptical responses monitored by the circular dichroism (CD) measurements with lowering the temperature in a poor solvent to promote the solvophobic segmental interaction in the vicinity of the axially chiral twisting unit.35

assembly states, i.e., micelles/vesicles,12−14 where the topological distinction of the single polymer molecule is amplified. Moreover, topology effects by cyclic polymers upon their dynamic properties, such as the diffusion behavior15 and crystallization kinetics,16−19 have been a subject of intensive investigation, as the chain-end directing reptation dynamics is apparently inapplicable to cyclic polymers in contrast to linear and branched counterparts. In this connection, a variety of cyclic polymers having diverse responsive groups have been prepared, and their topology effects have been explored in their dynamic conformational changes against any physical,20,21 chemical,22,23 or biological24,25 stimuli. And the eventual topological conversion between linear and cyclic polymer forms has also been attained.26−29 In the present study, we have introduced a new class of cyclic polymers having axially chiral units. The incorporation of such a twisting unit within the cyclic polymer backbone segment could cause entropy-promoted conformational constraint by the absence of free chain ends,1 in contrast to their linear counterpart to facilitate the conformational relaxation through the free chain ends. Notably, these are also considered relevant to topologically intriguing objects/substances like a Möbius strip30 and a supercoiled DNA.31 We have thus prepared a series of cyclic poly(THF)s having a pair of stereoisomeric forms of axially chiral, 2,2′disubstituted-1,1′-binaphthyl (BiNap) unit within the backbone segment, together with their relevant linear and cyclic analogues having one BiNap unit, by making use of an

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RESULTS AND DISCUSSION ESA-CF Synthesis of Cyclic and Linear Poly(THF)s Having Axially Chiral Units. A series of cyclic poly(THF)s having one or two axially chiral 2,2′-disubstituted-1,1′binaphthyl (BiNap) units, together with the corresponding linear analogue, were prepared by an electrostatic self-assembly and covalent fixation (ESA-CF) procedure. Thus, we first prepared a ring (single cyclic) polymer having a BiNap unit (CR‑1) by employing an ion pair of a bifunctional telechelic poly(THF) having pyrrolidinium salt end groups, accompanying a dicarboxylate counteranion having a BiNap unit, 2/1R (Scheme 1a), which was obtained by the ion-exchange reaction of 2/CF3SO3− with 1R (Scheme 1c,d). The effective formation of CR‑1 by the standard ESA-CF procedure was unequivocally B


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Figure 1. 300 MHz 1H NMR spectra of (top) a kentro-telechelic poly(THF) having an axially chiral unit and having pyrrolidinium salt end groups (3R/SbF6−), (middle) an ion-exchange product having an axially chiral counteranion (3R/1R), and (bottom) a cyclic poly(THF) having two axially chiral unit (CR‑R) (CDCl3, 40 °C).

confirmed through the 1H NMR characterization of the cyclized product CR‑1 together with the ionic polymer precursor, 2/1R (Figure S1, bottom and top, respectively), in addition to the MALDI-TOF mass (Figure S2) and GPC (Figure S3) characterization. Moreover, the relevant cyclic polymer having one BiNap unit, CR‑2, and a series of cyclic poly(THF)s having two BiNap units at the opposite positions, CR‑R, CR‑S, and CR‑R/S, were prepared by an alternative ESA-CF procedure with a kentrotelechelic precursor, 3R/SbF6− (Scheme 1c), prepared by a functional initiator (Scheme 1b). Thus, a diacid chloride derivative having a BiNap unit was first prepared from a diacid precursor 1R, by the treatment with thionyl chloride, and was used to proceed the living polymerization of THF by adding silver hexafluoroantimonate (AgSbF6). The subsequent endcapping reaction with N-phenylpyrrolidine could afford a kentro-telechelic precursor having a BiNap unit at the center position and having N-phenylpyrrolidinium salt end groups, 3R/SbF6− (Scheme 1c). 1H NMR of the product, 3R/SbF6− (Figure 1, top), showed signals due to binaphthyl unit (marked a−f), in accord with the relevant binaphthyl compounds reported before,36 together with those due to N-phenyl-

pyrrolidinium salt groups (marked l−n) at the 7.0−8.0 ppm region. Those due to the poly(THF) main chain are also visible at around 3.3 and 1.7 ppm. The effective initiation from both acid chloride units was confirmed by comparing the signal intensities of the binaphthyl and the N-phenylpyrrolidinium signals. The obtained kentro-telechelic poly(THF) precursor, 3R/ SbF6−, was then subjected to the ion-exchange reaction to replace the SbF6 anions by a designated dicarboxylate counteranion, either a chiral or a racemic form, 1R, 1S, or 1R/S, in addition to an achiral biphenyl dicarboxylate (Biph). The subsequent covalent conversion of these ionic polymer precursors was conducted by the heating treatment under dilution, optimized at the concentration of 0.2 g/L,3,32 to produce a series of cyclic poly(THF)s having a pair of stereoisomeric forms of axially chiral, BiNap units at the opposite positions, CR‑R, CR‑R/S, and CR‑S, in addition to the relevant cyclic poly(THF) having one BiNap unit, CR‑2 (Scheme 1b). Moreover, a linear poly(THF) having a BiNap unit at the center position (LR) was obtained from the precursor 3R having monofunctional benzoate counteranions (Scheme 1b). C


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Macromolecules The ion-exchange and the subsequent ring-opening reactions of the N-phenylpyrrolidinium groups in 3R/SbF6− by the prescribed anions were monitored by the 1H NMR. Thus, for a typical example, the comparison of the 1H NMR spectra of 3R/ SbF6− and 3R/1R (Figure 1, top and middle, respectively) showed the ion-exchange yield of as high as 97%, based on the comparison of the signal area ratio between the binaphthyl protons (marked a and d) and the naphthoxy-methylene protons (marked g). The subsequent quantitative covalent conversion to produce CR‑R from 3R/1R was evidenced by the change in the chemical shift of N-phenyl proton signals (marked l and m) at around 7.7 ppm in the latter toward the two separated ones at 6.6 and 7.2 ppm (Figure 1, middle and bottom). The MALDI-TOF mass spectra of LR/S and CR‑R (Figure 2, top and bottom, respectively) commonly showed a uniform

Figure 3. SEC traces of (top) a linear and (bottom) a cyclic poly(THF)s having an axially chiral unit (LR and CR‑R, respectively). The observed minor shoulder peak at the higher molecular weight direction in cyclic poly(THF) is assignable to the product formed by the intermolecular chain-extension reaction (THF as an eluent, 1.0 mL/min).

initiator system of a bifunctional acid chloride from 1R with AgSbF6. The comparison of the SEC peak molecular weights, as a measure of the hydrodynamic volume, of the linear LR (7700) with the cyclic CR‑R (6100), obtained by the same starting kenro-telechelic precursor, 3R/SbF6−, showed the reduction by ca. 20% along with the polymer cyclization, which is in good agreement with the preceding studies.37,38 Additional cyclic poly(THF) analogues having an axially chiral BiNap unit, CR‑2, or having a different pair of stereoisomeric forms of BiNap units at the opposite positions, i.e., CR‑S, and CR‑R/S, respectively, were prepared in similar manners (Scheme 1b). Thus, the effective ion-exchange yields of as high as 91% (for CR‑2), >99% (for CR‑S), and 91% (for CR‑R/S) were estimated by the 1H NMR inspection of the ionexchanged products, i.e., 3R/Biph (Figure S4, top), 3R/1S (Figure S5, top), and 3R/1R/S (Figure S6, top), respectively. And the subsequent covalent conversion by the ring-opening reaction of pyrrolidinium salt groups by the binaphthyl dicarboxylate or by the axially chiral dicarboxylate counteranions was also evidenced from the 1H NMR inspection (Figure S4, bottom, Figure S5, bottom, and Figure S6, bottom, respectively) to give the corresponding CR‑2, CR‑S, and CR‑R/S as in the case of CR‑R. The MALDI-TOF mass spectra of CR‑2, CR‑S, and CR‑R/S (Figure S7, top, middle, and bottom, respectively) showed commonly a uniform series of peaks with an interval of 72 mass units. And for CR‑2, CR‑S, and CR‑R/S, the peaks at the mass/ charge = 6118.0, 6280.8, and 6277.9, respectively, were observed as the adduct with Na+ and correspond to those possessing the expected chemical structures with a DPn of 72 having the calculated mass of 6117.76, 6277.93, and 6277.93, respectively. Finally, the SEC examination of CR‑2, CR‑S, and CR‑R/S (Figure S8, top, Figure S8, middle, and Figure S8, bottom, respectively) showed commonly unimodal traces with the PDI range of 1.19−1.35. The reduced apparent peak

Figure 2. MALDI-TOF mass spectra of (top) a linear and (bottom) a cyclic poly(THF)s having an axially chiral unit (LR/S and CR‑R , respectively). Linear mode; matrix: dithranol with sodium trifluoroacetate. DPn denotes the number of monomer units in the product.

series of peaks with an interval of 72 mass units corresponding to the repeating THF monomer unit, and each peak exactly matched the total molar mass of the LR and CR‑R. Thus, for the former, the peak at the mass/charge = 6119.8, which is assumed to the adduct with Na+, corresponds to LR possessing the expected chemical structures with a DPn of 72; (C4H8O) × 72 + C58H50N2O8 plus Na+ equals 6119.78. And for the latter, the peak at the mass/charge = 6277.9, which is assumed to the adduct with Na+, corresponds to CR‑R possessing the expected chemical structures with a DPn of 72; (C4H8O) × 72 + C68H58N2O10 plus Na+ equals 6277.93. The SEC inspection of the LR and CR‑R (Figure 3, top and bottom, respectively) showed a unimodal trace with narrow molecular weight distribution (PDI of 1.05 and 1.09, respectively) to confirm the effective initiation by the employed D


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ature. Thus, the solvophobic interaction of poly(THF) segments is crucially involved in hexane, particularly at the temperature toward −10 °C. We have thus conducted the CD measurements for a series of cyclic polymers CR‑R, CR‑R/S, and CR‑1 in comparison with the linear analogue LR, in order to monitor the temperaturedependent change in the wavelength interval between the positive and the negative Cotton effect peaks (Δλ). And remarkably, we have observed the noticeable extension of Δλ for the cyclic CR‑R, CR‑R/S, and CR‑1 (Figure 5, a, b, and c, respectively), in contrast to the absence of any relevant chiroptical response for the linear counterpart LR (Figure 5d) by decreasing the solution temperature toward −10 °C. According to the preceding theoretical and experimental studies on various axially chiral binaphthyl or biphenyl compounds,45,46 the dihedral angle, θ is reasonably correlated to Δλ, and the incremental change of the interval between the two Cotton effect peak wavelengths (Δλ) of 3.5 nm should correspond to the decrease of the dihedral angle of the binaphthyl or biphenyl units (θ) by 10°.47 And this leads to quantitative estimation of the observed chiroptical response results on the intervals between the Cotton effect peak wavelengths at the temperatures from 20 °C (Δλ20) to −10 °C (Δλ−10) shown in Figure 5. As a result, it was indicated that the intervals between the two Cotton effect peak wavelengths, |Δλ20 − Δλ−10|, for CR‑R, CR‑R/S, and CR‑1 extend by 4, 5, and 2 nm, respectively (Figures 5a, 5b, and 5c, respectively) by lowering the temperature from 20 to −10 °C. And these changes are corresponding to the decreases of the dihedral angle by 11°, 14°, and 6°, respectively. We have then carried out the DFT calculation using a series of model compounds, namely three cyclic BiNap compounds having different ring sizes (MC1, MC2, and MC3) together with a linear open-chain BiNap counterpart, ML (Figure 6). The DFT results indicated that the open-chain compound, ML, and the two cyclic counterparts having three and four oxytetramethylene units, MC2 and MC3, commonly possess the dihedral angle (θ) of around 100°, in contrast to the reduced angle of 79° for the smaller cyclic analogue, MC1, having two oxytetramethylene units. These results agree with the experimental ones on various open-chain and bridged (or cyclized) BINOL derivatives, showing the θ of approximately 90° or more for the former depending on the steric hindrance of the atomic groups linked to the two hydroxy groups of BINOL, in contrast to the θ of less than 90° for the bridged counterparts.47,48 Upon the obtained experimental and calculation results, it is postulated that the dihedral angle, θ, of the BiNap unit in a series of cyclic and linear poly(THF)s in the present study is assumed to be around 100° in hexane at 20 °C as well as in a good solvent of THF. And the dihedral angle θ was reduced to 89° for CR‑R, to 86° for CR‑R/S, and to 94° for CR‑1, by lowering the temperature toward −10 °C in hexane. The solvophobic interaction of poly(THF) segments in the vicinity of the axially chiral BiNap unit is considered to cause this chiro-optical response exclusively for the cyclic polymer frameworks, i.e., in CR‑R as well as in CR‑R/S and CR‑1, in contrast to the linear counterpart, LR. The related solvophobic interactions of polymer segments have so far been reported for the intramolecular polymer chain folding processes,49,50 where the intramolecular solvophobic interaction rather than the intermolecular random aggregation proceeds predominantly. Since cyclic polymers are topologically more constrained in

molecular weights of CR‑2, CR‑S, and CR‑R/S were observed again in comparison with the corresponding linear LR, though with somewhat smaller extent presumably due to the partial loss of the product of the lower molecular weight fraction during the purification procedure by the reprecipitation treatment. To conclude, a series of cyclic poly(THF)s having one or two axially chiral BiNap units were successfully synthesized through the ESA-CF process. Thermally Induced CD Response of Cyclic Poly(THF)s Having Axially Chiral Units. A series of cyclic poly(THF)s having axially chiral BiNap units, i.e., CR‑1, CR‑R, CR‑S, and CR‑R/S, together with the linear analogue, LR, were then subjected to the CD measurements in hexane at different temperatures. The axially chiral BiNap unit has frequently been employed as a chiro-optical conformational probe to monitor the static or dynamic behaviors of chain segments adjacent to the twisted unit.39−44 Thus, first, the CD measurements were performed in THF at 20 °C, where both cyclic and linear poly(THF) samples were apparently soluble (Figure 4). The BiNap group within cyclic

Figure 4. CD spectra of cyclic poly(THF)s having two axially chiral units (CR‑R, (in red), CR‑R/S, (in blue), and CR‑S (in black)) and a linear poly(THF) having one axially chiral units LR (in green) (1.0 × 10−7 mol L−1 in THF, 20 °C).

and linear poly(THF) segments showed commonly a pair of positive and negative Cotton effect peaks at the wavelength of around 225 and 235 nm, equivalent to the low molecular weight (R)- and (S)-1,1′-bi-2-naphthol (Figure S9). Moreover, cyclic poly(THF)s having a pair of stereoisomeric forms of the R−R and R−R/S(racemic) BiNap units, i.e., CR‑R and CR‑R/S, showed the relevant CD profiles with that of CR‑1 (Figure S10). The observed Cotton effect peak intensity was obviously higher for CR‑R than those for CR‑R/S and for LR (Figure 4), confirming the additivity of the chiroptical response by the BiNap groups introduced in the poly(THF) segment. On the contrary, CR‑S having the opposite stereoisomeric forms of the BiNap units showed the substantially reduced Cotton-effect peak signals obviously by the canceling out of the optical responses of the opposite stereoisomeric structures (Figure 4). And in THF, a good solvent of poly(THF), no sign of temperature-dependent chiroptical response was detected. The CD measurements were then conducted in hexane by lowering the temperature toward −10 °C. Any poly(THF) samples used in this study caused partial precipitation toward −10 °C, regardless of the presence or the absence of the BiNap units within the backbone poly(THF) segment. On the other hand, the low molecular weight analogues of the BiNap compounds itself remained soluble in hexane at this temperE


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Figure 5. Temperature-dependent 220−260 nm region CD spectra of cyclic poly(THF)s having one or two axially chiral units, (a) CR‑R, (b) CR‑R/S, and (c) CR‑1, together with (d) a linear poly(THF) having one axially chiral units LR at 20 (in red), 10 (in green), 0 (in black), and −10 °C (in blue). The spectra recorded at −10 °C were magnified by the factor of (a) 3, (b) 1.5, (c) 6, and (d) 1.5, as indicated in the figures. The peak positions of the CD traces recorded at 20 and −10 °C were indicated with red and blue circles, respectively.

Figure 6. DFT optimized structures of cyclic model compounds having an axially chiral unit with different ring sizes (MC1, MC2, and MC3) and a linear analogue (ML) together with the calculated dihedral angles (θ) of the binaphthyl unit.

units exclusively for cyclic polymers having axially chiral units, i.e., CR‑R, CR‑R/S, and CR. This new topology effect on the thermally induced chiroptical response is presumably caused by the solvophobic interaction of topologically constrained poly(THF) segments in the vicinity of the axially chiral units.

their conformation than the linear counterpart by the absence of the chain ends, the dynamic intramolecular polymer segment association in the cyclic poly(THF) products, CR‑R as well as CR‑R/S and CR‑1, could cause higher conformational strain in the vicinity of the BiNap unit and eventually reduce the dihedral angle in the poor solvent of hexane by lowering the temperature.

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EXPERIMENTAL SECTION

Materials. A series of binaphthyl dicarboxylic acid derivatives, 1R/S, 1R, and 1S, were prepared from the corresponding BINOLs, i.e., (±)-1,1′-bi-2-naphthol (Aldrich), (R)-(+)-1,1′-bi-2-naphthol (Aldrich), and (S)-(−)-1,1′-bi-2-naphthol (Aldrich), by the etherification reaction with methyl bromoacetate,51 followed by the acid hydrolysis and the neutralization with NaOH. N-Phenylpyrrolidine was synthesized according to the procedure described before.52,53 A telechelic poly(THF) having N-phenylpyrrolidinium salt end groups

CONCLUSIONS

A series of cyclic poly(THF)s containing axially chiral BiNap units at the prescribed positions were prepared by the ESA-CF process and were fully characterized. The subsequent CD measurements by lowering the temperature in hexane revealed the detectable reduction of the dihedral angle of the BiNap F


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MHz, CDCl3): δ ppm 1.10−2.11 (br, −CH2CH2O−), 2.15−2.50 (m, endo-, exo-NCH2CH2−), 3.09−3.60 (br, −CH2CH2O−), 3.63−4.45 (m, −OCH2COOCH2−, endo-, exo-NCH2CH2−, −CH2CH2NPh), 4.53 (m, −ArOCH2−), 7.02−7.70 (m, ArH, −NPhH), 7.74−7.96 (m, ArH). A 200 mL THF solution containing a weighed amount of 3R/1R (75 mg) was heated to reflux for 3 h after stirring for 30 min at ambient temperature. After removing the solvent by evaporating, the crude product, CR‑R, was recovered by the precipitation into deionized water at 0 °C and was subjected to the silica gel column chromatography using acetone−hexane (1/2, v/v) as an eluent. The product CR‑R was finally isolated as a slightly yellow solid by removing the solvent under reduced pressure. The yield was 48 mg. 1H NMR (300 MHz, CDCl3): δ ppm 1.10−2.11 (m, −CH2CH2O−, −NCH2CH2CH2−), 3.09−3.83 (m, −CH 2 CH 2 O−, −CH 2 CH 2 N−, −NCH 2 CH 2 −), 4.09 (t, −OCH2COOCH2), 4.53 (s, 8H, ArOCH2−), 6.61−6.72 (m, 6H, PhH), 7.10−7.50 (m, ArH and PhH), 7.88−7.96 (m, 8H, ArH). Mn(GPC) = 5800, Mp(GPC) = 6100, and Mw/Mn = 1.09. Synthesis of a Linear Poly(THF) Containing an Axially Chiral Binaphythyl Group, LR. The covalent conversion of 3R/SbF6− with benzoate counteranions was performed according to the procedure reported in the literature.55 To a THF (50 mL) solution of 3R/SbF6− (75 mg, 0.010 mmol), tetrabutylammonium benzoate (75 mg, 0.24 mmol) was dissolved, and the solution was refluxed for 3 h. After the removal of THF under reduced pressure, the residue was purified by silica gel column chromatography using acetone−hexane (1/2, v/v) as an eluent to give LR (70 mg, 93%). 1H NMR (300 MHz, CDCl3): δ ppm 1.10−2.11 (m, −CH2CH2O−, −NCH2CH2CH2−), 3.09−3.84 (m, −CH2CH2O−, −CH2CH2N−, −NCH2CH2−), 4.02 (t, 4H, −OCH2COOCH2−), 4.28 (t, 4H, −CH2OCOPh) 4.53 (4H, s, ArOCH2−), 6.64−6.68 (m, 6H, NPhH), 7.15−7.46 (m, ArH), 7.56 (t, 2H, PhH), 7.84 (d, 2H, ArH), 7.92 (d, 2H, ArH), 8.04 (d, 4H, PhH). Mn(GPC) = 7200, Mp(GPC) = 7700, and Mw/Mn = 1.05. Measurements. 1H NMR spectra were recorded on a JEOL JNMAL300 spectrometer operating at 300 MHz with CDCl3 as a solvent at ambient temperature. The chemical shifts were reported relative to the signal of tetramethylsilane (TMS) (δ = 0.00 ppm). SEC measurements were conducted by a Tosoh model CCPS at 40 °C with a column of a Tosoh TSK G3000HXL and with a Tosoh RI 8020 refractive index detector. THF was used as an eluent at a flow rate of 1.0 mL/min. The molecular weights of the products were estimated by the polystyrene standard samples with the conversion factor of 0.556 for poly(THF)s.56 MALDI-TOF mass spectra were recorded on a Shimadzu AXIMACFR MASS spectrometer by using a nitrogen laser (λ = 337 nm) and with the operation condition at an accelerating potential of 20 kV in a linear-positive ion mode with pulsed ion extraction. A sample solution was prepared by mixing a THF solution containing a polymer specimen (10 μL, 10 mg/mL), a THF solution of dithranol (100 μL, 20 mg/mL), and a THF solution of sodium trifluoroacetate (100 μL, 10 mg/mL), and a portion of the mixture solution was deposited onto a sample target plate. Mass values were calibrated by the three-point method using peaks of α-cyanohydroxycinnamic acid dimer plus H+ at m/z = 379.35, insulin β plus H+ at m/z = 3497.96, and insulin plus H+ at m/z = 5734.62. UV−vis and CD spectra were recorded at different temperatures on a JASCO Ubest V-560 spectrophotometer with a Peltier temperature control system. Density Functional Theory (DFT) Calculations. The computational calculations based on the density functional theory (DFT) method were carried out using Dmol3 module in Materials Studio 6.0 program (Accelrys, Inc.).57−59 The nonlocal generalized gradient approximation (GGA) exchange correlation functional was employed with the gradient-corrected exchange-correlation functional BLYP.60 The double-numeric-quality with polarization functions (DNP) basis set was used with a medium quality of orbital cutoff. The size of the DNP basis set is reported to be comparable to that of the Gaussian 631G** basis set.61,62 The tolerances of the energy, gradient, and displacement convergences were 2 × 10−5 Ha, 4 × 10−3 Ha Å−1, and 5 × 10−3 Å, respectively.

(2; Mn(NMR) = 5100) was prepared by the procedure reported before.54 THF (Godo Co., Inc.) was distilled over Na. All other reagents were used as received unless otherwise noted. Synthesis of a Cyclic Poly(THF) Containing an Axially Chiral Binaphthyl Group, CR‑1. Into a 1 L flask containing an aqueous solution (500 mL) of disodium salt of 1R (450 mg, 1.0 mmol) was added dropwise a 10 mL THF solution containing 500 mg (0.10 mmol) of a telechelic poly(THF) having N-phenylpyrrolidinium salt end groups (2; Mn(NMR) = 5100). The reaction was allowed to proceed for 30 min at 0 °C under vigorous stirring, and the formed precipitates were collected by filtration to give the ion-exchanged product 2/1R (384 mg) with quantitative ion-exchange yield. 1H NMR (CDCl3 ): δ ppm 1.15−2.10 (m, −CH 2 CH 2 O−, endo-, exoNCH 2 CH 2 −), 3.09−3.55(m, −CH 2 CH 2 O−), 3.63−4.05 (m, −CH2CH2NPh, −OCH2COO−), 4.13 (m, exo-NCH2CH2−), 4.51 (m, endo-NCH2CH2−), 7.07 (m, ArH), 7.16 (m, ArH), 7.46(m, PhH), 7.81 (m, ArH). A 500 mL THF solution containing 100 mg of the ion-exchange product, 2/1R, was refluxed for 3 h after stirring for 30 min at ambient condition. The solvent was then removed by evaporation, and the residue was subjected to the silica gel column chromatography with acetone−hexane (1/2, v/v) as an eluent. The crude product CR‑1 was recovered by evaporating the solvent and was further purified by the precipitation into hexane. The yield of CR‑1 was 35 mg. 1H NMR (300 MHz, C DCl 3 ): δ ppm 1.20−1 .88 (m , −CH 2 C H 2 O−, −NCH2CH2CH2−), 3.08−3.75 (m, −CH2CH2O−, −CH2CH2N−, −NCH2CH2−), 4.05 (t, 4H, −OCH2COOCH2−), 4.52 (s, 4H, ArOCH2−), 6.61 (m, 6H, PhH), 7.10−7.50 (m, ArH and PhH), 7.83− 7.96 (m, 4H, ArH). Mn(GPC) = 4400, Mp(GPC) = 5100, and Mw/Mn = 1.32. Synthesis of a kentro-Telechelic Poly(THF) Having a Binaphthyl Unit, 3, by Using a Diacid Chloride of 1R. A telechelic poly(THF) having an axially chiral binaphthyl group at the center position and having N-phenylpyrrolidinium salt end groups was prepared by the end-capping reaction of a living poly(THF) obtained with a bifunctional initiator using a diacid chloride of 1R. Thus, first, into a 100 mL flask containing a weighed amount of a diacid 1R (50 mg, 0.12 mmol) was added an excess amount of SOCl2 (1 mL, 42 mmol) by a syringe. The resulting solution was allowed to reflux for 2 h to prepare a diacid chloride from 1R. After removing the excess of SOCl2 under reduced pressure, 50 mL of dried THF was introduced. Thereupon, a THF solution (4 mL) of silver hexafluoroantimonate (0.24 g, 0.68 mmol) was added to proceed the polymerization of THF, with the precipitation of AgCl, in a thermostated bath at 0 °C for 12.5 min. A weighed amount of N-phenylpyrrolidine (0.93 g, 6.3 mmol) was then added to cause the end-capping reaction at 0 °C for 30 min under stirring. After removing the precipitated AgCl by the filtration, the crude product, 3R/SbF6−, was recovered by the precipitation into hexane cooled at −78 °C and purified by the silica gel column chromatography using acetone−hexane (1/2, v/v) as an eluent. The product, 3R/SbF6−, was finally isolated as a red waxy solid by removing the solvents under reduced pressure. The yield was 0.72 g. 1H NMR (300 MHz, CDCl3): δ ppm 1.43−1.92 (br, −CH2CH2O−), 2.15−2.50 (m, endo-, exo-NCH2CH2−), 3.17−3.68 (br, −CH2CH2O−), 3.72− 4.25 (m, endo-, exo-NCH2CH2−, −COOCH2−, −CH2CH2NPh), 4.53 (s, 4H,−OCH2COO−), 7.10−7.43 (m, 8H, ArH), 7.50−7.72 (m, 10H, −NPhH), 7.85 (d, 2H, ArH), 7.93 (d, 2H, ArH). Synthesis of Cyclic Poly(THF)s Containing One Binaphthyl Group or the Two at the Opposite Positions: CR‑2, CR‑R, CR‑S, and CR‑R/S. A series of cyclic poly(THF)s having one binaphthyl group, CR‑2, or the two at the opposite positions, CR‑R, CR‑S, and CR‑R/S, were prepared by means of the ESA-CF process with the kentro-telechelic precursor having a binaphthyl unit, 3R/SbF6−. The preparation procedure of CR‑R is given below as a typical example. Thus, a few milliliters of MeOH solution containing a weighed amount of 3R/SbF6− (100 mg) was added dropwise into a 400 mL of MeOH/H2O (1/1, v/v) mixture containing a weighed amount of disodium salt of 1R (300 mg, 670 mmol) at 0 °C. The ion-exchange product 3R/1R was formed as the precipitate and was collected by filtration after stirring for 30 min. The yield of 3R/1R was 75 mg with 97% ion-exchange yield. 1H NMR (300 G


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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.7b00839. 1 H NMR spectra of 2/1R, CR‑1, 3R/BiPh, CR‑2, 3R/1S, CR‑S, 3R/1R/S, CR‑R/S, MALDI-TOF mass spectra of CR‑1, CR‑2, CR‑S, CR‑R/S, SEC charts of CR‑1, CR‑2, CR‑S, CR‑R/S, and CD spectra of (R)- and (S)-1,1′-bi-2-naphthol, CR‑1 in THF (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (Y.T.). ORCID

Satoshi Honda: 0000-0001-5289-5078 Takuya Yamamoto: 0000-0001-9716-8237 Yasuyuki Tezuka: 0000-0001-5264-9846 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to Professor Masa-aki Kakimoto and Toshikazu Takata at the Tokyo Institute of Technology for our access to the NMR and CD apparatus. We also thank Kenichiro Nakashima for his assistance on the synthesis of linear and cyclic polymers. This work was supported by KAKENHI (26310206 and 17H06463 Y.T.).

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DEDICATION This paper is dedicated to Professor Shohei Inoue on the occasion of his 85th birthday. REFERENCES

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