**6.1. Copolycondensation of 3-aminopropyltrialkoxysilane with chiral groupcontaining trialkoxysilane**

To prepare chiral ladder-like PSQs, the introduction of a chiral moiety into the PSQs was first investigated by acid-catalyzed copolycondensation of two organotrialkoxysilanes containing chiral and amino groups, respectively (Kaneko & Iyi, 2009).

The chiral trialkoxysilanes (R- and S-Monomers) were synthesized by reaction of 3- (triethoxysilyl)propyl isocyanate with (R)-(+)- or (S)-(–)-1-phenylethylamine in dichloromethane at room temperature for 15 min, respectively, followed by evaporation of the dichloromethane. The sol–gel copolycondensation of the resulting chiral trialkoxysilanes with 3-aminopropyltriethoxysilane (APTEOS) (feed molar ratio is 1 : 9) was performed in a mixed solvent of aqueous hydrochloric acid and methanol by heating in an open system until the solvent was completely evaporated (Scheme 5a). The products were isolated as the fractions insoluble in acetone, washed with acetone and chloroform, and then dried under reduced pressure at room temperature to yield the white powdered PSQs.

The 1H NMR spectra in D2O at 60 ºC of the products showed the signals indicating the presence of both the components of the chiral trialkoxysilanes and APTEOS; this indicates that the products were copolymers composed of both trialkoxysilanes. The unit ratio of the chiral groups to the ammonium chloride groups in the products was calculated to be 6 : 94. Therefore, the resulting PSQs are denoted as R6- and S6-PSQs, according to the stereostructure and functionality of the chiral groups. The IR spectra of R6- and S6-PSQs showed absorptions at 1620 cm–1 attributed to the C=O bond of the urea groups, indicating the existence of the units of chiral groups in the products.

In the IR spectra of R6- and S6-PSQs, large absorption bands at 1135 and 1040 cm–1 assigned to the Si–O–Si bonds were observed, indicating the formation of PSQs. In addition, the 29Si NMR spectra in DMSO-*d*6 at 40 ºC of these PSQs exhibit the large peaks in the regions of T3. These results indicate that the complete progress of sol–gel copolycondensations of the chiral trialkoxysilanes and APTEOS, and the formation of Si–O–Si bonds. The *M*ws of R6- and S6- PSQs estimated by the *Zimm* plot method using SLS apparatus were assessed to be 10700 and 9800, respectively, indicating that the products were not oligomeric compounds but polymers.

The XRD patterns of the films of R6- and S6-PSQs showed three diffraction peaks with the *d*value ratio of 1 : 1/√3 : 1/2, indicating the formation of the hexagonal phases. Because these PSQs were soluble in water and DMSO, it was supposed that these hexagonal phases originated not from porous-type structures but from the stacking of rod-like polymers. The diameters of the rod-like PSQs calculated from *d*-values of (100) peaks (1.47–1.48 nm) were assessed to be *ca*. 1.7 nm.

As aforementioned, R6- and S6-PSQs had rod-like structures with relatively small diameter (*ca*. 1.7 nm) in spite of the presence of large T3 peak in the 29Si NMR spectrum. In addition, these PSQs were soluble in water and DMSO, despite the *M*ws of the PSQs were relatively high (*ca*. 9800–10700). These results satisfy the aforementioned conditions for ladder-like structure of PSQ. Therefore, the present chiral PSQs would also have one-dimensional ladder-like structure.

The vibrational circular dichroism (VCD) spectroscopy, which is the extension of the electronic circular dichroism (ECD) into the IR region, is powerful technique to obtain conformational information of chiral molecules (Tang et al., 2007). The VCD spectra of R6 and S6-PSQs showed the reversed absorptions at *ca*. 1140–1165 cm–1, respectively (Fig. 3), corresponding to the absorptions assigned to Si–O–Si bond of polymer main-chains. These results indicate that R6- and S6-PSQs had chiral conformations of main-chains.

84 Ion Exchange Technologies

**containing trialkoxysilane** 

assessed to be *ca*. 1.7 nm.

ladder-like structure.

**6.1. Copolycondensation of 3-aminopropyltrialkoxysilane with chiral group-**

containing chiral and amino groups, respectively (Kaneko & Iyi, 2009).

reduced pressure at room temperature to yield the white powdered PSQs.

the existence of the units of chiral groups in the products.

To prepare chiral ladder-like PSQs, the introduction of a chiral moiety into the PSQs was first investigated by acid-catalyzed copolycondensation of two organotrialkoxysilanes

The chiral trialkoxysilanes (R- and S-Monomers) were synthesized by reaction of 3- (triethoxysilyl)propyl isocyanate with (R)-(+)- or (S)-(–)-1-phenylethylamine in dichloromethane at room temperature for 15 min, respectively, followed by evaporation of the dichloromethane. The sol–gel copolycondensation of the resulting chiral trialkoxysilanes with 3-aminopropyltriethoxysilane (APTEOS) (feed molar ratio is 1 : 9) was performed in a mixed solvent of aqueous hydrochloric acid and methanol by heating in an open system until the solvent was completely evaporated (Scheme 5a). The products were isolated as the fractions insoluble in acetone, washed with acetone and chloroform, and then dried under

The 1H NMR spectra in D2O at 60 ºC of the products showed the signals indicating the presence of both the components of the chiral trialkoxysilanes and APTEOS; this indicates that the products were copolymers composed of both trialkoxysilanes. The unit ratio of the chiral groups to the ammonium chloride groups in the products was calculated to be 6 : 94. Therefore, the resulting PSQs are denoted as R6- and S6-PSQs, according to the stereostructure and functionality of the chiral groups. The IR spectra of R6- and S6-PSQs showed absorptions at 1620 cm–1 attributed to the C=O bond of the urea groups, indicating

In the IR spectra of R6- and S6-PSQs, large absorption bands at 1135 and 1040 cm–1 assigned to the Si–O–Si bonds were observed, indicating the formation of PSQs. In addition, the 29Si NMR spectra in DMSO-*d*6 at 40 ºC of these PSQs exhibit the large peaks in the regions of T3. These results indicate that the complete progress of sol–gel copolycondensations of the chiral trialkoxysilanes and APTEOS, and the formation of Si–O–Si bonds. The *M*ws of R6- and S6- PSQs estimated by the *Zimm* plot method using SLS apparatus were assessed to be 10700 and 9800, respectively, indicating that the products were not oligomeric compounds but polymers. The XRD patterns of the films of R6- and S6-PSQs showed three diffraction peaks with the *d*value ratio of 1 : 1/√3 : 1/2, indicating the formation of the hexagonal phases. Because these PSQs were soluble in water and DMSO, it was supposed that these hexagonal phases originated not from porous-type structures but from the stacking of rod-like polymers. The diameters of the rod-like PSQs calculated from *d*-values of (100) peaks (1.47–1.48 nm) were

As aforementioned, R6- and S6-PSQs had rod-like structures with relatively small diameter (*ca*. 1.7 nm) in spite of the presence of large T3 peak in the 29Si NMR spectrum. In addition, these PSQs were soluble in water and DMSO, despite the *M*ws of the PSQs were relatively high (*ca*. 9800–10700). These results satisfy the aforementioned conditions for ladder-like structure of PSQ. Therefore, the present chiral PSQs would also have one-dimensional

**Figure 3.** Vibrational circular dichroism (VCD) spectra in DMSO of R6- and S6-PSQs.

### **6.2. Polymer reaction of chiral group-containing compound with PSQ-NH3+Cl–**

To prepare ladder-like PSQs containing higher compositional ratios of chiral side-chain groups, the aforementioned acid-catalyzed copolycondensation was investigated with a higher feed molar ratio of chiral trialkoxysilanes (>20%). However, the resulting PSQs were insoluble in all solvents owing to the formation of irregular three-dimensional cross-linked network structures. This is because the number of ion pairs formed by the amino groups of APTEOS and the acid-catalysts decreased.

Therefore, to prepare soluble ladder-like PSQs containing higher ratio of chiral groups, *i.e.*, a lower ratio of ammonium chloride groups, the introduction reaction (polymer reaction) of chiral isocyanate compounds into the aforementioned PSQ-NH3+Cl– was investigated (Kaneko et al., 2011).

Synthesis was performed by reaction of (R)-(+)- or (S)-(–)-1-phenylethyl isocyanate (R- or S-PEI) with PSQ-NH3+Cl– in the presence of triethylamine in DMSO/water (9 : 1 (v : v)) mixed solvent at room temperature for 10 min (Scheme 5b). The products were isolated by precipitation in acetone. The compositional ratios of chiral groups to ammonium chloride groups in the resulting products were estimated from their 1H NMR spectra and were found to depend on the feed molar ratio of PEI to ammonium chloride group of PSQ-NH3+Cl–. Here, soluble PSQs with the compositional ratio of chiral groups to ammonium chloride groups = *ca*. 80 : 20 were prepared. These PSQs are denoted as R80- and S80-PSQs, respectively. The *M*ws of R80- and S80-PSQs were estimated by the *Zimm* plot method using SLS apparatus and were assessed to be *ca*. 54000 and 46000, respectively.

The diffraction peaks in the XRD patterns of the PSQs were broadened compared with those of PSQ-NH3+Cl–. This is due to the decrease in the number of ion pairs, *i.e.*, ammonium chloride groups. The ion pair has an important role in the construction of a regular higherordered structure. However, because the XRD pattern of the product film showed diffraction peaks with *d*-value of 1.80 nm, indicating a relatively regular stacking structure, the rigid structures of PSQs would be maintained.

The chiral conformations of many kinds of helical polymers are stabilized by intramolecular interaction, *e.g.*, hydrogen bonding (Zhao et al., 2004). Therefore, specific rotations of these polymers are generally changed by varying the solvents because their intramolecular interactions are affected by the nature of the solvent. The specific rotations []D22 of R80- and S80-PSQs in methanol were +17.4º and –18.9º, respectively, while those in DMF were +8.6º and –8.5º, respectively. Because these PSQs have urea groups as side chains, which are involved in intramolecular hydrogen bonding, their []D22 values were probably affected by solvent effects. Such a solvent effect on specific rotations indicates the presence of chiral conformations of these PSQs.
