**2.1. Sol–gel reaction of 3-aminopropyltrimethoxysilane**

Preparation of ladder-like PSQs with hexagonally stacked structures was achieved by sol–gel reaction of organotrimethoxysilanes containing amino groups. The first example of monomer to form these materials was 3-aminopropyltrimethoxysilane (APTMOS) (Kaneko et al., 2004a).

The sol–gel reaction of APTMOS was performed by stirring in an acid, *e.g.*, a hydrochloric acid, aqueous solution at room temperature for 2 h, followed by heating (*ca*. 50–60 ºC) in an open system until the solvent was completely evaporated (Scheme 2). The resulting product was dissolved in water and this aqueous solution was lyophilized to obtain ammonium chloride group-containing PSQ (PSQ-NH3+Cl–). Here, a feed molar ratio of the acid to APTMOS is very important factor for the formation of the regular structures of PSQ. The higher-ordered structure of the product was characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and nitrogen adsorption–desorption isotherm measurements, and the molecular structure was characterized by 29Si NMR, XRD, and static light scattering (SLS) measurements.

**Scheme 2.** Preparation of an ammonium chloride group-containing ladder-like PSQ (PSQ-NH3+Cl–) with a hexagonally stacked structure by sol–gel method.

**Figure 1.** XRD pattern of PSQ-NH3+Cl–. Relative humidity (RH) during XRD measurements was 50%.


**Table 1.** *d*-Values of diffraction peaks in the XRD patterns of PSQ-NH3+Cl– under various RH conditions.

For the XRD measurements, the films of the products on the glasses were obtained by drying the aqueous product solutions spread on flat glass substrates. The XRD pattern of PSQ-NH3+Cl– film showed diffraction peaks with the *d*-value ratio of 1 : 1/√3 : 1/2 : 1/3, strongly indicating that PSQ-NH3+Cl– had a hexagonal phase (Fig. 1). These three peaks were assigned to the (100), (110), (200), and (300) peaks, respectively. However, based on only these data, it could not be determined whether this hexagonal phase originated from a porous-type structure or a stacking of a rod-like polymer. Therefore, the influence of relative humidity (RH) was investigated on the *d*-value in the XRD measurements of PSQ-NH3+Cl–. As shown in Table 1, the *d*-values of the diffraction peaks changed by varying RH, *i.e.*, the *d*value increased for a high RH and decreased for a low RH, although the *d*-value ratios of (110)/(100) and (200)/(100) did not change. Such a behavior cannot be expected for hexagonal-structured porous materials. Therefore, it was assumed that this hexagonal phase originated from the stacking of rod-like polymers.

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**Scheme 2.** Preparation of an ammonium chloride group-containing ladder-like PSQ (PSQ-NH3+Cl–)

**Figure 1.** XRD pattern of PSQ-NH3+Cl–. Relative humidity (RH) during XRD measurements was 50%.

20 1.35 – – 30 1.37 0.79 0.69 40 1.40 0.81 0.70 50 1.43 0.82 0.71 60 1.45 0.84 0.73 70 1.48 0.86 0.74 80 1.52 0.88 0.76 90 1.58 0.92 0.79 **Table 1.** *d*-Values of diffraction peaks in the XRD patterns of PSQ-NH3+Cl– under various RH conditions.

(100) (110) (200)

RH (%) *d*-Value

with a hexagonally stacked structure by sol–gel method.

The TEM image of the product showed a stripe pattern, indicating that the rod-like PSQs were stacked parallel. In addition, the SEM image showed the aggregate, which lined up in a regular direction. This indicates that nano-ordered regular structure of PSQ affected the structures in the micro-ordered aggregate. Furthermore, the real image of PSQ-NH3+Cl– obtained by lyophilization seemed to be reflected by the regular nano- and micro-structures. The Brunauer–Emmett–Teller (BET) surface area of the product evaluated by the nitrogen adsorption–desorption isotherm measurement at 77K was much too small (*ca*. 6 m2/g), indicating that the rod-like PSQ stacked densely. These results supported the regular higher-ordered structure of PSQ-NH3+Cl– characterized by the aforementioned XRD measurements, *i.e.*, rod-like structure forming hexagonal phase.

So far, decisive analysis methods to prove the regular molecular structure such as ladderlike structure of PSQ have not been established. Therefore, necessary evidences for confirmation of the structures were collected by performing multiple analyses. The ladderlike PSQ simultaneously satisfies the following conditions: i) to be soluble in any solvents, ii) relatively high molecular weight, iii) relatively narrow molecular width, and iv) observation of large T3 peak and small T2 peak in 29Si NMR spectrum.

The PSQ-NH3+Cl– had a rod-like structure with relatively small diameter (*ca*. 1.6–1.7 nm, estimated from *d*-value of (100) peak in XRD pattern of Fig. 1) in spite of forming highly dense Si–O–Si bond network structure, which was confirmed by the observation of large T3 peak in the 29Si NMR spectrum of Fig. 2. In addition, the PSQ-NH3+Cl– was soluble in water, despite its *M*w was relatively high (*ca*. 12000, estimated by *Zimm* plot method using the SLS), which indicated no formation of three-dimensional network structure. These results satisfy the aforementioned conditions. All these things considered, it is reasonable to assume that the present PSQ has one-dimensional ladder-like molecular structure as shown in Scheme 1c-ii.

It was supposed that ladder-like PSQ-NH3+Cl– was twisted to form rigid rod-like structure in the solid state, resulting in the formation of the hexagonally stacked structure. The driving force for the formation of the twisted conformation is probably intramolecular

charge repulsion between the ammonium cations in side-chain groups of PSQ-NH3+Cl–. Therefore, to investigate correlation between intramolecular charge repulsion and regular structure of PSQ-NH3+Cl–, the XRD measurements were performed with changing RH. Stability of the ammonium cations is affected with RH because of hydration with water molecules. The XRD patterns of PSQ-NH3+Cl– with RH higher than 30% indicated three diffraction peaks derived from hexagonal phase, meanwhile those with RH lower than 20% did not show such the diffraction peaks. Because these results indicate the presence of correlation between the formation of the hexagonally stacked structure and higher RH, it is assumed that the twisted structure caused by intramolecular charge repulsion between the ammonium cations is plausible conformation of PSQ-NH3+Cl–.

**Figure 2.** Solid-state 29Si NMR spectrum of PSQ-NH3+Cl–.

On the basis of the aforementioned results, it was considered that self-organization of the ion pair composed of ammonium cations in the side-chains of the PSQ and chloride anions was the driving force for the formation of regular molecular, conformational, and higherordered structures.

#### **2.2. Sol–gel reaction of (3-(2-aminoethylamino)propyl)trimethoxysilane**

As another monomer, organotrialkoxysilane containing two amino groups, *i.e.*, (3-(2 aminoethylamino)propyl)trimethoxysilane (AEAPTMOS), was employed for the preparation of rod-like PSQ with hexagonally stacked structure (Kaneko et al., 2005a). The procedure for sol–gel reaction of AEAPTMOS was similar to that of APTMOS.

The XRD pattern of the resulting product film showed three diffraction peaks with the *d*value ratio of 1 : 1/√3 : 1/2, indicating that the product had a hexagonal phase. The *d*-values of the diffraction peaks were shifted by varying the RH, although the *d*-value ratios of (110)/(100) and (200)/(100) did not change (Table 2). The same behavior was observed with the aforementioned PSQ-NH3+Cl– (Table 1). Therefore, the PSQ containing doubleammonium groups in one repeating unit also had a hexagonal phase, which originated from the stacking of rod-like polymers. The *d*-value of (100) peak of this PSQ (1.85 nm for RH of *ca*. 50%) was larger than that of PSQ-NH3+Cl– (1.43 nm for RH of *ca*. 50%). This is because of difference in side-chain lengths between these PSQs.

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charge repulsion between the ammonium cations in side-chain groups of PSQ-NH3+Cl–. Therefore, to investigate correlation between intramolecular charge repulsion and regular structure of PSQ-NH3+Cl–, the XRD measurements were performed with changing RH. Stability of the ammonium cations is affected with RH because of hydration with water molecules. The XRD patterns of PSQ-NH3+Cl– with RH higher than 30% indicated three diffraction peaks derived from hexagonal phase, meanwhile those with RH lower than 20% did not show such the diffraction peaks. Because these results indicate the presence of correlation between the formation of the hexagonally stacked structure and higher RH, it is assumed that the twisted structure caused by intramolecular charge repulsion between the

On the basis of the aforementioned results, it was considered that self-organization of the ion pair composed of ammonium cations in the side-chains of the PSQ and chloride anions was the driving force for the formation of regular molecular, conformational, and higher-

As another monomer, organotrialkoxysilane containing two amino groups, *i.e.*, (3-(2 aminoethylamino)propyl)trimethoxysilane (AEAPTMOS), was employed for the preparation of rod-like PSQ with hexagonally stacked structure (Kaneko et al., 2005a). The

The XRD pattern of the resulting product film showed three diffraction peaks with the *d*value ratio of 1 : 1/√3 : 1/2, indicating that the product had a hexagonal phase. The *d*-values of the diffraction peaks were shifted by varying the RH, although the *d*-value ratios of (110)/(100) and (200)/(100) did not change (Table 2). The same behavior was observed with the aforementioned PSQ-NH3+Cl– (Table 1). Therefore, the PSQ containing double-

**2.2. Sol–gel reaction of (3-(2-aminoethylamino)propyl)trimethoxysilane** 

procedure for sol–gel reaction of AEAPTMOS was similar to that of APTMOS.

ammonium cations is plausible conformation of PSQ-NH3+Cl–.

**Figure 2.** Solid-state 29Si NMR spectrum of PSQ-NH3+Cl–.

ordered structures.


**Table 2.** *d*-Values of diffraction peaks in the XRD patterns of the PSQ obtained from AEAPTMOS under various RH conditions.

### **3. Ion-exchange behaviors of ladder-like PSQ with fatty acids**

Because PSQ-NH3+Cl– has ammonium groups as side-chains and chloride anions (Cl–) as counterions, the anion-exchange property can be expected. Therefore, the ion-exchange reaction of the PSQs was performed with anionic organic compounds and the higherordered structures of the resulting products were characterized. First, a fatty acid salt such as *n*-octanoic acid sodium salt was employed as an anionic compound (Scheme 3a) (Kaneko et al., 2004a). By pouring PSQ-NH3+Cl– aqueous solution into aqueous solution of *n*-octanoic acid sodium salt, precipitation immediately occurred. The XRD pattern of the resulting water-insoluble product showed peaks for a typical hexagonal phase and the *d*-value of (100) peak increase more than those of the original PSQs (PSQ-NH3+Cl–), indicating that the diameter of the rod-like PSQ increased when the Cl– as the counterion was exchanged with the bulky *n*-octanoate. Thus, the hexagonal phase of the rod-like PSQ was maintained, in spite of the increase in the *d*-value by ion-exchange reaction with *n*-octanoic acid sodium salt.

On the other hand, when the ion-exchange reactions were performed using the fatty acid salts containing longer alkyl chains (*n*-decanoic acid sodium salt, *n*-dodecanoic acid sodium salt, and *n*-tetradecanoic acid sodium salt), the peaks due to the typical hexagonal phase were not obtained. This is because the hydrophobic interaction between the guest fatty acid salts containing longer alkyl chains was too strong to maintain the hexagonally stacked structure of rod-like PSQ.

**Scheme 3.** Ion-exchange reaction of PSQ-NH3+Cl– with (a) *n*-octanoic acid sodium salt and (b) poly(acrylic acid sodium salt).
