**1. Introduction**

Silsesquioxanes (SQs: RSiO1.5), one class of the materials containing Si–O framework, have attracted much attention in the research fields of materials chemistry for academic and application reasons (Baney et al., 1995; Loy et al., 2000) because they can contain the various functional groups as side chains (R) and are inorganic materials indicating the remarkable compatibility with organic materials such as polymers (Choi et al., 2001; Kim & Chujo, 2003; Yu et al., 2010; Wang et al., 2011), in addition to having superior thermal, mechanical, and chemical properties derived from Si–O framework with high bond energy compared with C–C bonds.

However, even though various kinds of polyhedral oligomeric SQs (POSS) are known as SQs with controlled molecular structures (Scheme 1b) (Feher & Wyndham, 1998; Laine et al., 1998; Zhang et al., 2007; Cordes et al., 2010; Tanaka et al., 2010; Tanaka & Chujo, 2012), the regularly structured polySQs (PSQs) have only been obtained in the limited cases. This is because PSQs are prepared by polycondensation of the trifunctional silane monomers such as organotrialkoxysilanes and organotrichlorosilanes. These multifunctional monomers generally result in the formation of insoluble polymers with irregular three-dimensional network structures of Si–O–Si bonds (Scheme 1a) (Loy et al., 2000). If the molecular, conformational, and higher-ordered structures of PSQs can be controlled, they are expected to be applicable for a wide range of materials research fields.

Ladder-structured PSQs are one of a few PSQs with controlled molecular structures (Scheme 1c) (Brown et al., 1960; Brown et al., 1964; Unno et al., 2005; Zhang et al., 2006; Seki et al., 2010). These structures are classified into two types: "perfect ladder structure" (Scheme 1c-i) and "ladder-like structure" (Scheme 1c-ii) (Abe & Gunji, 2004). The latter has slight defects

in Si–O–Si bond main-chain. Even though oligomeric SQ with "perfect ladder structure" could be synthesized by a step-by-step method and its characterization methods were established (Unno et al., 2002), it is difficult to prepare PSQs with such structures and to characterize them. In most cases, the ladder-structured PSQs probably do not have "perfect ladder structure" but have "ladder-like structure" as shown in Scheme 1c-ii.

**Scheme 1.** Preparation of silsesquioxanes (SQs) with various structures.

The ladder-like PSQs exhibit rigidity and anisotropy in addition to the aforementioned superior physical properties of SQs because they have one-dimensional network structures of Si–O–Si bonds. Furthermore, ladder-like PSQs are colorless materials due to no absorptions of Si–O–Si bonds in the visible light region and can be used as transparent solutions owing to good solubility in any solvents. These properties of ladder-like PSQs would be useful for versatile applications, in particular, as inorganic fillers due to hybridization with organic functional materials.

Furthermore, control of the higher-ordered structures (nanostructures) of PSQs would also be significant to apply to various supramolecular organic–inorganic hybrid materials. For example, it has been reported that trifunctional silane monomers containing long alkyl chains were hydrolyzed to form amphiphilic molecules having silanol groups, resulting in the formation of multilayered PSQs by polycondensation (Scheme 1d) (Parikh et al., 1997; Shimojima et al., 1997). Another method for controlling higher-ordered structures of PSQs is sol–gel reaction (hydrolytic polycondensation) of 1,4-bis(trialkoxysilyl)benzene as a monomer in the presence of surfactants (Inagaki et al., 2002). The resulting material has a hexagonal array of mesopores and crystal-like frameworks. Self-organization of long alkyl chains by hydrophobic interactions is a driving force to form such regular higher-ordered structures.

74 Ion Exchange Technologies

in Si–O–Si bond main-chain. Even though oligomeric SQ with "perfect ladder structure" could be synthesized by a step-by-step method and its characterization methods were established (Unno et al., 2002), it is difficult to prepare PSQs with such structures and to characterize them. In most cases, the ladder-structured PSQs probably do not have "perfect

ladder structure" but have "ladder-like structure" as shown in Scheme 1c-ii.

**Scheme 1.** Preparation of silsesquioxanes (SQs) with various structures.

hybridization with organic functional materials.

The ladder-like PSQs exhibit rigidity and anisotropy in addition to the aforementioned superior physical properties of SQs because they have one-dimensional network structures of Si–O–Si bonds. Furthermore, ladder-like PSQs are colorless materials due to no absorptions of Si–O–Si bonds in the visible light region and can be used as transparent solutions owing to good solubility in any solvents. These properties of ladder-like PSQs would be useful for versatile applications, in particular, as inorganic fillers due to

Furthermore, control of the higher-ordered structures (nanostructures) of PSQs would also be significant to apply to various supramolecular organic–inorganic hybrid materials. For example, it has been reported that trifunctional silane monomers containing long alkyl From the aforementioned background, it is evident that the development of PSQs with regularly controlled molecular and higher-ordered structures is one of the important issues for research fields of SQs. In this chapter, therefore, the author first describes the preparation of cationic PSQs with controlled molecular and higher-ordered structures by simple sol–gel method and their detailed characterizations in section 2. The resulting PSQs indicated the anion-exchange properties due to existence of cationic functional groups as side-chains. Then, the author also describes the anion-exchange behaviors with various organic and inorganic compounds such as anionic surfactants (section 3), a polymer (section 4), layered clay minerals (section 5), and a dye molecule (section 6) to obtain the functional hybrid materials.
