1

Development of Element-Block Materials Based on Cage Silsesquioxanes

Polyhedral oligomeric silsesquioxane (POSS), also called cage silsesquioxane, is a typical example of an element-block consisting of a rigid, highly heat-resistant polyhedral low-dimensional inorganic backbone unit composed of Si–O bonds with flexible organic components introduced at each vertex. Controlling their symmetry and organic substituents provide interesting and unique properties. Precise control of spatial arrangement POSS moieties with linkers enables us to understand the structure–property relationship of silsesquioxane-based materials at the molecular level and design their properties more precisely than the conventional sol-gel method. We found that different molecular-level structures exhibit entirely different physical properties, even if the elemental composition is exactly the same. Systematic research of element-block materials based on POSS expected to create new materials with precisely controlled structures at the molecular level.

2

Single component Silsesquioxane-based Molecular Materials

The POSS compounds are used as fillers in matrix polymers and as co-monomers for co-polymerization with organic monomers. Another way of using the POSS compounds contains in the direct cross-linking POSS units with small organic molecules to form three dimensional networks. Optical transparent films of a single POSS compound are, however, hardly formed without cross-linking reagents due to their high symmetry and crystallinity. We have proposed that lower the symmetries of the POSS derivatives decrease their crystallinity and provided optical transparent film forming properties. We have shown that dumbbell-shaped trifluoropropyl substituted POSS derivatives and a star-shaped isobutyl-substituted POSS derivative linked by simple linker chains formed optical transparent films. The present molecules are first examples of optical transparent POSS films showing thermoplastic properties. We are developing single-component hybrid materials whose properties can be controlled by selecting combinations of POSS units of different structures, such as tripodal type POSS derivatives.

3

Development of Surface Segregation Technique based on Cage Silsesquioxanes

Among surface modification methods, surface segregation of small amounts of additives in a polymer matrix is the most convenient and low-cost method, because no special apparatus such as plasma, corona and gamma ray treatments is required. Although the surface segregation approach can increase the hydrophobicity of polymer surfaces, it is still a challenge to make the surfaces hydrophilic in an equivalent method. POSS based compounds are promising candidate of enhanced surface segregation due to their entropically advantage. We have succeeded in surface hydrophilization by entropy-driven surface segregation using a simple casting method with a POSS based compound having flexible hydrophilic organic chains at each vertex.

4

Development of Organoarsenic Chemistry Aimed at Emergent Functions

There are few attempts to use arsenic as a useful material, except for electronic materials such as gallium arsenide, because arsenic has been widely known to be highly toxic. On the other hand, certain microorganisms and algae are known to take up arsenic and convert into less toxic organic arsenic compounds. This means that the most toxic chemical form is inorganic arsenic, such as arsenite, and its toxicity is generally reduced by conversion to organic forms. Furthermore, arsenic is known to be an essential element, and recently the highly poisonous arsenous acid has been used as a treatment for leukemia. We have developed a safe, practical, and useful carbon-arsenic bond formation method using various arsenic intermediates that can be easily derived from nonvolatile arsenic precursors, allowing us to synthesize a wide variety of organic arsenic compounds and polymers. Based on these technologies, we are working on several projects to understand the unique properties of arsenic compounds and to create materials with useful functions.

5

Development of Polymer-based Photosensitizers by understanding the chemistry of arsenic

We synthesized arsenic-containing π-conjugated polymers, exhibiting the highest quantum yield of singlet oxygen generation (Φ = 0.54) in single component main-chain type π-conjugated polymers and high oxidation resistance in solution as well as in the solid state. In addition, when utilized as a recyclable photocatalyst for the oxidation reaction, the photosensitizer exhibited excellent oxidation resistance without losing its recognizable catalytic activity.

6

Organic-Inorganic Composite Particles Inspired by Biomineralization

Construction of organic-inorganic hybrid materials with controlled mineralization is now a current interest for both organic and inorganic chemists to understand the mechanism of natural biomineralization process as well as to seek industrial and technological applications. Most efforts of CaCO3 mineralization have been focused on the influence of specific additives and/or templates on the formation of CaCO3, and then the kinetics and the mechanisms of the subsequently phase transformation and control of morphology. There are, however, little studies applied the specifically binding kinetics and the mechanisms of polyelectrolyte-Ca2+ complexes to the mineralization process of CaCO3 so far. Therefore, the effects of the kinetics and the mechanisms of the interaction of a polymer and Ca2+ on the crystallization process of CaCO3 would provide an opportunity to gain a fundamental understanding on the biomineralization process. We have prepared calcium carbonate composite particles with size-controlled monodispersed spheres by a simple method, “delayed-addition method”.