Abstract
This paper deals with our recent studies on the preparation of ionic silsesquioxanes (SQs) with regular structures. Cationic ladder-like polySQs (PSQs) with hexagonally stacked structures were successfully prepared by the sol-gel reactions of amino group-containing organotrialkoxysilanes in strong acid aqueous solutions. Self-organization of an ion pair (a salt) prepared from the amino group in the organotrialkoxysilane and an acid is the key factor for the formation of such regular structures of the PSQs. It is also reported that the control of the conformational structure of the PSQs was performed by the introduction of the chiral moieties. In addition, we investigated the correlation between the of acid-catalysts and the structures of SQs prepared by the hydrolytic condensation of amino group-containing organotrialkoxysilane, that is, the use of the superacid aqueous solution resulted in the formation of cage-like octaSQ, while the ladder-like PSQs with hexagonally stacked structures were formed from the strong acid aqueous solutions under the same reaction conditions. Furthermore, anion-exchange behaviors of the cationic ladder-like PSQ were investigated with various organic and inorganic compounds, such as anionic surfactants, a polymer, and layered clay minerals, to obtain the functional hybrid materials.
Highlights
Silsesquioxanes (SQs), the materials containing the structure of RSiO1.5, have attracted much attention in the research fields of organic-inorganic hybrid materials for academic and application reasons [1, 2] 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 [3,4,5,6], in addition to exhibiting superior thermal, mechanical, and chemical stabilities derived from siloxane (Si–O–Si) bond frameworks with high bond energy compared with C–C bonds
We report the correlation between the pKa of acid-catalysts and the structures of cationic SQs prepared by hydrolytic condensation of an amino group-containing organotrialkoxysilane monomer
On the other hand, when the hydrolytic condensation of APTMOS was performed using a superacid trifluoromethanesulfonic acid (CF3SO3H) aqueous solution under the same reaction conditions as those used for the preparation of the ladder-like PSQ as described above, we found that cage-like octa(3-aminopropyl)SQ trifluoromethanesulfonate (OAP-polyhedral oligomeric SQs (POSS)-CF3SO3) was prepared in ca. 93% yield with a total reaction time of ca. 5-6 h (Scheme 4) [37]
Summary
Preparation of Ionic Silsesquioxanes with Regular Structures and Their Hybridization. Cationic ladderlike polySQs (PSQs) with hexagonally stacked structures were successfully prepared by the sol-gel reactions of amino groupcontaining organotrialkoxysilanes in strong acid aqueous solutions. Self-organization of an ion pair (a salt) prepared from the amino group in the organotrialkoxysilane and an acid is the key factor for the formation of such regular structures of the PSQs. It is reported that the control of the conformational structure of the PSQs was performed by the introduction of the chiral moieties. We investigated the correlation between the pKas of acid-catalysts and the structures of SQs prepared by the hydrolytic condensation of amino group-containing organotrialkoxysilane, that is, the use of the superacid aqueous solution resulted in the formation of cage-like octaSQ, while the ladder-like PSQs with hexagonally stacked structures were formed from the strong acid aqueous solutions under the same reaction conditions. Anion-exchange behaviors of the cationic ladder-like PSQ were investigated with various organic and inorganic compounds, such as anionic surfactants, a polymer, and layered clay minerals, to obtain the functional hybrid materials
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