Gao Jungang*, Zhang Xuejian, Wang Shichen, Run Mingtao
(College of Chemistry and Environmental Science, Hebei University, Baoding, 071002, China)

1. INTRODUCTION
In the field of inorganic-organic hybrid materials, there is growing interest in polyhedral silsesquioxane-based systems. The interest of these silica-like cage structures is driven by both their growing commercial availability and the relative ease of attaching functional groups to the cage, facilitating the incorporation of the organic component into a macromolecular system.
    Polyhedral oligomeric silsesquioxane (POSS) are a class of cage-shaped nanoscale building blocks that can self-assemble to construct hybrid organic/inorganic nanomaterials with enhanced physical properties^[1-3], POSS nanocubes consist of silicon and oxygen atoms linked into a well-defined, cubic inorganic framework with silicon atoms at the corners and oxygen atoms interspersed along the edges. Each of the silicon corners can be functionalized with a variety of organic substituents^[4,5] to confer precise control over the topology and architecture. Hu and Yuan^[6,7] had proved that the octahedral silsesquioxane can be synthesized in the presence of Me₄NOH. Scheme 1 illustrates the structural representation of the cubic silsesquioxane. In this paper, the hydrolyzation processing of the aliphatic aminosilsesquioxane was examined, and octaaminopropylsilsesquioxane (OAPS) was synthesized.

Scheme 1 The structural formula of the cubic silsesquioxane.

    In cubic macromonomers, all eight vertices are functionalized and equally reactive. Upon processing, the size of the cube core and the functionalized arms define the size of the organic/inorganic components in the resulting nanocomposites where both components are distributed uniformly and periodically.

3. RESULTS AND DISCUSSION
The process of formation of the silsesquioxane compounds is described as a multi-step hydrolysis-condensation reaction (see Scheme 2). The first step is the hydrolysis of an g-amino- propyltrioethoxysiloxane with water to form organic polysilanol compound. In the right environment, depending on the concentration of water, solvent and pH, these precursors can condense with each other, leading to the formation of oligosiloxanes. By means of thermo-dynamics^[8,9], kinetics and solubility of the products, the resulting product mixture can be determined, ranging from lower oligosiloxane dimers or tetramers to polyhedral oligomeric silsesquioxanes like the tri- and tetrasilanol silsesquioxanes.
    The hydrolysis of r-aminopropyltriethoxysilane in the presence of Me₄NOH was studied with various proportions. When the proportion is 3:1, crystal water of tetramethylammonium can provide adequate H₂O in hydrolyzation. The equal molar ratios of tetramethylammonium and ethoxy can provide hydrolytic condition completely and then the reaction selectively to form cube cage, while in other proportions the cage cannot be formed or impurity product obtained. Less solvent could lead to ladder molecules (Mn -20000), while more solvent decreased pH value so that the cage could not be formed.

Scheme 2 The process of formation of the silsesquioxane compounds

    Molecular masses and distributions were measured by GPC and VPO as in Table 1. OAPS data are also shown as comparison. Because the hydrodynamic volumes of "spherical" OAPS are smaller than the linear polystyrenes used for GPC calibration, the measured molecular weights were smaller than the theoretical values. But the molecular mass is 810 determined by VPO, which is close to the theoretical value.