Chunxin Zhang

Polyfunctional cubic silsesquioxanes as building blocks for organic/inorganic hybrids

Cubic silsesquioxanes, [RSiO1.5]x, potentially offer access to organic/inorganic hybrids wherein the exact shape, size and mechanical properties of the inorganic component are perfectly defined. Furthermore, by tailoring the organic functionality bound to silicon, the inorganic/ organic interface can also be perfectly defined. Finally, careful selection of the polymerizable groups in the organic moieties can provide goodto-excellent control of the crosslinked density or degree of polymerization of the resulting hybrid materials. Thus, cubic silsesquioxanes may be exceptional model materials for inorganic/organic hybrids. Methods of synthesizing cubes with liquid-crystalline and/or polymerizable organic moieties are described. Some thermal properties are discussed. The catalytic copolymerization of the octavinyldimethylsiloxy-functionalized cube with the octahydridodimethylsiloxy-functionalized cube to produce a material with well-defined microporosity and high surface area is described. # 1998 John Wiley & Sons, Ltd.

Silsesquioxanes as synthetic platforms. II. Epoxy-functionalized inorganic-organic hybrid species

The vinyl cubic polyhedral silsesquioxanes (vinylSiO1.5)8 and [(vinylMe2SiO)SiO1.5]8 were epoxidized using ten equivalents of m-chloroperoxybenzoic acid (m-CPBA) per cube. The [(vinylMe2SiO)SiO1.5]8 compound converts, quantitatively, to the octaepoxide, [(epoxyMe2SiO)SiO1.5]8 as demonstrated by 1H, 13C, and 29Si solution NMR, chemical and mass spectral analysis. The (vinylSiO1.5)8 cube was likewise fully epoxidized as determined by NMR; however, efforts to isolate it always led to intractable gels. Partial epoxidation was achieved using only three equivalents of m-CPBA. The partially epoxidized compound, when characterized by Cl mass spectra, chemical analysis and NMR, was shown to have an average of two epoxy groups per cube. Both polyepoxides readily polymerized in the presence of Lewis acid catalysts or on reaction with simple amines, which suggests their potential as coupling agents in the synthesis of novel inorganic-organic hybrids.

Octa(3-chloroammoniumpropyl) Octasilsesquioxane

The octahydrochloride salt of octa(3-aminopropyl)octasilsesquioxane can be isolated in 30% yields by controlled hydrolytic condensation of 3-aminopropyltriethoxysilane in strongly acidic methanol. The analytically pure product can be filtered from the reaction solution. The product was characterized by standard analytical and spectroscopic tools. Efforts were made to explore the potential utility of the product for preparing amide and imide compounds that serve as models of polyimides with the goal of making novel materials, especially those that offer high strength and that are flame-resistant. Efforts to make the octa-acetamide were unsuccessful as the hexadeca-acetamide was formed in preference. These results provided the motivation to explore the synthesis of the succinic-anhydride-derived octa-imide. This reaction was found to proceed quite readily. The latter compound is stable in nitrogen to ≈500 °C and more importantly, it appears to behave as a liquid-crystalline material in the temperature range 90–190 °C. This behavior is unusual, given that no aromatic or mesogenic groups are present on the cube. Copyright

Materials characterization of model epoxy-functionalized silsesquioxanes as potential underfill encapsulants

Preliminary data from cured epoxy functionalized silsesquioxane cubes, a novel inorganic/organic hybrid material system, have been presented to explore their potential as a possible advanced material to improve the underfill encapsulant process. The important underfill material properties considered here include the potential flow properties, T/sub g/, and CTE. The single phase nature of these materials has the advantage of reducing the intensive effort needed in filler particle optimization while retaining the ability to include up to 65% by mass silica content. Even for the model system here, using very flexible curing agents, substantial increases in T/sub g/ are observed. Unfortunately, the measured CTE values are comparable to unfilled epoxy resins, although T/sub g/ is observed to be greater than 200/spl deg/C. A large performance gap remains between this simple model system and current highly engineered underfill encapsulants, but these preliminary results show promise. Since the chemistry involved allows for the chemical tailoring of the cube functionality, sophisticated epoxy chemistries already developed for current underfill materials can be used as analogous components on these silica cube materials. Mixtures of different functional silsesquioxane cube materials may allow materials developers a larger range of components to tailor specific physical properties.

Structural Evolution of Silsesquioxane-based Organic/Inorganic Nanocomposite Networks

The basic tetrahedra of silica are readily assembled into eight cornered cages known as cubic silsesquioxanes ([RSiO 1.5 ] 8 ). Silsesquioxane cubes represent one of the smallest possible units of ceramic silica. The corners of these nanometer-sized ceramic cubes are readily functionalized with reactive groups and incorporated into organic polymers. In this work, we characterize the structures that result from varying the length of the flexible organic segments used to connect the cubes in a series of hybrid network materials. For very short organic segments, steric hindrances inhibit high degrees of network conversion and the resulting network is very inhomogeneous. As the length of the flexible organic segment increases, the added degrees of freedom allow a more ‘ordered’ glassy material to evolve. If the length of the organic segment becomes very long in comparison to the size of the cube, a disordered polymer-like network is obtained.

NMR characterization of hybrid systems based on functionalized silsesquioxanes

In this paper, the authors present recent NMR investigations on several silsesquioxanes (RSiO{sub 1.5}){sub 8} with R = H, CH{sub 3}, CH{double_bond}CH{sub 2}, OSi(CH{sub 3}){sub 2}R{prime} (R{prime} = H, CH{sub 3}, CH{double_bond}CH{sub 2}). The octameric polyhedral cubane like derivatives were analyzed by means of high resolution {sup 13}C and {sup 29}Si solid state NMR including CP (Cross-Polarization) and MAS (Magic Angle Spinning) techniques. The CP sequence including variable contact time was used in order to extract quantitative data. The 1D IRCP sequence (Inversion Recovery Cross Polarization), based on the standard CP scheme, allowed them to investigate the CP dynamics of the involved sites and to propose a complete spectral editing of the spectra. Furthermore, local molecular motions were determined through the careful analysis of CP dynamics. Finally, the NMR results related to crystalline cubane derivatives were extended to hybrid systems obtained by cross-coupling of monomeric entities (via hydrosilylation).