Pure octa, deca, and dodeca(4-nitrophenyl) cage silsesquioxanes were obtained by regio-selective 4-nitration of octa, deca, and dodeca(4-trimethylsilylphenyl) cage silsesquioxanes via ipso-substitution of trimethylsilyl-phenyl bonds by fuming nitric acid. 3-Nitration of octa(4-methylphenyl)octasilesquioxane was also described. The starting octa(4-methyl-, 4-isopropyl- and 4-trimethylsilylphenyl)octasilsesquioxanes were selectively formed in 9-21% isolated yield in the presence of hydrochloric acid. Mixtures of octa, deca and dodecasilsesquioxanes, with decasilsesquioxane as the main component, were formed in the presence of tetrabutylammmonium fluoride as a catalyst. All the cage compounds could be separated mainly by crystallization.
ortho-Methyl-and ethyl-substituted phenyl octasilsesquioxanes, (o-MePh, or o-EtPh) 8-T 8 , with cubic structure were synthesized in good yield (>70%) under mild basic conditions. The position of the alkyl substituent on the phenyl group (ortho-, meta-, para-) in the starting phenyltrimethoxysilane had a big effect on the yield of the product. (Meta-and para-methyl and-ethyl)phenyltrimethoxysilane did not give the desired products under basic conditions; instead, the methyl derivatives gave products in low yield under acidic conditions (<10%). (MePh) 8-T 8 showed different thermal properties and solubility, depending on the position of the methyl substituent on the phenyl group. (o-EtPh) 8-T 8 , the only obtainable isomer from ethyl-substituted starting materials, showed lower melting point and higher solubility in ordinary solvent than (o-MePh) 8-T 8 .
ABSTRACT:Products in hydrolysis of (4-substituted phenyl)trimethoxysilane in the presence of benzyltrimethylammonium hydroxide in benzene was studied by matrix-assisted laser desorption/ionization-time of flight mass spectroscopy. In the benzene soluble fraction of 4 h reaction, oligosilsesquioxanes containing 6 to 9 silicon atoms with or without loops were observed. (4-Dimethylaminophenyl)trimethoxysilane gave the fraction containing 6 silicon atoms the least (3%), and 9 silicon fraction the most (36%). Oligosilsesquioxanes containing 9 silicon atoms were formed the least among the products for [4-methoxy-(10%), 4-methyl-(22%), non-(3%), and 4-phenyl-(13%) substituted phenyl]trimethoxysilanes. Oligosilsesquioxanes containing 6 to 8 silicon atoms were the major components of the product irrespective of the substituent. Maximum degree of condensation ( f ) was 0.8 for S 8 , and fully condensed structure was not found. The maximum f ¼ 1:00, and completely closed loop was found in S 9 with one OH group remaining.
We describe the precision synthesis schemes of siloxane-containing polymers, i.e., the control of their molecular weight, stereoregularity, and higher-order structures. First, we found a new catalytic dehydrocoupling reaction of water with bis(dimethylsilyl)benzene to give poly(phenylene-disiloxane). Together with this reaction, we applied hetero-condensations to the synthesis of thermally stable poly(arylene-siloxane)s. The dehydrocoupling reaction was applied to the synthesis of syndiotactic poly(methylphenylsiloxane) and poly(silsesquioxane)s, which we also prepared by hydrolysis and deaminative condensation reactions. We discuss the tendency for loop formation to occur in the synthesis of poly(silsesquioxane) by hydrolysis, and provide comments on the design of functionality of the polymers produced. By taking advantage of the low energy barrier to rotation in the silicon-oxygen bond, we designed selective oxygen-permeable membrane materials and liquid crystalline materials. The low surface free energy of siloxane-containing systems allows surface modification of a blend film and the design of holographic grating materials.
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