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All siloxane-type siloxane-polyhedral oligomeric silsesquioxane [(HSiO 3/2 ) 8 , T 8 H ] copolymers were synthesized by the dehydrogenative condensation of T 8 H with diphenylsilanediol, tetraphenyldisiloxane-1,3-diol or silanol-terminated polydimethylsiloxanes in the presence of diethylhydroxylamine followed by trimethylsilylation. Coating films were prepared by spin-coating of the coating solutions prepared from the dehydrogenative condensation products. The hardness of the coating films was evaluated by a pencil hardness test and was found to increase up to 6H with increases in the curing temperature. Silica gels were prepared by concentrating the coating solution following by pyrolysis. These silica gels showed a specific surface area 449 m 2 /g at 650• C corresponding to the formation of a silica network in response to combustion of the phenyl groups.

Novel pentacyclic ladder oligomethylsilsesquioxane was synthesized using cis,trans,cis-[MeSi(NCO)O]4 as a building block. This compound was isolated in 13% yield by reprecipitation from the reaction mixture. X-ray crystallography revealed that pentacyclic rings assume a syn,anti,syn-configuration, resulting in the tube-like structure.

Organicinorganic hybrid gas barrier layers using 3-glycidoxypropyl silsesquioxane with random structures on plastic film were prepared by cross-linking reaction between glycidoxy functional group of 3-glycidoxypropyl silsesquioxane and amino functional group of p-xylylenediamine (PXDA). The effects of PXDA content on the gas barrier property of the membranes were investigated. Oxygen permeability coefficient and water vapor transmission rate of the hybrid layer were the same order of poly(vinylidene chloride). Pencil hardness (750 g load) of the hybrid layers on the polyethylene terephthalate (PET) substrate were HB. The pencil hardness of the PET was B. Thus, the pencil hardness of the hybrid layers was slightly higher than that of PET. These characteristics were attributed to the sufficient dispersion of inorganic segments (siloxane network, SiOSi) and organic segments in the hybrid.