A highly moisture-proof polysilsesquioxane coating was obtained from a new bis-silylated precursor, which was synthesized from 3-aminopropyltriethoxysilane (APTES) and m-xylylene diisocyanate (m-XDI) in tetrahydrofuran (THF) and verified by 1 H MAS NMR. For direct comparison purposes, an SiO 2 coating was also prepared by the Stöber method using tetraethoxysilane (TEOS) as the reactant. Interestingly, the coating obtained from the polysilsesquioxane sol exhibited a much higher moisture resistance capability than its counterpart, which was attributed to its more compact feature between nanoparticles as characterized by N 2 absorption experiment and transmission electron microscopy (TEM). Furthermore, its high transparency of about 92% showed potential for application in the protection of optical crystals. S ince Stöber developed the sol-gel method more than 30 years ago, 1 remarkable new opportunities have been created to prepare hybrid materials for employment in numerous fields, ranging from microelectronics to healthcare. 2-4 The hybrid materials obtained by the solgel reaction can provide high thermal stability 5 and good mechanical strength, 6,7 such as the large values of the ultimate strength and the rupture energy to the organic polymers, and show high transparency for optical materials 8,9 as well as contact lenses. 10 Recently, there has been a great deal of interest by chemists, physicists, material scientists and integration engineers in preparing polysilsesquioxane through the sol-gel process with the goal of developing low dielectric insulators in microelectronic devices, 11,12 and novel reinforcing elements for hybrid composites. 13-17 Because polysilsesquioxane with an organic group has a low dielectric constant and low moisture absorption compared to silica, it has already been proposed as a replacement for silicon dioxide. 15,18,19 To date, although several kinds of functional films derived from polysilsesquioxane sols have been reported, such as excellent hydrophobic films 15 and photoelectric films, 20,21 few reports on high quality polysilsesquioxane moistureproof coating have been published.In this work, we prepared a moisture-proof coating derived from m-xylylene diureidopropyltriethoxysilane (m-XDUPTES). The highly moisture resistance of the coating was clearly evidenced by putting several color-variable silica gel particles coated with polysilsesquioxane sol into water. It was found that these color-variable silica gel particles retained their original color unchanged for more than 100 hr.
EXPERIMENTAL
Synthesis of the New PrecursorThe following ingredients were used: 3-aminopropyltriethoxysilane (APTES, 99%, Acros), m-xylylene diisocyanate (m-XDI 99%, TOKYO KASEI), tetraethoxysilane (TEOS, 99%, Acros), NH 4 OH (Reagent Grade 26-30% NH 3 ), tetrahydrofuran (THF, dehydrated), EtOH (dehydrated), and deionized water.Scheme 1-Synthesis of m-XDUPTES.