Polyhydroxyurethane-silica nanocomposites were synthesized with 2-ethyl-2-(((3-((2-(2-oxo-1,3dioxolan- 4-ly) ethyl) thio) propanoyl) oxy) methyl) propane-1,3-diylbis(3-((2-(2-oxo-1,3-dioxolan-4-yl) ethyl) thio) propanate), Tris-CC, and 1,3-diaminopropane in the presence of 5e30 wt% of perhydropolysilazane, PHPS, which is a precursor of silica, in one step. During the synthesis of nanocomposite, three reactions, which are formation of hydroxy group by ring opening polymerization of cyclic carbonate, conversion of PHPS into silica, and the formation of Si-O-C bond by reaction between hydroxy group formed by ring opening and SiH group of PHPS, were competitively proceeded. The competitive reaction mechanism for polyhydroxyurethane-silica nanocomposite was quantitatively analyzed by using propylene carbonate, PC, and propylamine as model compounds of Tris-CC and 1,3-diaminopropane by H-1 NMR. The hydroxy group of polyhydroxyurethane was preferentially formed compared to the conversion of PHPS into silica, then the Si-O-C bond was formed between polyhydroxyurethane and PHPS until 5 h. The formation rate of Si-O-C bond was governed by the formation rate of the hydroxy group of polyhydroxyurethane. On the other hand, the conversion of PHPS to silica was preferentially performed than the formation of hydroxy group of polyhydroxyurethane over 5 h. The hydroxy group of polyhydroxyurethane was more slowly formed than the conversion of PHPS to silica over 5 h. Less competitive reaction between polyhydroxyurethane and PHPS occurred, which lead to the less formation of Si-O-C bond. (C) 2017 Elsevier Ltd. All rights reserved.