Polybenzoxazine/silica nanocomposites were synthesized with perhydropolysilazane (PHPS) and benzoxazines via thermal polymerization in one step. The reaction of benzoxazine's hydroxy group and PHPS was investigated via H-1 nuclear magnetic resonance and Fourier transform infrared spectrometry. At low heating temperatures, benzoxazine was converted to a polymer with a N, O-acetal structure, whereas at high heating temperatures, it was converted to a polymer with a Mannich structure because high temperatures allow the polymer to react with the Si-H groups of PHPS. Measurements of synthesized poly[6,6'-(1-methylethylidene)bis(3,4-dihydro-3-2H-1,3-benzoxazine)](PB-a)/silica nanocomposites showed that no reaction between PB-a hydroxy groups and PHPS Si-H groups occurred because of a stepwise heating process. Measurements of synthesized poly[6,6'-(1methylethylidene)bis(3,4-dihydro-3-2H-1,3-hexylbenzoxazine)] (PB-hda)/silica nanocomposites showed that no competitive reaction between PB-hda and PHPS occurred when materials were heated at 160 degrees C for 1 h because PB-hda formed no hydroxy group. Conversely, at 240 degrees C, a competitive reaction between PB-hda and PHPS occurred, which led to the formation of Si-O-C linkages. (C) 2016 Elsevier Ltd. All rights reserved.