Polybenzoxazine-silica nanocomposites with various silica contents were synthesized by ring opening reaction of benzoxazine in presence of perhydropolysilazane (PHPS). PHPS is a unique element-block and can be convert to silica at low temperature. We have already found that the great improvement of water vapor barrier property of polybenzoxazine formed at high temperature by addition of silica from PHPS. It was suggested that not only silica domains but also the combined polymer-silica layer increased the path of water vapor in the composites. In this work, we aimed to clarify the effect of hybridized domains in the composites on physical properties. 6,6’-(1-Methyl-ethelidene)bis(3,4-dihydro-3-2H-1,3-benzoxazine) (B-a) and 6,6’-(1-methyl-ethelidene)bis(3,4-dihydro-3-2H-1,3-hexylbenzoxazine) (B-had) were chosen as the monomers. The amount of the combined polymer-silica layer was estimated by TGA as the excess char of the composite from the silica content. The thermal stability of polybenzoxazines was greatly improved by silica. 7wt % of silica increased the char at 900 °C from 3 to 13 wt% for poly(B-a) and from 21 to 40 wt% for poly(B-had). Taking account of the numbers of isolated silica domains in polymer observed by transmission electron microscope, the whole composite domains concluding pure silica domain and the combined polymer-silica layer were estimated by using molecular model. It was found that the thickness of the combined polymer-silica layer around the silica domains strongly influenced on the properties rather than the silica content.

Polybenzoxazine-silica nanocomposites: Combined polymer-silica layer in the composite

255th National Meeting (2018)

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