B2O3/SiO2/Phenolic Resin Hybrid Materials Produced by Simultaneous Twin Polymerization of Spiromonomers

A synthetic procedure for boron oxide/silica/carbon polymer hybrid materials is presented, which does not need water as a reagent. For this purpose, the combined polymerization of the two twin monomers 2,2-spirobi[4H-1,3,2-benzodioxasiline] 1 and spiroboronate tetra-n-butylammonium bis(ortho-hydroxymethylphenolato)borate 2 is successful to produce homogeneous hybrid materials by thermal treatment in the melt at 180 degrees C. The achieved hybrid material shows a ternary composition. It consists of silica, polyborate-tetra(n-butyl)ammonium, and phenolic resin. The tetra(n-butyl)ammonium cation within the hybrid material, originating from monomer 2, can be easily sacrificed by Hofmann degradation at 300 degrees C. Thereby, it serves as the proton source for the BOH moiety. This thermal treatment finally results in the formation of the boron oxide network. The reaction between both inorganic networks under the formation of SiOB bonds occurs at 450 degrees C in air atmosphere, which is proven with infrared spectroscopy. Oxidation and carbonization of the hybrid materials provide composite materials with a similar composition of C/B2O3/SiO2. Their use as effective flame retardant materials is demonstrated.