Polymer-silica hybrid materials prepared from some functionalized polybenzoxazoles and polybenzobisthiazoles

Hybrid organic-inorganic composites were prepared by precipitating silica into hydroxypolybenzoxazole (HPBO) and sulfopolybenzobisthiazole (SPBT) polymers, with interfacial bonding between the phases improved by use of isocyanatopropyltriethoxy silane and N, N-diethylaminopropyltrimethoxy silane, respectively. The materials were transparent, and scanning electron micrographs indicated a uniform distribution of silica particles of domain sizes less than 1 μm. Values of the tensile modulus and tensile strength of the HPBO-silica composites were found to increase with the silica content. Values of the modulus of the SPBT-silica composites also increased in this manner, but the improvements in tensile strength were nearly independent of the amount of silica. The composites exhibited thermal decomposition temperatures of approximately 400–500°C, and the thermal stability was significantly increased for both HPBO and SPBT materials with increase in silica content. The water absorption amount for both types of composites decreased significantly compared to that of the pure polymers, suggesting excellent weatherability.