Synthesis, characterization, and properties of novel ladderlike phosphorus-containing polysilsesquioxanes

Novel ladderlike polysilsesquioxanes that contain phosphorus were successfully synthesized by the sol-gel method. The polysilsesquioxanes were characterized by Fourier transform infrared spectroscopy, Si-29 NMR, and X-ray diffraction. The characterizations demonstrated that the polymer possesses a typical ladderlike structure. The thermogravimetric and differential scanning calorimetric data revealed that the polysilsesquioxanes possess excellent thermal stability. A kinetic analysis of thermal degradation showed that the activation energy of thermal degradation is 187 kJ/mol, according to Kissinger's method. The activation energy of thermal degradation normally increases with conversion (from 171 to 309 kJ/mol) according to Ozawa's method. The average activation energy, calculated by Ozawa's method, was 209 kJ/mol. The scanning electron microscopic photograph and Si and P mappings of ladderlike polysilsesquioxanes showed that the particles were uniformly dispersed at the molecular level and that the sizes of the polysilsesquioxane particles were less than 100 nm. The ultraviolet-visible spectra of the ladderlike polysilsesquioxanes revealed no absorbance in the range of 400-800 nm. Ladderlike polysilsesquioxanes possess excellent optical transparency and excellent flame retardance. This transmittance may be used as a criterion for identifying the formation of a homogeneous phase. These polymers have great potential in waveguide applications. (C) 2003 Wiley Periodicals, Inc.