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, ²⁹Si 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. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1371–1379, 2003