Thermal softening behavior of poly (phenylsilsesquioxane) and poly (benzylsilsesquioxane) particles

The thermal softening behavior of poly(phenylsilsesquioxane) (PhSiO3/2) and paly(benzylsilsesquioxane) (BnSiO3/2) particles during heat treatment has been investigated from the results of gel permeation chromatography, therma l and structural analyses of the particles. Both PhSiO3/2 and BnSiO3/2 part icles thermally softened, and the on-set temperature of thermal sintering w as about 140 and 50 degrees C for PhSiO3/2 and BnSiO3/2. respectively. The thermal sintering of the PhSiO3/2 and BnSiO3/2 particles was caused by the decrease of viscosity at temperatures higher than the glass transition temp eratures. Glass transition was observed for BnSiO3/2 in the repeated heatin g runs, while for PhSiO3/2 glass transition was appreciable only in the fir st heating run. From Si-29 nuclear magnetic resonance spectra, the developm ent of siloxane network during heat treatment was found to be more signific ant in PhSiO3/2 than in BnSiO3/2. The difference in the structural evolutio n during heat treatment makes PhSiO3/2 particles thermosetting and BnSiO3/2 ones thermoplastic.