Effects of Silicon Substitution in the Main Chain Network Segments of Polycyanurates
AIR FORCE RESEARCH LAB EDWARDS AFB CA PROPULSION DIRECTORATE SPACE AND MISSILE PROPULSION DIV/PROPULSION MATERIALS APPLICATIONS BRANCH
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The incorporation of silicon into thermosetting polymers at the molecular level has been shown to have several significant effects, beyond improving thermo-oxidative stability, as demonstrated by studies of silicon-containing cyanate ester resins. These effects are generally traceable to the enhanced flexibility afforded by the substitution of C-Si and C-C bonds, and include increased free volume and thermal expansion. In cyanate esters, the increased specific volume leads to a decrease in cyanate ring density, which may explain the reduced water uptake in silicon-containing cyanate esters at high conversions. In addition, the increased flexibility provides for a greater degree of cure at lower temperatures than would otherwise be possible, leading, counterintuitively, to a higher glass transition temperature for a given cure schedule. Due to the molecular level mechanisms involved, many of these effects are expected to be present in other silicon-containing thermosetting resins as well.
- Inorganic Chemistry
- Polymer Chemistry