Reinforcement of silica aerogels using silane-end-capped polyurethanes.

Proper selection of silane precursors and polymer reinforcements yields more durable and stronger silica aerogels. This paper focuses on the use of silane-end-capped urethane prepolymer and chain-extended polyurethane for reinforcement of silica aerogels. The silane end groups were expected to participate in silica network formation and uniquely determine the amounts of urethanes incorporated into the aerogel network as reinforcement. The aerogels were prepared by one-step sol-gel process from mixed silane precursors tetraethoxysilane, aminopropyltriethoxysilane (APTES), and APTES-end-capped polyurethanes. The morphology and mechanical and surface properties of the resultant aerogels were investigated in addition to elucidation of chemical structures by solid-state (13)C and (29)Si nuclear magnetic resonance. Modification by 10 wt % APTES-end-capped chain-extended polyurethane yielded a 5-fold increase in compressive modulus and 60% increase in density. APTES-end-capped chain-extended polyurethane was found to be more effective in enhancement of mechanical properties and reduction of polarity.