Strong Silica Aerogels Crosslinked with Polynorbornene via Ring Opening Metathesis Polymerization (ROMP)
Silica aerogels are porous, self-assembled, 3D networks of silica nanoparticles. In general they are mechanically weak, which limits their applications in spite of their attractive bulk properties (low thermal conductivity, high acoustic impedance etc.). Weak interparticle necks between silica particles responsible for the poor mechanical properties can be reinforced with polymeric tethers to give strong, crosslinked silica aerogels.1 Here we report the crosslinking of silica aerogels by ring opening metathesis polymerization (ROMP) by providing the surface of silica particles with the norbornene functionality using a new nadimide derivative of 3-aminopropyltriethoxysilane (APTES). Norbornene monomer is introduced in the mesopores and a ROMP process is started using 2nd generation Grubbs' catalyst at ambient temperature. The growing polymer engages norbornene moieties bound on the surface of silica forming a conformal coating of polynorbornene on the mesoporous surfaces throughout the entire skeletal framework. The amount of polymer incorporated in the mesoporous structure is controlled by the concentration of the monomer in the mesopores. Despite the increase in bulk density (up to 0.6-0.7 g cm-3), decrease in porosity (down to ~50% v/v), and decrease in surface area (down to ~150 m2 g-1), the materials remain mesoporous. The mechanical properties in terms of strength, modulus and the energy absorption capability relative to the native (non-crosslinked) counterparts is increased dramatically.
D. Mohite et al., "Strong Silica Aerogels Crosslinked with Polynorbornene via Ring Opening Metathesis Polymerization (ROMP)," Abstracts of Papers of the American Chemical Society, American Chemical Society (ACS), Aug 2010.
240th ACS National Meeting and Exposition (2010: Aug. 22-26, Boston, MA)
Article - Conference proceedings
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