Inorganic−Organic Nanocomposite Based Hard Coatings on Plastics Using In Situ Generated Nano-SiO2 Bonded with ≡Si—O—Si—PEO Hybrid Network

Abstract

Inorganic−organic hybrid nanocomposite sols were prepared using tetraethyl orthosilicate (TEOS), 3-(glycidoxypropyl)trimethoxysilane (GLYMO), n-butanol, water, methanol, and catalytic amounts of HCl and Al(acac)3. Hydrolysis−condensation reactions of TEOS at pH ≈ 1.3 generates silica nanoparticles in the sol that remain bonded with the −Si−O−Si− network and protected by the organic functionality of GLYMO. The pH of the final sol was adjusted to close to the isoelectric point of silica (pH ∼ 2) to increase the shelf life of the sol. The resulting sol (obtained from the best optimized composition TEOS:GLYMO = 2.33:1) when deposited on CR-39 or related plastics yielded optically transparent and spot-free hard coatings after thermal curing at 95 °C. About 1.5−2 μm thick coatings serve all international specifications required for hard coatings. Thermal curing in the presence of Al(acac)3 ensured polymerization of GLYMO originated epoxy groups to polyethylene oxide (PEO). BET surface area measurement confirms ...