A high solid polyester polyol/silica nanocomposite resin with low
viscosity is synthesized by an in situ polymerization method, namely
conducting condensation polymerization of polyol/diacid monomer with a
molar ratio of 1.1.about.1.5 in the presence of colloidal silica
nanoparticles with a diameter of 10.about.150 nm. The resulted
nanocomposite resins has a solid content of >95%, molecular weight of
1000.about.5000 g/mol and hydroxyl value of 80-200 mg KOH/g, and a
viscosity in the range of 800-2000 mPa.s. The viscosities are especially
lower than those obtained by a blending method. The nanosilica content in
the nanocomposite resin is 1.about.15% (based on the total solid content
of nanocomposite resin). The high solid polyester polyol/silica
nanocomposite resin was curable with isocyanate or melamine to prepare
high solid transparent nanocomposite coatings with obviously improved
abrasion and scratch resistance, hardness, weatherability etc.