Properties of poly(2-hydroxyethyl acrylate)-silica nanocomposites obtained by the sol–gel process

Poly(2-hydroxyethyl acrylate) swollen in water forms a hydrogel with good biological acceptance but poor mechanical properties. Reinforcement by a nanometric silica phase obtained by acid catalyzed sol–gel reaction of tetraethoxysilane occurring simultaneously with the polymerization of the organic polymer leads to a hybrid material and is a way to improve the mechanical properties of the homopolymer. Dynamic mechanical measurements show a stiffness increase in the rubbery state as the silica content is increased, for both the xerogel (dry) and the swollen samples. Density measurements of the hybrid materials show that the silica phase has an apparent density close to that of vitreous silica, thus giving an indication of the intimate interpenetration of the organic and the inorganic phases in these nanocomposites. Thermogravimetric analysis has been used to probe the dependence of the thermal stability of the samples on the silica content, and to determine the actual silica amounts in each sample. Information about the percolation threshold of the silica phase could be gained from measurements of water uptake and mechanical moduli. All the results pointed out that the co-continuity of matrix and reinforcement starts at around 15 wt% of silica content.