Poly-2-hydroxyethilmethacrylate(pHEMA)-nanosilica composites  were prepared  by hydrolysis and polycondensation of ethoxysilanes (Stöber method) in the presence of HEMA monomers and successive hybrid polymer cure. Two procedures were followed.

Procedure A was used to prepare a nanocomposite with silica 30% weight content. The appropriate HEMA amount was dissolved into ethanol solution containing tetraethoxysilane (TEOS) (1.09 M), H₂O (12.8 M) and NH₃ (0.64 M). While stirring (50 min) the radical initiator (α, α’azoysobutyrronitrile (AIBN)) was added in concentration 0.1%. Water, ammonia and ethanol were removed at 60°C. The polymer was cured at 80°C (overnight) and 90°C (2h).

Procedure B differed mainly for the substitution of half TEOS amount with 3-aminopropyltriethoxysilane (APTS) that was preventively left to react (6d at 40°C) with an equimolar amount of HEMA. The coupling hybrid monomer formation was supported by ¹³CNMR and mass analysis. The mole ratios H₂O/TEOS+APTS and NH₃/TEOS+APTS were taken constant to the values 11.8 and 0.59 when preparing pHEMA nanocomposite with silica weigh concentrations of 10, 20 and 30%.

The procedure strongly affected the nanocomposite structure: the silica nanoparticle mean diameter changed from 500 nm to about 10 nm when the coupling hybrid monomer was used. Transparent composites containing well dispersed silica nanoparticles were obtained by procedure B.

The silica content made the thermal stability to strongly increase and allowed surface hydroxyapatite formation during exposition to simulated body fluids (SBF) so as on bioactive ceramics. The changes in thermal stability, bioactivity and swelling behaviour were well correlated to the silica content and nanocomposite structure.

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