Filler-coupling agent-matrix interactions in silica/polymethylmethacrylatecomposites

The interactions of the silane coupling agent methacryloxypropyltrimethoxys ilane (MPS) with both fumed silica and a polymethylmethacrylate (PMMA) resi n matrix were investigated using thermogravimetric analysis and Fourier tra nsform infrared spectroscopy. OX 50 fumed silica was silanated with MPS at concentrations of 1% and 5% in aqueous ethanol (95%), acetone, and anhydrou s toluene. Methyl methacrylate was polymerized with the silanated fumed sil ica (5% wt/wt) to form composites. The amount of NIPS adsorption on the fum ed silica and the amount of PMMA attached to the silanated fumed silica wer e determined by thermogravimetric analysis. MPS could be removed from the f umed silica after washing with methanol, but not after it underwent a dryin g process at 25 degreesC under vacuum. After vacuum drying at 25 degreesC, two types of adsorbed silane were found, i.e., firmly adsorbed and loosely adsorbed silane. The loosely adsorbed silane could desorb from silica and b e incorporated into the polymer matrix through copolymerization with monome ric methyl methacrylate, resulting in crosslinking of the matrix. Mien the silanated silica was dried at 110 degreesC for 2 h, the loosely adsorbed si lane was removed and the amount of firmly adsorbed silane increased. There was a positive correlation between the amount of firmly adsorbed MPS and th e amount of PMMA attachment. The highest efficiency for PMMA attachment was found when MPS was adsorbed as a monolayer, because the loosely adsorbed s ilane did not contribute to the bonding of PMMA, and this suggested that no t all of the double bonds of the MPS were accessible for reaction with the methacrylate monomer. Drying at 110 degreesC may also decrease the number o f unsaturated double bonds of NIPS. (C) 2001 John Wiley & Sons, Inc.