Characterization of the hydrolysis and polymerization processes of methacryloxypropyltrimethoxysilane
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The sol-gel synthesis of hybrid methacrylate-silica materials using methacryloxypropyltrimethoxysilane (MPS) as precursor, has been analyzed using 1H and 29Si liquid NMR as well as 29Si and 13C MAS-NMR. Under the present experimental conditions (H2O/MPS=3; pH=2), hydrolysis of methoxy groups is fast. However, 5% of unreacted alkoxy groups are still present in the sol after 14 days aging. Condensation reactions lead mainly to cyclic or short linear species. The number of cross-linking points never exceeds 20% of the Si units, which seems to prevent the formation of a gel. Polymerization of methacrylate groups occur easily under short times of U.V. irradiation. A quantitative analysis shows about 20% of residual unreacted groups in the polymerized materials. Addition of free methylmethacrylate in the hydrolyzed sols helps in getting a fully polymerized organic network.
Keywordshybrid materials NMR hydrolysis polymerization
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