Covalent Incorporation of 2,5-Diphenyloxazole in Sol−Gel Matrices and Their Application in Radioanalytical Chemistry

4-Hydroxymethyl-2,5-diphenyloxazole (4-HOCH 2 -PPO, 3 ) was reacted with 3-isocyanatopropyltriethoxysilane (3-ICPS, 4 ) to form a functionalized silicon alkoxide precursor (3-ICPS-PPO adduct 5 ). Transparent, colorless, monolithic sol−gel glasses with 3 covalently incorporated at different concentrations were prepared via the copolymerization of tetraethyl orthosilicate (TEOS) and 5 in a H 2 O/CH 3 COOH/C 2 H 5 OH solution. The gel samples were aged at room temperature, and dried in two stages: first at room temperature, and then at 70 °C, to reduce possible fracture. They have pore diameters in the range 2.2−2.4 nm. By comparison with the simple entrapment procedure, the leaching of scintillator from the sol−gel glass formed as a result of covalent bonding is greatly reduced. Furthermore, these sol−gel glasses are highly efficient at detecting β - radioactivity.