Synthesis and Photo-Polymerization of an Aryl Diphosphonic Acid-Containing Dimethacrylate for Dental Materials

A new dental dimethacrylate monomer containing phosphonic acid functionality, 2,5-bis(methacryloyloxy)-1,4-phenylenediphosphonic acid (1), was synthesized by silylation of 2,5-bis(diethoxyphosphoryl)-1,4-phenylene bis(2-methylacrylate) (2) with trimethylsilyl bromide (TMSBr) followed by the hydrolysis of the silyl ester. The monomer was solid and soluble in ethanol and water. The structure of this monomer was characterized by H-1-, C-13-, P-31-NMR and FT-IR spectroscopy. The aqueous solution of 1 is acidic (pH 1.65), so that it is expected to etch enamel and dentin, but is prone to hydrolysis over long storage periods. The co-polymerization behavior of this monomer with 2-hydroxyethyl methacrylate (HEMA) was investigated in water using photodifferantial scanning calorimeter at 40 degrees C with bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide (BAPO) as photoinitiator. It was observed that the addition of monomer 1 to HEMA slightly decreased both the maximum rate of polymerization and conversion. The thermal solution co-polymerization of this monomer with acrylamide (AAm) and HEMA gave cross-linked polymers, indicating its incorporation into the co-polymers. The interaction of this monomer with hydroxyapatite was observed using FT-IR spectroscopy. This monomer was found to be more suitable for dental composites than dental adhesives. (C) Koninklijke Brill NV, Leiden, 2010