Synthesis and evaluation of new dental monomers with both phosphonic and carboxylic acid functional groups

Novel dental monomers containing both phosphonic and carboxylic acid functional groups were prepared. The monomers were based on t ‐butyl α‐bromomethacrylate ( t ‐BuBMA) and synthesized in three steps: The reaction of o ‐hydroxyaryl phosphonates [diethyl (2‐hydroxyphenyl) phosphonate, tetraethyl (2,5‐dihydroxy‐1,4‐phenylene) diphosphonate and tetraethyl 5,5′‐(propane‐2,2‐diyl)bis(2‐hydroxy‐5,1‐ phenylene) diphosphonate] with t ‐BuBMA, the hydrolysis of phosphonate groups to phosphonic acid using trimethyl silylbromide, and the hydrolysis of the t ‐butyl groups to carboxylic acid with trifluoroacetic acid. The monomers were solids and soluble in water and ethanol. The structures of the monomers were determined by Fourier transform infrared (FTIR), 1 H, 13 C, and 31 P nuclear magnetic resonance (NMR) spectroscopy. The copolymerization behaviors of the synthesized monomers with glycerol dimethacrylate were first investigated in bulk using photodifferential scanning calorimetry at 40 °C with 2,2′‐dimethoxy‐2‐phenyl acetophenone as photoinitiator. Then, the solution copolymerization of the monomers with acrylamide in ethanol and water was studied, indicating that the synthesized monomers are incorporated into the copolymers. The acidic nature of the aqueous solutions of these monomers (pH values 1.72–1.87) is expected to give them etching properties important for dental applications. The interaction of the monomers with hydroxyapatite was investigated using 13 C NMR and FTIR techniques.