Synthesis and stability study of dental monomers containing methacrylamidoethyl phosphonic acids

Three new dental monomers containing methacrylamidoethyl phosphonic acids were synthesized. The structures of the synthesized monomers were determined with electrospray mass spectrometry (ESMS), Fourier transform infrared, and NMR. The hydrolytic stabilities of the synthesized monomers and a commercial monomer, 2-methacryloyloxyethyl phosphoric acid (MEP; used as a control), were studied with flow injection (FI)/ESMS, H-1 NMR, and P-31 NMR analysis of a CD3OD/D2O (4:1 v/v) solution of each monomer before and after storage at 60 degrees C for 2 months. The H-1 NMR and P-31 NMR chemical shifts of the monomers 2-methacrylamidoethylphosphonic acid (1) and N,N'-[4,4'-(propane-2,2-diyl)-bis(phenoxy-2-hydroxypropyl)]-bis(2-methacrylamidoethylphosphonic acid) (11) showed little change after storage at 60 degrees C for 2 months, but those of MEP changed significantly. FI/ESMS also showed that MEP was nearly completely decomposed, whereas monomers I and II remained largely intact. MEP could react with H2ZrF6 to form ternary zirconium fluoride complexes that were partially soluble in methanol, but all the monomers containing phosphonic acids formed precipitates. This study demonstrates that ESMS is a more sensitive and effective method than NMR for studying the hydrolytic stability or degradation of dental monomers. The new monomers containing methacrylamidoethyl phosphonic acids have higher hydrolytic stability than methacrylate phosphate monomers and may be used in dental bonding agents and other dental materials. (c) 2006 Wiley Periodicals, Inc.