Monomers for adhesive polymers, 13.1 Synthesis, radical photopolymerization and adhesive properties of polymerizable 2-substituted 1,3-propylidenediphosphonic acids

A family of polymerizable 2-substituted-1,3-propylidenediphosphonic acids was successfully synthesized for an application in dental adhesives. Methacrylates as well as N-alkyl-acrylamides were prepared. Those monomers were synthesized in 4 to 6 steps and were fully characterized by 1H NMR, 13C NMR, 31P NMR spectroscopy and by HRMS. In order to evaluate their reactivity, the copolymerization of each monomer with N,N′-diethyl-1,3-bis-(acrylamido)propane (DEBAAP) in DMF was investigated by photo-DSC. Bis-(4-methoxybenzoyl)diethylgermanium (BMDG) was added as the photoinitiator to each mixture of acidic monomer/DEBAAP/DMF (2/3/5: mol/mol/mol). It was demonstrated that each monomer efficiently copolymerized with DEBAAP. Self-etching enamel-dentin adhesives containing these new diphosphonic acids were formulated and used to mediate a bond between the dental hard tissues (dentin and enamel) and a restorative material. According to both dentin and enamel shear bond strength measurements, 2-methacryloyloxymethyl-1,3-propylidenediphosphonic acid 8, 2-[N-(2-methacryloyloxyethyl)-carbamoyloxymethyl]-1,3-propylidenediphosphonic acid 10a and 2-[N-(10-methacryloyloxydecyl)-carbamoyloxymethyl]-1,3-propylidenediphosphonic acid 10b were the best candidates to enter new formulations. Those diphosphonic acids were significantly more efficient regarding the etching of enamel than the 1,3-bis(methacrylamido)propane-2-yl dihydrogen phosphate 17, a monomer already used in some commercially available dental formulations.