Hydrolytically stable acidic monomers used in two steps self-etch adhesives

This study deals with the stability of new phosphonic monomers bearing an acrylamide moiety designed to increase the adhesion durability. Synthesis of monomers bearing acrylamide and methacrylate moieties, as well as their use in Self-Etch Adhesives is reported. The adhesion of a degraded methacrylate based adhesive has been evaluated. Homologous self-etching primers containing monomers bearing acrylamide or methacrylate were formulated and used either immediately after formulation or after 18 months. Their adhesive performances were assessed by shear bond strength testing and their degradation measured by NMR, HPLC-MS. While no differences were found in terms of adhesion between fresh and aged acrylamide based adhesive, the instability of methacrylate based ones was demonstrated. Nevertheless, methacrylate based SEAs still have good adhesion abilities. The co-monomer used, N,N′-diethyl-1,3-bis(acrylamido)propane is expected to be responsible for good mechanical properties even for degraded SEAs. Lastly, the stability of acrylamide monomer seems to be of interest in the prospect of developing SEA with longer shelf life.