Synthesis and photopolymerizations of new dental monomers from o-hydroxyaryl phosphonates

Abstract

New phosphonate, phosphonic and carboxylic acid containing monomers were synthesized from o-hydroxyaryl phosphonates and dimethyl 2-hydroxyethyl phosphonate for use in dental adhesives and composites. First set of monomers were synthesized from diethyl (2-hydroxyphenyl) phosphonate. Synthesis of the first monomer involved: (i) reaction of t butyl α bromomethacrylate (TBBr) and Bisphenol A, (ii) conversion to diacid chloride derivative using thionyl chloride, (iii) reaction of diacid chloride with diethyl (2-hydroxyphenyl) phosphonate. The second monomer was synthesized from the reaction of 2-chloromethacryloyl chloride (CMAC) and diethyl (2-hydroxyphenyl) phosphonate. Synthesis of the third monomer involved reaction of glycidyl methacrylate (GMA) with diethyl (2-hydroxyphenyl) phosphonate. Forth monomer was obtained by the ring opening reaction of bisphenol A diglycidylether with diethyl (2-hydroxyphenyl) phosphonate followed by reaction of the resulting diol with metharcyl chloride. Synthesis of the last monomer in this set involved reaction of diethyl (2-hydroxyphenyl) phosphonate with TBBr. Hydrolysis of the phosphonate groups of the first and second monomers with trimethylsilyl bromide (TMSBr) gave new monomers with phosphonic acid functionality. Hydrolysis of both phosphonate and t-butyl groups of the fifth monomer gave a new monomer with both phosphonic and carboxylic acid functionality. The homopolymerization and copolymerization behaviors of the synthesized monomers with 2,2-bis[4-(2-hydroxy-3-methacryloyloxy propyloxy)phenyl]propane (Bis-GMA) and glycerol dimethacrylate (GDMA) were investigated using photodifferential scanning calorimetry at 40 oC with 2,2’-dimethoxy-2-phenyl acetophenone (DMPA) as photoinitiator. The mono-functional (meth)acrylate synthesized from GMA was found to homo and copolymerize rapidly to give crosslinked polymers. This monomer can be used as a reactive diluent for BisGMA and improve the cure efficiency, material properties and binding ability of dental composites. The aqueous solutions of the acid monomers have a pH value in the range of acidity expected from a mild self-etching dental adhesive monomer (pH around 2.0). The interaction of the acid monomers with hydroxyapatite (HAP) was investigated using FT-IR technique. The second set of monomers were synthesized from tetraethyl 2,5-dihydroxy-1,4-phenylene diphosphonate. Reaction of tetraethyl 2,5-dihydroxy-1,4-phenylene diphosphonate with TBBr gave a new phosphonated monomer which was hydrolyzed to give a monomer containing both carboxylic and phosphonic acid groups. The copolymerization behaviors of the synthesized monomers with GDMA were first investigated in bulk using photodifferential scanning calorimetry at 40 oC with DMPA. Then solution copolymerization of the monomers with acrylamide in water was studied, indicating that the synthesized monomers were incorporated into the copolymers. The aqueous solutions of these monomers also have pH values (1.72-1.87) suitable for dental applications, therefore their interaction with HAP was also investigated, using 13C-NMR and FT-IR techniques. Last phosphonated monomer was synthesized from the reaction of dimethyl 2-hydroxyethyl phosphonate and CMAC and its photopolymerization reactivity was investigated.