Abstract:
Four novel phosphonated methacrylate, two novel phosphonic acid-containing methacrylate and one phosphate-containing methacrylate monomers have been synthesized using three different routes and studied for their potential in dental materials. First route for the synthesis of phosphonated monomers consists of a one step reaction of methacryloyl chloride with diethyl (2-hydroxyphenyl) phosphonate (monomer 1) and tetraethyl (2,5-dihydroxy-1,4-phenylene) bisphosphonate (monomer 2) in the presence of a base catalyst. Hydrolysis of the phosphonate groups of these monomers with trimethylsilyl bromide (TMSBr) gave phosphonic acid-containing monomers 1a and 2a. Second route for the synthesis of phosphonated monomers involved two steps: (i) reaction of dimethyl (2-hydroxyphenyl) phosphonate and α-(chloromethyl)acryloyl chloride (CMAC) to give an intermediate (ii) reaction of this intermediate with benzoic (monomer 3) and formic (monomer 4) acids. Third route involves reaction of glycidyl methacrylate (GMA) with diethyl hydrogen phosphate to give a phosphate-containing monomer (monomer 5). Thermal homopolymerization of monomers 1, 3, 4, and 5 and copolymerization of monomer 1 with methyl methacrylate (MMA) were investigated using azobisisobutyronitrile (AIBN) at 60 oC. Glass transition temperatures were observed for poly-1, poly(MMA-co-1) (50:50), poly(MMA-co-1) (90:10), PMMA, poly-3 and poly-5 at 52, 90, 99, 129, 50 and 70 ºC, respectively. Thermogravimetric analysis (TGA) of these polymers indicated formation of char on combustion. Homo- and/or copolymerization behavior of monomers 1-5 with 2,2-bis[4-(2- hydroxy-3-methacryloyloxy propyloxy) phenyl] propane (Bis-GMA) were investigated with photo-differential scanning calorimetry at 40 oC using 2,2’-dimethoxy-2-phenyl acetophenone (DMPA) as photoinitiator. The maximum rate of polymerizations decreased in the following order: Bis-GMA~3 > 1 > 4. The conversions of monomers 1, 3 and 4 (73.9, 85.9 and 98.2 %) were very high compared with Bis-GMA (40.5%). The aqueous solution of the acid monomer (2a) was acidic enough (pH= 1.65) to etch enamel and dentin, but is prone to hydrolysis at long storage periods. The copolymerization behavior of this monomer with 2-hydroxyethyl methacrylate (HEMA) was investigated in water using photo-differential scanning calorimeter at 40 oC with bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) as photoinitiator. The thermal solution copolymerization of this monomer with acrylamide (AAm) and HEMA gave crosslinked polymers, indicating its incorporation into the copolymers. The interaction of this monomer with hydroxyapatite was observed using FTIR spectroscopy. This monomer was found to be more suitable for dental composites than dental adhesives.
