Five novel phosphonated mono- and dimethacrylate monomers have been synthesized by two different routes. Monomers 1 and 2 were synthesized by reactions of methacryloyl chloride with diethyl (2-hydroxyphenyl) phosphonate or tetraethyl (2,5-dihydroxy-1,4-phenylene) bisphosphonate; monomers 3 and 4 by reactions of α-(chloromethyl)acryloyl chloride (CMAC) first with dimethyl (2-hydroxyethyl) phosphonate and then with benzoic or formic acids. The reaction of CMAC with two moles of dimethyl (2-hydroxyethyl) phosphonate gave 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 °C. 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 °C, respectively. TGA analysis of these polymers indicated formation of char on combustion. Homo- and/or copolymerization behavior of the synthesized monomers with 2,2-bis4-(2-hydroxy-3-methacryloyloxy propyloxy) phenyl propane (Bis-GMA) were investigated with photodifferential scanning calorimetry. The maximum rate of polymerizations decreased in the following order: Bis-GMA~3 > 1 > 4 > 5. The conversions of monomers 1, 3, 4, and 5 (73.9, 85.9, 98.2, and 62.2%) were very high compared with Bis-GMA (40.5%).