Summary: 2,4,6‐Trimethylphenyl 2‐[4‐(dihydroxyphosphoryl)‐2‐oxa‐butyl]acrylate (1) was synthesized by silylation of 2,4,6‐trimethylphenyl 2‐[4‐(dimethoxyphosphoryl)‐2‐oxa‐butyl]acrylate with trimethylsilyl bromide (TMSBr) and the hydrolysis of the silyl ester resulted in the formation of polymerizable phosphonic acid 1. The structure of this new monomer was characterized by IR, 1H, 13C and 31P NMR spectroscopy. The monomer dissolves well in ethyl acetate, ethanol or water and shows a high hydrolytic stability. 1 was homopolymerized with 2,2′‐azobisisobutyronitrile (AIBN), 2,2′‐azobis‐(2‐methylpropionamidine) dihydrochloride (AMPAHC) or dibenzoyl peroxide (DBPO) as the initiators. In a tetrahydrofuran (THF) solution, the deviations from the standard reaction kinetics were comparable with those of polymerizations of the other water soluble acrylate monomers. The unusual polymerization rate‐monomer concentration dependence with monomer intensity exponent less than 1 (m = 0.5) observed in THF solutions was even more declined from 1 in the polar medium EtOH‐H2O. The DBPO was a more effective polymerization initiator than AIBN. However, the overall activation energy of 81 kJ · mol−1 showed a usual temperature‐rate dependence observed in methacrylate ester polymerizations. In addition, monomer 1 was copolymerized with methyl methacrylate (MMA), ethyl 2‐[4‐(dihydroxyphosphoryl)‐2‐oxa‐butyl]acrylate (2), and N,N′‐diethyl‐1,3‐bis(acrylamido)propane (3), respectively, using THF as the solvent and AIBN as the initiator. The copolymerization curves revealed only slight deviations from the ideal copolymer‐feed composition. The estimated copolymerization parameters indicate a ready incorporation of comonomer units into polymer chains, preferably by alteration rather than at random.