[Specific physicochemical properties of apatites. 9. Organic phosphate ester monomer as a source of P]

Reactions of calcium ions and organic phosphate ester monomers were examined at 60 degrees C and 80 degrees C and at various pH. By a modification of the method used for HAp synthesis, calcium acetate was fed into aqueous solution of mechanically stirred mono (methacryloyloxyethyl) acid phosphate. Above a pH of 10, poorly crystallized hydroxyapatite was formed with lower crystallinity than that synthesized with inorganic phosphate as a source of P under the same conditions. This result suggested that phosphate ester and/or decomposed acrylic monomer may inhibit the diffusion of Ca2+ and PO4(3-) and the formation of the apatite crystal. On the other hand, the results of X-ray diffraction, chemical analysis, and infrared absorption analysis suggested that crystalline organic calcium phosphate ester was formed below pH 10, while in synthesis with inorganic phosphate, hydroxyapatite was formed at pH 7.4.