Hydrolysis of tetracalcium phosphate in the presence of a poly(alkenoic acid)

Ca₄(PO₄)₂O (TetCP) reacts with an acidic polyelectrolyte in the absence of a solvent to form a composite composed of Ca₁₀(PO₄)₆(OH)₂ (hydroxyapatite, or HAp) and the Ca salt of the polyelectrolyte. Mixtures of an acrylic copolymer and TetCP powders were hot-pressed, and the effects of temperature, pressure, and time on HAp formation were studied. Reaction starts when the copolymer is heated to above T_g. Initial carboxyl site neutralization liberates water, continued TetCP hydrolysis, liberates Ca²⁺ ions, which react with the copolymer forming its Ca salt. When 90% conversion to HAp was achieved, the composite had an average tensile strength of 51 MPa, a Vickers hardness of 145 kg/mm² and a T_g ˜50 °C.