Owing to their similarities to bone apatite, calcium phosphate bioceramics, such as hydroxyapatite (HAp), are used as biomaterials for hard tissue replacements. Composites of bioceramics and biomedical polymers can mimic bone structure and properties. The characteristics of composites comprising HAp and a biomedical polymer and prepared at low temperatures are described. The kinetics of HAp formation in the presence of a polyphosphazene polymer that carries carboxylic acid moieties (acid-PCPP) were established at temperatures from 25 degrees to 50 degrees C. Evolution in the compositions of the solids present, solution chemistry, and microstructure development were established as functions of reaction time and temperature. The polymer participated in HAp formation affecting its rates of nucleation and growth through the formation of calcium cross links. The presence of polymer also enhanced ductility.