Nanotemplating of calcium phosphate using a double-hydrophilic block copolymer

Atom transfer radical polymerization technique was used to synthesize poly(ethylene oxide)-block-poly(methacrylic acid) (PEO-b-PMAA) copolymer, which was employed as a template for the controlled precipitation of calcium phosphate from aqueous solution at different pH values. The interactions between polymer and inorganic ions were studied using Ca2+ ion selective electrode, which indicated a possible weak interaction between Ca2+ and PEO segments, in addition to the interaction between Ca2+ and MAA segments. Two interesting superstructures consisting of an organized inorganic/organic hybrid material were characterized by electron microscopy. At pH similar to 4.0 a nested structure consisting of hybrid nanofilaments was obtained. The fibers originate from a core of a size similar to that of the primary polymer aggregates, suggesting that cooperative interactions at a local level between dissolving calcium phosphate clusters and disassembling polymer segments may be responsible for the highly anisotropic character of the secondary growth process. At pH similar to 9.0 fractal growth morphology was obtained through the mineralization process. Such calcium phosphate/polymer nanohybrids with complex morphologies are interesting and might also be useful as novel ceramic precursors, reinforcing fillers, or biomedical implants.