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Synthesis and characterization of ionic block copolymer templated calcium phosphate nanocomposites

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2008-09-23
KANAPATHIPILLAI, M.
Yusufoglu, Y.
RAWAL, A.
HU, Y. -Y.
LO, C. -T.
THIYAIGARAJAN, P.
Kalay, Yunus Eren
Akinc, M.
MALLAPRAGADA, S.
SCHMIDT-ROHR, K.
Self-assembling thermo-reversibly gelling anionic and zwitterionic pentablock copolymers were used as templates for precipitation of calcium phosphate nanostructures, controlling their size and ordered structural arrangement. Calcium and phosphate ions were dissolved ill a block-copolymer micellar dispersion at low temperatures. Aging at ambient temperature produced inorganic nanoparticles, presumably nucleated by ionic interactions. The self-assembled nanocomposites were characterized by small-angle X-ray and neutron scattering (SAXS/SANS), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). H-1-P-31 NMR with 1H spin diffusion from polymer to phosphate proved the formation of nanocomposites, with inorganic particle sizes from similar to 2 nm, characterized by 1H-P-31 dipolar couplings, to > 100 nm. TEM analysis showed polymer micelles surrounded by calcium phosphate. SAXS attested that a significant fraction of the calcium phosphate was templated by the polymer micelles. SANS data indicated that the order of the polymer was enhanced by the inorganic phase. The nanocomposite gels exhibited higher moduli than the neat polymer gels. The calcium phosphate was characterized by TGA, X-ray diffraction, high-resolution TEM, and various NMR techniques. An unusual crystalline phase with >= 2 chemically and >= 3 magnetically inequivalent HPO42- ions was observed with the zwitterionic copolymer, highlighting the influence of the polymer on the calcium phosphate crystallization. The inorganic fraction of the nanocomposite was around 30 wt % of the dried hydrogel. Thus, a significant fraction of calcium phosphate has been templated by the tailored self-assembling ionic block copolymers, providing a bottom-up approach to nanocomposite Synthesis.