Inorganic/organic mesostructures with complex architectures: Precipitationof calcium phosphate in the presence of double-hydrophilic block copolymers

Double-hydrophilic block copolymers consisting of a long poly(ethylene oxid e) block and a short poly(methacrylic acid) block, modified by partial alky lation with dodecylamine (PEO-b-PMAA-C-12) were employed as dispersed templ ates for the controlled precipitation of calcium phosphate from aqueous sol ution at different pH values. Two new and nontrivial superstructures of an organized inorganic/organic hybrid material were characterized by ultracent rifugation, small- and wide-angle X-ray analysis, and electron microscopy. At pH 3.5 and 4.0, and pH 4.5, 5.0, and 6.3, two different types of discret e nested structures are obtained which consist of hybrid nanofilaments arra nged to give an unusual neuronlike morphology. The fibers originate from a core of similar size to the primary polymer aggregates, suggesting that coo perative interactions at a local level between dissolving calcium phosphate clusters and disassembling polymer units could be responsible for the high ly anisotropic nature of the secondary growth process. Aging of the nanofil aments grown in acidic solution results in a second hybrid morphology, cons isting of compact aggregates with a diameter of about 130nm, which show the interlocked layer structure of an ordered inorganic/organic mesophase with a repeat period of about 3 nm. Such calcium phosphate/polymer nanohybrids with complex morphologies are interesting from the viewpoint of prebiotic s tructure formation, and might also be useful as novel ceramics precursors, reinforcing fillers, or biomedical implants.