Synthesis of hollow CaCO nanospheres templated by micelles of poly(styrene- b -acrylic acid- b -ethylene glycol) in aqueous solutions

An asymmetric triblock copolymer, poly(styrene-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG), was synthesized via reversible addition-fragmentation chain transfer controlled radical polymerization. Micelles of PS-b-PAA-b-PEG with PS core, PAA shell, and PEG corona were then prepared in aqueous solutions, followed by extensive characterization based on dynamic light scattering, zeta-potential, and transmission electron microscopy (TEM) measurements. The well-characterized micelles were used to fabricate hollow nanospheres of CaCO as a template. It was elucidated from TEM measurements that the hollow nanospheres have a uniform size with cavity diameters of ca. 20 nm. The X-ray diffraction analysis revealed a high purity and crystallinity of the hollow nanospheres. The hollow CaCO nanospheres thus obtained have been used for the controlled release of an anti-inflammatory drug, naproxen. The significance of this study is that we have overcome a previous difficulty in the synthesis of hollow CaCO nanospheres. After mixing of Ca2+ and CO2- ions, the growth of CaCO is generally quite rapid to induce large crystal, which prevented us from obtaining hollow CaCO nanospheres with controlled structure. However, we could solve this issue by using micelles of PS-b-PAA-b-PEG as a template. The PS core acts as a template that can be removed to form a cavity of hollow CaCO nanospheres, the PAA shell is beneficial for arresting Ca2+ ions to produce CaCO, and the PEG corona stabilizes the CaCO/micelle nanocomposite to prevent secondary aggregate formation. © 2010 American Chemical Society.