Crystal Design of Calcium Carbonate Microparticles Using Double-Hydrophilic Block Copolymers

Small block copolymers, consisting of a hydrophilic poly(ethylene glycol) block and a second hydrophilic moiety which strongly interacts with alkaline earth ions, were employed to template the precipitation of calcium carbonate from aqueous solution. Depending on the type of polymeric functionalization pattern used, it was possible to grow two of the three different crystal modifications of CaCO3 (vaterite and calcite) under similar conditions. Vaterite could be successfully stabilized for more than 1 year by the polymer under conditions where it would normally transform into calcite within 80 h. Also the crystal size and shape respond to the polymeric template; for example, it was possible to grow monodisperse spherical particles with a diameter of ca. 2 μm or hollow spheres both consisting of aggregated nanocrystallites. The effect of different functional groups and of variable block length on the size, shape, and morphology of CaCO3 is discussed. It must be emphasized that these particles sediment, but are stabilized and protected by a dense layer of double-hydrophilic block copolymers, which enables direct use as pigments and fillers or in ceramic processing.