Biomimetic crystallization of calcium carbonate spherules controlled by hyperbranched polyglycerols

Abstract

Hyperbranched polyglycerols 1 and 2 have been synthesized from pentaerythritol and glycidol in a one-pot process by anion ring-opening polymerization. These polymers are modified easily to sulfate or carboxylate-based polyglycerols 3–5 with the SO₃–Py complex and sodium chloroacetate, respectively. Polyglycerols 3–5 have been used for the first time as additives for biomimetic crystallization of calcium carbonate. The morphologies of calcite crystals can be controlled by adjusting the functionality, the molecular weight and the secondary structure of the polymer as well as the Ca²⁺ concentration. Polyglyerol carboxylate 3-Na is capable of mediating the formation of uniform polycrystalline spherules with stacked multilayers. Interestingly, a successive rod–dumbbell–sphere transition can be observed directly, providing considerable insight into the mechanism of formation of calcite microspheres in the presence of 3-Na. Sulfate-based polyglycerols 5-H, 5-Na and 5-Im with different cations (e.g., H⁺, Na⁺, imidazolium, respectively) give rise to the mesocrystals with morphologies from truncated rhombohedra to rounded Chinese lantern-like particles to spherules, respectively. In this study, a structural transition from single crystal to mesocrystal to polycrystal has been carried out.