Morphological Control of Calcium Oxalate Dihydrate by a Double-Hydrophilic Block Copolymer

The crystallization of calcium oxalate in aqueous solutions of a double-hydrophilic block copolymer poly(ethyleneglycol)-block-poly(methacrylic acid) (PEG-b-PMAA) has been investigated, focusing on morphological control of the calcium oxalate dihydrate (COD) crystals. It has been shown that with increasing polymer concentration, the morphology of the obtained COD crystals gradually changed from tetragonal bipyramids dominated by the {101} faces to rodlike tetragonal prisms dominated by the {100} faces, which is a morphology adopted by some plant COD crystals but not obtained in vitro previously. The concentration of calcium oxalate and the [Ca2+]/[C2O4 2-] ratio were also found to show considerable effects on the morphology of the obtained COD crystals. Seed growth experiments further demonstrated the drastic effect of the polymer on the COD crystal morphology. This effect was preliminarily discussed in terms of possible structural correlation between the short PMAA chain of the polymer and the COD {100} planes.