Crystal growth of CaCO3 induced by monomethylitaconate grafted polymethylsiloxane

We report the preparation of a new monomethylitaconate grafted polymethylsiloxane (CO2H-PMS) copolymer and its effect as template for crystal growth of CaCO3. The in vitro crystallization of CaCO3 was carried out using the gas diffusion method at different pH values at room temperature for 24 h. The CO2H-PMS was prepared using polydimethylsiloxane-co-methylhydrogensiloxane (PDMS-co-PHMS), obtained through cationic ring opening polymerization, from cyclic monomers and monomethyltaconate (MMI) via hydrosilylation reactions with platinum complex as catalyst. FTIR results are in an agreement with the proposed template structure and confirmed that the hydrosilylation was complete. Experimental results from pH values and SEM analysis showed that the carboxylate groups of CO2H-PMS alter the nucleation, growth and morphology of CaCO3 crystals. SEM revealed single-truncated (ca. 5 mu m) modified at pH 7-9, aggregated-modified (ca. 20 mu m) at pH 10-11, and donut-shaped crystals at pH 12. These morphologies reflect the electrostatic interaction of carboxylic moieties with Ca2+ modulated by CO2H-PMS adsorbed onto the CaCO3 particles. EDS confirmed the presence of Si atoms on the crystals surface. XRD analysis showed the existence of only two polymorphs: calcite and vaterite revealing a selective control of CaCO3 polymorphisms. In summary, the use of grafted polymethylsiloxane template offer a good alternative for polymer controlled crystallization and a convenient approach for understanding the biomineralization process useful for the design of novel materials. (C) 2010 Elsevier Ltd. All rights reserved.