A New Pigment Type:  Colored Diblock Copolymer−Mica Composites

• Published in: Chemistry of materials 2005-07, Vol.17 (15), p.3837-3843
• Main Authors: Ghannam, Leïla, Garay, Hélène, Shanahan, Martin E. R, François, Jeanne, Billon, Laurent
• Format: Article
• Language: English
• Subjects: Chemical Sciences
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm0478024

New mica−polymer composite pigments have been prepared and characterized. The pigments are prepared from mica surfaces by block copolymerization of butyl acrylate (BA) and a mixture of styrene (S) and a modified alizarin (A; dye). This is performed after physical adsorption of a radical initiator with a cationic group. Some of the copolymer was desorbed from the surface and characterized by 1H NMR, size exclusion chromatography, and UV−visible spectroscopy. This desorbed copolymer fraction had a number-average molecular weight of 140 000 g·mol-1 with chemical compositions of 16% and 84% M, respectively, of poly(butyl acrylate) (PBA) and poly(styrene−alizarin) [P(S−A)]. In addition, it had a yellow coloration when in the bulk form. The remaining mica composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. It was found that 0.07 molecules of block copolymer per nm2 of mica remained adsorbed on the mica surface. This leads to a surprising pink color, which may be explained by the basicity of the mica surface due to the pH−color-sensitive character of the alizarin dye.