Synthesis and characterization of polypyrrole-coated poly(methyl methacrylate) latex particles

Abstract

A range of uniform, micrometer-sized poly(methyl methacrylate) latexes have been coated with ultrathin overlayers of polypyrrole from aqueous solution. Good control over the targeted conducting polymer overlayer thicknesses is achieved for a 1.19 µm diameter latex and latexes of up to 30 µm diameter can also be efficiently coated with this conducting polymer. Addition of sodium tosylate to the in situpyrrole polymerization leads to a smoother conducting polymer morphology, which in turn enables more uniform surface coverages and higher conductivities to be achieved for the coated particles. Laser diffraction studies of dilute aqueous suspensions indicate that the degree of dispersion achieved for the larger polypyrrole-coated latexes is comparable to that for the corresponding uncoated latex, although some incipient flocculation is observed for the smaller coated latexes. The FT-IR spectrum of 20 µm poly(methyl methacrylate) particles coated with a 20 nm polypyrrole overlayer is dominated by the underlying latex, since this is the major component (>99% by mass). On the other hand, the Raman spectrum of the same coated particles contains relatively strong features arising from the minor conducting polymer component due to a resonance Raman effect, although bands assigned to the underlying latex are also visible. Thermogravimetric analyses confirm that the tosylate-doped polypyrrole bulk powder is significantly more stable than chloride-doped polypyrrole bulk powder and that the polypyrrole-coated latexes are also more thermally stable than the uncoated poly(methyl methacrylate) latex. Since the chemical structure of individual polypyrrole-coated poly(methyl methacrylate) latex particles can be readily assessed using Raman microscopy, our results suggest that such thermally fragile particles will be useful model projectiles for assessing the extent of thermal ablation of organic cosmic dust in aerogel capture experiments such as those deployed during the recent Stardust space mission.