Jason Locklin, PhD , University of Georgia
The initial success in the first year of our project involved determining conditions suitable for the formation of surface-initiated Kumada-type catalyst-transfer polycondensation (SI-KCTP). This has led to densely packed conjugated polymer films that vary in thickness from 5-150 nm. We were successful in doing this, but there was a considerable amount of work remaining to fully understand the mechanism of polymer growth and thereby optimize the conditions for film formation. In the second year of the project, we have further explored this surface mediated coupling reactions and developed a more versatile method for fabricating SI-KCTP initiators on a variety of planar substrates incorporating bidentate phosphine ligands has been demonstrated. Indirect evidence of interfacial disproportionation reactions with nickel catalysts were observed electrochemically through the use of an aryl organomagnesium ferrocene probe. With respect to all self-assembled monolayers studied, incorporation of a methyl substituent ortho to the halogen on the thiophene ring helps prevent disproportionation, however an overall lower yield of initiators was observed due to the reduced packing density of SAMs containing the bulky methyl substituent. Initiators formed with phosphonic acids (for binding with transparent electrodes such as indium tin oxide (ITO)) anchor groups did not demonstrate any significant disproportionation reactions among the bidentate phosphine ligands used, since molecules on ITO are not as densely packed as SAMs formed on Au. We also observed that the use of LiCl or high concentration of Grignard reagent was incompatible with alkanethiol monolayers. Aryl(Ni(II)-Br monolayers could then be used to fabricate poly(3-methylthiophene) films on SiO2 and ITO surfaces. Uniform P3MT films with thicknesses between 40 and 65 nm were characterized using a variety of techniques. Studies using these films as modified interfaces in organic electronics are now possible and currently underway in our laboratory. We have also started to study the use of other metal catalysts to overcome the problems of disproportionation. Pd catalysts have shown to be the most effective, and films that are densely packed, with a high grafting density have been observed. Thicknesses greater than 300 nm are now possible using this catalyst combination.