Conjugated polymer synthesis via palladium-mediated catalysis
Description
We have attempted to participate in the advancement of polymer science through active research into the preparation of poly(aryleneethynylene) polymer chains (PAEs) (Figure 1). We have also investigated some other similar polymer systems. &parl0; - - ≡- Ar-≡ -Ar- ≡ -Ar- ≡-Ar -≡ - &parr0;n Figure1.General structureofap olyaryleneethynylene Poly(aryleneethynylene) systems contain carbon-carbon triple bonds within the main chain of the polymeric backbone and compose one of the relatively few groups of electrically conducting organic polymers. Interest in electrically conducting organic polymers was spawned by the discovery by Hatano et al. in 1961 that polyacetylene conducted an electric current, although it was about ten years later that serious research began. These materials are of synthetic interest not only for the possible exploitation of their expected electrical behavior, but also because they will potentially exhibit third order non-linear optical as well as photoluminescent properties. Poly(aryleneethynylene)s also display high thermal stability There are two major obstacles associated with poly(aryleneethynylene)s. The first is that without modification, the compounds typically exhibit very low solubility in organic solvents or water. The lack of solubility makes the processing and characterization of these types of polymers very difficult. The second obstacle is that the traditional method for PAE preparation (palladium catalyzed coupling of aromatic dihalides with terminal acetylenes) is laborious and usually utilizes rather harsh reaction conditions and/or less than desirable organic solvents (i.e. pyridine, dioxane, THF, etc.). Therefore, our work has concentrated on developing PAEs that are more soluble in organic and/or aqueous solvents, as well as modifying the methods of their preparation such that they are more easily performed and the conditions are less severe. We have tried to design novel materials in addition to incorporating desired qualities in both the polymers synthesized as well as the methods in which they have been prepared This research project has produced a series of highly conjugated poly(aryleneethynylene)s. These materials have been prepared through the careful selection and synthesis of polyhalogenated aromatic monomers and polymerized through the use of traditional and modified palladium catalyzed coupling reactions. The polymers generated from this research have a variety of physical characteristics that are potentially valuable in selected polymer applications. These new materials have been prepared without the need for the extensive monomer modification that is often associated with highly functional polymer species The preparation of the polymers for this project has led to the development of a very useful modification of the well known palladium mediated Sonogashira coupling reaction---the acetylene gas reaction. The procedure is mild with regard to temperature and solvent demands and is very flexible in these regards as well. The procedure can be performed at room temperature under completely aqueous conditions to produce a high weight poly(aryleneethynylene) Therefore, we have prepared several new polymer species as well as developed a unique polymerization method for doing so