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Abstract
Recently, palladium-catalyzed reactions have been extensively investigated to synthesize conjugated or other functional polymers. The mild reaction conditions enabled many functional groups to survive during these reactions. These developments are especially important for the syntheses of functional and multifunctional polymers. However, to effectively utilize these reactions for polycondensations, reaction conditions and scopes must be studied. The main direction of this thesis is focused on the exploration and development of the Stille and the Heck coupling reactions for polycondensations.
Several factors which affect the polymerization process of the Stille reaction were investigated, such as the catalyst composition and concentration, different solvents, ligands, and structures of monomers. As demonstrations of the versatility of the Stille reaction for polycondensations, different types of conjugated polymers with different properties and applications, such as conjugated photorefractive polymers, carbazole-containing photoconducting polymers, have been synthesized.
The Heck coupling reaction between organic halides and vinylbenzene compounds was also utilized to synthesize soluble and fusible conjugated polymers. It was first applied to the synthesis of poly(2,5-disubstituted-p-phenylene vinylene)s in order to demonstrate the feasibility of the Heck reaction for polycondensation. PPVs with high molecular weights were obtained. This reaction could be further expanded to the synthesis of metalloporphyrin-containing polymers. Different functional groups and various metal ions can be incorporated into the polymers because of the mild reaction conditions. Interesting electroactivity has been observed by measuring the large photoconductivity and photovoltaic effect. Using the same approach, rigid-rod metalloporphyrin oligomers and also oligomers with alternating metalloporphyrins were prepared using the Heck coupling reaction.
Finally, all the PPTs, PPVs, and PPPs synthesized from the Stille and the Heck reactions were found to be liquid crystalline polymers above their melting temperatures. Their nematic liquid crystalline properties were characterized by DSC, polarizing microscope, and x-ray diffraction measurements. The phase behavior of polymers with different side-chain lengths were studied.
