Boron containing vinyl aromatic polymers: synthesis, characterization and applications

Novel luminescent polystyrene-based organoborane polymers were synthesized via facile silicon-boron exchange reactions with boron tribromide. The Lewis acidity as well as the photophysical properties of the polymers were then fine tuned by variation of the organic pi-system. The key step is a selective boron-tin exchange that allows for controlled and selective replacement of one of the bromine substituents by the chromophoric system, followed by substitution of the second bromine by a sterically hindered aryl group. The polymers and model compounds were fully characterized by multinuclear NMR spectroscopy. Molecular weights were determined by GPC. DSC and TGA were used to determine their thermal properties. Both polymers and model systems are highly emissive and UV-visible and fluorescence spectroscopy were used to ascertain their photophysical characteristics. To probe the use of the polymers as potential anion sensors, they were subjected to complexation with fluoride ([Bu4N]F in THF) and their complexation was studied by 11B NMR as well as UV-vis and fluorescence spectroscopy. To counter the oxidative degradation of the systems a new strategy was adapted in which we prepared stannylcarbazole precursors which would act as chromophores. To further enhance the stability of the boron center in these systems the mesityl group was replaced by the bulkier 1,3,5-triisopropylphenyl group. The models and polymers synthesized show superior stability as compared to the compounds synthesized earlier. The compounds are also highly emissive in the blue region. Systems that contain electroactive ferrocenyl groups in the side-chain of polystyrene were also synthesized. Cyclic voltammetry studies confirm the electroactive nature of these polymers. A quasi-reversible boron redox couple and a ferrocene-centered redox process were observed. Finally, a trimethylsilyl-functionalized vinyl bithiophene monomer was prepared. This monomer was polymerized by a variety of methods including standard free radical polymerization (BPO, AIBN), via nitroxide-mediated polymerization (NMP) and also by anionic polymerization. Moderate molecular weights in the range of 4000 – 9000 were obtained.Ph.D.Includes bibliographical references (p. 146-161)by Kshitij K. Para