Conjugated polymer thin film formation via surface-initiated chain growth polymerization
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In this work, we have developed methods for forming surface-bound, covalently attached brushes of conjugated polymer via various chain-growth surface-initiated polymerizations. We report a new technique, surface-initiated Kumada-type catalyst transfer polymerization (SI-KCTP) which can be used to form thick, dense films of substituted and unsubstituted poly(p-phenylene) and polythiophene. This is the only known chemical technique for forming films of these unsubstituted polymers. We prepared brushes of soluble polymers by polymerizing alkoxy-substituted phenylene monomers, and examined the effect of substitutent chain length, aryl halide choice, initiator ligand, and salt additive upon the films formed by SI-KCTP. We have adapted ring-opening metathesis polymerization (ROMP) to a surface-initiated polymerization of cyclooctatetraene, forming polyacetylene, and characterized its growth via AFM. We have also end-functionalized this system with ferrocene and characterized the electron transfer kinetics between the electrode and the ferrocene endgroup, achieving substantially higher transfer rates than those observed in a non-conjugated polynorbornene film. We developed a method for electrochemical immobilization of a diazonium-terminated monolayer on an electrode surface for use in the formation of conjugated monolayer structures. We demonstrated this functional surface’s utility in the immobilization of a wide variety of electron-rich aromatic species, including ferrocene through an unusual radical-based Gomberg-Bachman-Hay coupling and other species via an azobenzene linkage. The resulting monolayers are densely packed and conjugated, displaying relatively rapid electron transfer. The diazonium layer can also be used to immobilize transition metal complexes, potentially allowing the technique to be used for surface-initiated polymerizations.