Surface Engineering Using Kumada Catalyst-Transfer Polycondensation (KCTP): Preparation and Structuring of Poly(3-hexylthiophene)-Based Graft Copolymer Brushes

Holy(4-vinylpyridine)-block-poly(4-iodo-styrene), P4VP-b-PS(l), block copolymers obtained by iodination of readily available P4VP-b-PS block copolymers strongly adhere to variety of polar substrates including Si wafers, glasses, or metal oxide surfaces by a polar P4VP block, forming polymer brushes of moderately stretched PS(l) chains. Kumada catalyst-transfer polycondensation (KCTP) from the P4VP-b-PS(l) brushes results into planar brushes of the graft copolymer in which relatively short (similar to 10 nm) poly(3-hexylthiophene), P3HT, grafts emanate from the surface-tethered PS(l) chains. Grafting of the P3HT leads to significant stretching of the PS(l) backbone as a result of increased excluded volume interactions. Specific adsorption of the P4VP block to polar surfaces was utilized in this work to pattern the P4VP(25)-b-PS(l)(350) brush. The microscopically structured P4VP(25)-b-PS(l)(350) brush was converted into the respectively patterned P4VP-PS(l)-g-P3HT one using KCTP. We also demonstrated that KCTP from functional block copolymers is an attractive option for nanostructuring with polymer brushes. P4VP(75)-b-PS(l)(313) micelles obtained in selective solvent for the PS(l) block form a quasi-ordered hexagonal array on Si wafer. The P4VP(75)-b-PS(l)(313) monolayer preserves the characteristic quasi-regular arrangement of the micelles even after extensive rinsing with various solvents. Although the grafting of P3HT from the nanopatterned P4VP(75)-b-PS(l)(313) brush destroys the initial order; the particulate morphology in the resulting film is preserved. We believe that the developed method to structured brushes of conductive polymers can be further exploited in novel stimuli-responsive materials, optoectronic devices, and sensors.