Book Description

Polymer brushes, thin polymer coatings consisting of polymer chains that are tethered with one chain end to a surface, have drawn extensive interest in the field of surface modification. The chemical bonding between polymer and substrate allows unique properties such as chemical resistance and stimuli responsiveness. Over the past decade, numerous new chemistry platforms have been established to synthesize polymer brushes with a variety of conformations, such as diblock copolymer brushes and mixed polymer brushes. Although various applications have been demonstrated, efforts to allow industrial scale-up are still required. This dissertation focuses on developing new chemistry platforms to allow more facile and eco-friendly chemistry for polymer brush manufacturing. Surface-initiated photoinduced electron transfer -- reversible addition-fragmentation chain transfer polymerization (SI-PET-RAFT) was introduced as a novel light-mediated polymerization technique with high oxygen tolerance under a wide wavelength range of visible light. The modularity and versatility of SI-PET-RAFT was highlighted through significant flexibility with respect to the choice of monomer, light source, wavelength, and photoredox catalyst. The reproducibility of polymer brush synthesis is also interrogated. Experiments compared the stability of initiating monolayers for surface-initiated (SI) reversible addition-fragmentation chain transfer polymerization (SI-RAFT) and SI atom transfer radical polymerization (SI-ATRP). Initiator-functionalized substrates were stored under various conditions and grafting densities of the resulting polymer brush films were determined via in situ ellipsometry. Decomposition of one of the examined SI-RAFT initiators resulted in limited reproducibility for polymer brush surface modification. In contrast, initiators for SI-ATRP showed excellent stability and reproducibility. While both techniques bring inherent benefits and limitations, the described findings will help scientists choose the most efficient technique for their goals in chemical and topographical surface modification. Studies on developing synthetic platforms for mixed polymer brushes are also provided. Two different pathways, sequential SI-RAFT/SI-ATRP and sequential dual SI-PET-RAFT, were attempted due to their highly versatile monomer choices. Optimizations on each polymerization and selective chain end passivation were successfully performed. Although there still lacked direct evidence in the formation of mixed polymer brushes, the co-existence of two polymers was confirmed by X-ray photoelectron spectroscopy (XPS). Current challenges and corresponding future works are also discussed. Finally, resonance soft X-ray reflectivity (RSoXR) is introduced as a novel characterization technique to probe vertical distribution of polymer brushes. Reflectance data of homopolymer brushes, diblock copolymer brushes, spin-coated bilayer films at carbon K-edge were investigated. The depth profiles obtained via RSoXR were in agreement with results from variable angle spectroscopic ellipsometry (VASE). Both techniques revealed a rougher polymer-polymer interface in diblock copolymer brushes than in spin-coated bilayer films.