This dissertation describes a study of the kinetics of formation of tethered polymer layers. Polymer chains diffuse from dilute solution to the surface a solid, to which they become attached by one end. Kinetics profiles composed of three distinct regimes are displayed by all tethering reactions studied in the absence of segmental adsorption, regardless of solvent quality, temperature, chemistry of polymer, architecture of polymer, and type of reactive site on the surface. The first regime, fast and predicted previously by theory, is controlled by diffusion of the polymer chains through solution to the bare surface. The second regime, slow and also predicted by theory, is controlled by diffusion of the polymer chains through the already tethered layer. The third regime, relatively fast and not predicted by theory, appears to be the consequence of cooperative interaction between incoming chains and tethered chains. During the tethering process, each tethered polymer chain changes from a random-coil-like configuration to a vertically stretched configuration. The end of the first regime corresponds to completion of a layer of nonoverlapping, coil-like tethered chains, called a mushroom layer. Cessation of tethering corresponds to a layer of vertically stretched chains, called a polymer brush. Transition from mushroom to brush mainly takes place in the third regime and develops in spatially nonuniform manner. The understanding gained about the kinetics of tethering was used to construct simply tethered layers, bi-component tethered layers, bidisperse (two molecular weights) tethered layers, and tethered layers of mixed architecture (linear and star-branched).

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京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20404号 / 工博第4341号 / 新制||工||1673(附属図書館) / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 澤本 光男, 教授 中條 善樹, 教授 竹中 幹人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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Organic semiconductors are widely studied as potential active components for consumer electronics due largely to their easily tuned properties and the promise of lower-cost solution-based processing technology. Imide-functionalized organic small molecule compounds have been one of the more important and studied organic semiconductors. However, very few imide-functionalized conjugated polymers have been reported in the literature. The body of this dissertation focuses on the synthesis, structure-property and device studies of imide-functionalized conjugated polymers. Reasons for choosing arylene imides as polymer building blocks include: a) they impart low-lying LUMOs to polymers, allowing band-gap engineering through choice of comonomers with variable electron-donating ability; b) imide-nitrogens provide points to attach side chains to manipulate solubility and solid-state packing; c) they are easily prepared. Structure-property studies include electrochemical measurements, UV-Vis absorption spectroscopy, differential scanning calorimetry (DSC), x-ray diffraction, and in some cases evaluation as active components in field-effect transistors (OFETs) and photovoltaic devices (PVDs). The published method to synthesize 3,6-dibromo-pyromellitic bisimides (PMBI) was streamlined and poly(phenylene ethynylene)s (PPEs) with variable band gaps were prepared from them (Chapter 2). As noted in all the chapters, electrochemical and optical measurements reveal that the LUMO of the polymers is indeed dictated by the arylene imide, while the HOMO, and therefore the optical energy gap is controlled through varying the electron donor monomer. Intramolecular hydrogen bonding was employed for increasing backbone coplanarity and therefore the polymer could have higher conjugation. One of these polymers demonstrated the narrowest band gap (1.50 eV) for any published PPE. Chapter 3 describes the first published conjugated copolymers from naphthalene bisimides (NBI), here using thiophene-based comonomers as donor units. Polymers with high molecular weight and decent solubility were obtained by choosing appropriate side chains. The optical energy gaps could be tuned across the visible and into the near IR. Preliminary OFET studies revealed electron mobility as high as ~0.01 cm2/Vs. One low band gap polymer provided OFETs with electron mobility of ~0.04 cm2/Vs and hole mobility of ~0.003 cm2/Vs, which is also among the highest mobilities of ambipolar polymeric semiconductors. Using the same approach as in Chapter 3, phthalimide-based monomers were incorporated into polymer backbones for developing new high performance p-type polymer semiconductors for OFETs and PVDs (Chapter 4). Some analogues based on benzothiadiazole, PMBI, and thiophene imides as acceptors were prepared for comparison. Again, high molecular weight, soluble polymers with band gaps spanning the visible and into the near IR were obtained. OFETs from one of the polymers yielded hole mobility ~0.3 cm2/Vs under ambient atmosphere without post-processing thermal annealing, which places it squarely within the state-of-the-art for conjugated polymers. Due to the high mobility and low band gap, this polymer also leads to PVDs with moderately good power conversion efficiency (PCE: ~2%).

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