Block Copolymers with Pendant Conjugated Chromophores: Syntheses, Properties, and Memory Device Application

• Main Authors: Pei-Hsuan Lin, 林佩萱
• Other Authors: Wen-Chang Chen
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/48328212271721349697

碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 99 === A wide range of vinyl monomers and their polymers bearing various conjugated chromophores have been extensively studied and applied in recent years. In contrast to wholly π-conjugated linear polymers, non-conjugated polymers containing pendant π-conjugated moieties systems are of interest for their advantages of excellent solubility, tunable morphology and precisely optoelectronic properties. However, the correlation between polymer architecture, charge transport and photophysical properties in the switching behavior of memory devices have not been fully explored yet. Therefore, this thesis mainly focuses on the synthesis and characterizations of polymers with pendant conjugated moieties combined with their applications on memory devices. In the first part of this thesis (Chapter 2), atom transfer radical polymerization (ATRP) and Suzuki coupling reaction were applied to synthesize the new non-conjugated diblock copolymers with different pendant conjugated chromophores, including 3,5-difluorophenyl, fluorene and pyrene groups. The targeted diblock copolymers were successfully synthesized and characterized by gel permeation chromatography (GPC) and 1H NMR spectrum. All the polymers have number average high molecular weight (>104) with polydispersity index (PDI) of 1.2 ~ 1.4, and soluble in common organic solvents such as chloroform, THF and chlorobenzene. The shifted absorption band of these diblock copolymers were shown as the increasing pendant conjugated moieties, and the band gaps calculated from absorption edge are in the range of 3.14 ~ 4.11 eV. Furthermore, adding pendant conjugated moieties to copolymers would shift the λmaxabs to longer wavelength in fluorescence spectra. Effects of side-chain chromophores structures and ratios on the optoelectronic and electrochemical properties were systematically investigated. In the second part of this thesis (Chapter 3), the new non-conjugated diblock copolymers based on polystyrene derivatives containing pendant 3,5-difluorophenyl, pyrene and fluorene groups were used to evaluate the memory applications. The prepared diblock copolymers are composed of three different block ratios of 3/1, 1/1 and 1/3 (polystyrene/pendent chromophores). The bistable memory behavior is conducted by a simple sandwich device configuration consisted of spin-coated polymer film between indium-tin oxide (ITO) bottom electrode and aluminum (Al) top electrode. For the pendant 3,5-difluorophenyl series of memory devices, the mechanism of the switching behavior is based on filamentary conduction, because the logarithmic plot of the I-V data for the ON state contains a linear region with a slope of 1.0. In the case of pyrene based polymers, the insulating characteristics of polystyrene could be served as hole-blocking moieties and provide the charge trapping environment. Thus, the pendant pyrene based polymers exhibit the electrical volatile nature which attributed to the back transferring of shallow trapped charges in the pendant functional groups. And for the last case of the devices with fluorene moieties, its insulating behaviors are due to the higher energy level between the work functions of the ITO bottom electrode and the HOMO level of the active polymer layer, which might prevent the hole injection process. The relationship between the chemical structure, electronic properties, and device performance were also established in this study.