Synthesis and Characterization of New Functional Brush Polymers Containing Electroactive Moieties

DoctorPolymeric memory devices have attracted a great amount of attention due to their low fabrication cost, good scalability, and simplicity of device structure Therefore, functional polymers have been considered as alternatives to traditional inorganic semiconductor materials for memory devices because they can be easily miniaturized indevice fabrication and their properties can easily be tailored through chemical synthesis. These merits have further accelerated the development of several types of polymer-based memory devices such as rewritable memory, write-once read-many times (WORM) memory, and dynamic random access memory (DRAM). However, none of reported studies can comprehensively account for the observed swiching properties of polymer memory, even though many operating mechanisms have benn proposed such as filamentary conduction, charge transfer, charge trapping and conformational chnge mechasinm. To figure out the operating mechanism of polymer memory device, the design of novel polymeric materials with controlled morphologies and electrical properties is required to elucidate the switching mechasnism because electrical behaviors is closely related to morphologies formed in thin films. First, different volume fraction of diblock copolymer is synthesized because block copolymers (BCP) can self-assemble into various ordered nanostructures (such as lamellae, cylinders, spheres and so on) with length scales ranging from 10 to 100 nm due to the repulsion between the chemically connected blocks. Secondly, correlation between memory and structure is studied by controlled morphologies and electrical properties. Lastly, development of a new polymeric materials system is needed for comprehensive understading, so various fluorinated brush polymers is synthesized and studied. In Chapter II, two series of crystalline-amorphous brush diblock copolymers bearing electroactive moieties were newly synthesized by sequential anionic ring-opening copolymerizations of glycidyl derivatives and subsequent selective post-functionalizations. Self-assembly structural details and electrical memory behaviors of these polymers in nanoscale thin films were investigated. The diblock copolymers revealed complex hierarchical self-assembly structures depending on the compositions. The self-assembly structure and orientation of the crystalline block chains were severely affected by the geometrical confinement (i.e., size and shape) resulted from phase-separation. Such film morphologies were found to cause significant influences on the electrical properties; they exhibited electrical properties from p-type permanent memory behavior to dielectric-like behavior. The permanent memory performances were further varied with the morphology parameters. The observed digital memory behaviors were originated from the electroactive moieties incorporated into the bristle ends. In Chapter III, perfluorinated and carbazole brush-containing block copolymer series, poly(3-((6-((7-(9H-carbazol-9-yl)heptanoyl)oxy)hexyl) thio)propyl glycidyl ether - b - glycidyl 12-((3,3,4,4,5,5,6,6,7,7,8,8,9, 9,10,10,10-heptadecafluorodecyl) oxy)-12-oxo dodecanoate) (PGCHHSP20-b-PGHFD60), (PGCHHSP40-b-PGHFD40), (PGCHHSP60-b-PGHFD20), were synthesized. The polymer was thermally stable up to 300 oC. Below the degradation temperature, it showed a glass transition, crystal melting transition, and a liquid crystal to isotropic melt transition. Most of the materials developed so far are only partially fluorinated materials with relatively low fluorine contents. Highly fluorinated polymers such as Teflon are difficult to process into high-quality films, thereby restricting their applicability. As a consequence, the innovative development of new types of highly fluorinated polymers with easy processability has become very attractive. Therefore, we demonstrates that well-defined linear homo polymer and diblock copolymers with the AGE and EEGE monomer, which are versatile and selectively functionalizable polyether platforms is used to synthesize polymer containing liquid crystalline and amorphous block for a variety of nanostructures and memory device applications. Most of all, synthesiezed brush diblock copolymer with different volume fraction is used to study relationship between memory and structure by controlled morphologies and electrical properties. In Chapter IV, fluorinated side chain liquid crystal polymers have been prepared and properties of synthesized polymers were studied. We report fluorinated polymers composed of hydrocarbon unit and semifluorinated side chain segments, where the number of fluorinated tails varies from one to eight. The polymeric structures described differed by the length of the perfluorinated chains and the spacer which joined the polymer backbone. The fluorinated brush polymers possessing different length of fluoroalkyl side group is used to study the correlation between the surface properties and liquid crystalline properties. By systematically probing the effect of structure on the surface organization of the fluorocarbon side chain, study of these brush polymers has helped optimize the semifluorinated side groups for creating low surface energy materials. In addition, electrical switching behaviors of fluorinated brush polymers are measured for memory device application, since research of electrical property with polymers bearing fluorine or fluuorocaron have not been reported except PVDF (polyvinylidene fluoride) and its copolymer. In Chapter V, we have prepared several polymers with mesogenic cores, coded PGBFn (PG : PolyGlycidyl-backbone, B : biphenyl-mesogenic core, Fn : the number of fluorocarbon-side chian). We designed the two types of polymer series with para-position and meta-position of biphenyl side group to study similarity and difference of crystalline structure and physical properties. The introduction of a mesogenic core will contributes to the stabilization and organization of fluorinated tails at the surface. The surface properties with contact angle measuremtn and surface energy is studied and all measured fluorinated brush polymer show the very low surface energy. This study will help us in the design of future liquid crystal polymers and low surface energy polymers opening an interesting field for the building of stable active surfaces with a favorable eco-toxic approach. In addition, quantitative studies on electrical properties of fluorinated polymer have not been carried out so far, electrical memory performance is measured with polymers which have the number of fluorinated tails varies from one to eight. In Chapter VI, we have synthesized a series of polymers bearing fluorinated aromatic ring side chains to investigate the effect of fluorine and trifluoromethyl group on the morphology, the crystal orientation, charge-carrier transport, and device performance. We have prepared several polymers with mesogenic cores and fluorinated aromatic ring, coded PGBaFbcCF3dP (PG : PolyGlycidyl-backbone, B : Biphenyl-mesogenic core, aFbcCF3dP : the number(a, c) and position(b, d) of fluorine or trifluoromethyl group on phenyl unit –fluorinated aromatic ring pendent). The fluorine atom has the highest Pauling electronegativity of 4.0 among electron-withdrawing groups and the electron density distribution of aromatic ring will be varied according to the position and the number of fluorine and trifluoromethyl group. This means the position of fluorine has significant effect on the crystalline behavior and thermal property