Liquid-crystalline conjugated polymer

More recently, Raman spectroscopy has been used to investigate the vibrational spectroscopy of polymer Hquid crystals (46) (see Liquid crystalline materials), the kinetics of polymerization (47) (see Kinetic measurements), synthetic polymers and mbbers (48), and stress and strain in fibers and composites (49) (see Composite materials). The relationship between Raman spectra and the stmcture of conjugated and conducting polymers has been reviewed (50,51). In addition, a general review of ft-Raman studies of polymers has been pubUshed (52). 

D. Neher, Polyfluorene homopolymers conjugated liquid-crystalline polymers for bright emission and polarized elecroluminescence, Macromol. Rapid Commun., 22 1365-1385,2001. 

M. Grell, D.D.C. Bradley, X. Long, T. Chamberlain, M. Inbasekaran, E.P. Woo, and M. Soliman, Chain geometry, solution aggregation and enhanced dichroism in the liquid-crystalline conjugated polymer poly(9,9-dioctylfluorene), Acta Polym., 49 439-444, 1998. 

B. Schartel, Y. Wachtendorf, M. Grell, D.D.C. Bradley, and M. Hennecke, Polarized fluorescence and orientational order parameters of a liquid-crystalline conjugated polymer, Phys. Rev. B, 60 277-283, 1999. 

The methods that have been examined for producing polarised EL include the use of liquid crystalline chiral oligomers and polymers. - Promising results have been obtained using conjugated polymers where fluorene makes up the backbone, e.g. (5.6), which was synthesised from the dibromo monomer via Yamamoto coupling. These types of material exhibit LC behaviour at transition temperatures of 100-200 °C, and produce blue polarised EL (425 nm) from thin flhns. °... 

Whether polymerized model membrane systems are too rigid for showing a phase transition strongly depends on the type of polymerizable lipid used for the preparation of the membrane. Especially in the case of diacetylenic lipids a loss of phase transi tion can be expected due to the formation of the rigid fully conjugated polymer backbone 20) (Scheme 1). This assumption is confirmed by DSC measurements with the diacetylenic sulfolipid (22). Figure 25 illustrates the phase transition behavior of (22) as a function of the polymerization time. The pure monomeric liposomes show a transition temperature of 53 °C, where they turn from the gel state into the liquid-crystalline state 24). During polymerization a decrease in phase transition enthalpy indicates a restricted mobility of the polymerized hydrocarbon core. Moreover, the phase transition eventually disappears after complete polymerization of the monomer 24). 

Main-chain thermotropic LC polymers such as those presented here combine the advantages of alignability and a well-characterized conjugation length with freedom from the solvent-removal problem of lyotropics. Since the conjugation in the present system can provide both liquid-crystalline and photonic behavior, it simultaneously provides us experience with a third harmonic material and a novel LC system. 

An important point in the science of conjugated polymers is the dependence of their optical properties as a response to their physical state (solution, aggregated, liquid crystalline, solid state, thermal treatment) [50]. Processable PPEs, particularly dialkoxy-PPEs, have been known since the early 1990s [1], and their spectroscopic behavior has been studied both in... 

Yu and co-workers [92,93] have prepared conjugated polymers exhibiting liquid crystallinity by allowing 2,5-bis(tributylstannyl)thiophene to react with aryl diodides or ditriflates, while van Haare et al. [94] have obtained oligomers containing thiophene and pyrrole units, starting from a stannylated pyrrole derivative. 

Kijima, M. Kinoshita, I. Hattori, T. Shirakawa, H. Poly(2,5-dialkoxy-/r-phenylenebutadiynylenejs. Novel rigid conjugated polymers with liquid crystalline property. Synth. Met. 1999, 70d(l), 61 69. 

In field-effect transistors based on the thin films of poly(3-alkyl)thiophene derivatives, high field-effect mobility has been observed because of the formation of crystal-like grains [116]. The mobility depends strongly upon the crystallinity of the thin films. Introduction of liquid crystallinity into conjugated polymers is expected to be effective for enhancing microscopic crystallization of conjugated polymers to increase their carrier mobilities. It can also cause anisotropy in various physical properties if macroscopic molecular alignment is achieved. 

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