Synthesis and Orientation of Fluorene Containing Reactive Mesogens

• Published in: Macromolecular chemistry and physics Vol. 207; no. 4; pp. 370 - 381
• Main Authors: Thiem, Heiko, Jandke, Markus, Hanft, Doris, Strohriegl, Peter
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 24-02-2006; WILEY‐VCH Verlag; Wiley
• Subjects: Applied sciences; crosslinking; Exact sciences and technology; fluorene; Organic polymers; orientation; photopolymerization; Physicochemistry of polymers; Polymers with particular structures; Preparation, kinetics, thermodynamics, mechanism and catalysts; reactive mesogen; Substituent effect; Thermotropic state; Photoluminescence; Oligomer; Phase transitions; Molecular orientation; Photopolymerization; Optical properties; Size effect; Crosslinked polymer; reactive mesogen; fluorene; Optical absorption; Ultrathin films; orientation; Bifunctional compound; Fluorene derivative polymer; Experimental study; Suzuki coupling; Oriented polymer; Acrylate polymer; Anisotropy; Liquid crystal polymers; Preparation; Prepolymer; crosslinking
• ISSN: 1022-1352; 1521-3935
• DOI: 10.1002/macp.200500455

The synthesis of new fluorene containing photocrosslinkable reactive mesogens is described. Both monodisperse trimers or pentamers and oligomeric mixtures containing two photocrosslinkable acrylate end groups were obtained by Suzuki‐cross‐coupling reactions. The pentamer 12a shows an ideal phase behavior for orientation experiments with a broad nematic phase between the glass transition at −10 °C and 123 °C. In the oligomeric mixtures 14a–g the transition temperature from the nematic to the isotropic phase can be tailored from 100 to 310 °C by adjusting the molecular weight of the oligomers by end‐capping. This process can be easily characterized by MALDI‐TOF spectroscopy. The pentamer 12a and the oligomeric mixture 14c were oriented on rubbed polyimide layers and orientation ratios of 15:1 in photoluminescence were obtained. Experiments with different film thicknesses show that the orientation is not homogeneous throughout the film but decreases with increasing distance from the orientation layer.