Molecular design of liquid crystalline poly(ester-amide)s with perfluoroalkyl spacers |
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Authors: | May May Teoh Tai-Shung Chung Si-Xue Cheng Ting Ting Lin K P Pramoda |
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Institution: |
a Department of Chemical and Environmental Engineering, National University of Singapore, Singapore 119260
b Department of Chemistry, Wuhan University, Wuhan 430072, PR China
c Institute of Materials Research and Engineering, Singapore 117602 |
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Abstract: | We have introduced a series of perfluoroalkyl dicarboxylic acids with different lengths of fluorinated aliphatic segments into the 2,6-acetoxynaphthoic acid (ANA) and acetoxy acetanilide (AAA) systems; and their effects on the evolution of liquid crystal texture and liquid crystallinity have been investigated. The perfluoroalkyl dicarboxylic acids are tetrafluorosuccinic acid (TFSA, n=2), hexafluoroglutaric acid (HFGA, n=3), perfluorosuberic acid (PFSUA, n=6) and perfluorosebacic acid (PFSEA, n=8). Computational results based on the 'RIS' Metropolis Monte Carlo method indicate that the ANA/AAA/perfluoroalkyl system may form thermotropic liquid crystalline polymers (LCPs) because the calculated persistence ratios are greater than 6.42. Computational results also predict that the systems containing even-numbered perfluoroalkyl acids have greater persistence length and molar stiffness than that containing odd-numbered acids. Experiments were carried out using the in situ thin film polymerization technique under a polarizing optical microscope. We observed that systems containing short aliphatic units (n=2, 3) tend to remain in the LC phase, while systems containing a long aliphatic spacer (n=8) tend to crystallize during the late stage of the polycondensation reaction. The liquid crystal domain formed in the early stage has a disclination strength S of +1. Ternary phase diagrams were plotted to show the relationship among monomer structure, composition, anisotropic and crystalline phases. FTIR results confirm the formation of LCPs. |
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