Thermotropic liquid‐crystalline poly(oxadiazole)s with poly(methylene) spacers: Preparation and extraordinary odd–even effect |
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Authors: | Cheng-Jang Tsai Yun Chen |
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Institution: | Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan 701, Republic of China |
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Abstract: | A novel synthetic procedure for the preparation of poly(oxadiazole)s was developed with nucleophilic substitution of α,ω-alkanediols with oxadiazole-activated bisfluoride. Seven poly(oxadiazole)s were successfully prepared by the solution polymerization of 2,5-bis(4-fluorophenyl)-1,3,4-oxadiazole and various α,ω-alkanediols HO (CH2)n OH, n = 5–10 or 12] in diphenyl sulfone at temperature greater than 230 °C with K2CO3 as a catalyst. The reduced viscosities of the poly(oxadiazole)s were 0.14–0.51 dL/g, and the decomposition temperatures were greater than 350 °C and decreased from 436 to 379 °C with increasing spacer length (n). Corresponding model compounds, consisting of two terminal mesogenic 2,5-bisphenyl-1,3,4-oxadiazole units and central poly(methylene) spacers, were also prepared for comparison. Both the polymers and model compounds exhibited an extraordinary odd–even effect: odd ones showed higher transition temperatures (melting and clearing temperatures). With differential scanning calorimetry, polarized optical microscopy (POM), and X-ray diffraction, we found that the nematic mesophase was the only texture in the melts except for the polymers with longer methylene units (n = 9), in which smectic mesophases were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 293–301, 2002 |
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Keywords: | poly(oxadiazole)s thermotropic liquid crystal odd– even effect smectic X‐ray polymerization differential scanning calorimetry (DSC) |
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