Thermotropic liquid-crystalline poly(oxadiazole)s with poly(methylene) spacers

Preparation and extraordinary odd-even effect

Cheng Jang Tsai, Yun Chen

Research output: Contribution to journalArticle

19 Citations (Scopus)

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 clearning 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.

Original languageEnglish
Pages (from-to)293-301
Number of pages9
JournalJournal of Polymer Science, Part A: Polymer Chemistry
Volume40
Issue number3
DOIs
Publication statusPublished - 2002 Feb 1

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Oxadiazoles
Crystalline materials
Liquids
Polymers
Temperature
Sulfones
Superconducting transition temperature
Optical microscopy
Differential scanning calorimetry
Melting
Substitution reactions
Textures
Polymerization
Viscosity
Decomposition
X ray diffraction
Catalysts
1,3,4-oxadiazole

All Science Journal Classification (ASJC) codes

  • Materials Chemistry
  • Polymers and Plastics

Cite this

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title = "Thermotropic liquid-crystalline poly(oxadiazole)s with poly(methylene) spacers: Preparation and extraordinary odd-even effect",
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 clearning 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.",
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