Thermotropic Liquid-Crystalline Polymers Having Five-Membered Heterocycles as Mesogens V. Relationship between Polymer Structure and Thermotropic Liquid-Crystallinity in Semi-Rigid Polyesters Composed of Twin 2-Phenyl-1,3,4-thiadiazoles Having Central Aliphatic Chains

Abstract

ABSTRACT:Semi-rigid polyesters based on twin biphenyl analogues of 1,3,4-thiadiazole (2-phenyl-1,3,4-thiadiazoles) with hepta-and octamethylene chains in the central part were synthesized by melt polycondensation of bismethyl ester derivatives of twin 2-phenyl-1,3,4-thiadiazole with a ,w-alkylenediols and dioxydialcohol derivatives of bi phenyl. The relationship between polymer structure and thermotropic liquid-crystallinity (LC) was investigated by differential scanning calorimetry (DSC), polarizing microscope observations, miscibility tests and temperature-dependent X-ray analysis. All the polymers derived from a ,w-alkylenediols appeared to form enantiotropic or monotropic nematic phase independent of the lengths of aliphatic chains. Among the polyesters containing the bi phenyl unit, most polymers with octamethylene segment between the twin 2-phenyl-1,3,4-thiadiazoles showed the nematic phase, but polymers composed of the twin bi phenyl analogue having the central heptamethylene chain had no LC melts.KEY WORDS Semi-Rigid Polyester/ 2-Phenyl-1,3,4-thiadiazole / Melt Polycondensation / Bismethyl Ester Derivative/ Liquid-Crystallinity / Nematic Phase/ Differential Scanning Calorimetry Measurement/ A terphenyl analogue of 1,3,4-thiadiazole (2,5-diphenyl-1,3,4-thiadiazole), a five-membered heterocyclic unit containing sulfur and nitrogen atoms, is a calamitic mesogen. 1 Derivatives composed of mesogen with flexible chains on both sides, twin terphenyl analogues of the 1,3,4-thiadiazole having alkylenedioxy segments in the center 2 -5 and main-6 -8 or side-chain 9 polymers containing the mesogen form nematic and smectic mesophases in spite of its bent molecular structure. 2 · 10 -12 Our previous articles described that twin 2,5-diphenyl-1,3,4-thiadiazole derivatives linking an octamethylenedioxy chain to the center 5 have stable nematic and smectic phases. Side-chain polymers with the 2,5-diphenyl-1,3,4-thiadiazole as a mesogen represent cholesteric and chiral smectic C * phases.9 Enantiotropic thermotropic liquid-crystalline (LC) phases emerge in semi-rigid polyesters derived from diacylchloride of the 2,5-diphenyl-1,3,4-thiadiazole and aliphatic diols, 8 although wholly aromatic polyesters consisting of calamitic mesogen have no LC melts. 13Biphenyl analogues of 1,3,4-thiadiazole (2-phenyl-1,3,4-thiadiazoles) have the monotropic smectic A phase, 1 · 14 · 15 although LC temperature range was narrow. 2 In recent years, Tschierske et al. found that homoand heterotrimeric or tetrameric derivatives with the 2-phenyl-1,3,4-thiadiazole ring linked to central flexible chains show the smectic C phase. 14 · 15 Thermotropic LC phases appear in semi-rigid LC polyesters based on twin biphenyl analogue of 1,3,4-thiadiazole having decamethylene chain in the central part. 16 The polymer with octamethylene spacer displayed the monotropic nematic phase and those having decamethylene and dodecamethylene chains showed enantiotropic smectic phases, but LC temperature range was narrow.The present work describes the synthesis of vario...

Thermotropic Liquid Crystalline Polymers Having Five-Membered Heterocycles as Mesogens, 7. Synthesis and Photoluminescent Properties of Semi-Rigid Thermotropic Liquid Crystalline Polyesters Based on a Quaterphenyl Analog of 2,2′-Bis(1,3,4-thiadiazole)

“…[1 -22] Aromatic derivatives, [23 -25] main- [26,27] and side-chain [28] polymers composed of terphenyl and quaterphenyl analogues [29] of 1,3,4-thiadiazole, being similar to 1,3,4-oxadiazole compounds (2,5-diphenyl-1,3,4-thiadiazole and 5,59-diphenyl-2,29-bis(1,3,4-thiadiazole)) form thermotropic liquid crystalline (LC) phases, but few papers on PL and EL properties of the 1,3,4-thiadiazole derivatives and polymers have been reported to our knowledge.…”

“…Very recently, we discovered [27] that semi-rigid polyesters prepared by melt polycondensation of a dioxydiundecanol derivative of 2,5-diphenyl-1,3,4-thiadiazole with diesters form stable thermotropic smectic phases and emit blue or bluish green fluorescence in solution and solid state, although they contain conjugation-interrupted aliphatic chain blocks in the backbones. [22] It was also found [29] that the quaterphenyl analogs of 2,29-bis(1,3,4-thiadiazole) (5,59-diphenyl-2,29-bis(1,3,4-thiadiazole)) not only have smectic melts, but also show PL and EL properties with blue and green light emission and act as electron-transporting and light-emitting materials.…”

Synthesis and Properties of Liquid-Crystalline Semi-Rigid Polyesters Based on Isophthalates of Nitro- or Methoxyazobenzene and Dioxydiundecanols of Biphenyl or 2,5-Diphenyl-1,3,4-Thiadiazole

“…Diethyl 5-hydroxyisophthalate [11,18] 2, 11,119-(4,49-biphenylenedioxy)diundecanol [19] 4 a, 2,5-bis[4-(11-hydroxyundecyloxy)phenyl]-1,3,4-thiadiazole [17] 4 b, 1-nitro-4-[4-(6-bromohexyloxy)phenylazo]benzene [20,21] 1 a, 1-methoxy-4-[4-(6-bromohexyloxy)phenylazo]benzene [21] 1 b, 1-nitro-4-[4-(10-bromodecyloxy)phenylazo]benzene [20] 1 c, and 1-methoxy-4-[4-(10-bromodecyloxy)phenylazo]benzene [22] 1 d were prepared according to published methods. Pyridine was purified by vacuum distillation.…”

Liquid crystalline homopolyesters having main chain calamitic mesogens and one or two side chain azobenzene moieties in the repeat units

“…We have also prepared a series of semi-rigid polyesters containing various aromatic derivatives of 1,3,4-thiadiazole (biphenyl [22,23], terphenyl [24,25], quarterphenyl [26,27], quinquephenyl [28] and distyrylbezene analogues [29]) in the main chain, and discovered that they show thermotropic LC properties arising from the good mesogenicity of aromatic 1,3,4-thiadiazole units, even though they have bent molecular structures (160 ‡).…”

“…Experimental 2.1. Characterization FTIR and 1 H NMR spectra were recorded as described previously [20][21][22][23][24][25][26][27][28][29]. DSC measurements, optical texture observations, X-ray diffraction (XRD) and molecular weight measurements by size exclusion chromatography (SEC) were carried out according to previously published procedures [20][21][22][23][24][25][26][27][28][29] …”