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Estroimidowe materiały ciekłokrystaliczne

Orzeszko A.

Wiadomości Chemiczne

2005

[Z] 59, 3-4

231--248

The credit for the discovery of liquid crystals must go to F. Reinitzer who in a paper submitted on May, 1888 described his observations of the colored phenomena occurring in melts of cholesteryl benzoate. He noted the "double melting" behavior in this case, whereby the crystals transformed at 145,5°C into a cloudy fluid, which suddenly clarified only on heating to 178°C. Mesophases are a state of order between crystals and liquids. They have imperfect long range orders of orientation and/or position. Thus, they can be fluid like a liquid and they can have anisotropic properties like crystals. The liquid crystals have a predominating orientational order. Despite intensive research activities of numerous research groups on polymers no systematic study on liquid crystalline polyimides had been published before 1985. Only two patents of Du Pont filed in 1979 reported on LC poly(ester imide)s. The fundamental study on this area was made by Kricheldorf. He found that the most promising substrate for synthesis of liquid crystalline poly(ester imide)s was trimellitic anhydride. It forms imide ester mesogenic group in main polymer chain. On the other hand it has been found that isolated phthalimide moiety not favor liquid crystalline order but connected with ester groups increases a possibility of forming mesophase. Low molecular weight cholesteric ester imides with oxyethylene spacers form liquid crystal SmA2 phase. It is possible due to microsegregation of hydrophobic parts of molecules. Similar compounds with polymethylene spacers exhibit monolayer SmA phase. In this case microsegregation is impossible. Also ester imides based on biphenyl mesogenic moiety show termotropic behavior. Cyanobiphenyl derivatives of such trimellitimides form a partially bilayered smectic Ad phase for the homologues with long N-alkyl substituents. The monolayer smectic A1 phase was observed for all members of 4'-undecyloxybiphenyl derivative series while the longer homologues exhibited SmA-SmC dimorphism. The reaction of imide compounds with Lawesson's reagent leads to monothio- and dithioimides, respectively. Liquid crystalline ester thioimides were obtained at first time by Orzeszko and Białecka. An incorporation of one or two sulfur atoms into an imide ring results in reduction of phase transition temperature values. This is a consequence of the considerable change of compound polarity and the increase of the molecular breadth.