Synthesis and liquid crystalline properties of models and polymers containing thiazolo[5,4-d]thiazole and siloxane flexible spacers

Model compounds and polymers were prepared by condensation of 3,5-bis(4-hydroxyphenyl)thiazolo[5,4-d]thiazole and 2,5-bis(4-hydroxy-3-methoxy)thiazolo[5,4-d]thiazole with chlorotrimethylsilane, dichlorodimethylsilane, dichlorodiphenylsilane and tetrachlorosilane respectively. The molecular weights of the synthesized polymers were calculated from intrinsic viscosity measurements using Mark-Houwink equation. The thermotropic liquid crystalline properties were examined by differential scanning calorimetry and microscopic observations. Model compounds do not exhibit mesomorphic properties while all the polymers except those derived from tetrachlorosilane, exhibit thermotropic liquid crystalline properties. They exhibit nematic thread-like or schlierene texture when examined by the polarizing microscopy. The mesophase type and formation is discussed in terms of chemical structure of the synthesized models and polymers. (C) 2001 Elsevier Science Ltd. All rights reserved.