Studies on synthesis and thermal characterisation of thermotropic liquid-crystalline poly(benzylidene-ether)s containing alkanones and methylene spacers in the main chain

Abstract

Two series of main chain thermotropic liquid-crystalline poly(benzylidene-ether)s were synthesised by Claisen–Schmidt polycondensation of 4,4'-diformyl-α,ω-diphenoxyalkanes (1–5) (series 1) and 4,4'-diformyl-2,2'-dimethoxy-α,ω-diphenoxyalkanes (6–10) (series 2) with alkanones. The molecular weight of the polymers determined by gel permeation chromatography was found to be moderate. The study of thermal properties by thermogravimetric analysis revealed that cyclopentanone-containing polymers are more stable than cyclohexanone- and acetone-containing polymers and, in addition, showed that series 1 polyethers displayed better stability when compared to series 2 polyethers. The influence of the length of methylene spacer on phase transition was investigated using differential scanning calorimetry and it was noted that the isotropic temperature decreases with an increase in the length of the spacer. Further, a study of the odd–even effect revealed that the decoupling function of the spacer plays a vital role. A polarised optical microscopic study showed that cyclohexanone-containing polymers exhibit well-defined textures in both the series.

Keywords:

• synthesis
• liquid-crystalline polymers
• differential scanning calorimetry
• odd–even effect

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Corrigendum

Acknowledgements

The authors gratefully acknowledge the Principal and Management, PSG College of Technology, Coimbatore, for providing the necessary facilities and the Department of Science and Technology, India, for financial assistance [Grant No.SR/S1/PC-21/2007]. Sincere thanks are also due to SAIF, Indian Institute of Science, Bangalore, for NMR spectral studies and STIC - Cochin University for TGA analysis.