Synthesis of imine-ester-linked benzothiazole mesogen containing liquid crystalline monomers with different terminal substituents

ABSTRACT

A series of imine-ester-linked benzothiazole mesogen-based liquid crystalline (LC) monomers (M1–M4) having polymerizable methacrylate functional group as the terminal were designed and synthesized. These monomers were differentiated from each other by varying the terminal substituents (-H, -CH₃, -OCH₃, and -OCH₂CH₃) at the sixth position on the benzothiazole moiety. The chemical structures of the synthesized monomers were characterized and confirmed by spectroscopic techniques such as FTIR, ¹H NMR, and ¹³C NMR. Thermogravimetric analysis (TGA) was used to study the thermal properties of the investigated monomers. The ethoxy substituted monomer (M4) showed higher thermal stability compared with the other monomers. The mesomorphic behavior of all the monomers was studied using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). DSC and POM studies revealed that the monomer (M1) having no substituent at the sixth position on the benzothiazole ring exhibited both smectic and nematic mesophases, whereas -CH₃-, -OCH₃-, and -OCH₂CH₃-substituted compounds revealed only nematic mesophase.

KEYWORDS:

• Benzothiazole
• imine-ester
• liquid crystal
• mesomorphic behavior
• monomers

Funding

The work was supported by the University of Malaya under Grant No. [FP043-2016].

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Additional information

Funding

The work was supported by the University of Malaya under Grant No. [FP043-2016].