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. 2021 May 22;13(11):1687.
doi: 10.3390/polym13111687.

Optical and Thermal Investigations of New Schiff Base/Ester Systems in Pure and Mixed States

Abeer S Altowyan  1 , Hoda A Ahmed  2   3 , Sobhi M Gomha  2   4 , Ayman M Mostafa  5   6   7
Affiliations

Optical and Thermal Investigations of New Schiff Base/Ester Systems in Pure and Mixed States

Abeer S Altowyan et al. Polymers (Basel). .

Abstract

New mesomorphic series, 4-hexadecyloxy phenyl-imino-4'-(3-methoxyphenyl)-4″-alkoxybenzoates (An), were prepared and investigated with different thermal and mesomorphic techniques. The synthesized homologous series constitutes four members that differ from each other in the terminal length of flexible chain (n) attached to phenyl ester moiety, which varies between n = 6, 8, 10, and 12 carbons. A lateral CH3O group is attached to the central benzene ring in the meta position with respect to the ester moiety. Molecular structures of all newly prepared homologues were elucidated via FT-IR, 1H and 13C NMR spectroscopy. Mesomorphic and thermal properties were examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and the mesophases identified by polarized optical microscopy (POM). DSC and POM examinations revealed that all members of the present series (An) exhibit a purely enantiotropic nematic (N) phase. Comparative evaluations and binary phase diagrams were established between the present homologues and their corresponding shorter one (Bn). The examination revealed that, the length of the flexible alkoxy chain incorporated into the phenylimino moiety is highly effective on the temperature range and stability of the mesophase observed. With respect to the binary mixtures An/Bn, the exhibited N phase showed to cover the whole composition range with eutectic behavior.

Keywords: Lateral methoxy; binary phase diagram; nematic stability; optical properties; schiff base/ester.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Prepared homologues series, An.
Scheme 2
Scheme 2
Synthesis route of title compounds An.
Figure 1
Figure 1
DSC thermograms of homologue A8 recorded from the second heating and cooling cycles at a rate of ±10 °C min−1.
Figure 2
Figure 2
N mesophase textures observed upon heating under POM for (a) homologue A8 at 107.0 °C and (b) homologue A16 at 102.0 °C.
Figure 3
Figure 3
Impact of alkoxy chain length (n) on the mesomorphic behavior of the present investigated series, An.
Figure 4
Figure 4
TG (a) and DTG (b) curves of the compound A8.
Scheme 3
Scheme 3
Homologues series, Bn.
Figure 5
Figure 5
Comparison of Tc (a); and ΔTc (b) of series An and Bn.
Figure 6
Figure 6
Phase diagrams for systems (a) A8/B8 and (b) A16/B16; the symbol “o” denotes the solid–N phase, “●” N–I phase transition upon second heating scan.
Figure 7
Figure 7
DSC curve of 80% mol of A8 for system A8/B8 at a rate of ±10 °C min−1 recorded upon heating and cooling cycles.
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