New liquid crystalline poly(azomethine esters) derived from PET waste bottles

Abstract

Nowadays, the disposal of non-biodegradable polyethylene terephthalate (PET) bottles is considered as an environmental issue faced by both developing and underdeveloped countries of the world. This research covers the historical development and the impact of structural concept of polyester and polyethylene terephthalate (PET) that contributes to the regeneration of terephthalic acid (TPA) from PET waste bottles to replace petrochemical resources and consequently act as a component in the production of liquid crystalline polymers focusing on liquid crystalline poly(azomethine esters). The experimental section covers four T-shaped azomethine bisphenols prepared via the reaction of 2,5-dihydroxybenzaldehyde with different aromatic amines, namely aniline, p-iodoaniline, p-bromoaniline and p-chloroaniline and subsequently reacted with TPA to produce the new thermotropic liquid crystalline poly(azomethine esters). The structures of the terephthalic acid, azomethine bisphenols and poly(azomethine esters) were confirmed by FTIR, 1H NMR, 13C NMR spectroscopy and elemental analysis (CHN). The liquid crystalline behaviors of these polymers were studied by differential scanning calorimetry (DSC), polarizing optical microscope (POM) and x-ray diffraction (XRD). All the synthesized poly(azomethine esters) possesses good thermal stability and exhibit nematic phases except for the polymer that derived from aniline did not show any mesophase.