Preparation and characterization of optically active and flame-retardant poly(amide–imide)/SiO2 nanocomposites having N-trimellitylimido-l-methionine linkages using ultrasonic irradiation

In the present investigation, at first, 2,3,4,5-tetrabromo-6-[(4-hydroxyphenyl)carbamoyl] benzoic acid (TBHBA) was synthesized and characterized by Fourier transform infrared (FTIR). Silica nanoparticles (SiO₂ NPs) were treated with TBHBA as coupling agent with ability of flame retardancy to introduce organic functional groups on the surface of SiO₂ and improved the dispersion of NPs. Furthermore, novel optically active and flame-retardant poly(amide–imide)/SiO₂ nanocomposites (PAI/SiO₂ NCs) were successfully synthesized via a simple and inexpensive ultrasonic irradiation process. For this purpose at first, PAI was selected as a polymer matrix and was synthesized by direct polycondensation reaction of N-trimellitylimido-l-methionine with 4,4′-diaminodiphenylether in molten tetra-n-butyl ammonium bromide/triphenyl phosphite as a green condensing agent. The resulting PAI/SiO₂ NCs were characterized by various techniques including FTIR, X-ray diffraction, and thermal gravimetric analysis (TGA), and their morphology were investigated by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) analysis. TEM and FE-SEM images showed that NPs were dispersed into the polymer matrix at nanoscale. TGA results showed that the addition of SiO₂ NPs into the NCs enhanced the thermal stability of the samples compared to the pure PAI.