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.