A series of aromatic polyimides based on the asymmetrical diamine 3,4ʹ-oxydianiline and various tetracarboxylic acid dianhydrides, both “rigid” and “flexible” structure, have been synthesized using the original method of one-pot high-temperature catalytic polycondensation in molten benzoic acid. The synthesized polyimides were investigated using fourier-transform infrared (FTIR) and ¹H NMR spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermomechanical analysis (TMA) and wide-angle X-ray scattering (WAXS). It was found that the synthesized polyimides, depending on the used dianhydride, are characterized by different solubility in organic solvent and molten benzoic acid, molecular weight, glass transition temperature (Tg) from 198 to 270 °C, an amorphous or semi crystalline structure with the degree of crystallinity from 41 to 52%. The influence of the method of synthesis on the formation of the crystalline phase of polyimides was studied, and the obtained results were compared with the literature data. The effect of dianhydride chemical structure on the performance of polyimide in pervaporation more specifically, dehydratation of azeotropic isopropanol solution was investigated and compared with the commercially available polyetherimide Ultem 1000™. Membrane structure was studied using scanning electron microscopy. It was found that polyimide PI-DA is the most effective for separation of 88 wt.% isopropanol/12 wt.% water mixture compared to the polyimide PI-6FDA and commercial polyetherimide Ultem 1000™ demonstrating normalized permeation flux of 2.77 kg µm m⁻² h⁻¹ and separation factor of 264 (water content in permeate 97 wt.%).

By the method of one-stage high-temperature polycondensation of 1,4-phenylene-bis-(5-oxy-1,3-phenylenediamine) (B4 monomer) with 4-(3-aminophenoxy)phthalic acid (AB monomer) in molten benzoic...

High-temperature thermoplastic semicrystalline polyamide imide (PAI) with T_g = 250°C, and T_m = 370°C was synthesized from 4,4’-diaminobenzanilide, and 2,2-propylidene-bis (1,4-phenyleneoxy) diphthalic anhydride using three different methods: one-pot high-temperature catalytic polycondensation in molten benzoic acid (BA), low-temperature polycondensation (LTP) in dimethylacetamide (DMAA) followed by chemical imidization, and LTP followed by imidization. The influence of the synthetic route on the crystallinity of PAI was studied by wide-angle X-ray scattering. The PAI synthesized in molten BA comprised a reactive oligomer, which on heating up to 360°C easily transformed into high-molecular-weight PAI. The thermal and rheological properties of the high-molecular-weight PAI thus prepared were studied using differential scanning calorimetry, trimellitic acid, thermogravimetric analysis, and capillary viscosimetry. The rheological characteristics indicate that the obtained PAI can be melt processed by extrusion and hot pressing at 370–380°C.