Investigation on synthesis and morphology characteristic of novel chiral poly(amide-imide)/TiO2 nanocomposites derived from L-isoleucine-based diacid and 4,4'-methylenebis(3-chloro-2,6-diethylaniline)

In the present investigation, a new optically active poly(amide-imide) (PAI) was synthesized from the polymerization reaction of N-trimellitylimido-L-isoleucine diacid with 4,4'-methylenebis(3-chloro-2,6-diethylaniline) using molten tetra-n-butylammonium bromide and triphenyl phosphite as a condensing agent and green media. Then the surface of titanium dioxide (TiO2) nanoparticles was modified with γ-aminopropyltriethoxyl silane as a coupling agent. The obtained polymer and inorganic metal oxide nanoparticles were used to prepare of PAI/TiO2 nanocomposites (NCs) through ultrasonic irradiation. The formation of PAI was confirmed by 1H NMR, fourier transform IR spectroscopy (FT-IR), specific rotation and elemental analysis. The resulting polymer was synthesized with good yield and moderate inherent viscosities around 0.27 dL/g. The resulting NCs were also characterized by FT-IR, powder X-ray diffraction, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The TEM and FE-SEM results indicated that the nanoparticles were dispersed homogeneously in PAI matrix on nanoscale. TGA confirmed that the heat stability of the NCs was improved in the presence of TiO2 nanoparticles. Transmittance behavior of the obtained PAI/TiO2 NCs was investigated by UV-vis spectroscopy.

Design and preparation of novel fluorescent polyimides containing ortho-linked units and pyridine moieties

A novel pyridine-containing aromatic diamine monomer, 4-[4-hydroxyphenyl]-2,6-bis[4-(2-aminophenoxy)phenyl]pyridine (p,o-HAPP), was synthesized by a modified Chichibabin reaction of p-Hydroxybenzaldehyde and a substituted acetophenone, 4-(2-nitrophenoxy)acetophenone (p,o-NPAP), followed by a reduction of the resulting dinitro compound 4-[4-hydroxyphenyl]-2,6-bis[4-(2-nitrophenoxy)phenyl]pyridine with Pd/C and hydrazine monohydrate. The aromatic diamine was employed to prepare a series of pyridine-containing polyimides (PIs) by polycondensation with various aromatic dianhydrides in N,N-dimethylformamide (DMF) via the conventional two-step method. The inherent viscosities of the resulting poly(amic acids) and PIs were in range of 0.62-0.76 and 0.52-0.64 dL/g, respectively. The obtained novel PIs exhibited high solubility in common organic solvents, such as m-Cresol, DMF, N,N-dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone (NMP), tetrahydrofuran, and chloroform. Meanwhile, flexible PI films were obtained, which had excellent thermal stability, with the glass transition temperature (T g) of 259.8-323.4 °C and the temperature at 10% weight loss of 485.5-576.4 °C in nitrogen atmosphere. The protonated polymer showed UV-vis absorption in the region 200-400 nm and displayed strong fluorescence intensity (470 nm) in NMP solution.