Synthesis and characterization of new organosoluble aromatic polyamides and polyazomethines containing pendent pentadecyl chains

Abstract

New aromatic polyamides and polyazomethines containing pendent pentadecyl chains were synthesized by polycondensation of pentadecylbenzene-1,3-diamine with (i) four commercially available aromatic diacids, viz., biphenyl-4,4′dicarboxylic acid, 4,4′-oxybisbenzoic acid, terephthalic acid and isophthalic acid, and (ii) dialdehydes, viz., terephthaldehyde, isophthaldehyde and a 50 : 50 mol% mixture of terephthaldehyde, and isophthaldehyde, respectively. Inherent viscosities of polyamides and polyazomethines were in the range 0.35–0.56 dL g−1 and 0.33–0.38 dL g−1, respectively, indicating the formation of medium molecular weight polymers. The presence of pendent pentadecyl chains in polyamides and polyazomethines led to an improvement in their solubility in organic solvents. Polyamides could be cast into flexible, transparent and tough films from their solution in N, N-dimethylacetamide while polyazomethines could be solution cast into transparent, flexible and stretchable films from their CHCl3 solution. 1H-NMR studies based on amide proton signals and azomethine proton signals indicated the presence of constitutional isomerism in the polyamides and polyazomethines. Wide-angle X-ray diffraction patterns exhibited broad halo indicating that the polymers were amorphous in nature. X-ray diffractograms also displayed sharp reflections in the small angle region (2 θ ≈ 3°) indicating the formation of layered structure arising from packing of flexible pentadecyl chains. The glass transition ( Tg) temperatures of polyamides were in the range 169–215 °C while Tg values for polyazomethines were in the range 16–55 °C. The temperature for the 10% weight loss of polyamides and polyazomethines were in the range 430–460 °C and 425–440 °C, respectively, in a nitrogen atmosphere, which indicated their good thermal stability. Polyazomethines were also characterized by UV-Vis and photoluminescence spectroscopy and optical band gap ( Eg) values, calculated according to the maximum of the UV absorption, were found to be in the range 2.82–3.10 eV.