Structural symmetry breaking of silicon-containing poly(amide-imide) oligomers and its relation to electrical conductivity and Raman-active vibrations

Abstract

Optically active poly(amide-imide) oligomers were synthesized by direct polycondensation between an aromatic diamine and a dicarboxylic acid both containing a diphenylsilylene unit. The reaction was carried out using triphenyl phosphite/pyridine in the presence of CaCl2 and N-methyl-2-pyrrolidone as solvent. Oligomers were obtained in good yields and showed high solubility in common aprotic polar solvents. The precursors, monomers and poly(amide-imide) oligomers were characterized using elemental analysis and Fourier transform infrared and NMR (1H, 13C, 29Si) spectroscopy. Additionally, themain vibrations of the functional groups (C O, C C or N–H) in the oligomers with respect to temperature were characterized using Raman spectroscopy. The glass transition temperature was determined by studying the Raman spectra and corroborated using differential scanning calorimetry. The thermal stability was studied using thermogravimetric analysis. The molecular mass of the compounds was obtained from matrix-assisted laser desorption ionization time-of-flight mass spectrometry and their optical properties were analyzed using UV-visible diode array spectrophotometry. The electronic properties of the oligomers as well as the delocalization of charge carriers within their structures were analyzed using conductance-voltage curves, which showed that thesematerials are excellent candidates for integrated optoelectronic applications.