Thermal and dielectric properties of newly developed L-tryptophan-based optically active polyimide and its POSS nanocomposites

Abstract

A new chiral diamine L-methyl-2-[(3,5-diaminobenzoyl)amino]-3-(1H-indol-3yl)propanoate was synthesized using L-tryptophan (essential amino acid) as starting material. The structure of the synthesized diamine was supported by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (1H and 13C-NMR) and mass spectral techniques. The diamine was polymerized with 3,3’,4,4’-benzophenone tetracarboxylic dianhydride via thermal imidization method to produce thermally stable chiral polyimide (PI) with low dielectric constant. Additionally, polyimide nanocomposites were also prepared by incorporating amino functionalized polyhedral oligomeric silsesquioxane (POSS) into the PI matrix. The polyimide and PI/POSS nanocomposites were characterized by FT-IR spectroscopy. The PI was found to have specific optical rotation of –41.4°. The inherent viscosity was found to be 0.77 dLg−1 indicating that a high molecular weight PI was formed. Surface morphology of the neat PI and nanocomposites was studied by scanning electron microscopy, transmission electron microscopy and atomic force microscopy (AFM) that reveal uniform distribution of the nanoparticles in the PI matrix. DSC analysis indicates that the Tg of the PI and its nanocomposites are in the range of 222–250 °C. The T10% was found to be in the range of 402.4–470.5 °C for the PI and its nanocomposites. The dielectric constant values are in the range of 3.5–2.1.