Synthesis of Optically Active and Thermally Stable Polyamides With Bulky Aromatic Side Chain in an Ionic Liquid (Tetrabutylammonium Bromide)

Abstract

A new class of wholly aromatic and optically active polyamides (PAs) having phthalimide and L-leucine pendant groups were synthesized via polycondensation of chiral diacid, (2S)-5-[4-(4-methyl2-phthalimidylpentanoyl-amino)benzoylamino]isophthalic acid and different aliphatic and aromatic diisocyanates. Polymerization reactions were performed both in the presence of dibutyltin dilaurate as a catalyst and without a catalyst, using molten tetrabutylammonium bromide (TBAB) as a green solvent, and was compared with polymerization in 1-methyl-2-pyrrolidone as a conventional solvent. The resulting polymers were obtained in good yields and inherent viscosities ranging between 0.26 and 0.96 dL g-1. These polymers are optically active, thermally stable and readily soluble in amide-type solvents. All of the above polymers were characterized by Fourier transform infrared spectroscopy, specific rotation and in some cases by 1H-NMR and elemental analysis techniques. Thermal properties of PAs were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry. TGA showed that the 5% weight loss temperature in a nitrogen atmosphere for two representative samples were more than 283 and 354 °C, which indicates that the resulting PAs have good thermal stability.