Fast synthesis of optically active polyamides containing l-methionine linkages in ionic liquid via a microwave-assisted process

Abstract

Several optically active aromatic polyamides have been synthesized via direct polycondensation of chiral diacid monomer 1 containing l-methionine moiety with diverse aromatic diamines 2a–2h in a green medium, namely 1,3-dipropylimidazolium bromide as a room temperature ionic liquid. In order to evaluate the advantages of microwave promotion of these polymerization reactions, we compared microwave irradiation (method I) with conventional oil bath heating (method II) by means of reaction rates, conversions, and inherent viscosities. The inherent viscosities of resulting polymers were ranging between 0.47–0.65 and 0.35–0.57 dL/g in methods I and II, respectively. These polymers were characterized by means of 1H-NMR, FT-IR, elemental, organosolubility, differential scanning calorimetry, and thermal gravimetric analysis techniques. The obtained polymers show thermal stability up to 273 °C under nitrogen atmosphere and good solubility in polar organic solvents. Polymerization reactions proceeded in higher yields and moderate inherent viscosities under microwave irradiation conditions besides the dramatically shorter reaction times and achieving the more pure products.