The Polymer Society of Korea

Abstract

In this study, the effect of a choline chloride–urea-based deep eutectic solvent (DES) on the polymerization behavior and structural properties of polyamide 66 (PA66) was investigated under reduced-pressure and high-pressure polymerization conditions. Under reduced-pressure polymerization, the DES-containing sample (#2) exhibited enhanced polymerization performance compared to the DES-free sample (#1). Specifically, #2 relative viscosity (ηᵣ) increased from 4 to 54, approaching that of commercial PA66 (approximately 64). In addition, the DES-assisted sample distinct amide-related absorption bands in the FT-IR spectram, particularly the amide band at 1630cm⁻¹ and ~1536 cm⁻¹. These observations indicate that the presence of DES effectively promotes the amidation reaction and stabilizes polymer chain growth during vacuum polymerization. Consistently, ¹H NMR spectra of the #2 revealed structural features comparable to those of commercial PA66, including amide at 8.0–8.5 ppm and characteristic methylene signals at 3.4 and 1.5–2.5 ppm. Thermal analysis by DSC and TGA further demonstrated that the #2 exhibited superior thermal stability compared to #1. Specifically, the Tm increased from 252 to 257 °C, while the Td₅% showed increase from 293 to 360 °C, indicating enhanced thermal stability. These results demonstrate that choline chloride–urea-based DES can act as an effective reaction promoter for PA66 synthesis under reduced-pressure conditions.