Synthesis of nylon 1 in supercritical carbon dioxide and its crystallization behavior effect on nylon 11

Abstract

Nylon 1 (PA1), with the highest density of hydrogen bonds and dipoles among odd-numbered nylons, was synthesized in supercritical carbon dioxide using urea as the raw material. In this method, CO₂ not only played the role of a reaction mediator but also acted as an absorbent of the small molecular by-product (NH₃). The chemical structures of PA1 were characterized by means of Fourier transform infrared spectroscopy, ¹³C NMR, intrinsic viscosity, energy dispersive spectrometry and WAXD. A sharp and intense diffraction peak occurred at 27.68°, indicating its highly crystalline nature. The obtained PA1 was quite thermally stable below 340.0 °C, and temperatures at 2% and 5% weight loss were 340.4 and 378.0 °C, respectively. The glass transition temperature (T_g) of PA1 was 135.4 °C. The crystallization behavior effect on nylon 11 after adding PA1 was investigated by DSC. The results showed that both the crystallinity degree and crystallization rate of nylon 11 increased with the addition of PA1 according to isothermal and non-isothermal crystallization analyses. The PA1, a new family member of nylons, is a potential multifunctional material and can serve as a high-performance material in many areas.