Abstract:

The Brill transition of even\|even nylon-6 18 was investigated by using differential scanning calorimetry(DSC),  temperature-dependent wide angle X-ray diffraction(WAXD) and Fourier transform infrared(FTIR). The X-ray diffraction results indicate that the melt-crystallized sample of nylon-6 18 transforms from the triclinic unit cell to the pseudo-hexagonal phase in the  temperature range of 120—180  ℃. In this range,  the thermograph of nylon-6 18 presents a broad endothermal peak. From the FTIR spectra,  it can be found that,  during the transition process of nylon\|6 18,  the intensity of the intrasheet hydrogen bonds  becomes weak. At the same time,  the CH₂-amide bonds twist and the all\|trans conformation of methylene sequences is disordered by inserting the gauche conformation. The CH₂ segments are in a mobile state because of the enhanced stretching and twisting vibrations of  C—CO and C—N bonds.

Key words: Brill transition;  Nylon-6 18;  Conformation;  Triclinic crystalline model;  Pseudo-hexagonal crystalline model