The crystal-form transition behaviours and morphology changes in a polyamide 6 cyclic dimer

• Published in: Royal Society open science Vol. 5; no. 11; p. 180957
• Main Authors: Peng, Lu, Li, Jie, Peng, Shumin, Yi, Chunwang, Jiang, Feng
• Format: Journal Article
• Language: English
• Published: England The Royal Society 01.11.2018
• Subjects: characteristic; Chemistry; cyclic dimer; melting; sublimation; transition; α- and β-form; melting; α- and β-form; cyclic dimer; characteristic; transition; sublimation
• ISSN: 2054-5703; 2054-5703
• DOI: 10.1098/rsos.180957

The characteristics of pure - and -form of the cyclic dimer (1,8-diazacyclotetradecane-2,9-dione) were systematically and integrally investigated during this study. The results showed that the -form could dissolve and rapidly transform into the -form in methanol, and in caprolactam solution at a lower temperature, an interesting transition occurred and formed co-precipitates, which refract colourful light under PLM. However, these dimers can aggregate in water, and they are then transformed into multi-slice layers and compact structures. The detailed transition behaviours between the two forms were further measured by FT-IR, XRD and DSC by varying the temperature from 25°C to 360°C, respectively, which showed that there are two endothermic transitions over the course of the heating programme. At a temperature of approximately 242°C, the crystals were initially converted into crystals, and then they melted when the temperature reached over 345°C. A video recorded under a light microscope also showed that the sublimation of the cyclic dimer occurred after the transition. However, the -form might sublimate at temperatures lower than 150°C when mixed with volatile matter.