Relaxation behavior, crystallization and mechanical property of long chain polyamides via thermodynamic technologies

Abstract

The relaxation spectra of Long Chain Polyamides (LCPAs) were obtained by adopting superposition principle of the characteristic structural information at different scales, which unveil the dynamic relaxation behaviors from local groups to whole chain over a broad frequency range of 107 − 10−2 Hz with Dielectric relaxation spectroscopy (DRS), dynamic mechanics analysis (DMA) and rheometer respectively and under a temperature interval of 150–30 °C. It has been systematically quantified the influences of the zero-shear viscosity (average macromolecular weight) and the density of hydrogen bonds on relaxation dynamics, the crystallization behavior and mechanical properties. Relaxation time is related to molecular weight, and the segment of LCPA with high molecular weight is difficult to be orderly arranged into crystalline structure, resulting in low crystallization temperature (Tc), thick lamellar thickness (Lc) determined by the increasing undercooling and high mechanical strength. A comparison of LCPAs with varying amide group density revealed the roles of the density of hydrogen bonds and the fraction of free amide groups on relaxation behaviors, which extended the relaxation spectra of LCPAs and furtherly clarified the relationship between structure and properties.