Phase Evolution of Polyamide 6 (PA6)‐Based Thermoplastic Elastomers during Heating and Cooling Investigated by Moving‐Window 2D Correlation Infrared Spectroscopy

To illustrate the complex phase evolution of polyamide 6 (PA6)‐based thermoplastic elastomer (TPAE‐50) with a three‐phase system (a pure PA6 crystalline phase, a phase‐separated mesophase, and a mixed phase) during cooling and heating, the in situ IR spectroscopy combined with moving‐window 2D correlation analysis is employed. The mixing of PA6 amorphous domains with soft domains and the melting of imperfect PA6 crystalline domains of TPAE‐50 occur from 60 °C with the increasing temperature. Brill transition happens to the elastomer during heating and cooling at 140–160 and 170–135 °C, respectively. Microphase separation of TPAE‐50 during cooling is formed and can be composed of three processes: the first process (200–180 °C) is motivated by the crystallization of the elastomer; the second process (170–140 °C) results from the transition of homo‐mixed domains in the mixed phase to PA6 amorphous and soft domains; the third process (125–60 °C) leads to the formation of imperfect PA6 crystalline domains in phase‐separated mesophase.