Thermal‐Oxidative Yellowing Mechanism of PEBA : Role of α,β‐Unsaturated Carbonyl Conjugation

ABSTRACT

Polyether block amide (PEBA), a block copolymer of polyamide and polyether segments, is valued for its low density, low water absorption, and high resilience, making it suitable for sports, electronics, industrial, and medical applications. However, it is prone to yellowing during processing and service, which compromises both aesthetics and performance. Unlike common aliphatic polyamides whose yellowing is attributed to structures like conjugated N‐acrylamides, the distinct two‐stage color evolution (yellowing followed by reddening) and the role of the polyether segment in PEBA remain unclear. Herein, the thermal‐oxidative aging mechanism of PEBA was systematically deciphered by combining colorimetry, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), X‐ray photoelectron spectroscopy (XPS), melt mass‐flow rate (MFR) and ultraviolet–visible spectroscopy (UV–vis) analyses. The results reveal that the color evolution stems from the sequential formation of chromophores via polyamide segment‐dominated oxidation. Initially, radical‐induced scission generates saturated aldehydes, which subsequently undergo aldol condensation to form α,β‐unsaturated aldehydes. The conjugation of these unsaturated aldehydes, extending to three or more double bonds, redshifts the π→π* transition into the visible region (380–500 nm), leading to yellowing. At elevated temperatures, further conjugation extension or the formation of additional chromophores contributes to the subsequent reddening. This study elucidates the segment‐specific and stage‐resolved yellowing mechanism of PEBA, providing a theoretical cornerstone for targeted anti‐yellowing strategies.