Degradation Structure of EPDM Revealed by Sequential PCA and Kendrick Mass Three-Dimensional Analysis of Temperature-Dependent High-Resolution Mass Spectra

Abstract

The structural changes in the ethylene–propylene–diene monomer (EPDM) during thermo-oxidative degradation were investigated using an evolved gas analysis coupled with a time-of-flight mass spectrometry (EGA-TOFMS)-based approach combined with multivariate and Kendrick mass defect analyses. Elucidating the degradation behavior of EPDM remains challenging owing to its cross-linked structure, and the presence of carbon fillers limits the applicability of conventional analytical techniques. Principal component analysis (PCA) of the temperature-dependent mass spectra corrected by EGA-TOFMS enabled the extraction of degradation-related features of EPDM, with the PCA scores identified as representing pyrolysis products. The assignment of accurate mass signals within the PCA loadings was achieved using a newly developed Kendrick mass three-dimensional (KM3D) analysis. Interpretation of the loadings revealed the progressive oxidation of diene units, leading to an increased contribution of thermally more stable PE and PP components compared to the diene-derived species. Furthermore, the formation of the degradation components in EPDM was evaluated using combined elected ion current (EIC) curves constructed from ion series containing oxygen atoms. Oxidation products, which were rarely observed in the undegraded EPDM, increased markedly with degradation. The number of ions containing one oxygen atom increased rapidly in the early stages followed by a gradual increase, whereas those containing two oxygen atoms showed a continuous increase, suggesting a sequential thermo-oxidative degradation pathway. These findings demonstrate that the integration of PCA with KM3D analysis provides a framework for interpreting temperature-dependent EGA-TOFMS data, enabling elucidation of degradation structures and pathways across a wide range of elastomers.