Tsai, Zong-YunZong-YunTsaiChang, Wei-CheWei-CheChangYu, Hui-YuHui-YuYuChen, Chin-WenChin-WenChenCHUIN-SHAN CHEN2026-01-082026-01-082026-01-0900323861https://www.scopus.com/record/display.uri?eid=2-s2.0-105023087816&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/735149Polyetherimide (PEI) is a high-performance polymer known for its excellent mechanical and thermal properties, yet its molecular-level deformation mechanisms under load remain poorly understood. In this study, we developed and validated a coarse-grained (CG) force field using a novel hybrid iterative Boltzmann inversion (IBI) and Bayesian optimization (BO) strategy. We then applied the validated CG force field to investigate the molecular mechanisms underlying PEI's tensile deformation. Our simulations successfully captured the stress–strain behavior of PEI — including the yield point and subsequent strain hardening — and provided insight into the underlying molecular mechanisms, including polymer chain orientation, entanglement dynamics, and free volume evolution. Among these, entanglement loss and free volume expansion emerged as the dominant mechanisms driving strain softening and post-yield deformation. These molecular-level insights can inform the design of PEI materials with enhanced mechanical performance.falseChain orientationCoarse-grained molecular dynamicsEntanglementFree volumePolyetherimideTensile testjournal article10.1016/j.polymer.2025.1293862-s2.0-105023087816