{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,8]],"date-time":"2026-10-08T09:49:22Z","timestamp":1791452962990,"version":"4.3.3"},"reference-count":46,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T00:00:00Z","timestamp":1791331200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T00:00:00Z","timestamp":1791331200000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100007129","name":"Shandong Provincial Natural Science Foundation","doi-asserted-by":"publisher","award":["ZR2024QE087"],"award-info":[{"award-number":["ZR2024QE087"]}],"id":[{"id":"10.13039\/501100007129","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100007129","name":"Shandong Provincial Natural Science Foundation","doi-asserted-by":"publisher","award":["ZR2025QC487"],"award-info":[{"award-number":["ZR2025QC487"]}],"id":[{"id":"10.13039\/501100007129","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Shandong Provincial Key Research and Development Program: Innovation Capability Enhancement Project for Technology-Based Small and Medium-Sized Enterprises","award":["2025TSGCCZZB0543"],"award-info":[{"award-number":["2025TSGCCZZB0543"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>Predicting the glass-transition temperature (Tg) helps select polymers for a service-temperature window, but accuracy on familiar structures may not transfer to a new family. We compare validation protocols on 7367 curated homopolymers. Histogram gradient boosting gives R2 = 0.899 and mean absolute error (MAE) = 23.9 K under random cross-validation, 0.857 and 28.5 K under scaffold holdout, a class-macro mean of 0.355 and 43.3 K under curator-class holdout, and \u22123.79 and 79.5 K under high-Tg extrapolation. Similarity explains only 6\u201311% of within-protocol absolute-error variance in the first three settings. A separate density functional theory (DFT) band-gap dataset shows a moderate fingerprint-cluster holdout penalty and poor property-range extrapolation for the tested baselines. Random-forest split-conformal empirical coverage falls from 0.899 under random splitting to 0.683 and 0.214 under class and property holdout; the tested prospective similarity gate provides little protection. A fold-fitted group-contribution prior is more sensitive to uniform additive bias in a squared-loss penalty than as a neural-network input, but this comparison is architecture-dependent. Class-holdout intervals and tests are descriptive or nominal because training sets overlap. The 279 multiply reported polymers support only the between-source variability analysis. Validation should match the intended polymer family and property range.<\/jats:p>","DOI":"10.3390\/polym18192445","type":"journal-article","created":{"date-parts":[[2026,10,8]],"date-time":"2026-10-08T08:34:25Z","timestamp":1791448465000},"page":"2445","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["What Random Splits Measure in Polymer Glass-Transition Prediction: Chemistry Holdouts, Applicability Domains, and Prior Integration"],"prefix":"10.3390","volume":"18","author":[{"given":"Deao","family":"Han","sequence":"first","affiliation":[{"name":"College of Transportation, Ludong University, Yantai 264025, China"},{"name":"Analysis and Testing Center, Ludong University, Yantai 264025, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yangkun","family":"Shao","sequence":"additional","affiliation":[{"name":"College of Transportation, Ludong University, Yantai 264025, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xueru","family":"Zhong","sequence":"additional","affiliation":[{"name":"College of Transportation, Ludong University, Yantai 264025, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhanzhao","family":"Song","sequence":"additional","affiliation":[{"name":"Analysis and Testing Center, Ludong University, Yantai 264025, China"},{"name":"Graduate School of Convergence Science and Technology, Seoul National University, Seoul 08826, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Quanzhong","family":"Zhang","sequence":"additional","affiliation":[{"name":"College of Transportation, Ludong University, Yantai 264025, China"},{"name":"Analysis and Testing Center, Ludong University, Yantai 264025, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chuansheng","family":"Wang","sequence":"additional","affiliation":[{"name":"National Engineering Laboratory for Advanced Tire Equipment and Key Materials, Qingdao University of Science and Technology, Qingdao 266061, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0418-0953","authenticated-orcid":false,"given":"Deshang","family":"Han","sequence":"additional","affiliation":[{"name":"College of Transportation, Ludong University, Yantai 264025, China"},{"name":"Analysis and Testing Center, Ludong University, Yantai 264025, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0008-7990-1771","authenticated-orcid":false,"given":"Lin","family":"Wang","sequence":"additional","affiliation":[{"name":"College of Transportation, Ludong University, Yantai 264025, China"},{"name":"Analysis and Testing Center, Ludong University, Yantai 264025, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,10,7]]},"reference":[{"key":"ref_1","unstructured":"Van Krevelen, D.W., and Te Nijenhuis, K. 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