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oai:recercat.cat:2117/4138432026-02-01T02:17:21Zcom_2072_1033col_2072_452950

urn:hdl:2117/413843 Double glass transition in polyethylene naphthalate by MDSC, BDS, and TSDC Cañadas Lorenzo, Juan Carlos Diego Vives, José Antonio Díez Berart, Sergio López Pérez, David Orencio Mudarra López, Miguel Salud Puig, Josep Sellarès González, Jordi Àrees temàtiques de la UPC::Física Polymers Polymer liquid crystals Thermodynamic properties Thermally stimulated current spectroscopy Dielectric properties Glass transitions Broadband dielectric spectroscopy Arrhenius plot Differential scanning calorimetry Free-volume theory Polymers Polímers Cristalls líquids In this work, we present an experimental study of the primary and secondary relaxations of the semi-crystalline polymer polyethylene naphthalate by modulated differential scanning calorimetry, Thermally Stimulated Depolarization Currents (TSDCs), and Broadband Dielectric Spectroscopy (BDS) and how they are affected by physical aging. Three dipolar relaxation modes can be observed: from slowest to fastest: the primary a relaxation, which vitrifies at the glass transition temperature, Tga, and two secondary relaxations, named ß* and ß. Modulated differential scanning calorimetry results show how the secondary ß* relaxation also vitrifies, giving rise to an additional glass transition at Tgß* < Tga. In fact, the a and ß* relaxations can be considered as part of a very broad and distributed relaxation. Its main part is the primary a relaxation with a shoulder at the high-frequency region corresponding to a complex secondary ß* relaxation. BDS results about ß* can be modeled by a main contribution (ß3*) and two additional ones (ß1* and ß2*) with a weaker dielectric strength. TSDC results show that each single mode of the relaxation has its own glass transition temperature and they are compatible with the structure inferred by BDS. This scenario gives rise to an extended glass transition dually centered in the Tgß* ~ 305 K and Tga ~ 387 K temperatures. Peer Reviewed Postprint (published version) 2024-08-07 Article https://pubs.aip.org/aip/jcp/article/161/5/054507/3306961/Double-glass-transition-in-polyethylene http://creativecommons.org/licenses/by/4.0/ Open Access Attribution 4.0 International American Institute of Physics (AIP)