Real time dielectric spectroscopy and bond connectivity during polymerization of stoichiometric and amine-rich, diepoxide-diamine compositions
Anno: 1998
Autori: Ferrari C., Tombari E., Salvetti G., Johari G.P.
Affiliazione autori: CNR, Ist Fis Atom & Mol, I-56127 Pisa, Italy; McMaster Univ, Dept Mat Sci & Engn, Hamilton, ON L8S 4L7, Canada
Abstract: The dielectric spectra and thermodynamics of macromolecular growth in the diepoxide-diamine liquid mixtures have been studied simultaneously, and in real time, as the original molecular liquid transformed to a rigid state of a vitrified network structure. Both stoichiometric and the excess amine compositions were studied and the dielectric properties of their final polymerized state investigated. The rate of polymerization is remarkably increased in the diamine-rich composition, and vitrification occurs sooner. A change in the rate of heat release profile is attributed to the onset of another reaction at longer times, which does not require the diamine. The dc conductivity, sigma(0), decreases progressively more rapidly during the initial stage of polymerization, producing a sigmoid shape when it is plotted against time. This shape is stretched out when plots are made against the number of covalent bonds formed. For a fixed number of covalent bonds, n, formed at 324.5 K, the relaxation time, tau(0), for the diamine-rich composition is twice that of the stoichiometric composition;Interpretation in terms of the configurational entropy theory shows that this is due to the lowering of vibrational frequencies. The stretched exponential relaxation parameter. beta, increases from 0.25 for the stoichiometric to 0.36 for the diamine-rich composition. The product, tau(0) sigma(0), increases with increase in n, thus showing that tau(0) and sigma(0) are not inversely related, and that requires consideration of other mechanisms for dc conduction. A faster dipolar reorientation dynamics evolves on polymerization and, in the fully polymerized state of the amine-rich composition, its peak shifts to a lower frequency.
Giornale/Rivista: JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS
Volume: 94 (9) Da Pagina: 1293 A: 1300
Parole chiavi: DGEBA-BASED THERMOSETS; RELAXATION SPECTROSCOPY; GLASSY STATES; KINETICS; DOI: 10.1039/a800277kCitazioni: 12dati da “WEB OF SCIENCE” (of Thomson Reuters) aggiornati al: 2024-04-21Riferimenti tratti da Isi Web of Knowledge: (solo abbonati) Link per visualizzare la scheda su IsiWeb: Clicca quiLink per visualizzare la citazioni su IsiWeb: Clicca qui