Curing and thermomechanical properties of off-stoichiometric anhydride–epoxy thermosets
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In the present work, we report the preparation and characterization of a new family of thermosets based on off-stoichiometric anhydride–epoxy formulations in the presence of an anionic initiator. Diglycidyl ether of bisphenol A (DGEBA) and hexahydro-4-methylphthalic anhydride (HHMPA) have been used as epoxy and anhydride comonomers, respectively, and 1-methylimidazole (1MI) has been used as anionic initiator. The isothermal curing kinetics and the thermal properties of the stoichiometric and the off-stoichiometric systems have been compared. The kinetics of the isothermal curing has been analyzed by differential scanning calorimetry (DSC) using an isoconversional method and the Šesták–Berggren equation to determine the activation energy, the frequency factor and the reaction orders. The materials obtained were characterized by DSC and dynamic mechanical analysis. Gelation during epoxy–anhydride condensation was determined by thermomechanical analysis. At the same curing temperature, the reaction is faster in the system with excess of epoxy groups. However, the glass transition temperatures of the partially cured stoichiometric system are greater. The gelation time of the off-stoichiometric system is shorter than that of the stoichiometric one. The results indicate that the dual-curing character of off-stoichiometric DGEBA/HHMPA thermosets with 1MI as anionic initiator makes them suitable for multistage curing processes with easy control of degree of cure and material properties in the intermediate stage and enhanced final material properties.
KeywordsEpoxy networks Isothermal cure Kinetics Gelation
The authors would like to thank MINECO (Ministerio de Economía y Competividad) and FEDER (Fondo Europeo de Desarrollo Regional) (MAT2017-82849-C2-1-R and MAT2017-82849-C2-2-R) and Generalitat de Catalunya (2017-SGR-77 and Serra Húnter program) for the financial support.
- 1.Riew CK, Siebert AR, Smith RW, Fernando M, Kinloch AJ. Toughened epoxy resins: performed particles as tougheners for adhesives and matrices. In: Riew CK, Kinloch AJ, editors. Toughened plastics II novel approaches in science and engineering, vol. 252., Advances in chemical seriesWashington: American Chemical Society; 1996. p. 33–44.CrossRefGoogle Scholar
- 3.Kang B-U. Interfacial fracture behavior of epoxy adhesives for electronic components. J Korea Acad Ind Cooper Soc. 2011;12:1479–87.Google Scholar
- 4.May CA, Tanaka GY. Epoxy resins. In: May CA, editor. Chemistry and technology, chap 1. New York: Marcel Dekker; 1988.Google Scholar
- 5.Petrie EM. Epoxy adhesive formulations. New York: McGraw-Hill; 2006.Google Scholar
- 15.Evans D, Canfer SJ. Radiation stable, low viscosity impregnating resin systems for cryogenic applications. Adv Cryog Eng. 2000;46:361–8.Google Scholar
- 22.Fernández-Francos X, Santiago D, Ferrando F, Ramis X, Salla JM, Serra À, Sangermano M. Network structure and thermomechanical properties of hybrid DGEBA networks cured with 1-methylimidazole and hyperbranched poly(ethyleneimine)s. J Polym Sci Part B Polym Phys. 2012;50:1489–503.CrossRefGoogle Scholar
- 24.Ramis X, Fernández-Francos X, De La Flor S, Ferrando F, Serra À. Click-based dual-curing thermosets and their applications. In: Guo Q, editor. Thermosets: structure, properties and applications, chapter 16. 2nd ed. Amsterdam: Elsevier; 2017.Google Scholar
- 30.Ivin KJ. Polymer handbook. Brandrup J, Immergut EH, editors. New York: Wiley; 1975Google Scholar