Phosphonium based ionic liquids (ILs) have been previously shown as a new emerging class of initiator of epoxy prepolymers. The present study aims at investigating the influence of ILs on the dielectric behaviour of epoxy-IL systems by dielectric spectroscopy. Here, the content of IL incorporated in the epoxy prepolymer has a significant impact on the final properties of the polymer networks displaying a high glass transition temperature (Tg > 160 °C). The excess of IL (>10 phr) acts as a plasticizer agent decreasing the Tg and leading to the formation of heterogeneities. Moreover, the study of α and β conventional relaxation modes by dielectric spectroscopy highlighted an increase of chain mobility due to IL excess. A ω relaxation mode has been noticed with the addition of high content of IL, probably relating to heterogeneities of the network. Unlike the most of polymer systems, the study of the DC conductivity by the application of an Arrhenius law demonstrated a thermal activation mechanism, independent from the free volume and the glass transition phenomenon. A discussion on the identification of charge carriers has been finally proposed.
Thibaut LEFORT, Jannick Duchet-Rumeau,
Sébastien Livi, Damien Bachellerie, Sébastien Pruvost
Published in Polymer (Volume 222, 22 April 2021, 123645)