Impact of Imidazolium-Based Ionic Liquids on the Curing Kinetics and Physicochemical Properties of Nascent Epoxy Resins

Andrzej Dzienia; Magdalena Tarnacka; Kajetan Koperwas; Paulina Maksym; Andrzej Ziȩba; Joanna Feder-Kubis; Kamil Kamiński; Marian Paluch

doi:10.1021/acs.macromol.0c00783

Impact of Imidazolium-Based Ionic Liquids on the Curing Kinetics and Physicochemical Properties of Nascent Epoxy Resins

Macromolecules. 2020 Aug 11;53(15):6341-6352. doi: 10.1021/acs.macromol.0c00783. Epub 2020 Jul 20.

Authors

Andrzej Dzienia^{1

2}, Magdalena Tarnacka^{3

2}, Kajetan Koperwas^{3

2}, Paulina Maksym^{3

2}, Andrzej Ziȩba⁴, Joanna Feder-Kubis⁵, Kamil Kamiński^{3

2}, Marian Paluch^{3

2}

Affiliations

¹ Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
² Silesian Center of Education and Interdisciplinary Research, University of Silesia, 75 Pulku Piechoty 1A, 41-500 Chorzow, Poland.
³ Institute of Physics, University of Silesia, 75 Pulku Piechoty 1, 41-500 Chorzow, Poland.
⁴ Department of Organic Chemistry, Faculty of Pharmaceutical Sciences in Sosnowiec, Medical University of Silesia in Katowice, Jagiellonska 4, 41-200 Sosnowiec, Poland.
⁵ Faculty of Chemistry, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland.

Abstract

We investigated the influence of anion type (salicylate, [(MOB)MIm][Sal], vs chloride, [(MOB)MIm][Cl]) of imidazolium-based ionic liquid (IL) and its content on the curing kinetics of bisphenol A diglicydyl ether (DGEBA of molecular weight M _n = 340 g/mol). Further physicochemical properties (i.e., glass transition temperature, T _g, and conductivity, σ_dc) of produced polymers were investigated. The polymerization of the studied systems was examined at various molar ratios (1:1, 10:1, and 20:1) at different reaction temperatures (T _reaction = 353-383 K) by using differential scanning calorimetry (DSC). Interestingly, both DGEBA/IL compositions studied herein revealed significantly different reaction kinetics and yielded materials of completely distinct physical properties. Surprisingly, in contrast to [(MOB)MIm][Cl], for the low concentration of [(MOB)MIm][Sal] in the reaction mixture, an additional step in the kinetic curves, likely due to the combined enhanced initiation activity of anion (salicylate)-cation (imidazolium-based), was noted. To thoroughly analyze the kinetics of all studied systems, including the two-step kinetics of DGEBA/[(MOB)MIm][Sal], we applied a new approach that relies on the combination of the two phenomenological Avrami equations. Analysis of the determined constant rates revealed that the reaction occurring in the presence of the salicylate anion is characterized by higher activation energy with respect to those with the chloride. Moreover, DGEBA/[(MOB)MIm][Sal] cured materials have higher T _g in comparison to DGEBA polymerized with [(MOB)MIm][Cl] independent of the IL concentration. This fact might indicate that, most likely, the products of hardening are highly cross-linked (high T _g) or oligomeric linear polymers (low T _g) in the former and latter cases, respectively. Such a change in the chemical structure of the polymer is also reflected in the dc conductivity measured at the glass transition temperature, which is much higher for DGEBA cured with [(MOB)MIm][Cl]. Herein, we have clearly demonstrated that the type of anion has a crucial impact on the polymerization mechanism, kinetics, and properties of produced materials.