VOC-free tricomponent reaction platform for epoxy network formation mediated by a recyclable ionic liquid

Abstract

Herein we propose a simple, volatile organic solvent (VOC)-free tricomponent reaction platform for the stoichiometric step-growth polymerization between diepoxy resins and dicarboxylic acid in an imidazolium IL medium. The established epoxy resin diglycidyl ether of bisphenol A (DGEBA), as well as the bio-based diglycidyl ether of methyl hydroquinone (DGEMHQ), were used as epoxy sources, while bio-sourced succinic acid was used as the binding building block in this reaction platform performed under mild conditions (T = 80–120 °C). Moreover, no co-solvents, co-catalysts or conventional polymerization initiators were used in our platform as the IL acted as both solvent and initiator/catalyst, and as no direct residue was produced, this concept fully complies with most of the 12 principles of green chemistry. In addition, post-reaction IL-recyclability was studied to further prove the sustainability and cost-effectivity of this platform. The ring-opening of DGEBA and DGEMHQ was followed by FTIR analysis and confirmed with NMR, showing a full consumption of the oxirane ring within 3 to 5 h of reaction. Also, MALDI-TOF mass spectrometry was used for the detection of the intermediates formed in different reaction steps to define the initiation mechanism. Finally, crosslinking and network structure of the optimized solid epoxy materials were characterized using dynamic-mechanical and thermogravimetric analysis.