Eugenol-based dual-cured materials with multiple dynamic exchangeable bonds

Abstract

In the present work, the preparation of sustainable thermosets has been approached simultaneously from three different points of view: a) the use of bio-based monomers chemically modified through green methodologies, b) the adoption of dual curing through click-type reactions to implement more efficient manufacturing processes, and c) inclusion of interchangeable groups in the network, to enable the reuse and recycling of the material at the end of its useful life and avoid waste generation.The first goal has been approached by synthesizing in a greener way an acrylate-epoxy derivative of eugenol (AEEU) and a glycerol triacrylate (GTA), both biobased resources. Then, the second approach was addressed by using biobased cystamine as a crosslinker to obtain materials through a dual-curing procedure based on a first “click” aza-Michael reaction and a second “click” epoxy-amine reaction. Intermediate and final materials could be prepared with different tailorable properties by controlling the molar ratio of the AEEU and GTA. By using DSC and rheology, we could evaluate the sequentiality and the gelation of the curing process. Finally, the covalent adaptable networks (CANs) prepared contained three different types of dynamic bonds (disulfide, esters, and β-aminoesters) and their thermomechanical properties were tested by DMA revealing Tgs above room temperature from 47 to 70 °C. Bending tests at break were performed to evaluate the mechanical properties reaching values up to 90 MPa of stress at break and 7 % of deformation. Stress relaxation tests showed that all materials could relax the stress at relatively low temperatures (120 °C) in less than 21 min. The associative and dissociative behavior of these materials was investigated through rheology revealing a clear drop of the modulus at high temperatures and frequencies when cystamine was used as a crosslinker. Moreover, their reprocessability was tested obtaining homogeneous samples with no significant changes in their chemical and thermal properties highlighting the great potential and wide range of possibilities in many different fields of these CANs.