Mechanically Robust,Self-Healable, and ReprocessableGeraniol-Based Epoxy Vitrimer by Dynamic Boronic Ester Bonds

Abstract

Covalent adaptable networks (CANs) are a pioneering member of the polymer family that have garnered significant attention in recent years and are characterized by covalent cross-links that exhibit reversible dynamic alterations in response to external stimuli. Additionally, unlike traditional thermosets, CANs, especially vitrimers, offer a range of properties such as self-healing, reprocessability, shape-reconfigurability, and recycling capabilities due to the dynamic nature of covalent cross-links. Recently, an increasing trend in the global production of thermosets involves the rapid consumption of petroleum-based resources, which has become a growing environmental concern. From this perspective, the development of eco-friendly thermosets from biobased feedstocks is a possible way to overcome these drawbacks. In this context, geraniol is one of the monoterpenoid alcohols, a primary component of several plant oils that has become a valuable replacement for petroleum-based resources. In this study, for the first time, a geraniol-derived epoxy vitrimer has been developed through a thermally triggered “thiol-epoxy click” reaction between the geraniol-based epoxy resin and a dynamic diboronic ester dithiol (DBDT) cross-linker. The resulting vitrimer exhibits excellent self-healing properties driven by topology alteration through the dynamic transesterification of boronic ester bonds. The fabricated Ger_epoxy-DBDT vitrimers possess excellent thermal stability and significant mechanical properties, with the absolute value of the glass transition temperature (T_g) of 38.43 °C determined from DMA analysis. Incorporating dynamic boronic ester linkages imparts an enhanced tensile strength of ∼19 MPa, enabling the vitrimer to recover its original shape after deformation (shape memory), solvent recycling ability, and excellent reprocessability with maximum restoration of mechanical strength. Moreover, the vitrimer was further characterized by a notably short relaxation time of around 9 s at 140 °C and an apparent activation energy of 22.44 kJ/mol. In a nutshell, the developed vitrimer demonstrates significant potential for use in various commercial sectors, and its reversible bond-breaking and bond-making ability under specific conditions offers opportunities for developing sustainable, high-performance materials.