Thioester-Based Latent Curing Agent for Thermally Conductive Epoxy Composites

Organic/inorganic hybrid composites are crucial in industrial applications for imparting the necessary physical properties. With the advancement of electronic components, managing heat dissipation has become vital. Research on thermal interface materials, particularly thermally conductive adhesives combining epoxy polymers, is gaining attention for their strong adhesion and thermomechanical properties. In these systems, curing agents like thiol are essential for enhancing properties due to their fast reaction rates and selectivity in thiol-epoxy reactions. However, thiol’s application in one-component epoxy systems is limited due to reduced latency with base catalysts. This study introduces a strategy using acylation to create a thioester from thiol acting as a latent curing agent. We also investigated incorporating boron nitride fillers for electrical insulation, lightweight design, and improved thermal conductivity. Our experiments showed that thioester-based epoxies cured differently than those with thiol, leading to addressing challenges in the curing process. We also analyzed thermomechanical properties by varying the ratios of curing agents and fillers. Adding 20 vol % filler to thioester-based epoxy resulted in a thermal conductivity of 0.68 W/m·K, a 4.53-fold increase over standard epoxy. The thioester composite maintained a viscosity of 765,000 cP after 3 days at room temperature and took about 8 days to solidify, offering longer storage times than thiol- and amine-based systems. This study proposes an effective solution to extend the use of thiol-type curing agents, overcoming their short shelf life and presenting a more industry-friendly method.