Synthesis and characterization of hyperbranched thiol hardener and their curing behavior in thiol–epoxy

Hyperbranched thiol (Hyperbranched mercaptopropionate, HBMP) was synthesized using a commercially available hydroxyl-terminal hyperbranched oligomer and 3-mercaptopropionic acid applying a low-temperature esterification reaction. The chemical structure and molecular weight analysis of synthesized HBMP were investigated by Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). The synthesized HBMP was analyzed with curing kinetics, thermal/mechanical properties, and adhesion trait with bisphenol-A-type epoxy resin compared to pentaerythritol tetra-mercaptopropionate (PETMP). The curing kinetics between HBMP and epoxy resin required higher activation energy compared to PETMP case. In addition, it was confirmed that as the content of HBMP increases, the thermal and mechanical properties decrease, but the adhesion property was greatly improved. These results indicate that incorporating hyperbranched thiol in epoxy resin is an efficient method to utilize the material as an adhesive layer.