Enhanced durability of a novel thiol-epoxy network thermosets with excellent hygrothermal and chemical resistance

Abstract

Epoxy resin is widely used in electronic packaging due to its exceptional performance, particularly the low-temperature curable thiol/epoxy system, which effectively minimizes thermal damage to sensitive electronic components. However, the majority of commercial thiol curing agents contain hydrolysable ester bonds and lack rigid structures, which induces most of thiol/epoxy systems still suffering from unsatisfactory heat resistance and hygrothermal resistance, significantly hindering their application in electronic packaging. In this study, we synthesized a tetrafunctional thiol compound, bis[3-(3-sulfanylpropyl)-4-(3-sulfanylpropoxy)phenyl]sulfone (TMBPS) with rigid and ester-free structures to replace traditional commercial thiol curing agents, pentaerythritol tetra(3-mercaptopropionate) (PETMP). Compared to the PETMP/epoxy system, the TMBPS/epoxy system exhibited superior comprehensive properties. The rigid structures of bisphenol S-type tetrathiol enhanced the heat resistance and mechanical properties of TMBPS/epoxy resin cured products, outperforming those of PETMP/epoxy resin cured products. Notably, the glass transition temperature of TMBPS/epoxy resin cured products was 74.2 °C which was 11.8 °C higher than that of PETMP cured products. Moreover, the ester-free structure in TMBPS contributed to its enhanced resistance to chemicals and hygrothermal conditions. After undergoing 1000 h of high-temperature and high-humidity aging, the tensile strength and adhesion strength of TMBPS-cured products were 73.33 MPa and 3.39 MPa, respectively exceeding 100% and 40% of their initial values, while PETMP-cured products exhibited a complete loss of both tensile strength and adhesion strength. This study provides a strategy for obtaining thermosetting polymers that can be cured at low temperatures and exhibit excellent comprehensive properties.