Phosphorus-Containing Polyimidothioether as a Latent Curing Agent and Flame Retardant for One-Component Epoxy Resins

The development of epoxy/thiol resins with long shelf life, satisfactory flame retardancy, good heat resistance, and high mechanical strength is challenging but essential for advanced applications. In this study, a phosphorus-containing polyimidothioether (DTPI) with good solubility was efficiently synthesized and employed as both a thermolatent curing agent and a flame retardant for the mixture of pentaerythritol tetra(3-mercaptopropionate) (PETMP) and diglycidyl ether of bisphenol A (DGEBA). The thiol exchange reaction between DTPI and PETMP occurred spontaneously prior to the ring-opening reaction of DGEBA, and the resulting aromatic thiols were dormant at 30 °C but reacted with DGEBA at temperatures above 130 °C, leading to good thermal latency of EP/DTPI systems. With a DTPI loading of 24.2 wt %, the EP/DTPI-3 system showed a shelf life of 20 days. Furthermore, the cured EP/DTPI exhibited simultaneously improved flame retardancy as well as enhanced thermal and mechanical properties. For example, the EP/DTPI-3 thermoset attained the UL-94 V0 rating and exhibited a 19.5 °C, 48.6%, and 32.1% increase in the glass transition temperature, ultimate tensile strength, and Young’s modulus, respectively, compared with the traditional DGEBA/PETMP thermoset. This work presents a simple and effective strategy for preparing flame-retardant and high-performance one-component epoxy resins with good thermal latency by bespoke multifunctional polyimidothioethers.