In situ Phase-Separated Epoxy Network with High Tg and Fracture Toughness

Abstract

This study investigated an in situ phase-separated epoxy network exhibiting high glass transition temperature (Tg) and enhanced fracture toughness for aerospace composite applications. A disulfide-containing curing agent, 4,4 '-dithiodianiline (4,4 '-DTDA), was introduced into a tetraglycidyl-4,4 '-diaminodiphenylmethane (TGDDM)/diaminodiphenyl sulfone (DDS) epoxy system. During curing, DTDA spontaneously aggregated to form a second phase, resulting in a phase-separated morphology. The optimal formulation-TGDDM with 3,3 '-DDS and 4,4 '-DTDA in a 7:3 ratio-achieved a fracture toughness of 2.0 MPa<middle dot>m1/2 and a Tg of 237 degrees C, surpassing many conventional aerospace-grade epoxies. In contrast, the TGDDM/3,3 '-DDS system without DTDA exhibited a higher Tg of 246 degrees C but significantly lower fracture toughness of 0.91 MPa<middle dot>m1/2, indicating a 120% improvement in toughness with only a modest reduction in Tg. These findings highlight the potential of utilizing in situ phase separation via mixed curing agents to enhance both mechanical and thermal properties without external toughening agents.