Dependence of epoxy toughness on the backbone structure of hyperbranched polyether modifiers

Abstract

The synthesis of epoxide-terminated hyperbranched polyethers (EHBPEs) with different backbone stiffness and molecular weight (MW) is obtained using simple one-pot A₂ + B₃ approach. When used as tougheners for DGEBA/TETA system, non-phase-separated cured networks are always obtained. Effects of MW and backbone stiffness on the toughening performance were systematically investigated. Among the EHBPEs studied, EHBPE-4C which has the lowest MW and stiffest backbone and EHBPE-10C which has the highest MW and most flexible backbone can simultaneously improve toughness, tensile strength, and T_g. In contrast, addition of EHBPE-6C and EHBPE-8C, which have medium MW and backbone stiffness, lead to incomplete cure and cannot improve or worsen the toughness and tensile strength. Both stiffness and MW of hyperbranched polyether play important roles in determining the crosslink density and structure of non-phase-separated networks, which dictate the toughness, strength and T_g of toughened epoxy.