Controllability of epoxy equivalent weight and performance of hyperbranched epoxy resins

Hyperbranched epoxy resins (HERs) is a group of thermoset resins which can be used to improve specifically the toughness and strength of popular diglycidyl ether of bisphenol-A (DGEBA). However, a relationship between the epoxy equivalent weight (EEW) of HERs and the level of property improvement has not been established due to the difficulty to control their EEW. Here we report the synthesis of a series of hyperbranched epoxy resins with different EEW (EHBP-n) through thiol-ene click reaction between thiol-ended hyperbranched polyesters and allylglycidyl ether. The rheological properties of the uncured EHBP-n/DGEBA blends are determined by viscosity and modulus changes, and are directly affected by the EEW of EHBP-n. Moreover, the EEW of EHBP-n also can tune the glass transition temperature and mechanical performances of the cured EHBP-n/DGEBA composites, and these properties first increased and then decreased with a decrease in the EEW of EHBP-n. At 9 wt % of EHBP-6, the improvements on the tensile, flexural, impact and adhesive strengths are 38.9%, 35.3%, 158.6% and 96.2%, respectively, compared with those of cured DGEBA. This result will give a basic guidance for obtaining epoxy resins with various performance.