A novel liquid hyperbranched polyether epoxy (HBPEE) based on commercially available hydroquinone (HQ) and 1

1

1-trihydroxymethylpropane triglycidyl ether (TMPGE) was synthesized through an A

2

+ B

3

one-step proton transfer polymerization. In order to improve the toughness

the synthesized HBPEE was mixed with diglycidyl ether of bisphenol A (DGEBA) in different ratios to form hybrids and cured with triethylenetetramine (TETA). Thermal and mechanical properties of the cured hybrids were evaluated. Results show that addition of HBPEE can improve the toughness of cured hybrids remarkably at

<

20 wt% loading

without compromising the tensile strength. However

the glass transition temperature (

T

g

) of the cured hybrids decreases with increasing HBPEE content. Fracture surface images from scanning electron microscope show oriented fibrils in hybrids containing HBPEE. The formation and orientation of the fibrils can absorb energy under impact and lead to an improvement of toughness. Furthermore

based on the morphology of fractured surfaces and the single

T

g

in each hybrid

no sign of phase separation was found in the cured hybrid systems. As a result

the toughening mechanism could be explained by in situ homogeneous toughening mechanism rather than phase separation mechanism.