Effect of hydroxyl ended and end-capped multiarm star polymers on the curing process and mechanical characteristics of epoxy/anhydride thermosets

•The use of a multiarm star as epoxy resin modifier was studied.•The end-capping of the final groups of the multiarm star allows increasing impact strength.•The addition of the multiarm stars reduced the generation of internal stresses.•The end-capped multiarm stars leads to a nanograined morphology. Multiarm star polymers have been synthesized by cationic ring-opening polymerization of ɛ-caprolactone from a hyperbranched poly(ethyleneimine) core and end-capped with acetic anhydride. These star polymers have been used as modifiers in diglycidylether of bisphenol A/methyl tetrahydrophthalic anhydride/benzyl dimethylamine formulations. The curing process is studied by dynamic scanning calorimetry and rheometry and the resulting thermosets are characterized by dynamic mechanical thermal analysis and thermogravimetry. Internal stresses generated during curing are measured and interpreted in terms of the thermal-mechanical properties of the cured materials. The influence of the modifier in the toughness improvement of the cured thermosets is determined by standardized impact tests and the microstructure of the material observed by scanning electron microscopy.