he use of commercially available hyperbranched poly(ethyleneimine)s (Lupasol TM , BASF) as polymeric modifiers in diglycidyl ether of bisphenol A thermosetting formulations using 1-methylimidazole (MI) as anionic initiator has been studied. Poly(ethyleneimine)s can get incorporated into the network structure by condensation of amine and epoxy groups. The excess, over-stoichiometric epoxy groups can undergo ani- onic homopolymerization initiated by MI. The thermal, dyna- momechanical, and mechanical properties of the resulting materials have been determined using DSC, thermomechanical analysis (TMA), dynamomechanical analysis (DMA), and me- chanical testing. The effect of the different amine modifiers on the MI networks, determined by their structure, is complex. Low initiator content and high molecular weight modifiers cre- ate significant mobility restrictions, which have a strong effect on the glass transition temperature and the apparent crosslink- ing density of the cured materials.