Structural analysis of the curing of epoxy thermosets crosslinked with hyperbranched poly(ethyleneimine)s

The network build-up process during curing of an epoxy resin using a hyperbranched poly(ethyleneimine) as crosslinking agent has been studied from a theoretical and experimental point of view. A systematic analysis taking into account the stoichiometry of the curing process has been performed. Conversion at gelation has been studied by thermomechanical analysis (TMA) and differential scanning calorimetry (DSC). Crosslinking density has been studied by dynamomechanical analysis (DMA). Gel fraction after extraction in organic solvents has also been determined. The experimental results have been compared with a theoretical network build-up model based on the random recombination of structural fragments, showing good agreement between theory and experimental results, but deviations from the ideal epoxy-amine polycondensation appear as a consequence of the dilution of the hyperbranched crosslinker in off-stoichiometric formulations.