Investigation on the effect of the presence of hyperbranched polymers on thermal and mechanical properties of an epoxy UV-cured system

The use of hydroxyl-functionalized hyperbranched polymers (HBPs) (Boltorn((R)) H20, H30 and H40) was investigated with respect to a UV-cured epoxy system. Their presence induced an increase of the final epoxy conversion, which was interpreted on the basis of a chain-transfer reaction. A decrease of the T(g) values in the photocured films was observed when the amount of HBP additive in the photocurable formulation was increased. When the amount of HBP in the photocurable resin was increased, the density of photocured films increased, indicating a decrease on the free volume. Moreover, a clear increase in toughness was observed and attributed to the plasticization effect induced by the presence of HBP. This effect is particularly interesting for epoxy thermosets, which are characterized by good mechanical properties, although they are brittle and fragile. By increasing the toughness properties of these photocured resins it may be possible to broad their applications. (c) 2005 Society of Chemical Industry.