Effect of a hyperbranched polymer over the thermal curing and the photocuring of an epoxy resin

In this study, the authors study by calorimetry the influence of hyperbranched polyester Boltron^®H40 on the thermal curing and the photocuring of a diglycidyl ether of bisphenol epoxy resin (DGEBA) using ytterbium (III) trifluoromethanesulfonate and triarylsulfonium hexafluorantimonate as thermal and photo cationic initiators, respectively. In the dynamic thermal curing at different heating rates, the authors have seen a decelerating effect when H40 is added to DGEBA, the system with 10% of H40 being the slowest. An isoconversional method has been used to determine the apparent activation energy of the thermal curing. In the isothermal photocuring at low temperatures, the authors have also appreciated a decelerating effect on adding H40, obtaining a minimum conversion when the H40 proportion is 15%. However, at high temperatures, the photocuring process can be accelerated at the first part of this process. This behavior is a consequence of the temperature dependence of H40 solubility in DGEBA, the viscosity of the system, and the hydroxyl-induced chain-transfer reaction. The values found of the maximum glass transition temperature in the thermal curing and in the photocuring, show that H40 is not completely solubilized in the reacted system.