New curing agents for epoxy resins: protoporphyrins

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Two similar macrocycles protoporphyrin IX and zinc protoporphyrin IX (ZPP) have been used as cross-linking agents for curing the epoxy resin of bisphenol A diglycidyl ether (BADGE, n = 0). The enthalpies and the activation energies of the esterification reaction of the 2 systems are very close to each other. However, the temperature of the minimum in the differential scanning calorimetry thermogram is 38°C lower for BADGE (n = 0)/ZPP, thus requiring a less energy expenditure for curing the system. By the contrary, the enthalpy and activation energies for the etherification reaction are lower and higher, respectively, for BADGE (n = 0)/ZPP suggesting that the zinc ion affects it, although the involved mechanism is unknown.