Effect of molecular spatial structure of alicyclic anhydride curing agents on the performance of bisphenol A epoxy resin curing systems

Understanding how the molecular topology of anhydride curing agents affects curing behavior and final properties is important for the rational design of high-performance epoxy thermosets. In this work, three alicyclic anhydride curing agents with different molecular topologies, namely methyl nadic anhydride (MNA), methyl ethyl tetrahydrophthalic anhydride (MeTHPA), and methyl hexahydrophthalic anhydride (MeHHPA), were comparatively investigated in diglycidyl ether of bisphenol A (DGEBA) epoxy systems. Non-isothermal differential scanning calorimetry combined with the Kissinger, Ozawa, and Crane methods was used to determine the characteristic curing temperatures, apparent activation energies, and reaction orders, based on which the gradient curing schedules for each formulation were established. Among the three systems, EP-MNA exhibited the highest characteristic curing temperatures and the highest apparent activation energy. After curing, EP-MNA showed the best overall performance, with a compressive strength of 126.2 MPa, a flexural strength of 86 MPa, and a glass transition temperature of 154.9 °C, all higher than those of the EP-MeTHPA and EP-MeHHPA systems. These results suggest that the bridged bicyclic structure of MNA contributes to higher molecular rigidity and restricted chain mobility, thereby improving the thermomechanical performance of the cured epoxy system. This study provides useful insight into the structure–property relationships of anhydride-cured epoxy thermosets.