Characterization of the Network Structure o Epoxy Resins Cured with Active Esters

Epoxy resins cured with polyfunctional active esters have no pendant hydroxyl groups but pendant ester groups. Epoxy resins without hydroxyl groups are expected to have high electric resistance, low dielectric constant, and low hygroscopicity. In this paper, the thermal, viscoelastic, dielectric, and hygroscopic properties are described on the epoxy resins cured with active esters in comparison with those of the resins with pendant hydroxyl groups that are cured with conventional curing agents. The network structure of epoxy resins with pendant ester groups is much looser than that of the resins with pendant hydroxyl groups. This is attributed to the lack of hydrogen bonds and to steric hindrance and plasticization of more bulky ester groups in the resins cured with active esters.