On epoxy network structure and dielectric performance

Epoxy resins are widely used in many different electrical applications. These materials are formulated using a resin that can be considered as an epoxy terminated bi-functional monomer, plus a hardener. Although it is generally assumed that optimal properties result from complete reaction of all epoxide and hardener groups, our previous work has revealed that systems containing an excess of the resin component can exhibit a higher breakdown strength than systems with a conventionally optimized stoichiometry and it was proposed that this may be associated with the formation of branched molecular structures within the network. This study set out to test the generality of this hypothesis by using a mono-functional reactive diluent as a means of varying the network structure in a more controlled way. By varying the composition of a designed three-component epoxy system appropriately, it has been possible to produce a range of samples in which the branch density within the network varies but where epoxy/amine stoichiometry is always maintained at the theoretical optimum. It has been shown that the introduction of a controlled degree of aliphatic branching may have beneficial consequences. More generally, the results suggest that the broad methodology could be used to introduce different moieties that can lead to different functionalities.