How to Optimize Performance of Dianhydride Epoxy Formulations

Dianhydrides leverage esterification reactions to cure epoxy resins to high degrees of crosslinking. This offers a range of performance improvements, including excellent resistance to chemicals, high temperatures, and electrical voltage.

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To take advantage of these resin systems, the resin formulator must be aware of several key factors.

As dianhydride-epoxy formulations are curing, there is a high probability that the formation of a densely crosslinked polymer network will result in early vitrification.

Vitrification results in a glassy state with unreacted groups such as diacids that may cause issues once the material is in service. Relying on post-curing as a remedy may create brittleness and far-from-optimum properties. 

Dianhydrides are suitable for use below stoichiometric levels versus monoanhydride curatives (Table 1). This approach adjusts the target crosslink density, helping optimize the resulting physical properties.  While excess epoxide groups may remain, these will be consumed via the beneficial side reaction of epoxy homopolymerization. This etherification reaction reduces brittleness versus a resin system that is fully crosslinked via esterification alone with a dianhydride.

Many epoxy formulators tend not to want this epoxide side reaction to occur, but dianhydride users regularly benefit from it and deliberately design it into their formulations.

Table 1. Suggested Anhydride/Epoxide ratios (A/E) for different anhydride curatives, with standard liquid epoxy resin (DGEBA with EEW 190 g/eq). Fully stoichiometry would mean A/E =1.00. Source: Jayhawk Fine Chemicals Corporation

Acknowledgments

Produced from materials provided by Vinay Mishra, PhD, Technical Director, Thermoset Additives, Jayhawk Fine Chemicals Corporation.

For more information on this source, please visit Jayhawk Fine Chemicals Corporation.