The Effect of Pendant Alkyl Chain Length in Epoxy/Amine Thermosets Materiel Properties and Water Barrier Properties

Aliphatic amido amine crosslinkers have been commercially used in epoxy coatings to enhance water barrier properties for corrosion prevention. However, there is only an empirical understanding of how these aliphatic polyamine crosslinkers affect properties of thermoset polymers, which limits our ability to design newer and more environmentally friendly coating systems. In this work, a series of model aliphatic amido amine curing agents are synthesized and used to create model epoxy/amine networks found in commercial coating formulations. These model systems were interrogated to understand the effects of pendant alkyl chain length material properties including storage modulus, glass transition temperature, solubility, diffusivity, and permeability of water. This work shows that the pendant alkyl chains form an “ideal mixture” with the polymer backbone, where material properties such as storage modulus and solubility of water are observed to be linearly dependent on the pendant alkyl chain volume fraction. Figure 1 shows our proposed hypothesis, where addition of pendant alkyl chains reduces the solubility of water by excluding some of the available free volume. We propose that the alkyl chains simultaneously enhances the diffusivity of water by the dispersal of higher water diffusivity segments (alkyl chains).