The effect of cross-linker structure on interfacial interactions, polymer dynamics and network composition in an epoxy-amine resin

Understanding interactions at the polymer / metal oxide interface is central to improving the performance lifetime of corrosion resistant coatings, where network polymers commonly form via step growth mechanisms in the presence of pigments. Here we employ a holistic analytical approach encompassing ATR-FTIR, DSC and molecular dynamics simulations to consider how crosslinker structure affects adsorption and incorporation into the network, using a stoichiometric mixture of diglycidylether of bisphenol-A (DGEBA) with m-xylylenediamine (MXDA) cured in the presence of hematite (Fe2O3) and goethite (FeOOH) powders. We find that the rigid MXDA molecule has two distinct binding modes on both hematite and goethite, and that synergistic hydrogen bonding modes observed on goethite limit interconversion between the two. Moreover, we find that binding persists in fully cured composite samples, determining the levels of residual amine. In contrast to previously reported results using triethylenetetramine (TETA) crosslinkers, however, we find that the Tg of composite specimens is inde-pendent of added hematite and goethite volumes. Molecular dynamics simulations demonstrate this is due to electrostatic binding between the cationic Fe sites and electronegative heteroatoms in MXDA. This renders both amine functionalities unavailable for incorporation into the network and hence, unlike TETA, MXDA adsorption does not determine polymer dynamics.

Automated summary

Understanding the interactions at the polymer/metal oxide interface is crucial for improving the performance of corrosion resistant coatings. In this study, we investigated how the structure of a crosslinker affects its adsorption and incorporation into the network. We found that the crosslinker has two distinct binding modes on both hematite and goethite, with hydrogen bonding modes observed on goethite limiting interconversion between the two. Additionally, we discovered that binding persists in fully cured composite samples, determining the levels of residual amine. Unlike previous studies using a different crosslinker, we found that the glass transition temperature (Tg) of the composite specimens is independent of the added hematite and goethite volumes.