Self-healing property characterization of reversible cross-linked polymer network coatings

Thermosets are irreversibly cross-linked polymer networks which have superior mechanical properties and increased thermal and chemical resistance in comparison to their linear, un-cross-linked analogues. However, these thermosets exhibit severe limitations such as restricted process-ability and certainly repair-ability. To overcome these drawbacks, the incorporation of reversible cross-linking functionalities in the polymer backbone, such as Diels-Alder (DA) adducts, has been explored. This built-in reversibility allows the material to behave analogous to melting, molding and dissolution.

The objective of this work is to asses the self-healing behaviour of a thermally reversible polymeric network for coating applications based on the Diels-Alder reaction (see figure below). The DA reaction is attractive as a reversible linkage as the retro-DA reaction occurs at moderate temperatures around 100 °C [1].
It is demonstrated that the network properties can be tailor-made by choosing the appropriate building blocks. In a first step, the furan functional compound is synthesized by an epoxy-amine reaction between furfuryl glycidyl ether (FGE) and a Jeffamine. The used Jeffamine series has a variable molar mass, resulting in different cross-linking densities in the final reversible network. Afterwards, the furan functional compound is mixed with a bismaleimide (BMI) in a 1:2 molar ratio and dissolved in chloroform. The epoxy-amine and Diels-Alder reactions were studied by micro-calorimetry and FTIR.

Bulk properties were assessed after removal of the solvent. The thermal transitions of the bulk material were studied by MTDSC. The thermal stability of the reversible thermosets was evaluated by TGA. The flow behaviour of the bulk material was studied by means of rheological experiments at different temperatures.

The reversible network coatings were applied on aluminum substrates by spincoating. Coating thicknesses were determined by local thermal analysis (LTA). The self-healing properties of the reversible thermoset coatings were evaluated by nanolithography and atomic force microscopy (AFM).


References

[1] A. Gandini, D. Coelho, A. Silvestre, European Polym. J. 44 (2008) 4029-4036.