Influence of Soft Segment Length and Crosslink Density on the Properties of Thermoreversible Diels-Alder Polyurethanes.

Highly crosslinked dynamic polymer networks composed of conventional polyurethane monomer starting materials modified with Diels-Alder (DA) compatible end groups are reported and shown to demonstrate beneficial properties of both thermoset and thermoplastic polymers. The design, synthesis, and evaluation of thermoreversible DA covalent polymer networks derived from modified conventional polyurethane monomers enable potential applications in high-performance coatings. The effects of soft segment chain length and cross-link density on thermal, mechanical, and self-healing properties are reported. Reversible covalent cross-linking was shown using dynamic mechanical analyses and elevated temperature in situ ssNMR analysis. We clearly demonstrate the excellent solvent stability and high temperature thermal reformation of the polymer, which together provide evidence of a cross-linked dynamic covalent network. This work represents the first demonstration of a facile approach to formulate DA coatings to target high performance coating specifications.