The primary objective of this project is the development of novel isocyanate-free polymer coating systems with dynamic self-healing capabilities. The Naval Research Laboratory and University of Alaska Fairbanks team will produce a durable, cross-linked coating system that is free of isocyanates and exhibits self-healing capability through the incorporation of dynamic bonding moieties from functionalized acrylate/methacrylate polymeric resins that will serve as the first demonstration of this technology’s feasibility for military coating applications.

This project employs a multi-pronged approach utilizing polymer chemistry, in situ spectroscopy and theoretical analysis to incorporate a unique combination of dynamic crosslinks to generate isocyanate-free coatings with inherent self-healing for military applications. Dynamic covalent bonds will be afforded through Diels-Alder [4+2] cycloadditions with furan and maleimide pendant group functionality, which have well established associative/dissociative behavior in solutions, small molecules, and oligomers. In situ spectroscopic evaluation of the dynamic crosslinking chemistry within the solid networks will be afforded through solid-state nuclear magnetic resonance spectroscopy, which will be utilized to provide mechanistic insight into the dynamic behavior to optimize formulations and guide end-use criteria. Traditional spectroscopic, thermal, and mechanical characterization of the polymer network dynamic mechanism and behavior will also be performed to ensure compliance of material properties with current performance standards. Furthermore, molecular modeling-based theory will direct synthesis and down-selection of formulation candidate systems by simulating the dynamic potential of the functionalized polymers and optimize polymer and coating properties. Two different levels of theory, coarse grain and atomistic scale molecular dynamics modeling simulations, will provide feedback to further the understanding and development of dynamic crosslinked polymers. Theory will reveal macroscopic intermolecular polymer dynamics and provide molecular-level feedback on the system run in parallel with experimental work.

Dynamic covalent crosslinking within the polymer is an alternative approach to generating crosslinkable networks with potential to replace isocyanate-based chemistries with the added benefits of self-healing characteristics. Current high performance military grade exterior topcoats are based upon polyurethane chemistries, which require the use of chemicals such as di- and poly-isocyanates that are sensitive to moisture and detrimental to human health and the environment [1]. Alternatively, the use of crosslinkable polymers with dynamic capabilities provides an opportunity to generate novel advanced coating systems with the ability to be repaired for enhanced longevity while potentially allowing easier removal and possible recyclability. The development of this coating system will have broad implications beyond coatings and lay the foundation for new classes of polymer technologies, ranging from self-healing and removable thermosets, to next-generation adhesives, and recyclable thermoset polymer-based materials.

[1] Kathalewar, M.K.; Joshi, P.B.; Sabnis, A.S.; Malshe, V.C. Non-isocyanate polyurethanes: from chemistry to applications. RCS Adv. 2013, 3, 4110-4129.