Activity: Talk or presentation › Talk at a school event
The thermally reversible Diels-Alder cycloaddition reaction between furan and maleimide has become one of the most popular chemistries for reversible network polymerization and the creation of self-healing materials. The thermal reversibility of the Diels-Alder reaction has been studied extensively, is well established in literature and is used extensively to create thermoresponsive polymer networks. Furthermore, stresses inside the reversible polymer network are able to relax by way of the dynamically reversible cycloaddition reaction and chain reorganisation. However, if the forces applied to the polymer chains are too high or the time to relieve the stresses too short, the polymer chain break. In view of self-healing applications, the mechanical activation of the Diels-Alder reaction was studied. A model monomer system consisting of a monofunctional furan compound FGE and a bifunctional maleimide compound M400 were reacted stoichiometrically to form the Diels-Alder adduct bonds. The mixture was then sonicated directly, without the addition of a solvent. The Diels-Alder conversion was followed with FTIR spectroscopy, showing that adduct bonds were broken to form the maleimide and furan groups. The thermal effect was quantified and found insignificant compared to the total change in conversion due to the mechanical activation. The system successfully recovered to its original equilibrium for 4 consecutive sonication and recovery cycles . Second, reversible polymer networks based on the same bismaleimide and a four-functional furan monomer were damaged by mechanical force. The material is able to successfully recover its original mechanical properties at room temperature, without the need for a thermal stimulus, in several days, showing excellent repeatability . Furthermore, thermoset and elastomeric coatings were damaged mechanically using nano-lithography. The healing behaviour was followed by AFM at temperatures between the glass transition and the gel transition of the material, retaining structural integrity while sealing the damage .
23 May 2019
EPF summer school 2019: Dynamic and Reversible Polymer Networks