A.A.Broekhuis@rug.nl with the processability and recyclability of thermoplastic ones. [ 6 ] The concept behind re-workable thermosets is that part of the polymer network can be de-crosslinked by applying an external stimulus, the latter being for example light [ 7 ] or heat. These networks can either consist of covalent or non-covalent crosslinks. Examples of non-covalent reversible crosslinks are hydrogen bonds, [ 8 , 9 ] and ionic [ 10 ] or Van der Waals interactions (e.g., SBS rubber). [ 11 , 12 ] All these physical bonds have been demonstrated to selectively break at a given de-crosslinking temperature. On the other hand, covalently reversible chemical crosslinks are based on chemical bonds that can be broken upon an external stimulus, mainly heat or radiation energy. The most studied thermoreversible chemical systems are based on the Diels-Alder (DA) reaction [ 13 ] probably because it ensures fast kinetics and a high number of recycles with little, if any, degradation [ 14 ] between 50 ° C and 200 ° C. In order to create a 3D crosslinked network, several systems have been employed based on the [4 + 2] DA reaction and its reverse. These systems consist of multiple dienophile and diene moieties of low molecular weight, [ 15 ] of dienes or dienophiles attached to polymer backbones crosslinked with bi-functional low molecular weight crosslinker, or of polymeric chains containing both diene and dienophile. [ 16 ]