Closed-loop chemical recycling of polymer networks via reversible Aza-Michael addition

A new type of closed-loop recyclable polymer network material was developed based on a reversible aza-Michael addition reaction between 2,6-di-t-butyl-7-phenyl-p-quinone methide (pQM) and secondary amine group. The polymer networks could be conveniently prepared at ambient conditions using the efficient aza-Michael addition to crosslink the difunctional monomers with pQM end groups and trifunctional crosslinker of tris[2-(methylamino)ethyl]amine (TMEN). By virtue of the reversible reaction property, the crosslinked polymer networks could be easily degraded using di-tert-butyl dicarbonate to trap the released secondary amine groups to stimulate the reverse aza-Michael addition reaction. The pQM monomers and TMEN crosslinkers could be recovered with high yields above 85 % and 75 % by this degradation approach, respectively. The thermal and mechanical properties of the resultant polymer network materials could be flexibly tuned ranging from elastomers to plastics, by simply manipulating the chemical structure of the pQM monomers.