Reprocessable Catalyst-Free Polymethacrylate Networks Containing Dynamic Hindered Urea Bonds and Exhibiting Full Recovery of Cross-Link Density after Recycling.

Conventional cross-linked polymers cannot be reprocessed due to the presence of permanent covalent cross-links, preventing reuse and recycling. Covalent adaptable networks (CANs) employ dynamic covalent bonds that undergo dynamic reactions under external stimulus, allowing recyclability of these network materials. Hindered urea chemistry is one of the recently discovered dissociative dynamic chemistries. While hindered urea bonds have traditionally been exploited in the synthesis of step-growth type CANs, the use of hindered urea bonds in the synthesis of addition-type dynamic networks has only been narrowly explored. Here, we present a simple, fast method to synthesize a hindered-urea-based dynamic cross-linker that can undergo a free radical polymerization with vinyl-type monomers or polymers to form reprocessable CANs. Using this cross-linker, we developed dynamic catalyst-free polymethacrylate networks that can be (re)processed multiple times and exhibit full recovery of cross-link density after three recycling steps. Unlike other dissociative dynamic polymer networks, polymethacrylate networks containing dissociative dynamic hindered urea bonds do not flow and maintain their network nature even at high temperature (T>300 °C).