Vinylogous Urea Vitrimers and Their Application in Fiber Reinforced Composites

Vitrimers are covalently cross-linked polymeric materials that can be thermally processed in a liquid state without losing their network integrity. In this work, novel vitrimers based on the dynamic amine exchange reaction of vinylogous urea moieties are introduced. Following a systematic exploration of different vinylogous acyl compounds (urethanes, amides, and urea), vinylogous urea dearly emerges as showing the fastest intrinsic exchange kinetics. The combination of these networks with a simple acid catalyst (0.5 mol % pTsOH) resulted in materials with good mechanical properties (T-g similar to 110 degrees C, E similar to 2.2 GPa) and remarkably short relaxation times above T-g, in the order of a few seconds when heated. This attractive combination of properties made it possible to prepare vinylogous urea based composites as enduring prepregs. We demonstrate that the dynamic material properties give fully cured composites that still allow an efficient thermal fusion of multiple layers as well as thermoforming. Finally, we also demonstrate fiber recycling by a simple chemical treatment.