Reprocessable vinylogous urethane cross-linked polyethylene reactive extrusion

Vitrimers are an emerging class of permanently cross-linked materials, where exchange reactions of cross-links provide malleability. The most promising application of these materials is to impart reprocessability to thermoset polymers, such as cross-linked polyethylene (PE). Here, a facile and easy to scale-up method for the preparation of cross-linked PE vitrimers is presented by combining reactive extrusion and injection molding using exchange reactions of vinylogous urethanes. Very low retention times (1.9 cross-links per chain, stress-relaxation is largely controlled by the exchange reactions of vinylogous urethanes. It was found that the activation energy depended on the cross-link density. Reprocessability of the vitrimers is demonstrated by four cycles of molding and tensile strength testing revealing minor degradation of the material. Reactive extrusion of a precursor polymer and a diamine cross-linker leads to reprocessable vinylogous urethane polyethylene vitrimers with desired rheological properties.