Synthesis of Polyethylene Vitrimers in a Single Step: Consequences of Graft Structure, Reactive Extrusion Conditions, and Processing Aids

Vitrimers have captured broad interest in academia and industry because they offer a compelling combination of mechanical performance, thermal stability, and recyclability. They are permanent polymer networks that contain dynamic covalent bonds that undergo thermally activated exchange reactions without decreasing the connectivity of the network. The introduction of such functionality to commercial thermoplastics via reactive processing is envisioned to be an economical way to access high-performance, recyclable materials. Polyolefins are of particular interest because they are the most widely used class of polymers today. Although reactive processing is widely practiced in the industry, it remains a nascent approach for accessing polyolefin vitrimers. Herein, we report a dimaleimide bis(dioxaborolane) that allows for commercial polyethylene (PE) to be transformed into a vitrimer in a single step without any small-molecule byproducts. The miscibility of the grafting agent with the PE melt is a critical consideration for optimizing the grafting protocol, as efficient mixing is essential for achieving quantitative grafting and a high gel content. We find that the degree of incompatibility of the grafting agent in the PE melt strongly affects the nano- and macrostructure of the resulting PE vitrimers, which in turn dictates the thermal and mechanical properties. Finally, the material properties can be finely tuned using a reactive processing aid.