Covalent Adaptable Networks from Commodity Polybutadiene and Rubber Waste.

Rubbers are polymer networks that are used in many everyday applications ranging from tires to apparel. Unfortunately, the cross-links that give these materials their desirable properties also make them difficult to recycle. Covalent adaptable networks (CANs) are a promising class of cross-linked polymers that rearrange their cross-links in response to a stimulus like heat, making them more recyclable than conventional thermosets. Herein we present a method of incorporating dithioalkylidenes, a catalyst-free associative dynamic bond, into polybutadiene rubbers using olefin metathesis. The modified polymers are cross-linked with a multiarmed thiol, and the resulting networks are chemically and mechanically recycled. Evolution of the network microstructure during recycling results in up to a 7-fold increase in toughness over three cycles of recycling. We incorporate common fillers like carbon fiber and silica into CANs to provide reinforced composites and recover these fillers through chemical recycling. Finally, we modify devulcanized rubber crumb derived from rubber waste, enabling the preparation of mechanically recyclable composites with 90% upcycled content. This work presents a new method of upcycling waste rubber to access materials with multiple lifecycles.