Recyclable and reprocessable elastomers relying on the vitrimer concept

Rubbers are usually cross-linked through static covalent bonds. Consequently, they cannot be reshaped after their synthesis. With the aim to extend the shelf life of elastomers, dynamic covalent chemistry was used to cross-link elastomers and develop recyclable rubbers. Thanks to the associative exchange reaction between boronic ester cross-links, incorporated into polybutadiene via thiol-ene chemistry, this elastomer was transformed into a vitrimer. The comparison with static networks showed the ability of the vitrimer to be recycled efficiently without detecting any side reactions during the synthesis nor the recycling process. As the exchange between dioxaborolanes is already occurring at room temperature, the polybutadiene vitrimer crept at service temperature. To avoid creep, dual networks, with both static and dynamic cross-links, were synthesised but their recyclability was decreased as compared to vitrimers. Aiming to slow down the exchange at room temperature while keeping its high rate at high temperatures, a new exchange reaction between dioxaborinanes was studied. Key parameters such as the rate constant and the activation energy were measured. Dioxaborinane based cross-links were incorporated into polybutadienes. In order to widen the range of recyclables elastomers, another grafting chemistry was tested, the nitrene chemistry. New molecules, bearing an azide and a boronic ester were synthesized and then introduced into polyisoprene.