Polybutadiene Vitrimers Based on Dioxaborolane Chemistry and Dual Networks with Static and Dynamic Cross-links

Vitrimers are polymer networks able to change their topology through degenerate exchange reactions. As a result, they behave like elastic solids when the topology of the network is frozen and like viscoelastic liquids at high temperatures. Controlling the dynamics of molecular exchange is essential to regulate the solid-to-liquid transition temperature in elastomeric vitrimers. In this study, such materials were prepared by the radical grafting of a bis-thiol dioxaborolane onto a low molar mass unentangled polybutadiene. All the resulting elastomeric vitrimers fully relax stress and are reprocessable and recyclable. Because of the low molar mass of the thermoplastic precursor, the low number of cross-links per chain, and the dynamics of the dioxaborolane exchange reaction, these vitrimers dissolve in tetrahydrofuran after prolonged immersion time at room temperature. Creep-recovery experiments at various temperatures show that both the viscosity and the viscosity activation energy of vitrimers can be controlled by manipulating the cross-linking density. This feature offers a new perspective on developing vitrimers with improved creep resistance at service temperatures and desirable flow properties at processing temperatures. In order to prepare reprocessable elastomers with improved creep resistance, we prepared dual networks that feature both dynamic and static cross-links. Even with fractions of static cross-links sufficient to form a percolated network, these dual networks are fully recyclable and exhibit strong adhesion with welding times as short as 2 min at 150 °C.