Fully recyclable and reprocessable polystyrene-based vitrimers with improved thermal stability and mechanical properties through nitrogen-coordinating cyclic boronic ester bonds

The cross-linked polystyrene (PS) are commonly used plastic materials, however, the greater brittleness and the difficulties in recycling severely limit their applications. In this work, we provide a new strategy for the crosslinking of PS based on the nitrogen-coordinating cyclic boronic ester (NCB) linkages. PS vitrimers are synthesized from PS with hydroxyl groups and isocyanate-terminated NCB oligomer. Incorporating NCB linkages can greatly improve the solvent resistance, thermal stability and mechanical properties of PS without sacrificing its dielectric properties. PS vitrimers exhibit rapid stress relaxation and improved creep resistance due to the stable NCB linkages. PS vitrimers were able to withstand multiple reprocessing cycles via the exchange reactions of NCB linkages without catalyst. The recycled PS vitrimers were shown to regain the structural integrity, mechanical strength and dielectric properties as the original. The glass fibre reinforced PS vitrimer composites were prepared to explore the application in copper clad manufacture, which showed good mechanical properties and can be conveniently recycled to resin solution and clean glass fibre. This work provides a new strategy for the development of the green dielectric polymer materials for copper clad laminates, and may serve as a guide for rational design of dynamic materials based on general-purpose plastics.