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Processable cross-linked polymers
Thermoplastics can be made stiffer and more durable by crosslinking them, but this makes it more difficult to reprocess and recycle them. Röttger et al. show that the transesterification of boronic esters grafted onto common polymers such as polyethylene and polystyrene improves their shape stability and chemical resistance. However, unlike traditionally cross-linked materials, their polymers can still be extruded or injection-molded. This is because the covalent cross-links can undergo rapid exchange reactions, which allows the material to flow at high temperatures while still retaining a cross-linked structure.
Science, this issue p. 62
Abstract
Windmills, cars, and dental restoration demand polymer materials and composites that are easy to process, assemble, and recycle while exhibiting outstanding mechanical, thermal, and chemical resistance. Vitrimers, which are polymer networks able to shuffle chemical bonds through exchange reactions, could address these demands if they were prepared from existing plastics and processed with fast production rates and current equipment. We report the metathesis of dioxaborolanes, which is rapid and thermally robust, and use it to prepare vitrimers from polymers as different as poly(methyl methacrylate), polystyrene, and high-density polyethylene that, although permanently cross-linked, can be processed multiple times by means of extrusion or injection molding. They show superior chemical resistance and dimensional stability and can be efficiently assembled. The strategy is applicable to polymers with backbones made of carbon-carbon single bonds.
