Closed-loop recycling of plastics enabled by dynamic covalent diketoenamine bonds

• Published in: Nature chemistry Vol. 11; no. 5; pp. 442 - 448
• Main Authors: Christensen, Peter R., Scheuermann, Angelique M., Loeffler, Kathryn E., Helms, Brett A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2019; Nature Publishing Group
• Subjects: 639/638/224/685; 639/638/455/941; Additives; Aliphatic amines; Amines; Analytical Chemistry; Biochemistry; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Closed-loop recycling; Commodities; Environmental impact; Flame retardants; Formulations; Impurities; Inorganic Chemistry; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Life cycles; Monomers; Organic Chemistry; Physical Chemistry; Plastics; Plastics recycling; Polymer synthesis; Polymerization; Polymers; Recycled materials; Recycling; Sustainability; Waste management; Waste streams
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/s41557-019-0249-2

Recycled plastics are low-value commodities due to residual impurities and the degradation of polymer properties with each cycle of re-use. Plastics that undergo reversible polymerization allow high-value monomers to be recovered and re-manufactured into pristine materials, which should incentivize recycling in closed-loop life cycles. However, monomer recovery is often costly, incompatible with complex mixtures and energy-intensive. Here, we show that next-generation plastics—polymerized using dynamic covalent diketoenamine bonds—allow the recovery of monomers from common additives, even in mixed waste streams. Poly(diketoenamine)s ‘click’ together from a wide variety of triketones and aromatic or aliphatic amines, yielding only water as a by-product. Recovered monomers can be re-manufactured into the same polymer formulation, without loss of performance, as well as other polymer formulations with differentiated properties. The ease with which poly(diketoenamine)s can be manufactured, used, recycled and re-used—without losing value—points to new directions in designing sustainable polymers with minimal environmental impact. It is difficult to recover materials for re-manufacturing and re-use from plastics that are compounded with colourants, fillers and flame retardants. Now, it has been shown that alternative plastics based on dynamic covalent poly(diketoenamine)s depolymerize in strong aqueous acids and enable triketone and amine monomers to be isolated and upcycled into new plastics.