Chemoselective Sequential Polymerization: An Approach Toward Mixed Plastic Waste Recycling

In nature, proteins are recycled through their metabolism, where mixtures of proteins are depolymerized to their monomers (the amino acids) that are then used to produce new proteins. Clearly, nature can convert mixed feedstocks into precise polymers. Inspired by this idea, the recycling of a mixture of synthetic polymers is herein reported. The polymers are first depolymerized together, yielding a mixture of monomers, that in turn undergoes chemoselective sequential polymerizations to yield the pure original polymers. This concept is established by using mixtures of poly(lactic acid), poly(2,2‐dimethyltrimethylene carbonate), and poly(pentadecalactone). All 3 polymers are depolymerized together into their cyclic monomers with high yield (>82%) via ring closing depolymerization, also in presence of other commodity polymers. A series of catalysts and reaction conditions is identified, enabling the sequential polymerization of each monomer into its respective polymer. The chemoselectivity of the polymerizations is illustrated by the chemical purity (>90% by NMR) and by the maintained mechanical and thermal properties of the polymers. A key limitation in plastic recycling is dealing with objects made of multiple polymers, the power of this approach is highlighted by showing that a multilayer film made of the three polymers can undergo this type of recycling.