Research Article

A synthetic polymer system with repeatable chemical recyclability

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Science  27 Apr 2018:
Vol. 360, Issue 6387, pp. 398-403
DOI: 10.1126/science.aar5498

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Recycle, recycle, recycle

Some polymers, such as polyethylene terephthalate in soft drink bottles, can be depolymerized back to the starting monomers. This makes it possible to repolymerize true virgin material for repeated use. Zhu et al. developed a polymer based on a five-membered ring cyclic monomer derived from γ-butyrolactone that could be produced at ambient temperature and mild conditions (see the Perspective by Sardon and Dove). The high-molecular-weight polymer exhibited high crystallinity and thermal stability. However, at hot enough conditions, or at lower temperatures in the presence of a zinc chloride catalyst, the polymer could be returned to its starting monomers and thus recycled into new material.

Science, this issue p. 398; see also p. 380

Abstract

The development of chemically recyclable polymers offers a solution to the end-of-use issue of polymeric materials and provides a closed-loop approach toward a circular materials economy. However, polymers that can be easily and selectively depolymerized back to monomers typically require low-temperature polymerization methods and also lack physical properties and mechanical strengths required for practical uses. We introduce a polymer system based on γ-butyrolactone (GBL) with a trans-ring fusion at the α and β positions. Such trans-ring fusion renders the commonly considered as nonpolymerizable GBL ring readily polymerizable at room temperature under solvent-free conditions to yield a high–molecular weight polymer. The polymer has enhanced thermostability and can be repeatedly and quantitatively recycled back to its monomer by thermolysis or chemolysis. Mixing of the two enantiomers of the polymer generates a highly crystalline supramolecular stereocomplex.

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