Concept of Recycling‐on‐Demand Investigated on Linear Poly(Ester‐Co‐Acetal)s

ABSTRACT Effective recycling of polymers into valuable resources is the basis for establishing a circular economy. Whereas mechanical recycling often leads to downcycling, the concept of recycling‐on‐demand (ROD) has high promise. The aim is to design next‐generation polymer materials that combine good material properties during use with convenient recycling abilities into higher‐value building blocks at the end of use. This work targets oligomers as desired degradation products to enhance energy efficiency in degradation and re‐polymerization steps. Therefore, selectively cleavable bonds are implemented into polyesters to degrade them by application of certain triggers. Poly(ester‐co‐acetal)s (PEAs) with model character are synthesized in a solution‐based sustainable process utilizing organo‐catalysis. In this approach, OH‐terminated oligoesters (OEs) are bridged by acid‐labile acetal groups, yielding polymeric materials that provide excellent recyclability. Two degradation‐repolymerization cycles by formation and cleavage of the acetal bonds were verified by nuclear magnetic resonance spectroscopy. At the same time, size exclusion chromatography confirms the effective polymerization and selective degradation of the acetals under full retention of the polyester oligomers. Additionally, the OH number of the degraded materials is determined to ensure good stoichiometry for effective repolymerization. These combined efforts result in an impressive proof of concept for the proposed ROD principle.