Chemically Recyclable Thermoplastic Polyurethane Elastomers via a Cascade Ring-Opening and Step-Growth Polymerization Strategy from Bio-renewable δ-Caprolactone

It is highly desirable to develop chemically recyclable polymers to address the challenge in establishing a sustainable circular polymer economy. Despite the mass production and widespread applications, there are limited reported examples for the polyurethanes capable of chemical recycling to monomers with high efficiency and purity. In this contribution, we report the "living"/controlled ring-opening polymerization (ROP) of bio-renewable δ-caprolactone (δCL) at room temperature in bulk using an organobase in combination with urea as a catalyst. The telechelic PδCL diol precursor with well-defined terminal groups can be prepared using catalyst loading as low as 0.05 mol %. A one-pot strategy by cascade ROP of δCL and step-growth polymerization of PδCL diol precursors with diisocyanate under solvent-free conditions produced thermoplastic polyurethane elastomers with excellent elastic recovery, tensile strength, ultimate elongation, and low residue strain. Remarkably, the polyurethanes can be chemically recycled to recover δCL with high purity and excellent yield (∼99%) by simple thermolysis.