Ring-Opening Polymerization of a Seven-Membered Lactone toward a Biocompatible, Degradable, and Recyclable Semi-aromatic Polyester

The widespread use of polymer materials and their improper disposal have resulted in significant environmental pollution and wastage of resources. Therefore, the design of chemically recyclable, environmentally compatible, and applicable polymers represents a new approach for a green and circular polymer economy, and it has become a major focus worldwide. Herein, we efficiently synthesized a seven-membered ether lactone, 3,4-dihydro-2H-benzo[b][1,4]dioxepin-2-one (BDXO), through a one-step reaction and successfully realized its controlled ring-opening polymerization (ROP). The ROP of BDXO in bulk and solvent conditions catalyzed by Sn(Oct)2 was investigated systematically, and the thermodynamic parameters obtained were Delta SP0 = -30.90 J center dot mol-1 center dot K-1 and Delta HP0 = -14.52 kJ center dot mol-1. The PBDXO polymer exhibits excellent thermal properties, applicable mechanical properties, excellent biocompatibility, and complete hydrolytic degradability. Notably, not only was the direct chemical recycling of PBDXO to BDXO monomer realized with high efficiency through bulk thermal depolymerization with a yield greater than 92% and a purity of up to 96% but also the regenerated PBDXO with almost the same structure and properties as the initial PBDXO was obtained through repolymerization of the recycled BDXO, establishing a polymer-monomer-polymer closed-loop life cycle.