Achieving Exceptional Thermal and Hydrolytic Resistance in Chemically Circular Polyesters via In-Chain 1,3-Cyclobutane Rings.

Polyesters, a highly promising class of circular polymers for achieving a closed-loop sustainable plastic economy, inherently exhibit material stability defects, especially in thermal and hydrolytic instability. Here, we introduce a class of polyesters, P(4 R -BL) (R=Ph, Bu), featuring conformationally rigid 1,3-cyclobutane rings in the backbone. These polyesters not only exhibit superior thermostability (T d,5% =376-380 °C) but also demonstrate exceptional hydrolytic resistance with good integrity even after 1 year in basic and acidic aqueous solutions, distinguishing themselves from typical counterparts. Tailoring the flexibility of the side group R enables the controlled thermal and mechanical performance of P(4 Ph -BL) and P(4 Bu -BL) to rival durable syndiotactic polystyrene (SPS) and low-density polyethylene (LDPE), respectively. Significantly, despite their high stability, both polyesters can be effectively depolymerized into pristine monomers, establishing a circular life cycle.