Ultratough Thermoplastic Elastomers Based on Chemically Recyclable Cycloalkyl-Substituted Polyhydroxyalkanoates

It remains a long-standing challenge for chemical recycling of polyhydroxyalkanoates (PHAs) to propiolactone-based monomers due to the high ring strain and many inevitable side reactions. In this contribution, a novel α-spiro-cyclohexyl-propiolactone (SHPL) has been designed with high reactivity toward ring-opening polymerization even at a catalyst loading of <1 ppm. The resulting poly(3-hydroxy-2-spiro-cyclohexylpropionate) (P3HSHP) exhibited high thermal stability with a <i>T</i>_d of 364 °C and a high <i>T</i>_m of 272 °C. Meanwhile, it could be depolymerized back to SHPL in 86% yield without decarboxylation or elimination side products. Notably, SHPL could be exploited to construct high-performance thermoplastic elastomers (TPEs) via one-pot copolymerization with ε-caprolactone (CL). Particularly, the resulting gradient P(CL₂₀₀₀-<i>grad</i>-SHPL₅₀₀) showcased an ultimate tensile strength of 58.8 ± 4.0 MPa, high stretchability of 1959 ± 53%, a record toughness of 600 MJ/m³, and high elastic recovery (>90%). This superior performance of SHPL could advance the development of new sustainable high-performance TPEs.