Sustainable Polyester Elastomers from Lactones: Synthesis, Properties, and Enzymatic Hydrolyzability

Chemically cross-linked elastomers are an important class of polymeric materials with excellent temperature and solvent resistance. However, nearly all elastomers are petroleum-derived and persist in the environment or in landfills long after they are discarded; this work strives to address these issues by demonstrating the synthesis of renewable, enzymatically hydrolyzable, and mechanically competitive polyester elastomers. The elastomers described were synthesized using a novel bis(β-lactone) cross-linker and star-shaped, hydroxyl-terminated poly(γ-methyl-ε-caprolactone). Using model compounds, we determined that the bis(β-lactone) cross-linker undergoes acyl bond cleavage to afford β-hydroxyesters at the junctions. The mechanical properties of the cross-linked materials were tunable and competitive with a commodity rubber band. Furthermore, the elastomers demonstrated high thermal stability and a low glass transition (-50 °C), indicating a wide range of use temperatures. The polyester networks were also subjected to enzymatic hydrolysis experiments to investigate the potential for these materials to biodegrade in natural environments. We found that they readily hydrolyzed at neutral pH and environmentally relevant temperatures (2-40 °C); complete hydrolysis was achieved in all cases at temperature-dependent rates. The results presented in this work exemplify the development of high performance yet sustainable alternatives to conventional elastomers.