Sourcing, thermodynamics, and ring-opening (co)polymerization of substituted δ-lactones: a review

Environmental concerns have escalated due to the extensive production of polymers from fossil resources and the resultant issues in waste management and environmental pollution. With the increased demand for more sustainable polymers, studies on the ring-opening polymerization of cyclic esters to obtain aliphatic polyesters, a relevant class of polymers with good mechanical performance, potential biodegradation and biocompatibility, have increased. Among them, substituted & delta;-lactones are interesting building blocks since a significant number of these monomers can be biobased and bring specific properties lacking in other lactones. Due to unfavorable ROP thermodynamic parameters, the polymerization of & delta;-lactones is challenging. However, various (co)polyesters have been synthesized from these lactones leading to valuable applications in drug delivery or thermoplastic elastomers. This review focuses on how to obtain these lactones, their particular thermodynamic parameters and different catalytic systems such as organocatalysts, alkali metals or metal complexes used to perform their ring-opening (co)polymerization. By providing an in-depth understanding of the synthesis and polymerization of substituted & delta;-lactones, this review aims to explore sustainable polyesters with improved properties and minimal environmental impact.