Recent advances in the controlled preparation of poly(α-hydroxy acids): Metal-free catalysts and new monomers

Polylactides (PLAs) are at the forefront of biodegradable polymer research. These poly(α-hydroxy acids) can be prepared by polycondensation of lactic acid or ring-opening polymerization (ROP) of lactide, both routes typically involving metallic promoters. The first part of this review focuses on the recent achievements reported with metal-free systems via organocatalytic (nucleophilic, cationic and bifunctional) as well as enzymatic approaches. The second part of the review concerns the heterocyclic monomers that give access to poly(α-hydroxy acids) such as PLAs. Two complementary approaches will be discussed: substituted 1,4-dioxane-2,5-diones and synthetic equivalents thereof.