Poly(α-hydroxy alkanoic acid)s derived from α-amino acids

Biodegradable polyesters derived from hydrophobic amino acids are synthesized by various techniques, resulting in a wide range of molecular weights. The polymers are prepared via a) direct condensation with p-toluenesulfonic acid (PTSA) as catalyst, b) ring-opening polymerization (ROP) of O-carboxyanhydrides, and c) ROP of cyclic dilactones. The polymers obtained by the first method reach a molecular weight ranging from 1000 to 3000 Da, whereas those formed by the second and third method yield extended molecular weights of 15 000-30 000 Da. The purity of the monomers as well as their steric bulkiness are key factors affecting the polymerizability of cyclic monomers by ROP. Other parameters such as spatial ring alignment and proximity organization may also play a role. Biodegradable polyesters derived from hydrophobic amino acids are prepared by ring-opening polymerization of O-carboxyanhydrides or of cyclic dilactones. Molecular weights in the range 15 000-30 000 Da are observed. The polymers are characterized by GPC, CD, and DSC.