Functional polyesters via ring-opening copolymerization of α–hydroxy–γ–butyrolactone and ε-caprolactone: La[N(SiMe3)2]3 as an efficient coordination-insertion catalyst

The growing awareness of environmental concerns and the fossil resources depletion have raised the need to develop sustainable and degradable polymers such as aliphatic polyesters. γ-Lactone-based polyesters are of great interest today due to their ability to depolymerize. The introduction of functional groups appeared also useful to tune the properties of such polyesters. This can be addressed by the use of functional monomers such as the sugar-based α-hydroxy-γ-butyrolactone (HBL). In this study, the synthesis of random copolyesters of HBL and ε-caprolactone (ε-CL) was investigated via ring-opening copolymerization in the presence of La[N(SiMe3)2]3 as a catalyst. High polymerization temperature (80 °C) was required for fast and high monomer conversions. The characterization of the copolyesters and kinetic investigations provided better insight into the polymerization mechanism and formation of various HBL monomer units (cyclic, linear and branched). La[N(SiMe3)2]3 catalyst afforded high HBL conversion ratio (over 85 %) for the copolymerization reaction enabling the synthesis of copolyesters with a ratio of HBL units ranging from 9 to 63 %.