Effect of Polymer Characteristics on the Thermal Stability of Retinol Encapsulated in Aliphatic Polyester Nanoparticles

The present study investigates how the thermal stability of retinol (vitamin A) encapsulated in polyester nanoparticles is influenced by the types of polyester used for the nanoparticles. A variety of polyester-retinol nanoparticles were prepared with various polyesters like: poly(ethylene adipate), PEA; poly(butylene adipate), PBA; poly(hexamethylene adipate), PRIMA; and three polycaprolactones, PCL, of different molecular weights (M-n similar to 10, 40, and 80K). The chemical stability of retinol in these nanoparticles, monitored in an aqueous solution at 25 degrees C and 40 degrees C for 4 weeks, was high in the following order of the nanoparticles prepared with PHMA > PCL 40K > PCL 10K > PCL 80K > PBA similar to PEA at 25 degrees C and PCL 10K > PCL 40K > PHMA > PCL 80K > PEA > PBA at 40 degrees C. More importantly, this study has also found that the thermal stability of the retinol in the nanoparticles was closely connected with the melting temperatures of polyesters and polyester nanoparticles. The results were further discussed with possible factors - such as sample preparation condition (or history) and miscibility between the polyesters and retinol - affecting T-m of the polyesters and the nanoparticles.