Raman Evaluation of the Crystallinity Degree of Star-Shaped Lactide Oligomers: An Influence of the Number, Length and Enantiomeric Composition of the Arms

The control of structure-dependent properties of materials widely applied in the manufacture of medical products is extremely important. The purpose of this study was the Raman evaluation of the crystallinity degree (CD) of star-shaped L-lactide (L-LA) and D,L-lactide (D,L-LA) oligomers with different structures of arms. Raman spectroscopy was applied for the first time to analyze the structure of these oligomers. They differed in the number of arms (three or six) and the degree of polymerization (DP) of each arm (about 25 or 100). L-LA oligomers were studied in two forms: semicrystalline and amorphous. It was shown that the Raman method for evaluation of the CD, previously proposed for pure L-polylactide (L-PLA), linear L-LA oligomers, and L-LA copolymers with ε-caprolactone (CL), is applicable to the star-shaped L-LA oligomers. The CD values of the star-shaped L-LA oligomers evaluated by Raman spectroscopy and X-ray diffraction analysis were in a good agreement. Raman analysis showed that the CD of star-shaped L-LA oligomers increased with decreasing arm number and increasing arm length. These results demonstrate that Raman spectroscopy is an effective tool for monitoring the CD of star-shaped L-LA oligomers, including operative control of CD during annealing.