Visualization of Changes in Crystallinity and Intermolecular Hydrogen Bonding of Poly(ε-caprolactone) during Marine Degradation Process by High- and Low-Frequency Three-Dimensional Raman Mapping

The samples investigated were prepared by seeking poly(ε-caprolactone) (PCL) films in seawater for the study of marine degradation processes. Raman mapping measurements in the low-frequency region and the C═O stretching region were used for investigating the strength of the CH···O═C hydrogen bonding and the changes in the crystallinity of PCL, respectively, in its marine degradation process. During the marine degradation of the PCL film, the amorphous parts of the film decomposed and flow away in the seawater. A band at around 60 cm–1 reflecting intermolecular CH···O═C hydrogen bonds showed a weakening of hydrogen bonds in the crystal structure of PCL. Three-dimensional (3D) Raman mapping developed by the C═O stretching region indicated that the marine degradation started from the surface of the annealed PCL film. However, 3D Raman mapping measurements in the low-frequency region showed no significant difference in the strength of the hydrogen bonding between a film surface and an inside after marine degradation of day 7. These findings suggest that the crystallinity changes mainly near the film surface, but changes in the strength of the hydrogen bonding occur both near the surface and inside of the PCL film.