Determining conformational order and crystallinity in polycaprolactone via Raman spectroscopy

Area of Science:

• Polymer Science
• Spectroscopy
• Materials Science

Background:

• Raman spectroscopy is vital for analyzing polycaprolactone (PCL) in tissue engineering and drug delivery.
• Interpreting PCL Raman spectra alongside dielectric spectroscopy and differential scanning calorimetry data presents challenges in melt and semi-crystalline states.
• Existing methods lack detailed correlation between spectral features and PCL's physical states.

Purpose of the Study:

• To develop a thermodynamically informed analysis method for Raman spectra of polycaprolactone.
• To establish a clear link between spectral features and polymer chain conformations, crystallinity, and dipole interactions.
• To enhance the interpretation of Raman spectroscopy data for PCL and other polymers.

Main Methods:

• Utilized a novel analysis method based on 'basis spectra' representing ideal polymer chain conformers.
• Identified three distinct basis spectra in the carbonyl region of PCL.
• Correlated basis spectra with crystallinity, dipole-dipole interactions (via dielectric spectroscopy), and amorphous chain behavior.
• Employed density functional theory calculations for spectral regions like C-COO stretch to differentiate between single chain modes and crystalline order.

Main Results:

• Discovered three basis spectra in PCL's carbonyl region, each linked to specific physical properties.
• Demonstrated a linear relationship between one basis spectrum and PCL crystallinity.
• Showed correlation of a second basis spectrum with dipole-dipole interactions and a third with amorphous chain behavior.
• Differentiated spectral peaks in other regions, attributing them to either all-trans single chain modes or crystalline order by comparing with DFT calculations.

Conclusions:

• The developed analysis method provides a robust framework for interpreting polycaprolactone Raman spectra.
• The method successfully correlates spectral features with fundamental polymer properties like crystallinity and chain conformation.
• This approach offers significant potential for advancing the analysis of polycaprolactone and other polymeric materials in various applications.