Investigation of the interaction of CO₂ with poly (L‐lactide), poly(DL‐lactide) and poly(ε‐caprolactone) using FTIR spectroscopy

Fourier transform infrared (FTIR) spectroscopy was used to reveal intermolecular interactions between carbon dioxide (CO 2 ) and the carbonyl groups of poly( L ‐lactide) (PLLA), poly( D,L ‐lactide) (PDLLA), and poly(ε‐caprolactone) (PCL). After exposing polymer films to high pressure CO 2 , the wave number of the absorption maxima of the polymer carbonyl groups shifted to higher values. Also, due to the interaction between CO 2 and the carbonyl groups of the polymers, a new broad peak in the bending mode region of CO 2 appeared. To distinguish between polymer‐associated and nonassociated CO 2 , and to quantify these contributions, the bending mode peaks were deconvoluted. From these contributions, it was found that in the case of PCL more CO 2 is interacting with the polymer carbonyl groups than in the case of PDLLA and PLLA. Under our experimental conditions, 40°C and pressures up to 8 MPa, a significant depression of the PCL melting temperature was observed.