Fourier transform infrared (FTIR) spectroscopy was used to reveal intermolecular interactions between carbon dioxide (CO2) and the carbonyl groups of poly(L-lactide) (PLLA), poly(D,L-lactide) (PDLLA), and poly(E-caprolactone) (PCL). After exposing polymer films to high pressure CO2, the wave number of the absorption maxima of the polymer carbonyl groups shifted to higher values. Also, due to the interaction between CO2 and the carbonyl groups of the polymers, a new broad peak in the bending mode region of CO2 appeared. To distinguish between polymer-associated and nonassociated CO2, and to quantify these contributions, the bending mode peaks were deconvoluted. From these contributions, it was found that in the case of PCL more CO2 is interacting with the polymer carbonyl groups than in the case of PDLLA and PLLA. Under our experimental conditions, 40 degrees C and pressures up to 8 MPa, a significant depression of the PCL melting temperature was observed. (C) 2008 Wiley Periodicals, Inc.