Investigation of the degree of homogeneity and hydrogen bonding in PEG/PVP blends prepared in supercritical CO2: Comparison with ethanol-cast blends and physical mixtures

The degree of homogeneity and H-bond interaction in blends of low-molecular-mass poly(ethylene glycols) (PEG, Mw = 400, 600, 1000) and poly(vinylpyrrolidone) (PVP, Mw = 9 × 103) prepared in supercritical CO2, ethanol and as physical mixtures were studied by differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMA) techniques. Homogeneity of samples prepared in supercritical CO2 were greater than physically mixed samples, but slightly less than ethanol-cast samples. PEG–PVP H-bond interaction was higher for ethanol-cast blends when compared to blends prepared in supercritical CO2. This reduced interaction was attributed to a combination of: (1) shielding of PEG–PVP H-bond interactions when CO2 is dissolved in the blend; (2) rapidly reduced PEG and PVP chain mobility upon CO2 venting, delaying rearrangement for optimum PEG–PVP H-bond interaction.