Effect of carbon dioxide sorption on the phase behavior of weakly interacting polymer mixtures: Solvent-induced segregation in deuterated polybutadiene/polyisoprene blends

In situ FTIR spectroscopic study of the effect of CO2 sorption on H-bonding in PEG-PVP mixtures

A study of the H-bonding between poly(ethylene glycol) (PEG) and polyvinylpyrrolidone (PVP) in the presence of supercritical carbon dioxide at various temperatures, pressures, different M(w) of PEG and PVP and different PEG/PVP ratios is presented. In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to investigate H-bonding by examining changes in the relative intensities and positions of peak maxima of the 2nd derivative ν(C=O) bands associated with 'free' and H-bonded C=O groups. In general, relative intensities of bands associated with H-bonded CO groups decreased upon CO(2) sorption and was accompanied by an increase in intensity of bands associated with 'free' C=O groups. At the same time, these bands were shifted to higher wavenumbers. These shifts were attributed to the shielding effect of CO(2) molecules on H-bonding interactions between PEG and PVP. The magnitude of the effects of CO(2) shielding generally increased with decreasing polymer M(w) and increasing CO(2) content. However, upon CO(2) venting the extent of the H-bonding between PEG and PVP reappeared. The extent of H-bonding recovery was greatest for blends with low M(w) PEG (M(w): 4×10(2)) and PVP (M(w): 9×10(3)) and PEG content ≥0.54 wt% under mild conditions of pressure (80 bar) and temperature (35°C). For the same low M(w) blends, increasing pressure to 150 bar, or temperature to 50°C, showed poor H-bond recovery upon CO(2) venting. Overall, it was shown that supercritical CO(2)-induced shielding of H-bonding interactions in polymer blends is reversible upon CO(2) venting, and the magnitude of both was influenced by processing conditions and blend composition.

Effect of density fluctuating supercritical carbon dioxide on polymer interfaces

We investigated an effect of CO2 sorption on the compatibility of immiscible polystyrene (PS) and polybutadiene (PB) bilayers by using in situ neutron reflectivity. By labeling either polymer with deuterium, we found that the excess CO2 molecules were adsorbed to both top PS and bottom PB layers when the bilayers were exposed to CO2 at the narrow T and P regime near the critical point of pure CO2. Furthermore, we clarified that this excess sorption of CO2 molecules increased the interfacial width between the layers up to 100 angstroms even near room temperature, while the interfacial width without CO2 exposure has been reported to be at most 40 A even at the highest temperature (T congruent with 175 degrees C).