High-pressure CO2-enhanced polymer interdiffusion and dissolution studied with in situ ATR-FTIR spectroscopic imaging

A novel application of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging to study polymer interdiffusion and dissolution under high-pressure or supercritical carbon dioxide environments has been demonstrated. Miscible systems of polyvinylpyrrolidone (PVP) and poly(ethylene glycol) (PEG) of different molecular weights have been chosen for this investigation. These systems were subjected to a controlled pressure of CO2 and the interfacial area of contact between the two polymers was studied by ATR-FTIR imaging in situ. Using this spectroscopic imaging approach, the phenomenon of polymer interdiffusion enhanced by CO2 dissolved in both polymers was investigated as a function of time. The evolution of spatially resolved images as a function of time was studied with FTIR imaging and the corresponding concentration profiles for both polymers were obtained. The chemical specificity of FTIR imaging also allowed us to measure the amount of CO2 dissolved in each domain of the polymer system. Effects of PEG molecular weight and pressure of CO2 on the mechanism and the rate of polymer interdiffusion was investigated. This approach has not only shown the ability to visualise the process of interdiffusion but also demonstrated the ability of high-pressure CO2 to 'tune' the rate of interdiffusion, this information is important for a better understanding of CO2-induced mixing of polymeric materials.