H-2 NMR INVESTIGATION OF THE PLASTICIZATION EFFECTS INDUCED BY HIGH-PRESSURE CARBON-DIOXIDE GAS ON THE MOLECULAR-DYNAMICS OF POLYMERS

2H NMR spectroscopy has been used to probe the effect of CO2 gas pressure on the molecular dynamics of polymers used as membrane materials in gas separation. A special cell was constructed for the experiment which was capable of pressures from vacuo to at least 35 atm. The investigation showed that the molecular dynamics of the polymer were unequivocally enhanced by dissolved CO2 (at relatively low pressures) for three polymers studied: polycarbonate, polyester carbonate, and polystyrene. In fact, the pressure dependence of the microscopic molecular dynamics of the polymer and the diffusivity of CO2 were quite similar. Two conclusions are possible from this observation. First, CO2 diffusion is directly related to the polymer dynamics monitored with2H NMR. If this conclusion is correct, then it suggests that concentration-dependent diffusion parameters are required to accurately model transport in these systems. However, an alternative conclusion is that CO2 diffusion is not related to the polymer dynamics measured by2H NMR because the specific frequencies and motions monitored by NMR are not dominant in the CO2 diffusion process. Instead, both the NMR determination and diffusion may be dependent on another process such as polymer swelling or plasticization. © 1990, American Chemical Society. All rights reserved.