High-pressure NMR of polymers dissolved in supercritical carbon dioxide

High-pressure, high-resolution proton nuclear magnetic resonance spectroscopy has been utilized to study the solution behavior of poly(1,1-dihydroperfluorooctyl acrylate) (PFOA) and poly(1,1-dihydroperfluorooctyl acrylate-block-styrene) (PFOA-b-PS) in supercritical carbon dioxide. The proton chemical shift was monitored as a function of solvent density and temperature. A change in the solvent quality of CO2 from that of a poor solvent to that of a good solvent is postulated to describe a discontinuous change in the H-1 NMR spectra of the polymers with increasing CO2 density and increasing temperature. At a CO2 density of 0.7 g cm(-3) at 64.6 degrees C (0.8 g cm(-3) at 41.2 degrees C) there is an apparent transition between a two-phase system-the coexistence of two polymer species in different environments-and a homogeneous solution. The volume fraction of CO2 in the polymer-rich phase is estimated from the proton chemical shift and the contributions from the bulk susceptibilities of PFOA and PFOA-b-PS.