Spectroscopic investigations of polymers processed by high pressure and supercritical carbon dioxide

Supercritical CO2, which is nontoxic, nonflammable, and environmentally benign, represents an attractive alternative to many traditional solvents for processing polymers. Supercritical CO2 offers enhanced mass transport properties which, along with its solvent strength, can be adjusted by simply changing the temperature and pressure of the system. Many polymers sorb significant amounts of CO2 inducing swelling and plasticization of the polymer matrix, resulting in an increase in the polymer's free volume and decreases in the glass transition and melting temperatures of the polymer. These properties may also be adjusted by changing the conditions of the supercritical CO2. To utilize supercritical CO2 effectively for processing polymers, it is imperative to understand the effects of CO2 on the polymer, and the resulting changes in the mass transport rates and thermodynamic partitioning of solutes within the polymer.; In this thesis we develop and apply spectroscopic techniques for gaining insight into the effects of CO2 on polymers and quantifying the resulting changes on solute mass transport rates and partitioning between the fluid and polymer. Transmission FTIR spectroscopy has been applied to eluicidate evidence of CO2 induced plasticization of PMMA, which results from increased mobility of the polymeric chains. FTIR, UV/visible, and RAMAN spectroscopy were then applied to quantify how process conditions, and resulting changes in polymer properties, affect dye uptake into polymers. A novel FTIR technique utilizing the near infrared region was then used to measure the sorption of CO2 into PET, and ATR-IR and RAMAN spectroscopies were applied to characterize the crystallinity of PET resulting from CO 2 processing. Finally, FTIR and UV/visible spectroscopy were utilized to investigate the effects of cosolvents on solute partitioning between a supercritical fluid and cross-linked rubbery polymer. These results were modeled with the Sanchez-Lacombe lattice fluid equation of state, and applied to calculate the stationary phase effects in supercritical fluid chromatography.