Intermolecular-Interaction-Dominated Solvation Behaviors of Liquid Monomers and Polymers in Gaseous and Supercritical Carbon Dioxide

The strong desire for the extensive application of supercritical carbon dioxide (scCO 2 ) as an environmentally benign solvent in polymers synthesis and processing has spurred numerous attempts to discern and improve its solvability toward monomers as well as polymers. The detailed solvation processes along with the phase behaviors of a fluorinated liquid monomer (LM) of 2,2,2-trifluoroethyl methacrylate (TFEMA), as well as another 13 non-fluorinated LMs in gaseous and supercritical CO 2, were respectively investigated by using a newly built high-pressure ATR-FTIR in situ monitoring system as CO 2 pressure stepwise increased from 0 to 38.0 MPa. Interestingly, an unexpected vibrational absorption variation, especially a distinct blue-shift in the in situ FTIR spectra of the functional groups in each LM + CO 2 binary system, was generally observed during the solvation process as CO 2 pressure increased. A similar variation trend of the vibrational absorption of the C–F bond in the TFEMA + CO 2 system was also obtained by ab initio calculation (MP2). We believe that the special evolution of the vibrational absorption is directly rooted in and dynamically induced by the variation of the intermolecular interactions in the LM + CO 2 binary systems as the pressure and/or the temperature varied and is closely related to the solvation behaviors of the LM in CO 2 . Based on this cognition, the solvation mechanism of the LMs in gaseous and supercritical CO 2 was systematically demonstrated by introducing the concepts of transition pressure ( P T ) as well as the resultant forces/interactions of σ(A–B) and σ(B–B). Poly(vinyl acetate) (PVAc), poly(hexafluoropropylene oxide) (PHFPO), and PTFEMA oligomers were prepared and characterized. The proposed mechanism was evaluated by investigating the solvation behaviors of the prepared oligomers and hexafluoropropylene trimer ((HFP) 3 ) in CO 2 and was successfully employed to expound the special CO 2 -philicity of the carbonyl compounds and the fluorinated organics (FOs).