Solubility of Poly (perfluoromonoitaconates) and Poly (perfluorodiitaconates) in Supercritical CO₂

Cloud-point data are reported at 25−150 °C and 100−560 bar for poly(perfluoromonoitaconates) (PFMIT_n) and poly(perfluorodiitaconates) (PFDIT_n, where n, the number CF₂ groups in the alkyl side chain, is equal to 3, 5, 7, and 9 for both types of itaconates) in supercritical CO₂. Cloud-point curves for the PFMIT_n−CO₂ system shift to lower pressures as the fluorinated alkyl tail length increases; however, this trend reverses going from PFMIT₇ to PFMIT₉. Hence, there is an optimum fluorocarbon side-chain length that balances energetic polymer−polymer, CO₂−CO₂, and polymer−CO₂ interactions with a favorable entropic effect associated with the increased free volume of the longer side chains. The PFDIT_n polymers readily dissolve in CO₂ at pressures as low as 140 bar at 25 °C, although, in this case, the cloud-point curves all superpose. The cloud-point data suggest that supercritical CO₂ is a suitable solvent for processing these fluoropolymers.