Impact of hexafluoroisopropylidene on the solubility of aromatic-based polymers in supercritical fluids

Three different supercritical fluids (SCF), CO2, dimethyl ether (DME), and propane, are investigated as potential solvents for processing two lactide-based terpolymers and two perfluorocyclobutyl (PFCB) aryl ether polymers. The repeat unit of the lactide-based terpolymers consists of a 1:1:1 ratio of L-lactide, diglycidyl ether of bisphenol A (DGEBA), and, in one case, 4,4ʹ-hexafluoroisopropylidenediphenol (6F-Bis-A) and, in the other case, 4,4ʹ-isopropylidenediphenol (6H-Bis-A). The PFCB-based polymers are synthesized from 1,1-bis[4-[(trifluorovinyl)oxy]phenyl]hexafluoroisopropylidene (6FVE) and from bis(trifluorovinyloxy)biphenyl (BPVE). For both classes of polymer the steric effect of the hexafluoroisopropylidene (6F) group reduces chain-chain interactions, disrupts electronic resonance between adjacent aromatic groups, and improves solubility. The two lactide-based terpolymers do not dissolve in CO2 or propane, but dissolve in DME. At room temperature the poly(lactide 6F-BisA DGEBA) terpolymer dissolves at 700 bar lower pressure in DME compared to the poly(lactide 6H-Bis-A DGEBA) terpolymer. Although the 6FVE polymer dissolves in all three SCF solvents, pressures in excess of 800 bar are needed to dissolve this polymer in CO2 and propane while 6FVE dissolves in DME at pressure below 150 bar. The other PFCB-based polymer (BPVE) only dissolves in DME, again at low pressure, although BPVE drops out of solution as the system temperature is raised above ~ 40 (degree) C, whereas 6FVE remains in solution in DME for temperatures up to 90 (degree) C.