Impact of Hexafluoroisopropylidene on the Solubility of Aromatic-Based Polymers in Supercritical Fluids

ABSTRACT: Three different supercritical fluids (SCF), CO2, dimethyl ether (DME), and propane, are investigated as potential solvents for processing two lactide-based ter-polymers 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 bis-phenol A (DGEBA), and, in one case, 4,4-hexafluoroiso-propylidenediphenol (6F-Bis-A) and, in the other case, 4,4-isopropylidenediphenol (6H-Bis-A). The PFCB-based polymers are synthesized from 1,1-bis[4-[(trifluoroviny-l)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 elec-tronic 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) ter-polymer dissolves at 700 bar lower pressure in DME com-pared to the poly(lactide 6H-Bis-A DGEBA) terpolymer. Although the 6FVE polymer dissolves in all three SCF sol-vents, 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 pres-sure, although BPVE drops out of solution as the system temperature is raised above 40°C, whereas 6FVE remains in solution in DME for temperatures up to 90°C. © 2005 Wile