Mixtures of CO2 and poly(fluoroacrylate) based on monomers containing only six or four fluorinated carbons: Phase behavior and solution viscosity

Abstract

Homopolymerization of fluoroacrylate monomers containing a segment with eight fluorinated carbons, (CH2CHCOO(CH2)2(CF2)7CF3), yield poly(fluoroacrylate) (PFA) with remarkably high solubility in CO2, but the corresponding ultimate PFA degradation product perfluorooctanoic acid (PFOA) is bio-accumulative. Based on cloud point loci in the 1–4 wt% PFA in CO2 concentration range at temperatures of 25, 50, 75, 100 and 125 oC, it is shown that C6F13-based and C4F9-based PFA, with relatively benign degradation products perfluorohexanoic acid (PFHxA) and perfluorobutanoic acid (PFBA), respectively, retain the same level of CO2-solubility as that of C8F17-based PFA. Further, both C6F13-based and C4F9-based PFA can increase the viscosity of single-phase CO2-PFA solutions (i.e. thicken CO2) as much as C8F17-based PFA in the 25–125 oC range. Therefore, the design of CO2-soluble PFA need not be constrained to monomers containing the C8F17 moiety; fluoroacrylate monomers containing shorter fluoroalkyl segments with only four or six fluorocarbons can be utilized.