Copolymerization of vinylidene fluoride and hexafluoropropylene in supercritical carbon dioxide

Vinylidene fluoride (VDF) and hexafluoropropylene (HFP) were copolymerized in supercritical carbon dioxide (scCO(2)) by a free radical mechanism with and without the use of a fluorinated graft poly(methyl vinly ether-alt-maleic anhydride) copolymer (F-g-PMVE-MA) stabilizer. A series of VDF-HFP copolymers, with composition varying from 1.46 to 25.62 mol % (HFP in copolymer), were synthesized with yields in the range 25-54 wt %. The reactivity ratios of VDF and HFP in CO2 were estimated as r(VDF) 5.13 and r(HFP) approximate to 0. The weight-average molecular weights of copolymers, relative to narrow standard poly(methyl methacrylate), were between 35 and 188 kg/mol, and the polydispersity was between 1.4 and 3.1. A solubility study demonstrated that VDF-HFP copolymers were more soluble in CO2 than in VDF or HFP. In addition, F-g-PMVE-MA was found to act as a stabilizer for the copolymerization.