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 CO 2 were estimated as r VDF = 5.13 and r HFP ≈ 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 CO 2 than in VDF or HFP. In addition, F- g -PMVE-MA was found to act as a stabilizer for the copolymerization of VDF and HFP in scCO 2, leading to products with higher molecular weight and improved morphology.