Abstract
Vinylidene fluoride (VDF) and hexafluoropropylene (HFP) were copolymerized in supercritical carbon dioxide (scCO2) 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 rVDF = 5.13 and rHFP ≈ 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 of VDF and HFP in scCO2, leading to products with higher molecular weight and improved morphology.
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