Continuous Copolymerization of Vinylidene Fluoride with Hexafluoropropylene in Supercritical Carbon Dioxide:  Low Hexafluoropropylene Content Semicrystalline Copolymers

Abstract

The copolymerization of vinylidene fluoride with hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide by precipitation polymerization using a continuous stirred tank reactor. Copolymers with ca. 10 mol % HFP were synthesized at 40 °C and pressures in the range of 207−400 bar using perfluorobutyryl peroxide as the free radical initiator. The effects of feed monomer concentration and reaction pressure were both explored at otherwise constant conditions. The rate of polymerization (R p) and the number-average molecular weight (M n) increased linearly with the total monomer concentration up to about 6 M, the highest concentration investigated. The R p and the M n were strongly influenced by the reaction pressure. An 80% increase in both R p and M n was observed when the reaction pressure rose from 207 to 400 bar. The molecular weight distributions of the synthesized copolymer showed a long tail that increased to become a broad shoulder with increasing total monomer concentration. This tail increased with increasing reaction pressure. The data suggest that the carbon dioxide-rich fluid phase is the primary locus of polymerization.

Homogeneous Phase Copolymerizations of Vinylidene Fluoride and Hexafluoropropene in Supercritical Carbon Dioxide

“…In contrast, homopolymerizations of VDF and copolymerizations of VDF and HFP carried out in heterogeneous phase (precipitation) at lower pressures resulted in bimodal MWDs. [19,20,33] It can be concluded that adding HFP to the reaction mixture leads to successful solution copolymerizations at noticeably lower temperature and pressures than in the case of pure VDF (140 8C, 1 500 bar) for f HFP > 0.10.…”

Copolymerization of VDF and HFP in Supercritical Carbon Dioxide: A Robust Approach for Modeling Precipitation and Dispersion Kinetics

“…Finally, for reactions at constant initiator concentration (such as the copolymerization reactions in CSTR at different pressures reported by Ahmed et al14), the following equation can be worked out combining Equation 32 and 35: …”

“…In recent years, the heterogeneous free‐radical homopolymerization of vinylidene fluoride (VDF) and its copolymerization with hexafluoropropylene (HFP) have been the subject of several experimental studies. Precipitation,14–17 as well as dispersion polymerizations18–22 have been analyzed. The reason of such an interest is twofold.…”

Synthesis and Processing of Organic Materials in Supercritical Carbon Dioxide

“…20 The first continuous copolymerization of vinylidene fluoride (VDF) with hexafluoropropylene (HFP) in scCO 2 was recently reported to give semicrystalline copolymers. 22 This also has industrial significance, as VDF-HFP copolymers are an important class of materials with applications in tubing, valves, and membranes. 22 The excellent mass-transfer properties of scCO 2 mean that good molecular weight control is achievable in radical polymerization reactions.…”

“…22 This also has industrial significance, as VDF-HFP copolymers are an important class of materials with applications in tubing, valves, and membranes. 22 The excellent mass-transfer properties of scCO 2 mean that good molecular weight control is achievable in radical polymerization reactions. Gregory et al recently exemplified the controlled dispersion polymerization of methyl methacrylate through reversible addition fragmentation chain transfer (RAFT) in scCO 2 .…”