Continuous Copolymerization of Vinylidene Fluoride with Hexafluoropropylene in Supercritical Carbon Dioxide: High-Hexafluoropropylene-Content Amorphous Copolymers

Abstract

Copolymerization of vinylidene fluoride (VF2) and hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide using a continuous stirred tank reactor. Three different HFP/VF2 molar feed ratios were studied, 59:41, 66:34, and 73:27, giving rise to amorphous copolymers containing about 23, 26, and 30 mol % HFP, respectively. The experiments were carried out at 40 °C with pressures in the range of 207–400 bar using perfluorobutyryl peroxide as the free radical initiator. Depending on the copolymer composition, the molecular weight, and the reaction pressure, either a homogeneous (solution) or a heterogeneous (precipitation) polymerization was observed. The effects of feed monomer concentration and reaction pressure were 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, independent of the mode of polymerization, i.e., homogeneous or heterogeneous. Both R p and M n increased by about 20–30% when the reaction pressure was increased from 207 to 400 bar. This increase could be accounted for by the effect of pressure on the reaction rate constants. The molecular weight distributions were perfectly unimodal except for the lowest HFP-content copolymers at the highest monomer concentrations. The data suggest that the carbon-dioxide-rich fluid phase is the main locus of polymerization, even when the polymer precipitates during the reaction.

Controlled/living heterogeneous radical polymerization in supercritical carbon dioxide

“…2,64,82 Homogeneous polymerizations in scCO 2 (conventional or CLRP) of common vinyl monomers can be performed provided that the monomer concentration is sufficiently high (monomer acts as cosolvent), the MW of the polymer is sufficiently low, and/or that the pressure and temperature are high enough. 83 Such polymerizations correspond to the conditions in a precipitation/dispersion CLRP in scCO 2 before nucleation (below J crit ) where the system is homogeneous.…”

A dynamically distributed reactor model for identifying the flow fields in industrial loop propylene polymerization reactors

“…The quick rise of reactor temperature and pressure usually results in breakage of the reactor and consequent release of flammable fluids 7, 8. In addition, the reactor pressure influences the polymerization rate, feed rate, and product properties 9–11. Thus, control of reactor pressure and temperature are necessary 10–12.…”

“…In addition, the reactor pressure influences the polymerization rate, feed rate, and product properties 9–11. Thus, control of reactor pressure and temperature are necessary 10–12. On the other hand, to achieve an optimum performance for the complete PP preparation process, the reactor should be comprehensively optimized 13.…”

Photoinitiated precipitation polymerization in liquid CO2: Fast formation of crosslinked poly(acrylic acid‐co‐methoxy polyethylene glycol acrylate) microspheres

“…In recent years, supercritical carbon dioxide (scCO 2 ) has been used as reaction medium in precipitation polymerization15–21 because it is chemically inert, low cost, nonflammable, and nontoxic. Because of the necessary of heating in thermal initiated polymerization, carbon dioxide had to work under supercritical state, and pressure of 200 bar or higher was needed, leading to the requirements of high pressure and specialized equipment.…”