Fluoroalkyl Acrylate Polymerization in Carbon Dioxide

Historically the widespread use of liquid and supercritical CO2 has been limited by the low solubility of most nonvolatile materials at reasonably low pressures. However, studies carried out over a decade ago established the solubility of oligometric perfluoropolyethers and poly(chlorotrifluoroethylene) in liquid CO2, and a few years later it was discovered that other highly fluorinated polymers such as fluorinated acrylates were also quite soluble in liquefied CO2 at relatively low pressures.  

Seheme 1. Free radical polymerization of fluorocarbon acrylates in supercritical COj. 

Initiator decomposition studies of AIBN in supercritical CO2 carried out by DeSimone et al. showed that there is kinetic deviation from the traditionally studied solvent systems. These studies indicated a measurable decrease in the thermal decomposition of AIBN in supercritical CO2 over decomposition rates measured in benzene. Kirkwood correlation plots indicate that the slower rates in supercritical CO2 emanate from the overall lower dielectric constant (e) of CO2 relative to that ofbenzene. Similar studies have shown an analogous trend in the decomposition kinetics ofperfluoroalkyl acyl peroxides in liquid and supercritical CO2. Rate decreases of as much as 30% have been seen compared to decomposition measured in 1,1,2-trichlorotrifluoroethane. These studies also served to show that while initiator decomposition is in general slower in supercritical CO2, overall initiation is more efficient. Uv-visual studies incorporating radical scavengers concluded that primary geminate radicals formed during thermal decomposition in supercritical CO2 are not hindered to the same extent by cage effects as are those in traditional solvents such as benzene. This effect noted in AIBN decomposition in CO2 is ascribed to the substantially lower viscosity of supercritical CO2 compared to that ofbenzene.  

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De Simone et al. synthesized poly(fluoroalkyl acrylate)-based block copolymers for use as lipophilic/C02-philic surfactants for carbon dioxide applications [181]. The particle diameter and distribution of sizes during dispersion polymerization in supercritical carbon dioxide were shown to be dependent on the nature of the stabilizing block copolymer [182]. 

A Cu(II) complex with a bipyridine-type ligand (Cu-4) is effective in the controlled polymerization of styrene and acrylates in the presence of Al(0-i-Pr)3, which most probably serves as a reducing agent of Cu(II) into Cu(I).93-94 A fluoroalkyl-substituted bipyridine ligand (L-7) was also employed in supercritical carbon dioxide for the polymerization of fluorinated acrylates and methacrylates.95 Similar pyridine-based bidentate ligands, 1,10-phenanthroline and its... 

Both dJorofluorocarbons (CFCs) and carbon dioxide appear to be very good solvents for amorphous, low-melting fluoropolymers. Since environmental restrictions have limited the use of CFCs drastically, carbon dioxide has become a highly viable alternative solvent for the production of amorphous fluoropolymers [59]. Examples of polymerization of fluorinated monomers in a homogeneous reaction medium of SCCO2 are the polymerization of fluorinated acrylates (see, for example Refs. 59-61, fluoroalkyl-derivatized styrene [62], fluorinated vinyl and cyclic ethers [63], and the telomerization of 1,1-difluoroethylene [64]. Other options to run a... 

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