Polymerization of fluoroolefins

Although the technological basis of all fluorine-containing plastics and most elastomers continues to be the free radical polymerization of fluoroolefins, which themselves are based on the vastly greater fluorocarbon refrigerant industry, important advances have been made in the past two decades These include primarily the production of polymers that are more resistant to degradation by heat, oxidation, bases, and solvents, as well as polymers that are more easily processable, that is, able to be converted mto their final forms for use, whether by thermoplastic or thermoset processes [1,2,3,4]... 

Indeed, free radical polymerization of fluoroolefins continues to be the only method which will produce high-molecular weight fluoropolymers. High molecular weight homopolymers of TFE, CFC1 = CF2, CH2CF2, and CH2=CHF are prepared by current commercial processes, but homopolymers of hexafluoro-propylene or longer-chain fluoroolefins require extreme conditions and such polymerizations are not practiced commercially. Copolymerization of fluoroolefins has also led to a wide variety of useful fluoropolymers. Further discussion of the subject of fluoroolefin polymerization may be found elsewhere and is beyond the scope of this review [213-215]. 

Heterogeneous Polymerization of Fluoroolefins in Supercritical Carbon Dioxide... 

Heterogeneous Polymerization of Fluoroolefins in Supercritical Carbon Dioxide 331 Table 1 Critical temperatures and pressures of substances useful as supercritical fluids [9]... 

The first reported polymerization of fluoroolefins in carbon dioxide was by Fukui and coworkers [39,40]. Tetrafluoroethylene, chlorotrifluoroethylene,and other fluoroolefins were polymerized in the presence of CO2 using ionizing radiation [39, 40] and free-radical initiators [40]. DeSimone and coworkers reported the homogeneous telomerization of tetrafluoroethylene [41] and vinylidene fluoride [42] in CO2 using AIBN as an initiator. The kinetics of AIBN decomposition in CO2 is well understood [4]. However, peroxide initiators are preferred over azo initiators for producing stable endgroups in fluoroolefins... 

The peroxy initiators bis(perfluoro-2-Ar-propoxypropionyl) peroxide (BPPP) and diethyl peroxydicarbonate (DEPDC) have had the greatest application in the heterogeneous polymerization of fluoroolefins in CO2. 

Romack TJ (1997) Polymerization of fluoroolefins in liquid and supercritical carbon dioxide (free radical). PhD Thesis, University of North Carolina at Chapel HUl, Chapel Hill,NC... 

Polymerization of fluoroolefins in liquid and supercritical carbon dioxide eliminates the use of water and C-8 surfactant that has been identified as a persistent organic pollutant (R. Carbonell) ... 

The principal method for synthesizing fluoropolymers is free radical polymerization, as the other typical methods, for example, cationic polymerization proves ineffective, due to the electrophilic nature of fluoroolefins. Fluoroolefins can be polymerized by anionic catalysts, but termination by fluoride ion elimination prevents formation of high molecular weights. Coordination catalysts do not effect polymerization of fluoroolefins. 

Some examples will illustrate the polymerization of fluoroolefins in supercritical carbon dioxide medium. 

---