Surfactant Design for Inverse Emulsion Polymerization

As noted above, surfactants used in inverse emulsion polymerizations in CO2 must dissolve in CO2 and create micelles that solubilize the monomer. Therefore, one end of these bifunctional molecules must interact favorably (in a thermodynamic sense) with CO2, while the other interacts favorably with the monomer. Creation of suitable hydrophiles for these molecules has been straightforward, while design of the C02-phihc portion has been difficult, and even at present cannot be considered to be an entirely solved problem. Thus, we consider the design of C02-philes in more depth. 

Designing C02-phiiic Compounds What Can We Learn from Fiuoropoiymer Behavior  

Fried and Hu used MP2 calculations (6-31-r+G basis set) in an effort to identify the nature of spedfic interactions between CO2 and fluorinated substituent groups on polymers [20]. They reported that quadrupole-dipole interactions are important contributors to the total energy of interaction. In experimental studies by McHugh et al., the favorable misdbihty of fluorocarbons has also been attributed to polar-quadrupole interactions [21]. The authors noted that fluorination imparts solubihty to the polymer provided that polarity is also introduced to the polymer via such fluorination. Too high a level of fluorination produces an adverse effect on miscibihty due to dominance of dipole-dipole interactions between the polymer chains [22]. 

Clearly, there is considerable controversy in the hterature surrounding the origin of the miscibility of some fluorinated polymers in CO2, yet there do seem to be some interesting lessons to be learned from this work regarding C02-phile design, namely  

In summary, combinations of theory and experiment are rapidly advancing our ability to design cost-effective C02-philic materials and hence surfactants that are both economical and effective. We would propose the following molecular characteristics for a C02-phile  

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