Polymerization in supercritical carbon dioxide

A supercritical fluid (SCF) is a substance above its critical temperature and critical pressure. The critical temperature is the highest temperature at which a substance can exist as a gas. The critical pressure is the pressure needed at the critical temperature to liquify a gas. Above the critical temperature and critical pressure, a substance has a density characteristic of a liquid but the flow properties of a gas, and this combination offers advantages as a reaction solvent. The liquidlike density allows the supercritical fluid to dissolve substances, while the gaslike flow properties offer the potential for fast reaction rates. Supercritical carbon dioxide (scC02) has a critical temperature of 31°C and critical pressure of 73 atm. 

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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]. 

Z. Guan, Homogeneous free radical polymerization in supercritical carbon dioxide, University of... 

Guan, Z. Combes, J. R. Menceloglu, Y. Z. DeSimone, J. M. Homogeneous Free Radical Polymerizations in Supercritical Carbon Dioxide 2. Thermal Decomposition of 2,2 -Azobis(isobutyronitrile), Macromolecules 1993, 26, 2663-2669. 

Charpentier, P. A Kennedy, K. A. DeSimone, J. M. Roberts, G. W. Continuous Polymerizations in Supercritical Carbon Dioxide Chain-Growth Precipitation Polymerizations. Macromolecules 1999, 32, 5973-5975. 

Xia, J. H. Johnson, T. Gaynor, S. G. Matyjaszewski, K. DeSimone, J. Atom Transfer Radical Polymerization in Supercritical Carbon Dioxide. Macromolecules 1999, 32, 4802-4805. 

Kendall, J.L., D.A. Canelas, J.L. Young and J.M. DeSimone, Polymerizations in Supercritical Carbon Dioxide, Chemical Reviews, 99, 543-563 (1999). 

Dispersion polymerization in supercritical carbon dioxide (SCCO2), pioneered by DeSimone and coworkers, has recently attracted considerable attention as an environmentally friendly alternative to the use of organic solvents. A wide range of monomers have been polymerized to produce the corresponding microspheres in the presence of C02-philic polymers and monomers, as reviewed in another chapter. 

Unique PVDF properties have been observed after polymerization in supercritical carbon dioxide [38,51-53,55] at certain conditions. The polymer synthesized in supercritical carbon dioxide exhibits a bimodal molecular weight distribution (MWD), as illustrated in Fig. 4 [52]. At molar VF2 feed concentrations less than about 1.9 M, the polymer has a unimodal distribution, at the conditions of Fig. 4. As the monomer concentration is increased, the distribution becomes broader and bimodal. Changes in temperature, pressure, and residence time also have an effect on the MWD [51,52]. In Fig. 4, ris the average residence time (the reactor volume divided by the inlet volumetric flow rate). 

Professor DeSimone, is the pioneer of heterogeneous polymerizations in supercritical carbon dioxide. 

DeSimone JM, Maury EE, Menceloglu YZ, McClain JB, Romack TJ, Combes JR. Dispersion polymerizations in supercritical carbon dioxide. Science 1994 265 356-359. 

Kendall JL, Canelas DA, Young JL, DeSimone JM. Polymerizations in supercritical carbon dioxide. Chem Rev 1999 99 543-563. 

The development of fluoropolymers began with the invention of PTFE in 1938, continued to 1992 when a soluble perfluoropolymer (Teflon AF) was introduced, and to 2002 when fluoroplastics polymerized in supercritical carbon dioxide were introduced. Table 1.3 summarizes the timeline for the development of fluoropolymers that have brought about major changes in properties and/or fabrication processes. 

The interest in C02-based processes has strongly increased over the past decades. Fig. 1.3 shows the number of papers and patents that have been published over the years concerning polymerizations in supercritical carbon dioxide (SCCO2). In the last ten years, a substantial rise in publications can be observed, which illustrates the increasing interest in SCCO2 technology for polymer processes. 

I 6 Heterogeneous Polymerization in Supercritical Carbon Dioxide Table 6.3 (continued)... 

In this chapter, a comprehensive model of heterogeneous polymerization in supercritical carbon dioxide has been applied to two different systems, with the aim of elucidating the key mechanisms underlying the process. The main mod-... 

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