Supercritical carbon dioxide polymeric materials

E Dada, W Lau, RE Merritt, YH Paik, G Swift Synthesis of poly(acryUc acid)s in supercritical carbon-dioxide. Polymeric Materials Science and Engineering, Proceedings of the ACS Division of Polymeric Materials Science and Engineering, Vol. 74, 1996, p. 427. 

Reprinted from H. Yokoyama, L. Li, T. Nemoto, Tunable nanocellular polymeric monoliths using fluorinated block copolymer templates and supercritical carbon dioxide. Advanced Materials, 16 (17) (2004) 1542-1546 with permission from John Wiley and Sons. 

Supercritical carbon dioxide has been used as a dispersing medium for the manufacture and processing of polymeric materials. The process allows for the synthesis of high molar mass acrylic polymers in the form of micrometer-sized particles with a narrow size distribution. This procedure represents an environmentally responsible alternative to aqueous and organic dispersing media for heterogeneous dispersion polymerizations (Fox, 1994). 

In this special volume on polymer particles, recent trends and developments in the synthesis of nano- to micron-sized polymer particles by radical polymerization of vinyl monomers in environmentally friendly heterogeneous aqueous and supercritical carbon dioxide fluid media are reviewed by prominent worldwide researchers. Polymer particles are prepared extensively as synthetic emulsions and latexes, which are applied as binders in the industrial fields of paint, paper and inks, and films such as adhesives and coating materials. Considerable attention has recently been directed towards aqueous dispersed systems due to the increased awareness of environmental issues. Moreover, such polymer particles have already been applied to more advanced fields such as bio-, information, and electronic technologies. In addition to the obvious commercial importance of these techniques, it is of fundamental scientific interest to completely elucidate the mechanistic details of macromolecule synthesis in the microreactors that the polymer particles in these heterogeneous systems constitute. 

These data also indicate where reasonable care needs to be exercised in the use of supercritical carbon dioxide for cleaning applications. Amorphous materials can show significant uptakes of carbon dioxide depending upon the conditions employed. Secondly, even semicrystalline materials can show property changes that result from the absorption of carbon dioxide that ultimately affects the amount of crystallinity in the polymeric material. 

Sawan, S. P., Shieh Y. T., and Su, J. H., Evaluation of the interactions between supercritical carbon dioxide and polymeric materials, Los Alamos National Laboratory Report No. LA-UR-94- 2341, New Mexico 87545, USA... 

Water has been shown to be an effective solvent in some chemical reactions such as free radical bromination. Supercritical fluids such as liquified carbon dioxide are already commonly used in coffee decaffeination and hops extraction. However, supercritical carbon dioxide can also be used as a replacement for organic solvents in polymerization reactions and surfactant production. Future work may involve solventless or neat reactions such as molten-state reactions, dry grind reactions, plasma-supported reactions, or solid materials-based reactions that use clay or zeolites as carriers. 

Polymerization and Grafting onto Nanotubes Supercritical fluids are widely used in the manipulation of porous materials. Supercritical carbon dioxide can be used for the impregnation of carbon nanotubes with NVK and AIBN with subsequent polymerization. ... 

ENCAPSULATION PROCESSES WITH SUPERCRITICAL FLUIDS INTERACTIONS BETWEEN SUPERCRITICAL CARBON DIOXIDE AND COMMON POLYMERIC CARRIER MATERIALS... 

Variations in the thomal properties (v and vi from above) and the mechanical properties (vii from above) for polymaic materials are discussed sq arately in Sec. 3. This section details our results on sorption and swelling of polymers by carbon dioxide and the dissolution characteristics of various polymeric materials under a variety of conditions. A comparison will be shown for wdght change data of twenty different polymers that have been treated in both sub- and supercritical carbon dioxide at seven different conditions. These results are discussed in general to isolate important factors which affect the weight change (and possibly dimensions) of polymers. 

Different tedmological processes can be used and the choice largely depends on the properties of the material treated and no general rules can be given. The poor solubility of polymeric materials in supercritical carbon dioxide can constitute a severe limitation in the use of RESS process even if the adoption of different supercritical fluids can overcome the limitation. 

Supercritical fluids have also been used purely as the solvent for polymerization reactions. Supercritical fluids have many advantages over other solvents for both the synthesis and processing of materials (see Chapter 6), and there are a number of factors that make scCCH a desirable solvent for carrying out polymerization reactions. As well as being cheap, nontoxic and nonflammable, separation of the solvent from the product is achieved simply by depressurization. This eliminates the energy-intensive drying steps that are normally required after the reaction. Carbon dioxide is also chemically relatively inert and hence can be used for a wide variety of reactions. For example, CO2 is inert towards free radicals and this can be important in polymerization reactions since there is then no chain transfer to the solvent. This means that solvent incorporation into the polymer does not take place, giving a purer material. 

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