Supercritical carbon dioxide was used as a solvent to produce polymeric films on fused silica plates and metal (Al, Mg) powders. Two polymers, poly(vinylidene fluoride) and poly(4-vinylbiphenyl) (PVB), were used. Polymer-coated particles of metal powders exhibit enhanced resistance to the dissolution in aqueous basic and acidic solutions. The protective properties of the films were quantified based on the dissolution rate. The average thickness of the PVB films (that contain aromatic rings) was evaluated using UV absorption spectroscopy. A technique to measure the solubilities of poorly soluble polymers in supercritical carbon dioxide was developed. The effect of the coating conditions on the protective properties of the produced polymeric films was evaluated.
Ind.Eng.Chem.Res. 2001, v.40, No.19, pp. 4058-4068

A novel method based on ex situ dispersion of silver nanoparticles within the monomers and subsequent emulsion polymerization using water-in-sc-CO2 medium is introduced in this paper. Silver nanoparticles were synthesized by chemical reduction of silver nitrate using sodium borohydrate as a reducing agent and polydimethylsiloxane (PDMS) as a stabilizer in the water-in-sc-CO2 medium. The stable dispersion of silver nanoparticles was added slowly during the polymerization of styrene in the water-in-sc-CO2 maintaining the temperature at 70oC and pressure at 20.68MPa respectively. The silver nanoparticles encapsulated within polymer particles were characterized by UV-visible spectroscopy, XRD, TGA, SEM and TEM. The silver/polystyrene nanocomposite particles exhibited antimicrobial activity against a number of bacteria. The current work represents a simple, reproducible and universal way to prepare a variety of metal–polymer nanocomposite particles.

Copper encapsulated polystyrene nanocomposite particles were prepared through ex-situ dispersion of Cu nanoparticles into monomer droplets and subsequent polymerization using water-in-sc-CO2 at 70oC. First, colloidal dispersion of copper nanoparticles were synthesized by chemical reduction of copper chloride (CuCl2) using sodium borohydrate (NaBH4) as reducing agent. Colloidal dispersion of copper nanoparticles was added slowly during the polymerization of styrene using water-in-sc-CO2 medium at 70oC and 20.68 MPa. Cu nanoparticle encapsulated polymer particles were characterized by UV, XRD, TGA, SEM and TEM. Cu nanoparticles were uniformly distributed inside the polymer matrix during the polymerization process. This work represents a simple way to prepare a variety of metal nanoparticles encapsulated polymer particles using water-in sc-CO2 medium. The Cu/polystyrene nanocomposite particles exhibit antimicrobial activity against a number of bacteria. The current work represents a simple and universal way to prepare a variety of metal–polymer nanocomposite materials.

Reported herein is the synthesis of stable dispersion copper nanoparticles by chemical reduction of Copper Chloride (CuCl2) in a water-in supercritical carbon dioxide (sc-CO2) medium using sodiumborohydrate (NaBH4) as reducing agent, polydimethylsiloxane (PDMS) as the stabilizer and Sodium (bis-2ethylhexyl) sulfosuccinate(AOT) as co-surfactant at temperature 40 o C and pressure in the range of 2000 psi-2400psi. UV-visible spectroscopy exhibits a typical emission peak at 560-590 nm for Cu nanoparticles. By changing the reaction pressure and the stabilizer concentration, the size and the shape of the copper nanoparticles could be easily controlled. The X-ray diffraction pattern reveals that the Cu nanoparticles formed in the range of 4-8 nm which are in consistent with the TEM images.

We have synthesized microparticles of polymer by emulsion polymerization of styrene in supercritical carbon dioxide (sc-CO2) using (polydimethylsiloxane) (PDMS) as a surfactant/stabilizer and azobisisobutyronitrile (AIBN) as initiator. The emulsion polymerization was carried out at different pressures (2000-2600 psi). At the end of polymerization, powdered polymeric micoparticles were collected by depressurizing CO2. The powdered polymeric microparticles were characterized by SEM, GPC, DSC and TGA. The influence of pressure on conversion, molecular weight, particle size and polydispersity index was studied. The molecular weight (Mn) of the polymer is in the range of 35,542 to 45,078 g/mol. Polydispersity is in the range of 1.45-1.86 and particle size in the range of 3.25m-6.3m.
DOI: 10.1080/10426914.2010.491008

Herein we report the successful emulsion polymerization of styrene monomers in supercritical carbon dioxide (sc-CO2) using (trifluoromethyl)undecafluorocyclohexane (C7F14) as a stabilizer and azobisisobutyronitrile (AIBN) as initiator. The emulsion polymerization was carried out using different percentage of stabilizers (0.2%-10%), different initiator concentrations (0.1%-0.5%) and different pressures (2100-2500 psi). The polymers were characterized by GPC, SEM and TGA. The influence of different process parameters (stabilizer concentration, initiator concentration and pressure of CO2) on conversion, molecular weight, particle size and polydispersity index was elaborately studied. Molecular weight of the polymer is in the range of 32,000 to 55,000g/mol, polydispersity is 1.43-2.33 and particle size in the range of 0.15m-1.0m.