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Extramural Research

1999 Progress Report: Nonionic Surfactants for Dispersion Polymerizations in Carbon Dioxide

EPA Grant Number: R826115
Title: Nonionic Surfactants for Dispersion Polymerizations in Carbon Dioxide
Investigators: DeSimone, Joseph M.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Karn, Barbara
Project Period: November 1, 1997 through October 31, 2000
Project Period Covered by this Report: November 1, 1998 through October 31, 1999
Project Amount: $370,000
RFA: Technology for a Sustainable Environment (1997)
Research Category: Nanotechnology , Pollution Prevention/Sustainable Development

Description:

Objective:

More than 30 billion pounds of organic and halogenated solvents are used worldwide each year as process aids, cleaning agents, and dispersants. Solvent-intensive industries are considering alternatives that can reduce or eliminate the negative impact that solvent emissions can have on the environment. Recently, the design and synthesis of surfactant molecules that are active in CO2 has enabled a variety of new processes that will reduce hazardous waste production and emission. With this innovation, we have demonstrated that CO2 can be used as a replacement for more hazardous volatile organic compounds (VOCs) and chlorofluorocarbons (CFCs) that are traditionally used as solvents in the polymer industry. The key feature of this work has been the rational design and utilization of surfactants, or soaps, that are amphiphilic and interfacially active in a CO2 continuous phase. It is apparent that the widespread use of CO2 by industries will depend strongly on the design and efficient synthesis of effective surfactants (amphiphilic macromolecules that act as soaps in CO2) for a variety of applications. This pursuit is the main focus of this research.

Progress Summary:

Recent efforts to synthesize methyl methacrylate (MMA) by dispersion polymerization in CO2 investigated the influence of helium concentration in CO2 on the resulting poly(methyl methacrylate) (PMMA) particle sizes and distribution (Hsiao and DeSimone, 1997). This study was important because many CO2 supply tanks are sold with a helium head pressure. It was found that the presence of 2.4 mol% helium in CO2 increased the PMMA average particle diameters from 1.9 to 2.7 µm, while decreasing particle size distribution from 1.29 to 1.03 µm. The reason for these effects has been ascribed to the decreased solvency imparted to the CO2 by the dissolved helium.

The dispersion polymerization of styrene in supercritical CO2 using various stabilizers has been studied in detail. Using a surfactant with a poly(styrene) (PS) anchoring block and a polydimethylsiloxane (PDMS) soluble block (PS-b-PDMS), spherical PS particles were obtained (Canelas and DeSimone, 1997). The resulting high yield (>90 percent) of PS was obtained in the form of a dry, free-flowing powder comprised of submicron-sized particles. The affinity of the amphiphilic diblock copolymers for the PS particle surface was confirmed by interfacial tension measurements in a CO2 continuous phase (Harrison, et al., 1998). The anchor-to-soluble balance (ASB), or ratio of the two block lengths, of the PS-b-PDMS stabilizer was found to be a crucial factor affecting both the stability of the resulting latex in CO2 and the particle morphology (Canelas and DeSimone, 1997). The monomer and stabilizer concentration affected the morphology of the resulting PS particles. Additionally, the temperature and pressure of the reaction mixture were found to affect results, such as average particle diameter and molecular weight, of the PS product.

Using random copolymers including 1,1-dihydroperfluorooctyl methacrylate (FOMA), styrene, and 3-[tris(trimethylsilyloxy)silyl]propyl methacrylate (SiMA), the dispersion polymerization of styrene was investigated (Shiho and DeSimone, 1999a). Spherical and relatively uniform, micron-size PS particles were obtained in high yield using various amounts of the random copolymers as a stabilizer. Although the copolymers with styrene can be good stabilizers when the incorporated ratio of FOMA is high (>92 weight/weight percent), the copolymers with SiMA can indeed be good stabilizers, even when the incorporated ratio of FOMA is as low as 26 weight/weight percent. The particle diameter was shown to be dependent on the percent of FOMA incorporated in the stabilizer and the weight percent of added stabilizer.

The successful cationic dispersion polymerization of styrene in liquid carbon dioxide using amphiphilic block copolymers has been reported (Clark and DeSimone, 1997). Vinyl ether block copolymers consisting of a CO2-philic fluorinated segment and a poly(methyl vinyl ether) anchoring segment were employed to stabilize the growing PS particles. The effect of stabilization in these polymerizations on molar mass, molar mass distribution, and polymer yield was studied as a function of temperature and surfactant composition. Scanning electron microscopy confirmed the formation of PS particles ranging in size from 300 nm to 1 µm in diameter.

The preparation of stable dispersions of poly(vinyl acetate) (PVAc) and ethylene-vinyl acetate copolymers in liquid and supercritical CO2 recently has been investigated (Shiho and DeSimone, 1999a; Canelas, et al., 1997; Canelas, et al., 1998). Both fluorinated and siloxane-based stabilizers, including homopolymers, block copolymers, and reactive macromonomers were employed. The vinyl acetate polymerization stabilized by PDMS homopolymer, vinyl-terminated PDMS macromonomer, or PVAc-b-PDMS all produced collapsed latexes of high yield and high molecular weight polymer, whereas the polymerization stabilized by PVAc-b-PFOA provided stable latexes. Turbidity showed that PFOA and PVAc-b-PFOA with a short anchoring group (PVAc Mn = 4 x 103 g/mol) inefficiently anchored to the PVAc particles. The PVAc-b-PFOA with the longest blocks (PVAc Mn = 3.1 x 104 g/mol; PFOA Mn = 5.4 x 104 g/mol) produced the smallest diameter polymer particles.

We recently have reported the successful dispersion polymerization of acrylonitrile in carbon dioxide using a block copolymer consisting of polystyrene and poly(1,1-dihydroperfluorooctyl acrylate) as a stabilizer (Shiho and DeSimone, 1999b).

The dispersion polymerization of 1-vinyl-2-pyrrolidone in supercritical CO2 has been examined using poly(1,1-dihydroperfluorooctyl acrylate) (PFOA) as a polymeric stabilizer. The polymerizations produced stable latexes that resulted in high yields of polymer with high molecular weights (MW = 3.1 x 106 g/mol). Spherical and relatively uniform particles were formed with diameters ranging from 0.56 to 2.89 m, while the surfactant concentration was varied from 0.25 to 6 weight/volume percent. Upon increasing the initial concentration of the monomer from 20 to 60 weight/volume percent, the latex stability decreased, while the particle size increased.

We have illustrated the use of temperature and solvent quality to regulate the degree of association of block copolymer amphiphiles in highly compressible supercritical carbon dioxide (Triolo, et al., 1999). Small angle neutron scattering (SANS) has been used to examine the association behavior of a block copolymer containing a CO2-phobic moiety, poly(vinylacetate), and a CO2-philic block, poly(1,1-dihydroperfluorooctyl acrylate). By adjusting the density of the medium through pressure and temperature profiling, the self-assembly can be reversibly controlled from unimers to core-shill spherical micelles; this establishes a critical micelle density (CMD), a phenomenon distinctive of highly compressible fluids, such as supercritical CO2.

The behavior of polymeric surfactant PVAc-b-poly(1,1,2,2-tetrahydroperfluorooctyl acrylate) (PTAN) in supercritical CO2 was investigated using static and dynamic light scattering (Triolo, et al., 1999). We observed three regions on the phase diagram of the copolymer in supercritical CO2: (1) two-phase region at low CO2 density, (2) solutions of spherical micelles at intermediate CO2 densities, and (3) solutions of unimers (individual copolymer chains) at high CO2 densities. This light-scattering study is the first to report a solvent density-induced transition between spherical micelles at lower supercritical CO2 density and unimers at higher CO2 density. The light-scattering technique appears to be a very powerful tool for the analysis of the carbon dioxide density-induced micellization transition.

Future Activities:

We intend to study more fundamental aspects of reversible self-assembly of amphiphilic block copolymers in CO2 as a function of temperature, CO2 density, and composition of block segments.


Journal Articles on this Report : 9 Displayed | Download in RIS Format

Other project views: All 21 publications 15 publications in selected types All 15 journal articles

Type Citation Project Document Sources
Journal Article Buhler E, Dobrynin AV, DeSimone JM, Rubenstein M. Light scattering study of diblock copolymers in supercritical carbon dioxide CO2 density-induced micellization transition. Macromolecules 1998;31(21):7347-7355. R826115 (1999)
R826115 (Final)
not available
Journal Article Canelas DA, DeSimone JM. Dispersion polymerizations of styrene in carbon dioxide stabilized with poly(styrene-b-dimethylsiloxane). Macromolecules 1997;30:5673-5682. R826115 (1999)
R826115 (Final)
not available
Journal Article Canelas DA, Betts DE, DeSimone JM. Preparation of poly(vinyl acetate) latexes in liquid and supercritical carbon dioxide. Polymer Preparation (American Chemical Society, Division of Polymer Preparation) 1997;38:628-629. R826115 (1999)
R826115 (Final)
not available
Journal Article Canelas DA, Betts DE, DeSimone JM, Yates MZ, Johnston KP. Poly(vinyl acetate) and poly(vinyl acetate-co-ethylene) latexes via dispersion polymerizations in carbon dioxide. Macromolecules 1998;31(20):6794-6805. R826115 (1999)
R826115 (Final)
not available
Journal Article Carson T, Lizotte J, DeSimone JM. Dispersion polymerization of 1-vinyl-2-pyrrolidone in supercritical carbon dioxide. Macromolecules 2000, Volume: 33, Number: 6 (MAR 21), Page: 1917-1920. R826115 (1999)
R826115 (Final)
not available
Journal Article Clark MR, DeSimone JM. Cationic dispersion polymerizations in liquid carbon dioxide. Macromolecules 1997;30:6011-6014. R826115 (1999)
R826115 (Final)
not available
Journal Article Harrison KL, da Raocha SRP, Yates MZ, Johnston KP, Canelas DA, DeSimone JM. Interfacial activity of polymeric surfactants at the polystyrene-carbon dioxide interface. Langmuir 1998;14:6855-6863. R826115 (1999)
R826115 (Final)
not available
Journal Article Hsiao YL, DeSimone JM. Dispersion polymerization of methyl methacrylate in supercritical carbon dioxide: Influence of helium concentration on particle size and particle size distribution. Journal of Polymer Science Part A-Polymer Chemistry 1997;35(10):2009-2013
abstract available  
R826115 (1999)
R826115 (Final)
not available
Journal Article Shiho H, DeSimone JM. Dispersion polymerization of acrylonitrile in supercritical carbon dioxide. Macromolecules 1999;33(5):1565-1569. R826115 (1999)
R826115 (Final)
not available
Supplemental Keywords:

carbon dioxide, VOC, CFCs, alternatives, innovative technology, waste reduction, waste minimization, environmentally conscious manufacturing., RFA, Scientific Discipline, Sustainable Industry/Business, cleaner production/pollution prevention, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Economics and Business, Chemistry and Materials Science, cleaner production, non-ionic surfactants, environmentally benign solvents, dispersion polymerization, emission controls, green process systems, carbon dioxide, plastic, chlorofluorocarbons, pollution prevention, source reduction, Volatile Organic Compounds (VOCs), polymer design, green chemistry, solvents, polymeric coatings

Relevant Websites:

http://www.unc.edu/depts/chemistry/faculty/desimone/resact.htm Exit EPA icon
http://www.nsfstc.unc.edu Exit EPA icon
http://www2.ncsu.edu:80/champagne/Exit EPA icon

Progress and Final Reports:
Original Abstract
2000 Progress Report
Final Report

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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