With collaboration and financial support of NASA-Johnson Space Center (Houston, Texas), Dr. Caneba’s group has recently embarked on research involving polymer composites with single-wall carbon nanotubes (SWCNTs). Continuous fibers of SWCNTs have been shown to be 100 times stronger than steel and 17 times stronger than Kevlar™ per weight. They also possess similar thermal and electrical conductivities compared some metals, while their density is just over 2 g/cm3. Even though they currently cost about $800 per gram, they are suitable in space applications and they exhibit dramatically enhanced properties at relatively low loadings (about 0.5 wt % in a polymer composite). The key is to be able to attain its percolated structure by proper dispersion of SWCNT bundles.

Current efforts in this area involve the formulation of SWCNT/high performance polymer composites as components of fuel cells in space missions. Also, efforts are underway to develop SWCNT-based lightweight dosimeters for the international space station (ISS). Finally, research is ongoing for the development of lightweight radiation shields and thermal films.

With funding from the National Science Foundation through the Nanoscale Science and Engineering – Nanoscale Undergraduate Education (NSE-NUE) Program, education of undergraduate students regarding SWCNT/polymer composites as well as societal aspects of various nanotechnology systems are currently ongoing.

The focus of this effort is the free-radical retrograde-precipitation polymerization (FRRPP) process that Dr. Caneba discovered in the late 1980s. Here, polymerization occurs above the lower critical solution temperature (LCST). The local heating that occurs in exothermic chain polymerization reactions places FRRPP systems closer to the spinodal curve, wherein diffusional mass fluxes have been found to vanish. Apparently, even the more mobile monomer and solvent molecules cannot diffuse from high-concentration to low-concentration regions that are adjacent to the reactive sites. Also, an apparent reduction of heat transfer rate from the reactive sites has been found to occur in the system. The underlying reason for the heat-trapping phenomenon is still in question, but it might be rooted from the observed nanometer-scale features of the reactive sites.

Other apparent results of the FRRPP process are efficient trapping of polymer radicals, relatively narrow molecular weight distributions, stable molecular weight and polydispersity index, reduced conversion rate, and persistence of nanometer-scale polymer-rich domains. Materials from and variants of the FRRPP process are the basis of the following industry, federal, and state-funded applied oriented projects.

Block Copolymer Emulsions

Styrene- and methyl methacrylate-based block copolymer emulsions in water have been efficiently produced from the FRRPP process. Typical products are specialty adhesives, low VOC paints and coatings, and even intermediate latices with relatively stable polymer radicals. These intermediate polymer (polystyrene or poly(methyl methacrylate)) radical emulsions can be used to generate various block copolymers by addition of another monomer mixture.

Controlled Statistical Free-Radical Copolymerization

In conventional statistical free-radical copolymerization, monomer reactivity ratios and addition protocol dictate monomer distribution in the resulting polymer chains. In a selectively precipitating medium that also involves radical trapping and molecular weight control, a more effective monomer distribution control in the product copolymer has been obtained. An example product is a sharply tapered vinyl acetate/acrylic acid block copolymer that was produced in a single-stage operation; this indicates a segmental self-assembly mechanism. Also, vinyl acetate/acrylic acid copolymers were produced with equal acrylic acid spacing in a group of vinyl acetate segments (roughly one acrylic acid segment per 10 vinyl acetate segments). These materials have been proposed to have the following unique applications: coupling agent for plastics-natural fiber composites, surfactants for oil recovery, soil remediation, water-based degreasers, biodegradable plastic materials and foams, froth flotation for iron and copper processing, wood preservation, longterm water-dispersible adhesives, water-based coating primers, silicone-organic coatings, and water-based pesticide formulations.

Radiation-Initiated FRRPP

If the reaction rate in FRRPP systems is under control, then it means that polymer-rich domain growth will also be under good control if domain interaction is minimized. If the reaction is carried out in a quiescent fluid, then one should expect the formation of nanometer-scale particles. Indeed, morphological and X-ray scattering experimental results confirm this hypothesis. Nanometer-scale particles produced by this method could be used in bioseparations and drug delivery systems.

If polymerization is induced by radiation with nanometer-sized wavelengths, it is possible to control the dimensional features of the polymer product within the radiation zones.

It is evident that this approach (bottom-up method) is different from established lithographic methods (top-down approaches); which involve casting a polymer film, irradiating the film, and then dissolving away irradiated or unirradiated regions. The FRRPP-based bottom-up method produces nanometer-scale polymer structures from the monomer in situ, using low-wavelength low-divergence directed radiation (such as that of the synchrotron X-ray source at Argonne National Laboratory) for free-radical initiation. Current results are microlithographic patterns of pure thermoreversibe hydrogels that can be used in microfluidic and tissue engineering systems.

Enhanced Oil Recovery

At a time of uncertainty in foreign crude oil supplies, decreasing domestic oil production, and projected increases in demand for petroleum products, there is a need for new technologies to efficiently recover more of the oil-originally-in-place (OOIP) from existing oilfields in an environmentally responsible fashion. Around 300 billion barrels of oil is recoverable in the United States using enhanced recovery methods.

Newly-discovered vinyl acetate-acrylic copolymers from the FRRPP process are being investigated as surfactant/thickener for secondary and tertiary oil recovery operations. In secondary operations, recoveries of up to 90% of oil from water-wet formations were obtained with a sharp breakthrough and copolymer consumption of 1 lb per barrel of oil produced. As a foaming surfactant, the copolymer was found to outperform commercially available anionic and nonionic surfactants per lb of usage. These performance results are accompanied by the competitive cost of the copolymer compared to lower priced oil recovery surfactants in the market.

Recent Publications

Y. Dar and G.T. Caneba, “Transport Phenomena Aspects of the Free-Radical Retrograde-Precipitation Polymerization (FRRPP) Process”, Chemical Engineering Communications, 189, 571 (2002).

R. Saxena, L. Shi, and G.T. Caneba, “Studies of Spinodal Decomposition in a Ternary Polymer-Solvent-Nonsolvent System”, Polymer Engineering and Science, 42, 1019 (2002).
G.T. Caneba, Y. Zhao, and Y. Dar, “Amphiphilic Styrene-Acrylic Acid Copolymers from Free-Radical Retrograde-Precipitation Polymerization (FRRPP)”, ACS Polymer Preprints, 43(2) 156 (2002).

G.T. Caneba and Y.L. Dar, “Free-Radical Retrograde Precipitation Copolymers and Process for making the Same”, submitted to U.S. Patent and Trademark Office, January, 2002, Publication 2003/0153708..

G.T. Caneba, and J.E. Axland, “Vinyl Acetate-Acrylic Acid-based Copolymers for Enhanced Oil Recovery”, The Journal of Minerals and Materials Characterization and Engineering, 1(2), 97 (2002).

G.T. Caneba and L. Shi, “Lower Critical Solution Temperature of Polymer-Small Molecule Systems: A Review”, in: Phase Separation in Polymer Solutions and Blends, P.K. Chan (Ed.), Research Signpost, ISBN #81-7736-097-3, Chap. 4, pp. 63-104 (2002).

V.R. Tirumala, G.T. Caneba, N. Moldovan, ,D. Mancini, and H._H. Wang, “Self-Organization in Synchrotron X-Ray Induced Controlled Polymerization”, Proceedings of the A.I.Ch.E. Annual Meeting, Indianapolis, IN, November 3-8, 2002.

G.T. Caneba, Y.-L. Chen, and K. Solc, “Computer Simulation of Spinodal Decomposition in One, Two, and Three Dimensions”, Proceedings of the A.I.Ch.E. Annual Meeting, Indianapolis, IN, November 3-8, 2002.

G.T. Caneba, “Foaming Characteristics of Vinyl Acetate-Acrylic Acid Copolymers”, Proceedings of the A.I.Ch.E. Annual Meeting, Indianapolis, IN, November 3-8, 2002.

Yi Zhao, Y.L. Dar, M.-L. Kosonen, and G.T. Caneba, “Influence of Relative Block Sizes of Styrene-Acrylic Acid Copolymer Coupling Agent to the Tensile Behavior of Polystyrene-Wood Composites”, Proceedings of the A.I.Ch.E. Annual Meeting, Indianapolis, IN, November 3-8, 2002.

V. Tirumala, Y. Dar, H.-H. Wang, D. Mancini, and G.T. Caneba, “Nanopolymer Particles from a Controlled Polymerization Process”, Advances in Polymer Technology, 22, 126 (2003).

G.T. Caneba, Y. Zhao, and Y. Dar, “Amphiphilic Styrene-Acrylic Acid Copolymers from the Free-Radical Retrograde-Precipitation Polymerization (FRRPP) Process”, in press, J. Appl. Polym. Sci.

Y.L. Dar and G.T. Caneba, “Free-Radical Retrograde-Precipitation Polymerization: Mathematical Modeling of Styrene Polymerization in Diethyl Ether”, in press, Chem. Eng. Commun.

M.E.P Walinder, D.J. Gardner, M.-L. Kosonen, and G.T. Caneba, “Surface Energy Characteristics of Maple Wood Particles coated with Hydrophilic-Hydrophobic Polystyrene-Acrylic Acid (PSAA) Block Copolymers”, submitted to Holzforschung.

G.T. Caneba, E.R. Fisher, and D. Caspary, “Poly(dimethyl siloxane) Experiments for the Unit Operations Laboratory”, submitted to Chemical Engineering Education.

V.R. Tirumala, R. Divan, D.C. Mancini, and G.T. Caneba, “Lithographically-Assisted Synthesis of High Aspect Ratio Hydrogel Microstructures”, submitted to Microsystems Technologies Journal.

V.R. Tirumala, D.C. Mancini, and G.T. Caneba, “Synthesis of Ultrafast Response Microgels for MEMS Applications”, submitted to Smart Structures and Materials.

Y.L. Dar, V.R. Tirumala, G.T. Caneba, and D.C. Mancini, “Novel Sparse-Matrix Representations for Free-Radical Polymerization Simulations”, submitted to Journal of Macromolecular Theory and Simulations.

G.T. Caneba and Y.L. Dar, “Free-Radical Retrograde Precipitation Copolymers and Process for making the Same”, foreign submission to the Patent Cooperation Treaty, January, 2003, Publication WO 03/059974.

V.R. Tirumala, G.T. Caneba, D.C. Mancini, and H.H. Wang, “Spatially Controlled In Situ Synthesis of Polymers”, submitted to U.S. Patent and Trademark Office, June, 2003.

K.K. Mohanty and G.T. Caneba, “Enhanced Oil Recovery – A Review”, submitted to Encyclopedia of Chemical Processing.

G.T. Caneba, Y.L. Dar, and Y. Zhao, “Vinyl Acetate-Acrylic Acid Copolymers as Coupling Agents for Wood Flour-Vinyl Composites”, Proceedings of the 7th International Woodfiber-Plastic Composites Conference, Madison, WI, May 19-20, 2003.

V.R. Tirumala, R. Divan, D. Mancini, and G.T. Caneba, “Lithographically-Assisted Synthesis of High Aspect-Ratio Hydrogel Microstructures”, this paper was partly presented at the Fifth International Workshop on High Aspect Ratio Miscrstructure Technology (HARMST), Monterey, CA, June 15-17, 2003