Chapter 5
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Preparation and Characterization of Porous Polymers from Microemulsions 1
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S. Qutubuddin , E. Haque , W. J. Benton , and E. J. Fendler
1Chemical Engineering Department, Case Western Reserve University, Cleveland, OH 44106 Research and Development, BP America, Inc., 4440 Warrensville Center Road, Cleveland, OH 44128
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Polymerization of microemulsions containing styrene monomer have produced porous solid materials. The morphology and porosity are affected by the type and concentration of surfactant and cosurfactant. The middle phase microemulsions yield maximum porosity as observed using scanning electron microscopy. Permeability measurements were done to obtain the diffusion coefficient of gases through the porous solid. The polymerization process was investigated using a polarized light screen and enhanced video microscopy in order to follow the dynamics and evaluate the role of the initial microstructure. Differential scanning calorimetry was used to study the glass transition temperature and reaction kinetics. In addition to being porous, these materials exhibit interesting thermal properties. The anionic microemulsion systems containing sodium dodecyl sulfate yield solids with a glass transition temperature (Tg) higher than observed in bulk polystyrene. In contrast, the nonionic microemulsion produces solids with lower Tg. This is due to different interactions between the surfactant and polystyrene chains in the two systems. X-ray diffractometry, F T I R and N M R were used to investigate the structure of the solid polymers. The weight average molecular weight as obtained by gel permeation chromatography varied from 0.2 x 10 to 1 x 10 , depending on the initial microemulsion composition. Potential applications of the new materials include ultrafiltration, conductive polymers, polymer blends or composites, etc. 6
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In the last decade, polymers with unprecedented qualities have emerged from advances in synthesis and novel polymerization techniques. The area of polymerization reactions in organized systems or associated structures has recently become an important focus of research. A microemulsion may be defined as a thermodynamically stable isotropic solution of two immiscible fluids, generally oil and water, containing one or more surface active species (laJb). Microemulsions can be lower phase (water-continuous or oil-in-water type), upper phase (oil-continuous or
0097-6156/89/0384-0064S06.00/0 • 1989 American Chemical Society In Polymer Association Structures; El-Nokaly, M.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Downloaded by UNIV OF GUELPH LIBRARY on August 31, 2013 | http://pubs.acs.org Publication Date: December 30, 1989 | doi: 10.1021/bk-1989-0384.ch005
5.
QUTUBUDDIN ET AL.
Porous Polymersfront Microemulsions
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water-in-oil type) and middle phase. The middle phase microemulsions can be bicontinuous in microstructure (2). In bicontinuous microemulsions both the organic and aqueous phases coexist in interconnected domains with surfactant molecules located at the interface. The domain size in microemulsions is in the range of 100 to 1000 Â. A microemulsion is an example of the nonrandom systems which have been termed "organized solutions" by Shinoda (3). The surfactant molecules are mostly confined at the oil/water interface. Tne water, oil, and cosurfactant (usually a short-chain alcohol) in bicontinuous microemulsion systems diffuse at rates that are comparable to those of the neat components. Microemulsions differ from macroemulsions and miniemulsions. Macroemulsions, conventionally known as emulsions, are thermodynamically unstable mixtures of two immiscible liquids, one of them being dispersed in the form of fine droplets with diameter greater than 0.1 μτη. in the other liquid. Macroemulsions are turbid, usually milky white in color. The concentration of surfactants is usually very low (
