Synthetic Polymers in Water-in-Oil Microemulsions
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SYNTHETIC POLYMERS IN WATER-IN-OIL MICROEMULSIONS
FRANCOISE CANDAU Institut Charles Sadron Strasbourg Cedex, France
(CRM-EAHP),CNRS-ULP
6,
rue
Boussingault
67083
ABSTRACT High molecular weight water-soluble polymers are usually supplied in the form of water-in-oil emulsions which have advantages of low viscosity and easy storage and dissolution. Most uses in water treatment, flocculation, paper manufacture or mining fields require polymer latexes formed of finely dipersed particles. Polymerization in reverse micelles or microemulsions appears to be an attractive technique because it can lead, under appropriate formulations, to high molecular weight polymers entrapped within small-sized stable particles. The main characteristics and properties of the latexes and polymers formed by this process are described.
INTRODUCTION Polymerization of water-soluble monomers in hydrocarbon fluids has attracted a renewed interest over the past decade, owing to the suitability of the process for producing high molecular weight polymers at high reaction rates. In this process, a water-soluble monomer (usually in aqueous solution) is emulsified in a continuous oil medium using a water-in-oil emulsifier. Polymerization can be initiated with either oil -or -water-soluble initiators. The product is a dispersion of fine particles of an aqueous high polymer solution which can be easily inverted into water so that the water-swollen polymer particles dissolve rapidly, contrary to solid-powder which forms gels or aggregates when added to water. These high viscosity polymer solutions find applications in water-treatment, flocculation of colloidal suspensions, tertiary oil recovery as pushing fluids, fines retention in paper manufacturing etc [11. Inverse emulsion polymerization has been far less investigated than conventional (i.e. aqueous) emulsion polymerization. Apart from a large number of patents, there have been few fundamental studies. The pioneering work is due to Vanderhoff et al [2] who studied in 1962 the polymerization of sodium-p-vinyl benzene sulphonate in xylene. More recently, polymerization processes in different inverse colloidal systems, i.e. suspension [3], microsuspension [4,5], dispersion [6], and emulsion [7-12] have been described in the literature. In general, the problems of latex stability are more severe than for aqueous latexes, due to the absence of electrostatic forces between particles, and to the large difference in density between the organic continuous medium and the polymer core. This led us in the past years to investigate the possibilities offered by a polymerization reaction proceeding in a thermodynamically stable microemulsion rather than in an emulsion. Microemulsions are water-oil colloidal dispersions stabilized by an appropriate mixture of surface-active agents. While inverse emulsions are unstable, turbid and consist basically of two populations with a broad particle size distribution (fig.l ), microemulsions are thermodynamically stable and can adopt a large variety of labile structural o
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