High-performance surfactants have been developed for the preparation of water-in-oil high internal phase emulsions (HIPE), particularly for the preparation of polymerized HIPE foams. High-efficiency surfactants with poly(butylene oxide)/poly(ethylene oxide) (BO/EO) block copolymer backbones have been developed that can stabilize an HIPE through polymerization at concentrations as low as 0.006 wt% based on total emulsion weight. Polymerizable versions have been developed that bind into the polymeric foam backbone. BO/EO block copolymer surfactants also allow preparation of polymerized HIPE foams without salt in the aqueous phase. HIPE with the BO/EO surfactants have been prepared at room temperature and polymerized at temperatures exceeding 90°C. By minimizing the required amount of surfactant, allowing the surfactant to react during HIPE polymerizations, eliminating the need for salt, and stabilizing over a broad range of temperatures, BO/EO block copolymer surfactants have demonstrated their place as high-performance HIPE surfactants.Paper no. S1199 in JSD 4, 127-134 (April 2001) KEY WORDS: Polymerizable surfactants, polymerized water-inoil high internal-phase emulsions, poly(butylene oxide)/poly(ethylene oxide) surfactants.Emulsions comprise a continuous external phase and a discontinuous internal phase. High internal phase emulsions (HIPE) are a special type of emulsion wherein the internal phase makes up in excess of about 70 vol% of the emulsion. HIPE are routinely prepared with internal phases exceeding 98 vol%. The dispersed-phase droplets at these very high internal phase volumes are no longer free to move about in the external phase but are compressed against one another, taking on multifaceted geometries (1-3). The high-volume fraction of the dispersed phase in the HIPE led very early to their being considered for a variety of applications. Many of the applications utilized the shear thinning rheological properties of the HIPE (high viscosity at low shear rate and low viscosity at high-shear rates) (4). Some examples of this are: safety fuels (5), suspension media for transporting solids through pipelines (6-8), hydraulic fracturing of subterranean formations surrounding oil wells (9-11), cosmetic preparations (12), and emulsion explosives (13,14). In addition to the rheological properties, polymerized HIPE compositions found uses in other applications. Examples are: particles in the range of 0.1 to 0.3 µm (15), membranes for separation of water-ethanol mixtures by pervaporation (16), and polymeric foams for absorption of hydrophobic materials (17) and hydrophilic materials (18). The particles are obtained by polymerizing the dispersed monomers in an aqueous continuous phase, whereas the membrane and foams are obtained by polymerizing a continuous monomer phase in which an aqueous phase is dispersed. In all of these cases, the HIPE provides the template for the polymerization of the monomers. For the preparation of polymeric foams, the internal phase volume dictates the void volume of the foam, and the ...
The reduction of ZrCl4(PR3)2 with Li powder, in the presence of a stoichiometric amount of trans-1,4-diphenyl-1,3-butadiene, affords the Zr(II) diene complexes (1) in 90-93% yields. This reaction consists of a rate-limiting step for the formation of the chloride-bridged Zr(III) dimer (2) and a fast diene-driven disproportionation of 2 to 1 and ZrCl4(PR3)2 that re-enters the reduction cycle. The reaction of 1 with Li2{Me2Si(2-Me-4-Ph-Ind)2} in toluene produces quantitatively the desired racemic, divalent ansa-zirconocene (3) that is a highly active isospecific propylene polymerization catalyst upon activation with common activators.
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