Conventional heterogeneous dispersion polymerizations of unsaturated monomers are performed in either aqueous or organic dispersing media with the addition of interfacially active agents to stabilize the colloidal dispersion that forms. Successful stabilization of the polymer colloid during polymerization results in the formation of high molar mass polymers with high rates of polymerization. An environmentally responsible alternative to aqueous and organic dispersing media for heterogeneous dispersion polymerizations is described in which supercritical carbon dioxide (CO(2)) is used in conjunction with molecularly engineered free radical initiators and amphipathic molecules that are specifically designed to be interfacially active in CO(2). Conventional lipophilic monomers, exemplified by methyl methacrylate, can be quantitatively (>90 percent) polymerized heterogeneously to very high degrees of polymerization (>3000) in supercritical CO(2) in the presence of an added stabilizer to form kinetically stable dispersions that result in micrometer-sized particles with a narrow size distribution.

(NMR) analysis, using the tris [3-(trifluoromethylhydroxymethylene)-(ϩ)camphorato]europium(III) complex. The compound was hydrolyzed to the corresponding acid and then the optical purity was enhanced up to 97% ee by cocrystallization with commercially available R-PEA. The optical purity was checked by NMR and circular dichroism spectra:[␣] D 25 ϭ Ϫ63.2 (C ϭ 1.01 g/liter tetrahydrofuran). 5. The isotherms were measured from A ϭ 100 to 5 Å 2

letters to nature 368 NATURE | VOL 389 | 25 SEPTEMBER 1997 membrane lipid/water systems 19 . It has been suggested that two lipid bilayers transform through an inverted micellar intermediate to a cubic mesophase 20 . We propose that the 3-dH film is derived from the parent cubic film by constrained one-dimensional shrinkage during calcination 3 . The cubic → 3-dH transformation can be considered as a constrained one-dimensional distortion of the cubic cell along the [110]-direction. Comparable lattice parameters between the two mesophases allow seamless transitions between ordered domains and cause cubic and 3-dH domains to be essentially indistinguishable in plan-view (Fig. 4c).A surface acoustic wave technique 21 was used to determine pore accessibility of supported films. Figure 5 compares nitrogen sorption isotherms of the incipient 1-dH and cubic 3-dH films. Despite the substantially different degrees of ordering, the isotherms are qualitatively similar. The lack of hysteresis and absence of any appreciable adsorption at relative pressures above 0.3 is consistent with a unimodal porosity with no interparticle meso-or macroporosity 22 . The surface areas calculated for the cubic 3-dH and incipient 1-dH films are 734 and 648 m 2 g −1 , respectively, demonstrating the accessibility of the mesophase porosity. In addition, the trans-film flux of cubic 3-dH films prepared as supported membranes increased by over 1,000× upon calcination, establishing through-thickness pore connectivity (A. Tsai, unpublished results).We have demonstrated a rapid, continuous process, enabling the practical utilization of mesostructures in thin-film form. The uniform three-dimensional pore channel systems of cubic 3-dH films and the absence of granularity suggest applications in molecular separation, catalysis and sensors. The dip-coating procedure combined with the optical probe technique enables us to follow the progressive evolution of the mesostructured films and should provide insight into the synthesis of complex, self-organized organic/inorganic assemblies in general 23 . Ⅺ

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