Trifunctional poly(dimethylsiloxane) (PDMS) block copolymers PDMS-b-poly(tert-butyl acrylate (tBA)-co-acrylic acid (AA)), PDMS-b-poly(methyl methacrylate), PMMA-b-PAA, and PDMS-b-P(MMA-co-methyacrylic acid (MA)) were synthesized and utilized to stabilize PMMA latexes in both nonpolar (CO2) and polar (water) solvents. Submicron PMMA particles synthesized by dispersion polymerization in supercritical CO2 have been redispersed to form up to 40 wt % stable aqueous latexes. In CO2, the PDMS block provides steric stabilization. Upon transfer to water, the MA or AA groups ionize producing electrostatic stabilization, while the acrylate group anchors to the PMMA polymer surface. In both media, the particle size remained constant, indicating good Stabilization without agglomeration. The surfactant is "ambidextrous" in that stabilization is achieved in both CO2 and water and by different mechanisms in each medium. PMMA particles stabilized with a PDMS macromonomer could be transferred to an aqueous solution of sodium dodecyl sulfate in water to produce a stable latex.