Aqueous poly(phenylacetylene) dispersions were obtained by catalytic polymerization in emulsion with a phosphine-modified Pd(II) catalyst. A range of mono- and bidentate phosphines were screened. A tBu(2)P(CH2)(3)PtBu2-modified catalyst exhibits very high rates up to 2 x 10(5) TO h(-1) (TO = moles of monomer converted per mole of metal present in the reaction mixture) in the preparation of colloidally stable poly(phenylacetylene) dispersions. Polymerization in miniemulsion afforded dispersions with up to 36 wt % solids content and average particle sizes of ca. 130 nm. From microemulsions dispersions with ca. 25 nm particle size were obtained.