The synthesis and characterization of phenylethynyl (PE) end-capped polyimides derived from 4,4'-(2,2,2-trifluoro-1-phenylethylidene) diphthalic anhydride (3FDA), 4,4'-(hexafluoroisopropylidene) diplithalic anhydride (6FDA), and 3,3',4,4'-biphenylene dianhydride (s-BPDA) are described in this paper, with particular emphasis on the glass transition temperatures and viscosities. The phenylethynyl end-capped 3FDA- and 6FDA-containing oligomides demonstrate much lower minimum complex melt viscosities than s-BPDA-containing oligomides. The PE-3F and PE-6F oligomers also show greater viscosity stability at elevated temperature (310 degreesC) than s-BPDA oligomides. The lower viscosities can be explained by the presence of the bulky groups CF3 and phenyl on 3FDA and 6FDA relative to the planar configuration of the s-BPDA dianhydride. The greater viscosity stability of the PE-3F and PE-6F oligomers over the s-BPDA oligomers at 310 degreesC may be explained by the decreased electron density and hence lower reactivity of the ethynyl group in the PE-3F and PE-6F oligomers due to the influence of fluorine in the polymer chain.