Six exactly alternating, silphenylene-siloxane polymers containing either 3,3,3-trifluoropropyl, tridecafluoro-1,1,2,2-tetrahydrooctyl, hydrido, methyl, or vinyl substituent groups on the siloxyl silicons were prepared by low-temperature, solution polycondensation reactions of 1,4-bis(dimethylhydroxysilyl)benzene, DMHSB, and the respective dichlorosilane monomers. All of the polymers prepared were characterized by H-1 and C-13 NMR spectroscopy, gel permeation chromatography and differential scanning calorimetry. The polymers with tridecafluoro-1,1,2,2-tetrahydrooctyl substituents showed two glass transition temperatures, and the higher transition at -37-degrees-C was attributed to the mobility of the highly fluorinated substituents.