An acid-catalyzed polymerization of tribenzylborate (TBB) is described for the synthesis of soluble poly(phenylene methylene) (PPM). The polymerization proceeds via carbocationic mechanism with first-order kinetics with respect to TBB and 0.7th order with respect to acid concentration. The structure of PPM was characterized by H and C-13 NM R. analysis. Thermal properties of PPM were investigated by TGA and DSC, and thermally stable polymers displayed completly amorphous structure, which was attributed to nonrestricted rotation of the phenyl rings around bridged methylene units in the rodlike structure. PPM exhibits a broad fluorescence emission band with a maximum at 422 nm arising from the benzonoid transition. The extremely low dielectric constant of PPM suggests that these polymers can be used as polymer insulators.