he composite film of lightly sulfonated polystyrene(SPS)and polypyrrole(PPy)was prepared by in situ polymerization of pyrrole in SPS ionomer film using an oxidant.The polymerization of imbibed pyrrole brought about changes in the structure and proper ties of the SPS matrix.The FTIR results showed that there were stronger intermolecular interactions between PPy and SPS by the oxidated PPy as a cation exerted on a-SO3-anion in SPS.The ion-ion interactions led the band of antisymmetric stretching vibration of-SO-3 near 1200cm-1 to split into two bands (1180 and 1211 cm-1). The microphase separation in the SPS/PPy composites was observed by DMTA measurement.The DMTA results indicated that two Tg appeared at 124 and 145 ℃ respectively.The phenomenon of phase separation was considered that the ionic associations in parent SPS film were disrupted by the incorporation of PPy during the in situ polymerization in the mean while causing the variation of the microstructure of SPS.