A series of polyimides has been synthesized based on different dianhydrides and diamines. The microstructure of polyimide films has been analyzed by per-forming density measurements, X-ray diffraction and UV-visible spectrophotometry. The dynamic mechanical behavior was investigated according to both chemical and microstructural aspects. Thus, it was pointed out that the broadness of the beta sub-glass transition is dependent not only on dianhydride flexibility but also on para- or meta-diamine links. Such behavior is discussed in terms of intra-charge transfer complex, On the contrary, the temperature location of the gamma-transition appears to be controlled by interchain packing. Based on a statistical approach, a correlation between microstructural data and gamma. relaxation temperature is established.