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Two kinds of polyarylene ether nitriles (PEN) with different molecular structures were designed and synthesized by two kinds of bisphenol monomers. Then, solution casting method has been used to obtain three kinds of films based on the two kinds of pure PEN and their blends with a weight ratio of 1:1. The chemical structures of PEN were characterized by Fourier transform infrared (FTIR). Dynamic rheology behaviors were investigated to study the effects of inherent structures on the motion of molecular chains. Then, three kinds of foamed PEN films were prepared with supercritical carbon dioxide foaming method and the micro-morphology were monitored by scanning electron microscopy (SEM). Results indicated that microcellular foam films were obtained and dielectric properties of the foamed PEN films exhibited significant difference from that of un-foamed films. The dielectric constant of micro-foamed film decreased to 2.0. Moreover, the unusual dielectric properties of two kinds of PEN composite film were discussed in detail, which can be ascribed to the fact of micro-phase separation. [ABSTRACT FROM AUTHOR]