Dielectric and viscoelastic relaxation behaviours of polyethylene 2,6 naphthacene dicarboxylate (PEN)

PEN films of different morphologies, amorphous (300 /spl mu/m thick), semi-crystalline (300 /spl mu/m thick, obtained by thermally treating the amorphous samples at temperatures of 240/spl deg/C and 260/spl deg/C) and semi-crystalline biaxially stretched oriented films (25 /spl mu/m thick) have been studied by dielectrical (DEA) and mechanical dynamic (DMA) analysis. By both methods three relaxation phenomena are observed which are due to different molecular motions: the /spl beta/-, /spl beta/*- and /spl alpha/-relaxation in order of increasing temperature. The temperature dependence of the relaxation rate of the /spl beta/-relaxation can be described by an Arrhenius law with an activation energy E/sub A/ which is quite similar to values found for the /spl beta/-relaxation of PET. So it is concluded that the /spl beta/-process is due to local fluctuations of the ester linkage. The temperature dependence of the relaxation rate of the /spl beta/*-relaxation can be also described by an Arrhenius law but the activation energy is rather high. So probably the /spl beta/*-process is due to cooperative motions of the naphthalene groups or aggregates of it. Moreover dielectric and mechanical measurements gave different values for E/sub A/. This is discussed together with the morphology dependence of the /spl beta/*-process. For the a-relaxation the temperature dependence of the relaxation rate agrees with glass transition temperature measured by DSC. It is concluded that the /spl alpha/-process is due to the glass transition which is discussed also in dependence of the structure.