|Ronova, I. A.; Bruma, M.; Schmidt, H.-W.: Conformational rigidity and dielectric properties of polyimdes, Structural Chemistry, 23(1), 219-226 (2012) -- DOI: 10.1007/s11224-011-9865-1
On the basis of two series of polyimides it was shown that the conformational rigidity and the presence of side voluminous substituents determine the packing of macromolecular chains in glassy state. The presence of hexafluoroisopropylidene groups leads to the increase of free volume of polymers due to the repulsion of such groups belonging to different macromolecular chains. The physical properties studied here, such as dielectric permittivity and electrets properties depend on the size of free volume. The normalized surface potential is determined by the mass fraction of fluorine content and by the conformational rigidity of those polymers.