Electrical behaviour of a main chain liquid crystalline copolyester during melting and crystallisation

Dielectric measurements on a main chain liquid crystalline copolyester reveal that during crystallisation or melting no change in dipole activity occurs. However, interfacial polarisation appears during crystallisation, due to charge accumulation near the crystalline interfaces; it disappears when the polymer melts. The ohmic conductivity derived from the dielectric data increases during isothermal crystallisation. Unlike the liquid crystalline polymer, polyethylene terephthalate clearly exhibits changes in the dielectric properties due to the immobilisation of dipoles during crystallisation; the reverse occurs during melting. The build-up and decay of interfacial polarisation during crystallisation and melting occurs in PET as well; the ohmic conductivity decreases however during isothermal crystallisation.