Complex Dynamics of a Fluorinated Vinylidene Cyanide Copolymer Highlighted by Dielectric Relaxation Spectroscopy

The complex dynamics of a nearly alternating copolymer of vinylidene cyanide (1,1-dicyanoethylene, VCN) with 2,2,2-trifluoroethyl methacrylate (TFEMA), including two alpha-relaxations with diverging time scale in the glass transition temperature range, was thoroughly characterized by dielectric spectroscopy over wide temperature and frequency ranges and analyzed in the frame of the Ngai’s coupling model. The dielectric relaxation strength as well as the glass transition temperature, the temperature dependence of the α-relaxation time, and the corresponding distribution of relaxation times were all larger than those of a reference TFEMA homopolymer, as expected from the introduction of the stiffening VCN units all along the macromolecular chain. The effect of casting solvent and applied poling electric field on the copolymer dielectric strength suggests the onset of local orientational order involving the strong dipoles in the VCN units, a requirement for piezo- and pyroelectricity in amorphous polymers