Dielectric properties of block copolymers based on vinylidene fluoride and cyano comonomers

The syntheses of poly(vinylidene fluoride)-b-poly(AN, MAN, VCN) (PVDF-b-PMCN) block copolymers, using the iodine transfer polymerization (ITP) of acrylonitrile (AN), methacrylonitrile (MAN) and vinylidene cyanide (VCN), in the presence of PVDF-I, are presented. In a first step, the ITP of vinylidene fluoride (or 1,1-difluoroethylene, VDF) with C6F13I initiated by tert-butyl peroxypivalate is achieved. This ITP led to two different isomeric oligomers (PVDF-I) bearing either CH2I or CF2I end-groups. Second step, those fluorinated blocks were used latter as macromolecular chain transfer agents to achieve the ITP with cyanide monomers (MCN). The characterization of synthesized samples by 19F and 1H NMR spectroscopy allowed determining the average degree of polymerization. These block copolymers were characterized by SEC chromatography (4160–51100 g/mol) and by wide angle X-ray diffraction. Their thermal stabilities were studied using thermogravimetric analysis (TGA). The melting and glass transition temperatures as well as the degree of crystallinity were characterized by means of DSC. The influence of the copolymer compositions on dielectric properties has also been investigated. Dielectric analyses show several relaxations processes associated with long-range molecular motions, which are associated to the glass transition temperatures of both blocks (PVDF block and poly(cyano monomer blocks)). These behaviors are discussed in terms of dielectric proprieties as a function of molecular composition and mobility.