Etude diélectrique de deux copolymères du méthylcyanure de vinylidène avec le 4‐fluorostyrène et le 4‐chlorostyrène

The dielectric properties of 2 copolymers poly[(methyl vinylidene cyanide)‐co‐(4‐chlorostyrene)] and poly[(methyl vinylidene)‐co‐(4‐fluorostyrene)] have been studied. These products are chiefly alternating and have relatively high glass transition temperatures, respectively at 145°C and 160°C. α relaxation phenomena have been characterised around to these temperatures. The values of dielectrical increment Δε have been calculated and compared to those of similar copolymers synthesized from vinylidene cyanide with various substituted styrenes. The low values are due to the steric effect of the bulky aromatic cycles. The orientation abilities of CN dipoles decrease comparatively to that of the copolymer of vinylidene cyanide with vinylacetate and this could explain the low piezo or pyroelectric properties.