MECHANICAL, ELECTROCHEMICAL AND OPTICAL-PROPERTIES OF POLY(3,4-ETHYLENEDIOXYTHIOPHENE) SULFATED POLY(BETA-HYDROXYETHERS) COMPOSITE FILMS

Poly(3,4-ethylenedioxythiophene)/sulfated poly(beta-hydroxyethers) (PE DT/S-PHE) composite films were prepared by electrochemical polymerizat ion of 3,4-ethylenedioxythiophene (EDT) in the presence of S-PHE polye lectrolytes. The sulfate groups of S-PHE play the role of the counteri on to the positive charges of the oxidized PEDT. Moreover, as a conseq uence of the good mechanical properties imparted by S-PHE, we succeede d in preparing free-standing PEDT composite films. All composites show ed excellent mechanical properties, high conductivity and reversible e lectrochromic properties. In order to examine the influence of the S-P HE content on composite properties, a series of composites containing S-PHEs of differing molar ratios (MR) of sulfate groups to the monomer units of poly(beta-hydroxyethers) were synthesized. From the experime ntal results it was found that the conductivity of the composites is i ndependent of MR value and, hence, PEDT content. In situ absorption sp ectra of the composite films suggested that composites with larger con tents of PEDT possessed shorter pi-conjugation lengths. Electrochemica l properties of the composites were measured by means of cyclic voltam metry and potential step chronocoulometry and results demonstrated tha t the rate of switching between the doped and undoped states of the co mposites occurs within 0.5 s. The absorption band of the composites in the visible region almost disappeared upon doping. All results indica te that the composites are interesting candidates as materials for ele ctrochromic displays. (C) 1997 Elsevier Science Ltd.