Composite of poly(Dithienopyrrole) and poly(Vinylchloride) obtained by the electrode coating method

Journal of the Brazilian Chemical Society

UNICAMP, Campinas, Brazil¹  Casalbore-Miceli, Giuseppe¹  Geri, Alessandro¹  De Paoli, Marco-A¹  C.N.R, Bologna, Italy¹ 

关键词: conductive polymeric composite;    electrochromism;    thermoplastic;   

DOI  :  10.1590/S0103-50531997000300006

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

Processability is a property important for polymeric materials in general and, particularly, for conducting polymers to make them technologically useful. A convenient route to render a conducting polymer with electro-optic properties usable for technological processes is by its inclusion in a film of a non conducting but processable host polymer1. The combinations of two or more polymers produce a blend if the product is homogeneous or a composite if it is heterogeneous. Electrochemical techniques were largely used for these purposes, and conductive polymers were included in films of polyvinylchloride (PVC)2, nitrilic rubber3, ethylene-propylene-diene rubber4 and many other processable polymeric materials5. Preliminary results were reported in a previous paper describing the anodic polymerization of dithienopyrrole on films of PVC6. Adherent films cannot be obtained by the electrochemical polymerization of dithienopyrrole on different substrates. Nevertheless, an electrochemically deposited film of pure poly(dithienopyrrole), pDP, showed interesting electrochromic properties6. Films of pDP deposited on PVC coated electrodes also showed electrochromic properties in comparison to the pure polymer. On the other hand, they did not characterize the new material in detail and consequently it was not clear whether it was a composite, a blend or a copolymer. Furthermore, they did not do morphological and thermal analysis for the determination of the stability and the composition of this polymeric material. In this paper we report on results obtained by several techniques, which better explain the characteristics and the composition of the product obtained by the electropolymerization of dithienopyrrole on PVC films. We confirm the composite nature of the material and its electrochromic properties.   Experimental 4H-dithieno[3,2-b;2Â’,3Â’-d]-pyrrole (dithienopyrrole) was synthesized as described in the literature8. Films of poly(dithienopyrrole) on PVC were prepared by cycling ITO (glass slides coated with indium-tin oxide) electrodes coated with PVC films (thickness 2-7 mm) between -0.5 and 1.5 V in acetonitrile solutions of dithienopyrrole (1 x 10-2 M) and 0.1 M tetrabutylammonium perchlorate (TBAP) or 0.1 M tetrabutylammonium tetrafluorborate (TBAF). The electrode potentials in this work are referred to the saturated calomel electrode, moreover, a salt bridge was used to connect the reference electrode and the organic electrolyte solution. Acetonitrile (Merck p.a.) was dehydrated with CaCl2, twice distilled over CaH2, and stored under nitrogen atmosphere. TBAP and TBAF were purified by crystallization from methanol. Dynamic spectro-electrochemical experiments were carried out using an electrochemical cell with optically transparent windows in the sample compartment of an Hewlett-Packard 8452A diode-array spectrophotometer with a response time of 0.1 s. The electrode potential was controlled with a FAC 200A potentiostat driven by a computer and a home made program. Cyclic-voltammetric experiments were done with an AMEL Electrochemolab instrument. Thermogravimetry (TGA) determinations and the experiments of Differential Scanning Calorimetry (DSC) were performed with a Dupont 9900 Thermal Analysis system. The Fourier-transform infrared spectra were obtained with a FT-IR DX Nicolet instrument.   Results and Discussion The cyclic voltammetries of dithienopyrrole dissolved in acetonitrile and of films of poly(dithienopyrrole)/PVC, pDP/PVC, are shown in Fig. 1. These were prepared on ITO electrodes, as described in the experimental part, both with ClO4- and BF4- as counterions. These were used to study the effect of anions with different ionic radius on the redox processes of the composite material. Curves a and b demonstrate the small interference of the anion of the electrolyte on the electrochemical properties of the monomer. Curve 1c clearly demonstrate that, the PVC matrix produces a strong broadening of the redox waves, probably caused by the hindrance for ion diffusion. The insulating host, however, does not hinder the reversibility of the redox process of pDP.   The variation of the optical spectrum as a function of applied potential for a film of pDP (BF4- as counterion)/PVC on ITO electrode is reported in Fig. 2. The potential was scanned at 50 mV s-1 from 0 to +1.5 V and then back to 0 V (in relation to SCE). A good agreement is observed when comparing the spectra of Fig. 2 with those previously obtained at stationary conditions with a film of pDP(ClO4- as counterion)/PVC9. In these previous experiments, 2 or 3 s after the potential change, the equilibrium at the new condition was nearly reached, without evidence of intermediate species between the initial and final states. The redox process of the conductive polymer depend on the diffusion of ions between the polymer film and the electrolyte solution. The results obtained with pDP/PVC is an indication that the hindrance to the ion diffusion process caused by the PVC phase is not sufficiently large to impede the optical response of the material. Moreover, the change of the counterion (ClO4- in the stationary, BF4- in the dynamic experiments) did not affect the electrochromic results. The dynamic experiments (measurement of the absorption spectra during a cyclic voltammetry scan) reveal intermediate absorptions at 650 nm under an applied potential of 1.3 to 1.4 V (in relation to SCE), in cathodic or anodic scan, Fig. 2. This absorption was also observed in the stationary experiments9. When the film is polarized at 1.5 V the absorption is lower producing a valley in this region of the curve, indicating a high chromatic contrast between the reduced and the oxidized species.   Thermogravimetric experiments on pure pDP samples, with ClO4- and BF4- as counterions, are reported in Figs. 3 and 4, respectively. In both cases two different thermogravimetric steps are visible. The first one is assigned to dedoping of the polymer with a mass loss corresponding to counterion elimination. This step is centered at 232 °C in the

【 授权许可】

Unknown