Copolymerization 22’-bithiophene-pyrrole

The equation was applied to 2,2 -bithiophene-pyrrole copolymerization. The result plotted in the Unear form, Eq. (11.17), is shown in Figure 11.29. These authors confirmed the copolymerization equation. Recently, Dung et al. investigated the same system with similar results. 

The determination of the type of copolymers formed in the preparation process is an important characterization step. One method of characterization is cyclic voltammetry as shown, e.g., by Yohannes et Cyclic voltammograms of copolymerization of pyrrole and bithiophene is shown in Figure 11.30. 

Fig. 3 Fabrication of type II conducting polymer heterolayer superlattice by the electro-copolymerization of pyrrole (2.5x10 M) and bithiophene (2.5x10" M) LiC104 (1.0x1 O M) CH3CN solution. Sweep potentials, copolymer compositions and AEq, AEy of the resulting heterolayers.

In addition to the routine characterization of these copolymers with UV-visible, near IR and FTIR spectroscopy, XPS, elemental analysis and four-point probe conductivity measurements, Mossbauer [17] and photoluminescence (PL) [18,19] spectroscopy of the copolymer were used. When the thiophene content in the copolymer is higher than 50 mole%, there are three peaks at 2.0, 1.8 and 1.7 eV in the PL spectra of the copolymer. Below 50 mole%, the copolymer does not exhibit photoluminescence. Details of the fabrication of a type II conducting polymer heterolayer superlattice by the electrochemical copolymerization of pyrrole and bithiophene by the potential-programmed electropolymerization (PPEP) method are given in a recent review [19]. 

The random copolymerization of pyrrole with thiophene, bithiophene and terthiophene is reviewed in Section 11.2.1.1(a). 

Electrochemical copolymerization of pyrrole and 2,2 -bithiophene also yielded a conducting copolymer... 

There are several examples of the copolymerization of pyrrole with bithiophene [77-80] and pyrrole with a-terthiophene [78,81]. The lowered oxidation potentials of the thiophene dimers and trimers facilitates copolymerization with pyrrole. Nevertheless, early research showed that bithiophene content in polymers of pyrrole/ bithiophene was not linearly related to the bithiophene... 

Figure 2 shows the band structures of several homopolymers and pyrrole-bithiophene copolymers estimated by electrochemical and optical methods as examples. A combination of these homopolymers and/or copolymers implies various kinds of superlattice structures. The electrochemical preparation of both homopolymer multiheterolayers and/or copolymer multiheterolayers results in a superlattices. The electrochemical copolymerization method as used to prepare heterolayers was easier than in the homopolymer heterolayers. The copolymer multi heterolayers are prepared by simply changing the applied electrode potential. On the contrary, the latter needs exchange of the mother solutions. The present electrocopolymerization method which makes compositionally modulated copolymer heterolayers possible is considered to be one of the most fascinating methods to fabricate organic superlattices. 

A significant study [13] of the copolymerization in acetonitrile with t-butyl ammonium perchlorate as the electrolyte confirmed that the composition of the copolymer depends on applied potential as well as feed ratio. The authors demonstrated that the copolymer composition obeys the Mayo-Lewis copolymer equation [14] and reported reactivity ratios for the pyrrole/ bithiophene pair for the first time. At a polymerization potential of 1.3 V, r, =4.9 and r2 = 0.04 for pyrrole and bithiophene, respectively, and at 1.5 V, r — 4.3 and a-2 = 0.24. 

The reactivity of pyrrole and thiophene during copolymerization with their derivatives depends strongly on the oxidation potentials of the monomers. Accordingly, the use of a monomer feed of bithiophene and pyrrole is the optimum method for preparing thiophene/pyrrole copolymers. But the best route to thiophene/1-methylpyrrole copolymers is to homo-polymerize A/-methyl-2,5-di-(2-thienyl)-pyrrole. 

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