Electrochemical synthesis and characterization of conducting copolymers of biphenyl with pyrrole

Abstract

Copolymer films of biphenyl and pyrrole were synthesized by electrochemical polymerization. The influence of the applied potential used for the electropolymerization on the structure, morphology, electrical conductivity, and stability of the films was examined. From the analysis of the current–time curves, it was found that the growth of the copolymer films starts immediately. The films were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, X‐ray diffraction analysis, and scanning electron microscopy–energy‐dispersive X‐ray analysis, and their electrical conductivity (σ), energy gap (Eg), and electrochemical stability were also determined. Based on the results, the copolymers were classified into three groups. The first includes the (PP‐PPy)0.80 copolymer synthesized at the lowest potential Eox (0.80 V), having the highest ratio R (R = 0.35) of quinoid to benzenoid rings (calculated from FTIR), the highest value of σ (σ = 0.9 S/cm), the lowest Eg (Eg = 1.20 eV), and has compact morphology. The second group concerns the copolymers synthesized at higher potential (0.82 up to 0.86 V), having lower R (∼ 0.20), lower σ (below 0.4 S/cm), higher Eg (∼ 1.35 eV), and they are less compact with many pores. The third group includes the copolymers synthesized at even higher applied potential (0.88 and 0.90 V), having even lower R values (∼ 0.10), significantly lower σ (∼ 10−3 S/cm), even higher Eg (∼ 1.70 eV), and they are very porous. The applied potential during electropolymerization strongly affects the properties of the synthesized copolymers. Because of the combination of high conductivity, low energy gap, and partial solubility with significant electrochemical stability, these new copolymers are attractive candidates for many applications. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Influence of electrochemical copolymerization conditions of 3‐methylthiophene and biphenyl on the morphology and nanomechanical properties of the films

“…It seems that the presence of biphenyl affords more compact films. This can be supported from previous works about copolymers of biphenyl with thiophene 6 or biphenyl with pyrrole, 7 where the copolymers were generally more compact compared to the thiophene or pyrrole homopolymers. Copolymer (3MTh-Biph) 1 [Figure 7(b)] has completely different morphology: again, the main feature of the film are the thin flat lamellae, but this time they appear thinner and more porous; however, it also has a uniform morphology.…”

“…6,7 The values are presented in Table IV. The morphology of the copolymers can also be correlated with the ratio of structural units.…”

“…Thus, according to the mechanism of the deposition, the (i)-(t) curves can be analyzed in regions where specific steps of the film deposition take place. 6,7,22 Namely, there are the following regions:…”

“…It has already been proven that for polyphenylenes x 5 1 and that for 3PMTh x 5 0.5, independent of the applied potential. 6,7 This means that the NGM is instantaneous, two-dimensional nucleation (IN2D) in both cases, controlled by charge transfer in the former case and diffusion in the latter. The copolymers also have x 5 1 in the whole range of applied potentials which was investigated.…”

“…In all these cases, the films synthesized showed a wide variation in their morphology and properties. 4,[6][7][8][9][10] The films that were deposited through electropolymerization have been studied using plenty of methods, particularly spectroscopies, microscopies, and analytical techniques; however, their mechanical properties have only seldom been studied, even though their importance for the applications of these materials is widely recognized. The main reason for the absence of this kind of investigation is the difficulty to perform measurements into such thin films (with thickness a few micrometers at most).…”