Pyrrole monomer, polymerization

Significant variations in the properties of polypyrrole [30604-81-0] ate controlled by the electrolyte used in the polymerization. Monoanionic, multianionic, and polyelectrolyte dopants have been studied extensively (61—67). Properties can also be controlled by polymerization of substituted pyrrole monomers, with substitution being at either the 3 position (5) (68—71) or on the nitrogen (6) (72—75). An interesting approach has been to substitute the monomer with a group terminated by an ion, which can then act as the dopant in the oxidized form of the polymer forming a so-called self-doped system such as the one shown in (7) (76—80). 

Cyclic voltammetry is most commonly used to investigate the polymerization of a new monomer. Polymerization and film deposition are characterized by increasing peak currents for oxidation of the monomer on successive cycles, and the development of redox waves for the polymer at potentials below the onset of monomer oxidation. A nucleation loop, in which the current on the reverse scan is higher than on the corresponding forward scan, is commonly observed during the first cycle.56,57 These features are all illustrated in Fig. 3 for the polymerization of a substituted pyrrole.58... 

Fig. 122. Polymerization of pyrrole monomer in a preformed ferric stearate multilayer film (black dots represent electrically conducting polypyrrole) [764]...

Recently the mechanisms of pyrrole electropolymerization have been reviewed in Ref. [9b]. By the anodic reaction, an electron is withdrawn from the pyrrole monomers and cationic radicals are formed. The cationic radicals undergo a series of chemical-electro-chemical-chemical reactions and, as the result, the polymerization proceeds. If the cationic... 

Vinylpyrrole and several of its derivatives have been studied. Free radical polymerization has been shown to lead to low molecular weight (2000-13 000) polymers (20) (80MI11102). Similar results were obtained for homopolymerization of pyrrole monomers in which the polymerizable group was attached at the 2-position (73MI11101), as in monomers (21) and (22). Low molecular weights can probably be attributed to chain transfer reactions involving the pyrrole nucleus. 

Polypyrrole thin film doped with glucose oxidase (PPy-GOD) has been prepared on a glassy carbon electrode by the electrochemical polymerization of the pyrrole monomer in the solution of glucose oxidase enzyme in the absence of other supporting electrolytes. The cyclic voltammetry of the PPy-GOD film electrode shows electrochemical activity which is mainly due to the redox reaction of the PPy in the film. Both in situ Raman and in situ UV-visible spectroscopic results also show the formation of the PPy film, which can be oxidized and reduced by the application of the redox potential. A good catalytic response to the glucose and an electrochemical selectivity to some hydrophilic pharmaceutical drugs are seen at the PPy-GOD film electrode. 

The utility of the ionic liquid as a recyclable medium for the polymerization was also demonstrated. More than 90% of [EMIM][OTf] after the polymerization was easily recovered simply by extracting the remaining pyrrole monomer with chloroform. The recoved [EMIM] [OTf could be reused five times without significant loss of reactivity for the polymerization. 

The discovery that doped forms of polypyrroles conduct electrical current has spurred a great deal of synthetic activity related to polypyrroles [216-218], Reviews are available on various aspects of the synthesis and properties of polypyrroles [219,220]. In addition, summaries of important aspects of polypyrroles are included in several reviews on electrically conducting polymers [221-226]. Polypyrrole has been synthesized by chemical polymerization in solution [227-231], chemical vapor deposition (CVD) [232,233], and electrochemical polymerization [234-240]. The polymer structure consists primarily of units derived from the coupling of the pyrrole monomer at the 2,5-positions [Eq. (84)]. However, up to a third of the pyrrole rings in electrochemically prepared polypyrrole are not coupled in this manner [241]. 

The polymerization of pyrrole over Cu(II)-exchanged ZSM-5 zeolites was studied with resonance Raman spectroscopy. The authors found that a critical concentration of cupric ions must be exceeded to observe polymerization. Hosts with low Si/Al ratios gave partially oxidized pol5rpyrrole (having quinoidal and aromatic structures) and pyrrole monomer. The quinoidal structure was associated with the charge carriers. Residual oxygen degraded the polymer. 

Ultrasound was also used for the dispersion of a surfactant pyrrole, prior to electrooxidation to the conducting polymer [233]. An amphiphilic (pyrrolylalkyl) ammonium monomer dispersion was used to coat the electrode surface with monomer, subsequently electropolymerized to thin films using an aqueous electrolyte for this step. Ultrasound has also been used to assist impregnation of pyrrole monomer into, for example, a conventional polymer matrix prior to polymerization to yield a composite of the conducting and conventional polymers, but is also a pretreatment effect of ultrasound rather than a sonoelectrochemical one [234],... 

Polypyrroles (PPy s) are formed by the oxidation of pyrrole or substituted pyrrole monomers. In the vast majority of cases, these oxidations have been carried out by either (1) electropolymerization at a conductive substrate (electrode) through the application of an external potential or (2) chemical polymerization in solution by the use of a chemical oxidant. Photochemically initiated and enzyme-catalyzed polymerization routes have also been described but are less developed. These various approaches produce polypyrrole (PPy) materials with different forms—chemical oxidations generally produce powders, whereas electrochemical synthesis leads to films deposited on the working electrode, and enzymatic polymerization gives aqueous dispersions. The conducting polymer products also possess different chemical/electrical properties. These alternative routes to PPy s are therefore discussed separately in this chapter. 

Pyrrole polymerizations have a significant advantage in terms of flexibility over polyaniline syntheses, described later in Chapter 4, in that they may be carried out in neutral aqueous solution (i.e., no acid is required). A range of organic solvents may also be employed, the limitation being the requirement to dissolve both the pyrrole monomer and the oxidant. 

Aizawa and Wang have reported123 that the copper-containing enzyme, bilirubin oxidase (BOX), catalyzes the oxidative polymerization of pyrrole to give thin films of PPy on substrates such as glass, plastic, or platinum plates. The BOX was first adsorbed onto the matrix support from an aqueous acetate buffer solution (pH 5.5), followed by incubation with the pyrrole monomer (0.2 M) in acetate buffer (pH 6) for several hours at room temperature. The deposited PPy film was reported to have similar properties to PPy made by conventional chemical or electrochemical methods. 

The simplest approach is to have a suitable host structure imbibe the oxidant or monomer. This material is then exposed to the monomer or oxidant, respectively, and the polymer material is grown throughout. For example, Bjorklund and Lund-strom27 described a procedure in which cellulose paper was first exposed to a metal salt (FeCl3) that would act as the polymerization agent. The metal salt-soaked paper was then exposed to the pyrrole monomer in liquid or vapor form. Materials with conductivities of approximately 2 S cm-1 could be produced using this approach. 

Coral-hke nanowires and nanowire networks of conducting PPy have been synthesized by chemical oxidation polymerization of pyrrole monomers in a dodecyl-benzene sulfonic acid (DBSA) aqueous solution with FeCla as oxidant and poly(vinyl-alcohol) (PVA) as... 

There have been efforts to put scanning tips to different uses in which the scanning probe is employed neither as an electrode nor as a monomer/CP delivery mechanism, but as a nanomechanical tip to create scratches on a substrate to guide the growth or promote selective adhesion of CP nanofeatures. For example, it has been shown that a tip can be used to scratch the poly(methyl methacrylate) (PMMA) layer on top of electrolyte and catalyst underlayers to achieve selective chemical polymerization of pyrrole monomer on... 

Figure 10.16 A general concept for the production of nanowires an AFM is used as a nanomechanical tool for scratching a resist layer, to result in selective exposure of the underlying polymeric dopant surface containing the catalyst for polymerization. Treatment with the pyrrole monomer results in polymerization in the nanochannels. (Reprinted with permission from ChemPhysChem, In Situ Polymerisation of Pyrrole in Nanochannels Produced by Means of AFM Lithography by S. Jahromi, ). Dijkstra, E. van der Vegte and B. Mostert, 3, 8, 693-696. Copyright (2002) Wiley-VCH)...

Poddar et al. [56] successfully extended the UV-irradiation technique [73] for PPy formation to composite fabrication. In this technique, silver nitrate (10-5 mol%) was added to the pyrrole monomer as the electron acceptor for pyrrole photopolymerization. A photoinitiator was used to increase the polymerization rate and uniformity. A cationic... 

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