Polymerisation polypyrrole

Kojima and co-workers [52] identified the major thermal decomposition products of plasma polymerised polypyrrole as nitriles with less than four carbons and alkyl pyrroles. Evolution of only monosubstituted alkyl pyrroles, such as 2-methylpyrrole and 2-ethylpyrrole, suggests that polypyrroles consist of monosubstituted pyrrole rings. This is also supported by the result that the IR spectrum of polypyrroles differs from that of the electrochemically polymerised pyrrole, which consists of disubstituted pyrrole rings. Evolution of linear nitriles shows evidence that a polypyrrole molecule has the main chain containing nitrogen atoms. The mechanism of polymerisation of pyrrole in the discharge is considered to be similar to that of aromatic hydrocarbons, which mechanism involves a process of production of acetylene. 

Elemental analysis shows that the polymer generally contains four monomer units per dopant ion [20], and that there is also more hydrogen than would be expected (cf. polypyrrole) [20, 395], although this may vary depending on the starting material [409,410,414], Even in the neutral form, the polymer contains a small quantity of anions (0.5-1%) [19], although Waltman et al. [400] found that the extent to which the counter ion is incorporated into the polymer on polymerisation depends strongly on the nature of the /J-substituent (if present). 

A typical example of such a polymer is polypyrrole. The exact mechanism by which the electropolymerisation of pyrrole occurs remains a source of controversy however, by assuming 100% growth efficiency, then it can be calculated that 2.25 electrons are removed per monomer unit. Only two electrons are required to polymerise the monomer however, the film is formed in a highly oxidised state, corresponding to one electron per four units, see Figure 2.20. 

The quaternary groups in viologens can be derivatised to produce compounds capable of chemically bonding to a surface, especially electrode surfaces. These include symmetrical silanes, e.g. (1.93), which can bond to the oxide lattice on the electrode surface, and a viologen with pyrrole side chain (1.94) that undergoes anodic polymerisation to form a film of the viologen bearing polypyrrole on the electrode. Polymeric bipyridilium salts such as (1.95) have also been prepared for use in polymeric electrolytes. ... 

The other important electrochromic polymers are the polypyrroles and polythiophenes, obtained by polymerisation of the parent pyrrole and thiophene or, more importantly, their 3,4-substituted derivatives. The most widely studied of these two classes of polymers in electrochromic outlets are the poly thiophenes, which are readily synthesised by the reaction of the substituted monomer with FeClj in chloroform solution. The colour change properties of a variety of poly thiophenes in the presence of a counter-ion are shown in Table 1.14. ... 

Polypyrrole/poly(ethylene-co-vinyl acetate) conducting composites with improved mechanical properties were prepared by a similar method [167], In addition, polyaniline/polystyrene [168] and polyaniline/poly(alkyl methacrylate) [169] composites have been synthesised. A solution of persulphate in aqueous HC1 was added to an o/w HIPE of polymer and aniline in an organic solvent, dispersed in aqueous SDS solution, causing aniline polymerisation. Films were processed by hot- or cold-pressing. 

Dall Acqua et al.45 reported the development of conductive fibres made by cellulose-based fibres embedded with polypyrrole. Several efforts with cotton, viscose, cupro and lyonell have followed. The conductivity is directly related to the amount of polypyrrole, oxidant ratio and fibre structure with significant differences between viscose and lyonell. Polymerisation occurs uniformly inside the fibre bulk, by producing a coherent composite polypyrrole/cellulose. The mechanical and physical properties of cellulose fibres were not significantly modified as they are the best available45. 

Similar structures will occur in conjugated polymers such as polypyrroles and polythiophenes prepared from monomers with one or more different substituents at the positions on the aromatic ring not involved in the polymerisation, see Fig. 1.5. The reactivity of one particular site in the monomer usually predominates, so that the effect is relatively small. A 1 % head-to-head content may, however, seriously upset crystallisation. 

Fig. 18.9. Metal complex polymerised to give polypyrroles containing complexing cavities [128].

All of the above applications of ICPs have significant commercial potential. However, in most cases, this has not been exploited due to the lack of convenient polymer processing and device fabrication protocols. For example, while polypyrroles exhibit the desirable properties mentioned above, polymerisation usually results in the formation of an insoluble, infusible material not amenable to subsequent fabrication. Conducting polyaniline and polythiophene salts are similarly intractable. Several approaches have recently been employed to overcome this problem of intractability. 

Solubility has been Induced for polypyrroles by attaching alkyl [102,103] or alkyl sulfonate [104] groups to the pyrrole monomer prior to polymerisation. This results in markedly enhanced solubility in organic or aqueous medias, respectively. For example, we have shown that the electrochemical method [105] can be used to produce alkylated polypyrroles with high (400 g/L) solubility in organic solvents and reasonable (1-30 S cm ) conductivity. 

Both electrochemical and chemical oxidation have been used to produce 3-substituted alkylsulfonated pyrroles [106]. Electrochemical polymerisation was achieved using acetonitrile as solvent to form a solid deposit on the electrode. Alternatively, FeCl3 was used as oxidant. Conductivities in the range 0.001-0.500 S cm were obtained, with lower conductivity products obtained from chemical polymerisation. Others [107,108] have prepared homopolymers and copolymers of polypyrroles with alkyl sulfonate groups attached via the N-group. This N-group substitution decreases the polymers inherent conductivity. 

Several types of monomers have been used for this (Fig. 6), especially easily polymerisable molecules. Acrylate monomers [46-51 ] and acrylamides have been used the most [52-56]. Systems with polystyrene [47, 57-63] and poly-siloxane [64] backbones have also been synthesised. Recently, other types of polymer such as polyurethanes [65],polypyrroles [66-68], and polyimidazoles [69,70] have been used in special applications. Renewed interest has also been shown in silicas and sol-gel glasses [71]. 

The polypyrrole (Ppy)/dextrin nanocomposite is synthesised via in situ polymerisation and the preparation of this nanocomposite is shown in Figure 5.4. The backbone chain of this nanocomposite polymer contains hydrophobic side chains, which disrupt the microbial cell membrane leading to leakage of the cytoplasm in bacteria including Escherichia coli. Pseudomonas aeruginosa. Staphylococcus aureus and Bacillus subtilis. This material can be implemented in the fields of biomedicine, biosensors and food packaging due to the biodegradable property of dextrin as well as the antibacterial properties of the Ppy [79]. 

A. Ramanaviciene, W. Schuhmann, and R. Ramanavicius, AFM study of conducting polymer polypyrrole nanoparticles formed by redox enzyme - glucose oxidase - initiated polymerisation, Colloid Surf. B., 48(2), 159-166 (2006). 

Conducting organic polymers such as polyacetylenes, polyanilines and polypyrroles are of interest in electronic devices. One of the difficulties associated with their application is that they are degraded upon exposure to the atmosphere. For this reason, attempts have been made to prepare them encapsulated within zeolites, for example by polymerising acetylene over metal-exchanged zeolites. A recent report shows that polyacetylenes can also be prepared inside functionalised MOFs (see Section 10.3.3). It remains a challenge to prepare materials of acceptable properties for applications. 

Confocal Raman microprobe spectroscopy was used to characterise polyaniline/poly(V-vinyl carbazole), polypyrrole/poly(V-vinyl carbazole) and polypyrrole/ polyaniline films (or reverse order of each pair in the films). Two types of film were observed, depending on the conditions. Either the second polymer was incorporated into the initially coated layer or a doublelayer film with a well-defined interface was formed. Electrolysis of pyrrole and aniline monomer mixtures gave films rich in pyrrole when the pyrrole aniline molar ratios were greater than 0.12. However, polymerisation of V-vinyl carbazole and pyrrole monomer mixtures gave only polypyrrole over a wide range of molar ratios (121). 

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