Poly-N-methyl pyrroles

During the last decade, immobilization of oxidase type enzymes by physical entrapment in conducting or ionic polymers has gained in interest, particularly in the biosensor field. This was related to the possibility for direct electron tranfer between the redox enzyme and the electroconducting polymers such as polypyrrole (1,2), poly-N-methyl pyrrole (3), polyindole (4) and polyaniline (5) or by the possibility to incorporate by ion-exchange in polymer such as Nafion (6) soluble redox mediators that can act as electron shuttle between the enzyme and the electrode. 

Immobilization matrix poly-N-methyl pyrrole glucose [9]... 

Zhou, Q.-X., Miller, L. L., and Valentine, J. R., Electrochemically controlled binding and release of protonated dimethyldopamine and other cations from poly(N-methyl pyrrole)/polyanion composite redox polymers, J. Electroanal. Chem., 261, 147-164 (1989). 

Salmon et showed that the nature of the monomer was important in determining the switching potential. Specifically, he found that poly-N-methyl pyrrole was more difficult to oxidize/reduce than PPy and that intermediate potentials were required to switch copolymers of these two pyrroles. An elegant study by Delabouglise and Gamier showed how attaching various amino acids to the polymer backbone could be used to modify the switching characteristics. ... 

What happens if one introduces substituted analogs of the pyrrole monomer unit, e.g. N-methyl pyrrole in place of pyrrole This is seen in Fig. 4-8 the voltammetric behavior of the substituted analogs is very similar to that of P(Py), but with an anodic shift of the redox peak potentials. This is explained by the likely participation of protons in the facilitation of the redox of P(Py), which is not possible in N-substituted analogs. Another effect of N-substitution in poly(pyrroles) is of course increased environmental stability, as oxidants invariably first attack the exposed, electron rich N-atom of unsubstituted pyrrole. That monomer structure can sometimes directly influence polymer behavior is also seen in the plot of oxidation potentials of monomer vs. polymer for poly(thiophene) analogs in Fig. 4-9 here the two oxidation potentials exactly parallel each other, i.e. a monomer more difficult to oxidize implies a polymer also more difficult to oxidize. On the other hand, alkoxy-substituted P(ANi) show voltammetric behavior very close to that of the unsubstituted P(ANi), with peaks shifted less than 90 mV anodically (Fig. 4-10). 

Pyrroles do not react with alkyl halides in a simple fashion poly alkylated products are obtained from reaction with methyl iodide at elevated temperatures and also from the more reactive allyl and benzyl halides under milder conditions in the presence of weak bases. Alkylation of pyrrole Grignard reagents gives mainly 2-alkylated pyrroles whereas N-alkylated pyrroles are obtained by alkylation of pyrrole alkali-metal salts in ionizing solvents. 

PNMA, poly(N-methylaniline) PANI, poly(aniline) PEDOT, poly(3,4-ethylenedioxythiphene PSS, poly(styrene-sulfonate), PPy, poly(pyrrole) PEO, poly(ethylene oxide) DBSA, dodecylbenzene sulfonic acid CSA, camphor sulfonic acid PTSA, poly(o-toluene sulfonic acid) PFOA, perfluoro-octanolc acid TSA, toluene sulfonic acid CNF, carbon nanofiber SWCNT, single-walled carbon nanotube NP, nanoparticle MWCNT, multiwalled carbon nanotube PTh, poly(thlphene) CNT, carbon nanotube POA, poly(o-anisidine) SPANI, poly(anilinesulfonlcacld) PB, Prussian Blue DAB, 1,2-diamino benzene POEA, poly(o-ethoxyanlllne) PMMA, poly(methyl methacrylate). 

In contrast to the N-substituted polypyrroles, substitution at the 3-position results in polymers with a similar oxidation potential as the unsubstituted pyrrole and a higher conductivity. Some examples include methyl substituted bipyrroles (25a-c) [96], poly(3-hydroquinonylpyrrole) (26) [99], and poly(3-alkylsul-fonate pyrrole)s (27a-c) [100]. Unfortunately, because 3-substitution of the pyrrole ring is synthetically demanding and the resulting polymer shows a higher degree of sensitivity to air in the neutral state, more focus has been placed on iV-substitution as opposed to 3-substitution of the pyrrole monomer unit. 

Because the results of elemental analysis of the doped A/-methyl- and A/-phenylpyrrole copolymers with pyrrole do not accurately measure copolymer composition, Reynolds and others [5,6] prepared poly(pyrrole-co-A/-(3-bromophenyl)pyrrole tosylate). CV indicates that this comonomer has an oxidation potential of 1.7 V versus SCE, confirming its similar electrochemical behaviour to A/-phenylpyrrole. Elemental analysis of the copolymer prepared from a monomer feed of 95 moI% A-(3-bromophenyl)pyrrole contains only 9.3 mole% N-(3-bromopenyl)pyrrole units, based on the results of its elemental analysis. This means that only 30% of the pyrrole monomer used is inserted into the copolymer, and it is therefore difficult to prepare pyrrole/A/-phenylpyrrole copolymers of uniform composition containing more than 10% phenyl-substituted monomers. 

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