Polypyrroles alternating copolymers

In one other report on polypyrrole alternating copolymers, Geissler et al. [143] synthesized and electrochemically polymerized 3,6-bis(N-methylpyr-role-2-yl)-A -ethylcarbazole to obtain the alternating copolymer of bi-A -methylpyrrole and A/-ethylcarbazole, but they gave few details. 

Polypyrrole copolymers with perfectly alternating units of pyrrole with another single heterocycle are not known. Alternating copolymers of pyrrole with bithiophene are prepared by electrochemical polymerization of the three-membered oligomer, 2,5-di-2-(thienyl)-pyrrole [11,12]. Even the homopolymerization of 2-thienylpyrrole does not really lead to alternating units of pyrrole and thiophene because this monomer must dimerize after oxidation. What results is a copolymer of bipyrrole and bithiophene because of the different values for the oxidation potentials of pyrrole, thiophene, bithiophene, etc. 

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. 

Poly (thiophene)s are of particular interest as electfochromic materials owing to their chemical stability, ease of synthesis and processability. For the most part, current research has been focused on composites, blends and copolymer formations of several conjugated polyheterocyclics, polythiophene and its derivatives, especially PEIX)T. In one example, poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(2-acrylamido-2-methyl-l-propanesulfonate) (PAMPS) composite films were prepared by Sonmez et al. for alternative electrochromic applications [50]. Thin composite films comprised of PEDOT/PAMPS were reported to switch rapidly between oxidized and neufial states, in less than 0.4 s, with an initial optical contrast of 76% at A.max. 615 nm. Nanostructured blends of electrochromic polymers such as polypyrrole and poly(3,4-ethylenedioxythiophene) were developed via self-assembly by Inganas etal. for application as an electrochromic window [26]. Uniir etal. developed a graft-type electrochromic copolymer of polythiophene and polytetrahydrofuran for use in elecfiochromic devices [51]. Two EDOT-based copolymers, poly[(3,4-ethylenedioxythiophene)-aZ/-(2,5-dioctyloxyphenylene)] and poly[(3,4-ethylenedioxythiophene)-aft-(9,9 -dioctylfluorene)] were developed by Aubert et al. as other candidates for electrochromic device development [52],... 

This chapter is divided into two main parts polythiophene copolymers and polypyrrole copolymers. Each part reviews the random copolymerization of the heterocyclic monomer and important derivatives, principally those with substituents at the 3-position of thiophene and at the 1- and 3-positions of pyrrole. Alternating, block and graft copolymers are covered in both segments. Because applications of conducting polymers are reviewed in Volume 4, only applications unique to specify copolymers are covered here. In addition, a few theoretical studies dealing with conducting copolymers are reviewed. 

Cyclic voltammetry of the copolymer shows three anodic peaks, two matching the oxidation potentials of the parent homopolymers and a third which is intermediate. Authors attributed the data to the formation of blocks of polypyrrole and polythiophene cormected by blocks of random alternating groups of pyrrole and bithiophene. Increasing the amount of bithiophene in the copolymer produced a strong drop in the final conductivity of the materials, from 17 S cm at 1 mol% to I S cm at 14 mol%. 

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