ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The galvanostatic electropolymerization of thiophene (1), 3-methylthiophene (2) and 2,2′-bithiophene (3) in acetonitrile, containing 0,002 to 20 mol/L water, was studied in detail. The current efficiency γ for the polymer film formation decreased rapidly for 1, but much slower for 2 and 3 with increasing water concentration cH2O. For cH2O = 0,1 mol/L, γ was found to be 10, 82 and 95% for 1-3. It was possible to describe the experimental γ vs. cH2O plots quantitatively by a model where the electrogenerated radical cations (rc) of the thiophene (derivative) are consumed by two competing second-order follow up reactions, the nucleophilic attack of the rc by water (i) and the rate-determining dimerization of two rc's (ii). Their rates are given by: (i) v1 = k1 crc cH2O and (ii) v2 = k2 c2rc. The side reaction (i) leads to soluble products, while reaction (ii) contributes to the polymer film growth. The ratio k1/k2 was found to be 3 · 10-7, 2 · 10-8 and 4 · 10-9 for 1, 2 and 3, respectively, and this shows that the electropolymerization of 2,2′-bithiophene is by a factor of about 100 less sensitive toward the present water than thiophene. The steady state concentration crc is in the order of 10-9 mol/L in all three cases. The relative insensitivity of doping/undoping cycles with respect to the presence of water is discussed in terms of a lessened reactivity of the polarons and a low solubility of water in the heteroaromatic polymer.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1993.021941008
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