Synthesis and investigations of new electronically and ionically conducting polymers

Mao, Huanyu (1991) Synthesis and investigations of new electronically and ionically conducting polymers. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The electronically and ionically conducting ion exchange polymers, protonatedpoly-[3-(pyrrol-l-ylmethyl)pyridine](poly-HPMP+), poly-[l-methyl-3- (pyrrol-l-ylmethyl)pyridinium tetrafluoroborate] (poly-MPMP+BF4-), poly-[l-(3- [pyrrol~3-yl]propyl)pyridinium tetrafluoroborate] (poly-PPP+BF4-) and poly-[(3- [pyrrol-3-yl]propyl)trimethylammonium tetrafluoroborate] (poly-PPTA+BF4-) have been electrochemically synthesised. Elemental analysis, cyclic voltammetry, gravimetry and scanning electron microscopy have been used to characterize the prepared polymers. The structures and electrochemical properties of these polymers are similar to those of other N- and 3-substituted polypyrrole based polymers. However, the high concentration (5 ~ 6 M) of permanent positively charged sites improve their electrochemical properties. -- The in situ electronic conductivity of poly-MPMP+ was measured using rotating disc voltammetry. An empirical method was developed to extract potential profiles and conductivities from rotating disc voltammograms of ferrocene at poly-MPMP+ coated electrodes. This treatment was tested using in situ dual electrode methods, and confirmed. A relationship between the polymer conductivity and potential was obtained. The electronic conductivity increases exponentially with potential (90 mV per decade) and levels off when the potential is more positive than the polymer's formal potential. -- Ion exchange properties, such as the binding of an anionic electroeatalyst, for poly-MPMP+, poly-PPP+ and poly-PPTA+ have been quantitatively investigated. The partition coefficients of ferrocyanide for these polymers range from 3.2 x 104 to 5.5 x 104 and their saturation concentrations are 1.3 ~ 1.4 M. The charge transport of ferrocyanide is faster in poly-PPP+ and poly-PPTA+ than in poly-MPMP+ due to the significant difference in each polymer's conductivity at the formal potential of ferrocyanide. -- Transport of I-, CI-, and Fe(CN)64- in poly-MPMP+ have been studied using rotating disc voltammetry and ionic conductivity methods. Ion transport in the film is strongly dependent on the solvent. The diffusion coefficient of I- in water (1.5 x 10-7 cm2 s-1) is over 2 orders of magnitude higher than in acetonitrile. Poly- MPMP+ is significantly more permeable in water than polypyrrole. The diffusion coefficient for Fe(CN)64- is over 3 orders of magnitude higher than in reduced polypyrrole. The increased solvation and swelling of poly-MPMP+ in water, which are due to the high concentration of positively charged sites in the polymer, result in improved ion transport properties. -- Ascorbic acid oxidation is catalysed by these polymers (pH = 7.4) and mediated by electrostatically bound Fe(CN)64- (pH = 2.3). Cyclic voltammograms for ascorbate oxidation show that the peak potential at poly-PPTA+ coated Pt electrodes can be as much as 350 mV less than that at a bare Pt electrode. The peak current for poly-PPP+ coated electrodes is more than 10 times greater than that at a bare Pt electrode. The 3-substituted polymers (poly-PPP+ and poly- PPTA+) show a greater electron transfer rate than does the N-substituted polymer (poly-MPMP+), mainly due to the higher electronic conductivity for 3-substituted polymers at the ascorbate oxidation potential. The three polymers have enhanced, analytically significant peak currents which have allowed the generation of linear calibration curves for the analysis of ascorbic acid in aqueous solution.

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