[Show abstract][Hide abstract] ABSTRACT: Studies of the hydrogen evolution reaction (HER) were carried out on base-inhibited vapor phase polymerized (BI-VPP) poly(3,4-ethylenedioxythiophene) (PEDOT)-poly(ethylene glycol) (PEG) thin films synthesized on several substrates, including gold, glassy carbon, and titanium, in an acidic electrolyte. The proton reduction overpotential became smaller and the current–potential (i-E) scans moved toward the thermodynamic potential with time. However, they did not move below the proton reduction potential of the substrate. Collectively, the results suggested to us that the polymer film was porous and that the porosity increased with time when the electrode was immersed in solution, with the hydrogen evolution catalysis taking place on the conducting substrate beneath the polymer rather than on our BI-VPP PEDOT-PEG thin films. Comparison of the HER on gold substrates with different impurities was also studied and traces of Pt and Pd at the ppm level significantly improved the HER activity of Au.
[Show abstract][Hide abstract] ABSTRACT: Using stopped flow and other spectroscopic techniques, the thermodynamic parameters of the coupling reaction between 1,3-dimesitylimidazolylidene and phenyl isothiocyanate were determined (H(o) = -96.1 kJ mol(-1) and ΔS(o) = -39.6 J mol(-1) K(-1)). On the basis of these data which indicated that the reaction was reversible (K(eq) = 5.94 × 10(14) M(-1) at 25 °C; k(f) = 252 M(-1) s(-1); k(r) = 4.24 × 10(-13) s(-1)), the adduct formed from the two aforementioned coupling partners was used as a latent catalyst to facilitate the [2 + 2 + 2] cyclotrimerization of phenyl isocyanate and the polymerization of DL-lactide.
The Journal of Organic Chemistry 01/2011; 76(1):301-4. · 4.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Conjugated polymers (CPs) have become essential to a diverse array of fields, ranging from biosensing to photovoltaics to optoelectronic materials. Given their widespread use, there is a growing need for variants whose functions may be modulated via exogenous stimuli. Alteration of CP structure could effect the desired changes and may be actuated in response to (1) chemical, (2) electrochemical, (3) photochemical, or (4) thermal impetuses. In this Perspective, we present a review of CPs reported to respond to chemical, electrochemical, and photochemical stimuli along with our own efforts using thermal stimuli. A particular emphasis has been directed toward structurally dynamic CPs that exhibit changes in their electronic properties, which could enable access to new classes of smart and other functional materials. During the course of our discussion, we consider the advantages and disadvantages inherent to each of the aforementioned methods, along with the potential applications of the polymers derived therefrom. We conclude this Perspective with a brief overview of the accomplishments in this nascent field, reflecting upon the unconquered challenges and contemplating the opportunities present for future discoveries involving structurally dynamic CPs.
[Show abstract][Hide abstract] ABSTRACT: Using the copper-catalyzed 1,3-dipolar “click” cycloaddition reaction, poly(sulfone)s containing pendant azide moieties were functionalized with various quantities of sodium 3-(prop-2-ynyloxy)propane-1-sulfonate and crosslinked with 1,7-octadiyne. The degrees of sulfonation and crosslinking were systematically varied by changing the ratios of the aforementioned reagents. The polymers were cast into membranes, acidified, and then tested for proton conductivity, methanol permeability, and membrane-electrode assembly (MEA) performance. The membranes showed a reduction in methanol permeability with increasing concentration of crosslinker and exhibited performance on par with direct methanol fuel cells containing Nafion-based membranes.
[Show abstract][Hide abstract] ABSTRACT: Sulfonated poly(ether ether ketone) (sPEEK) membranes were blended with various functionalized imidazoles. The effect of the pKa of the added heterocycle on the dry proton conductivities of the blended membranes was evaluated over the temperature range of 40-150 degrees C. These membranes showed nonmonotonous conductivities with respect to temperature, as well as a clear correlation of peak temperature conductivity to the pKa of the heterocycle. We use a theoretical model based on the reaction equilibria between sPEEK's sulfonic acid groups and the basicity of the added heterocycles in order to better understand the mechanistic origins of the observed temperature-conductivity profiles.
The Journal of Physical Chemistry B 08/2009; 113(30):10063-7. · 3.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A click by any other name: Coupling bis(N-heterocyclic carbene)s with bis(azide)s afforded a novel class of conjugated polytriazenes. These polymers were rendered electrically conductive upon doping, and fluorene-containing variants exhibited luminescence. This adaptation of N-heterocyclic carbene (NHC)/azide coupling chemistry to polymer synthesis reveals the potential of NHCs as building blocks for accessing polymers having useful electronic properties.
Angewandte Chemie International Edition 07/2009; 48(28):5187-90. · 11.34 Impact Factor