Jennifer A. Irvin

Progress in using conductive polymers as corrosion-inhibiting coatings

Abstract A general review of the chemistry and corrosion control properties of electroactive polymers will be presented. These polymers are also known as conductive polymers (CPs), and this term will be used throughout this article. This paper will focus on both the synthesis of applicable CPs used for corrosion protection in various environments and their potential benefits over common organic barrier coatings.

Low-oxidation-potential conducting polymers: Alternating substituted para-phenylene and 3,4-ethylenedioxythiophene repeat units

The effect of alkoxy substituents on the physical and electronic properties of a series of poly1,4-bis[2-(3,4-ethylenedioxy)thienyl]-2,5-dialkoxybenzenes is reported. Monomers containing methoxy, heptoxy, dodecyloxy and hexadecyloxy substituents were obtained from Negishi couplings in yields ranging from 42 to 83%. The methoxy, heptoxy and dodecyloxy monomers electropolymerized efficiently to form electroactive films, with irreversible monomer oxidation peak potentials ranging from +0.46 to +0.51 V versus Ag/Ag + . The hexadecyloxy-substituted derivative exhibited a higher oxidation potential of +0.66 V and a slower rate of film formation owing to solubility of the oligomer. Cyclic voltammetry of the polymer films revealed reversible redox processes with quite low E 1/2,p potentials ranging from −0.28 to −0.35 V. Band gaps of 1.75 eV for the methoxy-substituted polymer and 2.0 eV for the longer-chain-substituted polymers were determined from the onset of the π to π * transition observed by optoelectrochemical techniques. Oxidative chemical polymerization of the dodecyloxy and hexadecyloxy monomers with ferric chloride, followed by reduction with ammonium hydroxide, produced slightly soluble polymers.

Conductive polymer-based nanoparticles for laser-mediated photothermal ablation of cancer: synthesis, characterization, and in vitro evaluation

Laser-mediated photothermal ablation of cancer cells aided by photothermal agents is a promising strategy for localized, externally controlled cancer treatment. We report the synthesis, characterization, and in vitro evaluation of conductive polymeric nanoparticles (CPNPs) of poly(diethyl-4,4′-{[2,5-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-1,4-phenylene] bis(oxy)}dibutanoate) (P1) and poly(3,4-ethylenedioxythiophene) (PEDOT) stabilized with 4-dodecylbenzenesulfonic acid and poly(4-styrenesulfonic acid-co-maleic acid) as photothermal ablation agents. The nanoparticles were prepared by oxidative-emulsion polymerization, yielding stable aqueous suspensions of spherical particles of <100 nm diameter as determined by dynamic light scattering and electron microscopy. Both types of nanoparticles show strong absorption of light in the near infrared region, with absorption peaks at 780 nm for P1 and 750 nm for PEDOT, as well as high photothermal conversion efficiencies (~50%), that is higher than commercially available gold-based photothermal ablation agents. The nanoparticles show significant photostability as determined by their ability to achieve consistent temperatures and to maintain their morphology upon repeated cycles of laser irradiation. In vitro studies in MDA-MB-231 breast cancer cells demonstrate the cytocompatibility of the CPNPs and their ability to mediate complete cancer cell ablation upon irradiation with an 808-nm laser, thereby establishing the potential of these systems as agents for laser-induced photothermal therapy.

Poly(propylenedioxy)thiophene-Based Supercapacitors Operating at Low Temperatures

A mixture of the ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIBTI) and 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIPF6) was formulated. The thermal properties of the 50/50 binary mixture were determined by differential scanning calorimetry and cloud point measurement. No evidence of crystallization or phase separation during cooling at 1°C/min to - 60°C was found. The devices constructed in this study were light weight, flexible, and hermetically sealed. These sealed devices proved effective against electrolyte leakage and performance degradation during temperature cycling. The performance of poly(propylenedioxy) thiophene (PProDOT)-based type I supercapacitors using a 50/50 wt % EMIBTI/EMIPF6 electrolyte mixture was compared to the performance using neat EMIBTI. It was difficult to deposit PProDOT films directly from the ionic liquid mixtures. However, it was possible to deposit PProDOT films from EMIBTI and then assemble and test the devices using the 50/50 mixture. The low temperature performance of the EMIBTI/EMIPF6 supercapacitors was superior to that of the EMIBTI-based supercapacitors, evidenced by the retention of capacitive behavior below -30°C. The high temperature performance of the EMIBTI/EMIPF6 supercapacitors was nearly as good as the EMIBTI-based supercapacitors with 10% loss after 10,000 cycles at 70% depth of discharge at 60°C.

Electrochemical Deposition of a New n-Doping Polymer Based on Bis(thienyl)isopyrazole

A novel donor-acceptor polymer based on thiophene and isopyrazole has been prepared for use in n-doping applications. Nonpolymerizable monomer radical cations appear to be the predominant oxidation product, resulting in a need for extended cycling to produce adequate quantities of polymer for characterization. The electrochemical behavior of the polymer films produced is strongly dependent upon the conditions applied during electrodeposition and on the solvent used during cycling of the films. Cycling to reductive potentials during oxidative polymerization in acetonitrile was necessary to produce a polymer film capable of n-doping, likely resulting from a need to establish pathways for cation migration. The neutral polymer undergoes oxidation to the p-doped form at ca. 2000 mV vs Ag/Ag + in propylene carbonate and reduces back to neutral at ca. 0 mV. Conversion of the neutral polymer to its n-doped form involves reductions at -700 and -1300 mV, with reoxidation at -800 and -200 mV to return to the neutral form of the polymer.

Biodegradable DNA-enabled poly(ethylene glycol) hydrogels prepared by copper-free click chemistry

Abstract Significant research has focused on investigating the potential of hydrogels in various applications and, in particular, in medicine. Specifically, hydrogels that are biodegradable lend promise to many therapeutic and biosensing applications. Endonucleases are critical for mechanisms of DNA repair. However, they are also known to be overexpressed in cancer and to be present in wounds with bacterial contamination. In this work, we set out to demonstrate the preparation of DNA-enabled hydrogels that could be degraded by nucleases. Specifically, hydrogels were prepared through the reaction of dibenzocyclooctyne-functionalized multi-arm poly(ethylene glycol) with azide-functionalized single-stranded DNA in aqueous solutions via copper-free click chemistry. Through the use of this method, biodegradable hydrogels were formed at room temperature in buffered saline solutions that mimic physiological conditions, avoiding possible harmful effects associated with other polymerization techniques that can be detrimental to cells or other bioactive molecules. The degradation of these DNA-cross-linked hydrogels upon exposure to the model endonucleases Benzonase® and DNase I was studied. In addition, the ability of the hydrogels to act as depots for encapsulation and nuclease-controlled release of a model protein was demonstrated. This model has the potential to be tailored and expanded upon for use in a variety of applications where mild hydrogel preparation techniques and controlled material degradation are necessary including in drug delivery and wound healing systems.

Synthesis and characterization of chiral conjugated polymers for optical waveguides

In the pursuit of new photonic devices, the unique waveguide properties of chiral films made from single-handed helical molecules are under investigation. The synthesis of polymers with a hierarchical structure is the first step. In this paper we present results on the synthesis and characterization of poly(p-phenylenes) (PPPs) and polythiophenes possessing amine and amide chiral side-chains. A regioirregular PPP possessing one chiral side group per repeat unit was prepared. Regioregular PPPs possessing two chiral side groups per repeat unit were also synthesized; however, lower molecular weights were achieved due to steric constraints. The PPPs exhibited total optical rotation that was a function of the concentration of the chiral side group, with 35- per chiral group or 70- per repeat unit. A regioirregular polythiophene was prepared using oxidative polymerization. A molecular structure that leads to helical polymer chains that undergo supramolecular packing in spin-cast films is the goal.

Low oxidation potential conducting polymers based on 1,4-bis[2-(3,4-ethylenedioxy)thienyl]-2,5-dialkoxybenzenes

Abstract Palladium-catalyzed coupling techniques have been used to prepare a series of 1,4-bis[2-(3,4-ethylenedioxy)thienyl]-2,5-dialkoxybenzenes which can be polymerized chemically or electrochemically. The polymers have been characterized by electrochemistry, spectroelectrochemistry, in situ EPR electrochemistry, and in situ conductivity. The highly electron rich nature of these polymers leads to extremely low oxidation potentials (E 1/2.p = −0.15 to −0.35V vs . Ag/Ag + ). Mild polymerization conditions can be used, resulting in fewer side reactions and more stable polymers; e.g. only a 25% loss in electro activity occurs over 3000 redox cycles when switching polymer 2c. These polymers are stable over a broad potential range, allowing them to be used as modified electrode materials; for example, ferrocene can be repeatedly oxidized and reduced on the polymer surface. In situ EPR electrochemistry and in situ conductivity were used to better understand the polymer redox processes, which are solvent-dependent. Maximum conductivity is attained in the bipolaronic state, but stable polarons can be formed in certain solvents. The polymers are electrochromic, reversibly switching from red to blue upon oxidation with electronic bandgaps at ca . 1.9 eV.

Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step process that finishes with Negishi coupling. Negishi coupling is a cross-coupling process in which a chemical precursor is first lithiated, followed by transmetallation with ZnCl2. The resultant organozinc compound can be coupled to a dibrominated aromatic precursor to give the conjugated monomer. Polymer films can be prepared via electropolymerization of the monomer and characterized using cyclic voltammetry and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. Nanoparticles (NPs) are prepared via emulsion polymerization of the monomer using a two-surfactant system to yield an aqueous dispersion of the polymer NPs. The NPs are characterized using dynamic light scattering, electron microscopy, and UV-Vis-NIR-spectroscopy. Cytocompatibility of NPs is investigated using the cell viability assay. Finally, the NP suspensions are irradiated with a NIR laser to determine their effectiveness as potential materials for photothermal therapy (PTT).