Electroinitiated Polymerization Research Articles

Biomedical Applications of Electro-Initiated Polymerisation on Ti6Al4 V Titanium Alloy using Silk Fibroin Coatings for Antibiotic Delivery and Improved Cell Metabolism.

Silk fibroin interactions with metallic surfaces can provide utility for medical materials and devices. Toward this goal, titanium alloy (Ti6Al4 V) was covalently grafted with polyacrylamide via electrochemically reducing 4-nitrobenzene diazonium salt in the presence of acrylamide. Analysis of the modified surfaces with FT-IR spectra, SEM and AFM were consistent with surface grafting. Functionalised titanium samples with a silk fibroin membrane, with and without impregnated therapeutics, were used to assess cytocompatibility and drug delivery. Initial cytocompatibility experiments using fibroblasts showed that the functionalised samples, both with and without silk fibroin coatings, supported significant increases between 72-136 % in cell metabolism, compared to the controls after 7 days. A 7-days release profiling showed consistent bacterial inhibition through gentamicin release with average inhibition zones of 239 mm2. Over a 5-week period, silk fibroin coated samples, both with and without growth factors, supported better human mesenchymal stem cell metabolism with increases reaching 1031 % and 388 %, respectively, compared to samples without the silk fibroin coating with.

Multifunctional polymeric surface coatings of carbon fibre electrodes for enhanced energy storage performance

We report a proof-of-concept study on the development of multifunctional surface coatings for carbon fibre (CF) electrodes in structural energy composites, which for the first time addresses three key properties of CF: capacitance, tensile properties and interfacial adhesion, simultaneously. Multifunctional coatings have been designed by covalently grafting conductive and redox active poly(o-phenylenediamine) (PoPD) on CF via surface electro-initiated polymerisation using different diazonium salts. This has resulted in improvements in specific capacitance, tensile strength, tensile modulus and interfacial shear strength (IFSS) up to 30 F g−1, 4.58 GPa, 276 GPa and 43.5 MPa, respectively, all of which are higher than the values reported for pristine CF. To further improve the IFSS, a bilayered polymeric coating has been designed by electro-grafting polyacrylamide on top of the conductive PoPD layer, which led to specific capacitance, tensile strength, tensile modulus and IFSS (up to 9 F g−1, 4.28 GPa, 256 GPa and 55.6 MPa, respectively). The non-conductive polyacrylamide layer on top of the PoPD layer is thought to be the reason for depressed capacitive performance, though this does come at a trade-off for improved fibre–matrix adhesion. Thus, a means to tailor this material based on end user priorities is presented herein. In contrast to the conventional methods of surface activation for improving the capacitance of CF, which often result in a trade-off between electrochemical and mechanical/interfacial properties of CF, this method offers a means to simultaneously enhance the electrochemical, mechanical, and interfacial performance of CF with great tunability.

Examining the Role of Aryldiazonium Salts in Surface Electroinitiated Polymerization.

Historically, the irreversible reduction of aryldiazonium salts has provided a reliable method to modify surfaces, demonstrating a catalogue of suitable diazonium salts for targeted applications. This work expands the knowledge of diazonium salt chemistry to participate in surface electroinitiated emulsion polymerization (SEEP). The influence of concentration, electronic effects, and steric hindrance/regiochemistry of the diazonium salt initiator on the production of polymeric films is examined. The objective of this work is to determine if a polymer film can be tailored, controlling the thickness, density, and surface homogeneity using specific diazonium chemistry. The data presented herein demonstrate a significant difference in polymer films that can be achieved when selecting a variety of diazonium salts and vinylic monomers. A clear trend aligns with the electron-rich diazonium salt substitution providing the thickest films (up to 70.9 ± 17.8 nm) with increasing diazonium concentration and electron-withdrawing substitution achieving optimal homogeneity for the surface of the film at a 5 mM diazonium concentration.

Expanding the Scope of Surface Grafted Polymers Using Electroinitiated Polymerization.

The ability to rapidly modify the surface of materials is a powerful means of tailoring interfaces and interphases for a variety of applications. In this work, we demonstrate the extensive scope of an electrochemically mediated surface modification technique, able to install a range of surface grafted polymers of varying polarity and functionality. The irreversible reduction of aryldiazonium salts initiates polymer growth and provides a "priming layer" for the polymers to attach to, covalently anchoring them to the surface. We show the broad applicability of this technique through polymerization of 19 acrylate monomers, as well as a noncarbonyl bearing monomer species, styrene. Surface bound films were characterized using FT-IR, ellipsometry, and water contact angle.

Methyl methacrylate reactivity under electric field in view of an electrically induced polymerization process

Abstract We have studied the effect of a static external electric field on electronic properties of methyl methacrylate (MMA) and its consequences in an electro-initiated polymerization by density functional theory (DFT). The Conceptual-DFT scheme is used to obtain hardness (η), electrophilicity (ω) and nucleophilicity (N) for MMA in gas phase and in a dielectric media. These changes on ω and N have been determined as a function of the direction and strength of the external electric field. This study give some insight on the enhancement of reactivity and, therefore, on the polymerization process under the presence of electric fields.

Grafting of PMMA brushes layer on Cu surface to create a stable superhydrophobic surface

In this paper, poly(methyl methacrylate) (PMMA) brushes were grafted on Cu micro-cone structured substrate by a simple one-step cathodic electro-initiated polymerization method which was carried out in aqueous solution at room temperature in the open air. The PMMA brushes were continuous, uniform and thickness-controllable, and it covalently bonded to the Cu surface. In the brushes, nitrophenyl moieties acted as cross-linker between PMMA chains. After removed from the solution followed by treated with water, the PMMA brushes (basically a hydrophilic material)/micro-cone structured Cu surface was hydrophilic with water contact angle (CA) of 74.4°. However, it exhibited superhydrophobicity by treating it in the acetone. The conversion from hydrophilic surface to superhydrophobic one may due to rearrangement of nitrophenyl moieties and PMMA chains at the topmost of the brushes. In addition, its water CA increased with grafting time of the brushes from 145° to about 166°, because there was no available space in thinner film for group reorientation. The surface was conversed to hydrophilic again after treated with hot water, but it was still superhydrophobic after treated in water at room temperature. This revealed that the group reorientation also easily occurred in hot water like in the acetone. More importantly, the surface retained good superhydrophobic stability in acidic environment and in long-time storage. Furthermore, the superhydrophobic surface had excellent resistance that can provide effective protection for the bare Cu substrate.

Cathodic Aqueous Polymerization of Acrylamide with ZnCl2

The electroinitiated polymerization has been described here. The polymerization mixture consisted of monomer dissolved in an aqueous solution of ZnCl2, and was subjected to electrolysis in a divided cell. The rates of polymerization increased linearly with increase in applied current level and monomer concentration. Polymers of high molecular weights (≍105) were obtained from intrinsic viscosity measurements that increased with monomer concentration. The cyclic voltammogram of acrylamide in H2O -ZnCl2 solution suggests that the monomer gets directly reduced at cathode and the polymerization mechanism is anoinic.

Electro-initiated cationic polymerization in the presence of potassium hexafluoroantimonate

The kinetics of electro-initiated polymerization of vinyl ethers in the presence of potassium hexafluoroantimonate are investigated by RT-FT-NIR. The apparatus for real time monitoring of the kinetics of the reaction is set up by using ITO conductive glasses. Potassium hexafluoroantimonate has been proven to be an efficient initiator for electro-initiated polymerization of vinyl ethers.

Polycarbonate-based solid polymer electrolytes for Li-ion batteries

Pressing demands for high power and high energy densities in novel electrical energy storage units have caused reconsiderations regarding both the choice of battery chemistry and design. Practical concerns originating in the conventional use of flammable liquid electrolytes have renewed the interests of using solvent-free polymer electrolytes (SPEs) as solid ionic conductors for safer batteries.In this thesis work, SPEs developed from two polymer host structures, polyethers and polycarbonates, have been investigated for all-solid-state Li- and Li-ion battery applications. In the first part, functional polyether-based polymer electrolytes, such as poly(propylene glycol) triamine based oligomer and poly(propylene oxide)-based acrylates, were investigated for 3D-microbattery applications. The amine end-groups were favorable for forming conformal electrolyte coatings onto 3D electrodes via self-assembly. In-situ polymerization methods such as UV-initiated and electro-initiated polymerization techniques also showed potential to deposit uniform and conformal polymer coatings with thicknesses down to nano-dimensions.Moreover, poly(trimethylene carbonate) (PTMC), an alternative to the commonly investigated polyether host materials, was synthesized for SPE applications and showed promising functionality as battery electrolyte. High-molecular-weight PTMC was first applied in LiFePO4-based batteries. By incorporating an oligomeric PTMC as an interfacial mediator, enhanced surface contacts at the electrode/SPE interfaces and obvious improvements in initial capacities were realized. In addition, room-temperature functionality of PTMC-based SPEs was explored through copolymerization of e-caprolactone (CL) with TMC. Stable cycling performance at ambient temperatures was confirmed in P(TMC/CL)-based LiFePO4 half cells (e.g., around 80 and 150 mAh g-1 at 22 °C and 40 °C under C/20 rate, respectively). Through functionalization, hydroxyl-capped PTMC demonstrated good surface adhesion to metal oxides and was applied on non-planar electrodes. Ionic transport behavior in polycarbonate-SPEs was examined by both experimental and computational approaches. A coupling of Li ion transport with the polymer chain motions was demonstrated.The final part of this work has been focused on exploring the key characteristics of the electrode/SPE interfacial chemistry using PEO and PTMC host materials, respectively. X-ray photoelectron spectroscopy (XPS) was used to get insights on the compositions of the interphase layers in both graphite and LiFePO4 half cells.

Vinyl-functionalized imidazolium ionic liquids as new electrolyte additives for high-voltage Li-ion batteries

Four functionalized ionic liquids based on imidazolium cations with vinyl or alllyl group and TFSI− anion were synthesized as electrolyte additives for high-voltage Li-ion battery to stabilize carbonate-based electrolytes on the surface of 5 V class cathode materials. The electrochemical behaviors and surface morphology of LiNi0.5Mn1.5O4 cathode had been investigated by cyclic voltammetry, charge–discharge test, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), respectively. Cycle life and rate performance of the Li/LiNi0.5Mn1.5O4 cells containing 1.2 M LiPF6 in ethylene carbonate/ethyl methyl carbonate can be improved by adding 1-allyl-3-vinyl imidazolium bis(trifluoromethanesulphonyl)imide ([AVIm][TFSI]). The addition of 3 wt.% [AVIm][TFSI] results in high discharge capacity of above 130 mAh g−1. Surface analysis of the cathode material (XPS and SEM) suggested that a stable and compact polymer film was formed on the LiNi0.5Mn1.5O4 cathode by electroinitiated polymerization of imidazolium cation with vinyl and allyl group.

Synthesis, electropolymerization and characterization of a cross-linked PEDOT derivative

The synthesis of a novel electropolymerizable monomer, 2,2′,3,3′-tetrahydro-2,2′-bithieno[3,4-b][1,4]dioxine (THBTD), based on two 3,4-ethylenedioxythiophene (EDOT) moieties connected through the ethylenedioxy bridge is reported. The new monomer paves the way for the development of cross-linked networks based on the EDOT moiety. Polymer films were electrogenerated from monomeric solutions by consecutive potential sweeps or by flow of constant anodic currents and the polymer structure was studied using FTIR. The relationship between the mass of the electrogenerated polymer (after reduction) and the polymerization charge gives the productivity of the consumed charge (mg C−1) while the charge stored and delivered by the films was determined by cyclic voltammetry getting the specific charge (C g−1). Simultaneously with the electroinitiated polymerization a chemical polymerization occurs around the electrode by monomer protonation giving protonated and no electroactive polymer chains. This chemical polymerization was followed in solution by UV-Vis spectroscopy using different conditions. Productivities and specific charges change with the conditions of synthesis in opposite directions. The voltammetric control presents a main redox couple (0.54/0.50 V) and a strong reduction process at −2.89 V that only can be reoxidized at more anodic potentials than 0.3 V as usual for charge trapping effects. EQCM studies indicate a remarkable difference between PEDOT and poly(THBTD). While poly(THBTD) shows a predominantly reversible anionic exchange during oxidation from the neutral state, the parent pristine PEDOT presents a mixed anionic and cationic exchange. Electrochromic color changes from an intense blue color of the oxidized film to a clear orange color in the reduced films as observed by in situUV-Vis spectroscopy. Interestingly, the electrochromic changes in poly(THBTD) are opposed to those of PEDOT. Both thiophene derivative polymers present a similar thermal degradation at 305 and 314 °C, respectively.

Simultaneous novel synthesis of conducting and non-conducting halogenated polymers by electroinitiation of (2,4,6-trichloro- or 2,6-dichlorophenolato)Ni(II) complexes

NiL 2(Ph) 2· xH 2O [L=3,5-dimethylpyrazole or N-methyl imidazole; Ph=DCP or TCP; x=0, 1 or 3] complexes were synthesised and characterised by analytical and spectroscopic methods using elemental analysis and FTIR. The electrochemical behavior of the complexes was studied by cyclic voltammetry in tetrabutylammoniumtetrafluoroborate– N, N-dimethylformamide electrolyte–solvent couple. Cyclic voltammogram of the complexes displayed two-step oxidation processes under the nitrogen gas atmosphere. The polymerization of the complexes was accomplished in the same solvent–electrolyte couple by the constant potential electrolysis of NiL 2(Ph) 2· xH 2O, synthesizing the poly(di- or monochlorophenylene oxide)s via free radical mechanism. The simultaneous polymerization of non-conducting polymer and conducting polymer (the conductivity of 0.7 S cm −2) were achieved by electroinitiated polymerization of Ni(DMPz) 2(TCP) 2. The structural analysis of the polymers were performed using FTIR, 1H NMR and 13C NMR spectroscopic techniques and DSC for the thermal analysis. The kinetics of the polymerization was followed by in situ UV–vis spectrophotometer during the electrolysis. The low temperature ESR spectrum of the electrolysis solution also confirmed the formation of phenol radical ( g=2.0028). One electron oxidation process of NiL 2(DCP) 2· xH 2O produces a new Ni(II) complex, Ni(L–L)(DCP) 2(S) by the rapid decomposition of Ni IIIL 2(DCP) 2 into a ligand radical producing a singlet with the g value of 2.0015. Second electron oxidation process generates oligemers, which could not be isolated from the electrolyte solution.

Synthesis of acrylic polymer networks by electroinitiated polymerization

A polyurethane oligomer bearing acrylate end groups has been cross-linked at ambient temperature by electroinitiated polymerization. The initiator-free water-based resin was coated onto a metallic plate serving as cathode by electrodeposition or drying, only its tip being dipped into the electrolyte. The curing of the coating in contact with air was followed by infrared spectroscopy and found to proceed efficiently by applying a 100 mA current, with formation of a hard and insoluble polymer. Electroinitiated polymerization can be associated to photoinitiated polymerization to ensure an effective curing of shadowed areas on tridimensional objects protected by UV-cured coatings.

Electroinitiated polymerization of 2-allylphenol

Redox behaviour of 2-allylphenol (2APhOH) was studied by using cyclic voltammetry (CV) and electroinitiated polymerization was conducted at the measured peak potentials. Constant potential electrolysis (CPE) of the monomer was carried out in acetonitrile-sodium perchlorate, solvent-electrolyte couple, at room temperature. Polymerization of the monomer yielded insoluble polymer films on the surface of the electrode together with the low molecular weight polymers in the bulk of the solution. The structural analysis of the polymers were carried by 1H-NMR and FTIR spectroscopy. Molecular weight of the soluble polymer was determined by GPC. Thermal properties of the polymer film and soluble polymer were studied by DSC. The course of electroinitiated polymerization was monitored by in-situ UV-VIS spectroscopy.

Electroinitiated polymerisation of methyl methacrylate mediated by titanium(III)–hydroxylamine redox system: a kinetic study

Methyl methacrylate was polymerised in an aqueous sulphuric acid–methanol medium in a divided cell by an electrolytically generated mediator species titanium(III). Titanium(III)–hydroxylamine sulphate was used as the initiator redox system. The reaction was confined to the cathode compartment and was found to proceed via a free radical mechanism. Kinetics of polymerisation were investigated for different initial monomer concentrations, acid concentrations, electrical currents, dielectric constants of the solvent and electrode materials. Chain termination of the polymer was due to coupling of growing macroradicals, also a fraction of the termination took place by chain transfer mechanism involving the organic solvent molecules. A suitable mechanism for titanium(III)–hydroxylamine sulphate mediated indirect electropolymerisation of methyl methacrylate has been proposed.

Kinetics of electroinitiated polymerization of acrylonitrile mediated by titanium (III)-dimethylglyoxime redox system

Acrylonitrile was polymerized in an aqueous sulphuric acid–methanol medium by an electrolytically generated mediator species, titanium(III). Titanium(III)–dimethylglyoxime was used as the initiator redox system. The reaction was confined to the cathode compartment and was found to proceed via a free radical mechanism. The kinetics of polymerization were investigated for different initial monomer concentrations, acid concentrations, electric currents, dielectric constants of the solvent and electrode materials. A suitable mechanism for titanium(III)–dimethylglyoxime-mediated indirect electropolymerization of acrylonitrile is proposed. Copyright © 1999 John Wiley & Sons, Ltd.

Electrochemically induced redox polymerization of acrylamide

Polymerization of acrylamide (AA) has been studied in aqueous solution in the presence of Ce(IV) salt-oxalic acid initiator system in an electrochemical cell with and without separation of anolyte and catholyte. For reactions that required the cathode and anode sections to be analyzed individually, a cell whose compartments were divided by a sintered glass disk of the medium porosity was employed. Polymerization was initiated by a free radical that is formed by the fast reaction of oxalic acid and Ce(IV). The electrolysis of the reaction solution results in regeneration of Ce(IV), which can oxidize oxalic acid to produce radicals. The effect of sulfuric acid and cerium (IV) salt concentration and temperature on the yield of electroinitiated polymerization in different cell designs and structural identification of products were performed. Reaction was also followed by cyclic voltametric measurements, and a mechanism was proposed. Results indicated that the electrolysis method with a divided cell (85% conversion) shows advantages, compared with nonelectrolytic (5% conversion) and with undivided electrochemical cell (25% conversion) methods where a high concentration of initiator was used.

Electroinitiated polymerization of maleic anhydride with 1,4-dimethylpyridiniumiodide—kinetics of polymerization

The polymerization of maleic anhydride was investigated under constant current electrolysis in a simple H-type divided cell with 1,4-dimethylpyridiniumiodide as supporting electrolyte. The polymer formation depends on polymerization time, current intensity and on the nature of the supporting electrolyte. The polarographic measurements showed that the reduction potential of the supporting electrolyte is less than that of the monomer or the solvent. The product of the electrolysis arising from the supporting electrolyte initiates the polymerization. The mechanism of polymerization is assumed to be an anionic one.

Monitoring of electroinitiated polymerization of aniline by Raman microprobe spectroscopy

It was observed that some water soluble products were formed during the electrochemical synthesis of polyaniline, and Raman spectroscopy can be used to detect those products. The amount of water soluble products increases with increasing electrolysis potential and the peak observed at 1620 cm −1 is characteristic for these products. Rinsing the polyaniline coated electrode with water even once removes the soluble products from the polymer, which indicates that care must be taken in polyaniline characterization studies during washing, solvation and doping-undoping processes. The transition of H 2SO 4-doped polyaniline to undoped form by treating with 1.0 M NaOH takes place very rapidly in high yields which can be followed by in situ Raman spectroscopy.

Conducting Polymer Composites of Polypyrrole and a Pqly(Arylene Ether Ketone)

Electrically conducting composites of polypyrrole and a poly(arylene ether ketone) were synthesized by electroinitiated polymerization of pyrrole on a poly(arylene ether ketone)-coated platinum electrode. The electrolysis medium was water and p-toluene sulfonic acid. The conductivities of the composites were in the range 1–10 S/cm. The composites were characterized by scanning electron microscopy, Fourier transform infrared, and thermal analyses. The composites were found to be composed of bilayers which can be peeled into two free-standing polymer films. The solution side of the polypyrrole layer of the alloy film contains globular structures, whereas the other side is smoother.