Synthesis and characterization of vinyl ester networks containing phthalonitrile moieties

A new styrenic monomer, 4-vinylphenoxyphthalonitrile, was synthesized by nucleophilic aromatic substitution of 4-vinylphenolate onto 4-nitrophthalonitrile. The new monomer was reacted with dimethacrylate-styrene resins (so-called vinyl esters) via free radical copolymerization at 90, then 120 °C with benzoyl peroxide as the initiator to form networks. The networks were further post-cured at 220, 240, or 260 °C for 4 h to convert the last portion of the methacrylates, and to partially cross-link the pendent phthalonitrile groups. A dimethacrylate-styrene network containing 30 wt% of the phthalonitrile-functional monomer exhibited a 70% reduction in peak heat release rate by cone calorimetry measured at an incident heat flux of 50 kW m⁻² relative to control vinyl ester networks. This still remains somewhat higher than peak heat release rates exhibited by brominated vinyl ester networks, but the CO/CO₂ ratio in the smoke is much lower for these non-halogenated materials.     

Curable resins based on recycled poly(ethylene terephthalate) for coating applications

Poly(ethylene terephthalate) waste was depolymerised in the presence of diethylene- or tetraethylene glycol and manganese acetate as a catalyst. An epoxy resin was then prepared by the reaction of these oligomers with epichlorohydrin in presence of NaOH as a catalyst. The produced oligomers were condensed with maleic anhydride and ethylene glycol to produce unsaturated polyester. The chemical structures of the resulting epoxy and unsaturated polyester resins were confirmed by ¹HNMR. The vinyl ester resins were used as cross-linking agents for unsaturated polyester resin diluted with styrene, using free radical initiator and accelerator. The 2-amino ethyl piprazine was used as hardener for epoxy resins. The curing behaviour of the unsaturated polyester resin, vinyl ester resins and styrene was evaluated at different temperatures ranged from 25 to 55 °C to calculate the curing activation energy of the system. The cured epoxy and unsaturated polyester resins were evaluated in coating application of steel.     

Effect of cation structure on the electrochemical and thermal properties of ion conductive polymers obtained from polymerizable ionic liquids

Several onium cations having vinyl group formed ionic liquids after coupling with bis(trifluoromethanesulfonyl)imide. These monomers were polymerized, and the relation between onium cation structure and properties of thus polymerized ionic liquids was investigated. The polymerized ionic liquid having ethylimiadzolium cation unit showed the highest ionic conductivity of around 10⁻⁴ S cm⁻¹ at 30 °C among the obtained polymers reflecting the lowest glass transition temperature of −59 °C. These polymers were thermally stable and their decomposition temperatures were about 350 °C. The ionic conductivity of the polymerized ionic liquids decreased by both the addition of lithium bis(trifluoromethanesulfonyl)imide and the polymerization in the presence of cross-linker. However, the polymerized ionic liquid having 1-methylpiperidinium cation structure showed good lithium ion transference number of 0.43 at room temperature.     

Inorganic-organic hybrid protonic polymeric materials for fuel cells based on polycondensed and organically cross-linked sulfonyl- and styrene-functionalized alkoxysilanes

A new class of proton conducting inorganic-organic polymer (ORMOCER^®) electrolytes for fuel cells based on polycondensed and organically cross-linked sulfonyl- and styrene-functionalized alkoxysilanes has been developed [1]. Different synthesis processes are used to take account of the different acidities of the starting alkoxydes. System-I is based on the separate hydrolysis and condensation of the acid and basic alkoxysilanes. Sulfonated alkoxysilanes and a styrene derivative functionalized alkoxysilane are hydrolyzed and co-condensed in parallel to the alkoxysilane containing at least a nitrogen heterocycle, an amine group or a sulfonamide group and a styrene derivative functionalized alkoxysilane. The two polycondensates are then mixed; the resulting resins are shaped into thin films and organically cross-linked via UV and/or thermal curing. Improvements of mechanical and electrochemical properties lead to System-II in which the sulfonated functionalized alkoxysilane is first hydrolyzed and condensed, then the two other alkoxysilanes are added for co-condensation. In system-III the three alkoxysilanes used for system-I are hydrolyzed and co-condensed without any partial hydrolysis of one of the components.The three systems present a good thermal stability up to 180 °C. The conductivity of the materials shows an Arrhenius behavior in the temperature range 25-110 °C with activation energies of 0.45 up to 0.78 eV depending on sample composition. A 1.0 × 10⁻² S cm⁻¹-conductivity value was measured for system-II/imidazole membranes at 110 °C under an inert gas atmosphere. The conductivity of anhydrous system-III/imidazole membranes goes from 9.1 × 10⁻³ S cm⁻¹ at 100 °C to 2.0 × 10⁻² ± 1.5 × 10⁻³ S cm⁻¹ at 140 °C.     

Compressive Properties and Curing Behaviour of Unsaturated Polyester Resins in the Presence of Vinyl Ester Resins Derived from Recycled Poly(ethylene terephthalate)

Poly(ethylene terephthalate) waste was depolymerised in the presence of tetraethylene glycol and manganese acetate as a catalyst, so as to produce oligomers. An epoxy resin was then prepared by the reaction of these oligomers with epichlorohydrin in presence of NaOH as a catalyst. New diacrylate and dimethacrylate vinylester resins were then synthesized by reaction of the terminal epoxy groups with acrylic and methacrylic acid in the presence of triphenyl phosphite as a catalyst. The chemical structures of the resulting vinyl ester resins were confirmed by ¹HNMR. The vinyl ester resins were used as crosslinking agents for unsaturated polyester resin diluted with styrene, using free radical initiator and accelerator. The curing behaviour of the unsaturated polyester resin, vinyl ester resins and styrene was evaluated at temperatures from 25 to 55 ^○C. The compression properties of the cured resins, having different vinyl ester contents and different cure temperatures, were evaluated. Increasing the cure temperature and the vinyl ester content led to a pronounced improvement in the compression strength and Young’s modulus.     

Online monitoring of synthesis and curing of phenol-formaldehyde resol resins by Raman spectroscopy

The synthesis and curing of phenol-formaldehyde resol resins were monitored online by Raman spectroscopy. The synthesis of the resins (F/P 2.0, alkalinity 4.5 wt%) was studied at rising temperature (40-90 °C) for 90 min and at constant temperatures (80 °C, 90 °C, 100 °C, and 110 °C) for 120 min. The progress of the curing was investigated isothermally (80 °C, 90 °C, 100 °C, and 110 °C) for 120 min for three resins with different degrees of condensation. The synthesis and curing of the resins were started in the reactor and the advancement of the methylolation and condensation reactions was followed through the window of the reactor in the wave number region of 2000-400 cm⁻¹ with use of a fiber optic probe for the data collection. The Raman spectra of six model compounds (formaldehyde, phenol, 2-hydroxybenzyl alcohol, 4-hydroxybenzyl alcohol, 2-benzylphenol, and 4-benzylphenol) were analyzed to facilitate the interpretation of the spectra of the resins. The consumptions of free phenol and free formaldehyde, as well as the progress of the methylolation and condensation reactions were easily monitored by following the changes in intensity of the characteristic Raman bands. The results for the cured resins obtained by Raman spectroscopy were in good agreement with the structures and residual reactivities studied by CP/MAS ¹³C NMR spectroscopy and differential scanning calorimetry (DSC), respectively. The results of the study show Raman spectroscopy to be a promising tool for the online monitoring and control of phenol-formaldehyde resol resin synthesis and curing; in addition, Raman spectroscopy offers an effective and fast method for structural study of the solid state resins.     

Fatty acid-based monomers as styrene replacements for liquid molding resins

One method of reducing styrene emissions from vinyl ester (VE) and unsaturated polyester resins (UPE) is to replace some or all of the styrene with fatty acid-based monomers. Methacrylated fatty acid (MFA) monomers are ideal candidates because they are inexpensive, have low volatilities, and free-radically polymerize with vinyl ester. The viscosity of VE resins using these fatty acid monomers ranged from 700-2000 cP, which is considerably higher than that of VE/styrene resins (∼100 cP). In addition, the T_g of VE/MFA polymers were only on the order of 80 °C, which is significantly lower than that of VE/styrene polymers. Decreasing the length of the base fatty acid chains from 18 to 12 carbon atoms improved the T_g by 20 °C, while lowing the resin viscosity from ∼2500 to ∼1000 cP. Residual unsaturation sites on the fatty acid backbone decreased the cure rate of the resins thereby decreasing polymer properties. Ternary blends of VE, styrene, and fatty acid monomers also effectively improved the flexural, fracture, and thermo-mechanical properties and reduced the resin viscosity to acceptable levels, while using less than 15 wt% styrene, far less than commercial VE resins.     

Synthesis of sulfonated poly(arylene-co-naphthalimide)s as novel polymers for proton exchange membranes

A series of novel sulfonated poly(arylene-co-binaphthalimide)s (SPPIs) were successfully synthesized via Ni(0) catalytic coupling of sodium 3-(2,5-dichlorobenzoyl)benzenesulfonate and bis(chloronaphthalimide)s. Bis(chloronaphthalimide)s were conveniently prepared from 5-chloro-1,8-naphthalic anhydride and various diamines. Tough and transparent SPPI membranes were prepared and the electrolyte properties of the copolymers were intensively investigated as were the effects of different diamine structures on the copolymer characterisitics. The copolymer membrane Ia-80, with an ion exchange capacity (IEC) of 2.50 meq g⁻¹, displayed a higher proton conductivity, i.e. 0.135 S cm⁻¹ at 20 °C, as compared to Nafion 117 (0.09 S cm⁻¹, 20 °C). The copolymer membrane Id-70, containing 3,3′-dimethyl-4,4′-methylenedianiline (DMMDA) units, exhibited excellent stability toward water and oxidation due to the introduction of hydrophobic methyl groups on the ortho-position of the imido bond in the copolymer. The mechanical property of Id-70 remained virtually unchanged after immersing membrane in pressured water at 140 °C for 24 h. Furthermore, the introduction of aliphatic segment a hexane-1,6-diamine (HDA) in copolymer led to a significant increase in proton conductivity and water uptake with increasing temperature; the proton conductivity of the Ic-70 membrane reached 0.212 S cm⁻¹ at 80 °C, which was higher than Nafion 117 as well as of the membranes based on aromatic diamines at equivalent IEC values. Consequently, these materials proved to be promising as proton exchange membranes.     

Preparation and surface characteristics of low-temperature curing fluorinated cathodic electrodeposition coating

Fluorinated cationic cathodic electrodepositing (CED) resins were synthesized by copolymerization of several acrylic monomers including Zonyl. Water dispersible cationic blocked-diisocyanate (denoted as TId) was also synthesized from isophorone diisocyanate (IPDI), cationic triethanolamine (TEOA), and dimethylpyrazole as the cross-linker for the low temperature curing at 90–120 °C. The emulsion stability of the cationic fluorinated CED resin was improved by ionization of the cross-linker TId, showing a mean particle diameter of 140–150 nm and a narrow distribution. 0.5 wt% of curing catalyst dibutyltin dilaurate (DBTL) was enough to accelerate the curing reaction and the gel content of the TId cured fluorinated CED film was higher than 90 wt% after being cured at 130 °C for 40 min. The contact angle and XPS spectrum of the CED film demonstrated that the surface enrichment of C–F₂ and C–F₃ groups effectively reduced the surface tension of the fluorinated CED coating and its surface tension γ_sv is even lower than 15 mN m⁻¹ for PTFE. The preheating of the CED film above T_g but below curing temperature promoted this surface enrichment of the fluorinated groups. Thermal fragmentation of the fluorinated side chains in the CED resins was successfully avoided due to using TId for low temperature curing.     

Preparation of star copolymers with three arms of poly(ethylene oxide-co-glycidol)-graft-polystyrene and investigation of their aggregation in water

The star graft copolymers with three arms composed of poly(ethylene oxide) (PEO) as main chain and polystyrene (PS) as side chains were prepared by sequential anionic ring-opening copolymerization of ethylene oxide and ethoxyethyl glycidyl ether (EEGE), and then atom transfer radical polymerization (ATRP) of styrene. The anionic ring-opening copolymerization of EO and EEGE was carried out using 2-ethyl-2-hydroxymethyl-1,3-propanediol as trifunctional initiator and diphenylmethyl potassium (DPMK) as deprotonating agent. The resulting three-arm star copolymer [poly(EO-co-EEGE)]₃ could be easily hydrolyzed to unmask the pendant hydroxyl groups without affecting the PEO chains. The switch from the first to the second mechanism was completed by the reaction of the multi-pendant hydroxyl groups of three-arm PEO chain with 2-bromoisobutyryl bromide. The obtained poly(ethylene oxide-co-2-bromoisobutyryloxyglycidyl ether), [poly(EO-co-BiBGE)]₃, was used as macroinitiators to initiate the polymerization of styrene in bulk at 90 °C by ATRP. The final products and intermediates were characterized by NMR, SEC and IR in detail. The amphiphilic star graft copolymers synthesized can form micelles in water. The critical micelle concentration (cmc) determined by fluorescence spectra was about 5 × 10⁻⁷ g/mL. Sphere micelles were observed by transmission electron microscopy (TEM) at low copolymer concentration (6 × 10⁻⁵ g/mL), but the micelle shape became irregular when the copolymer concentration increased to 6 × 10⁻⁴ g/mL.     

Semi-interpenetrating polymer networks of Nafion and fluorine-containing polyimide with crosslinkable vinyl group

Fluorine-containing polyimide with crosslinkable vinyl group (FPI) was synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), and 4-amino styrene (AS). The reinforced composite membranes based on semi-interpenetrating polymer networks (semi-IPN) were prepared via solution casting of FPI and Nafion^®212, and crosslinking thereafter. The water uptake, swelling ratio, mechanical properties, thermal behavior, proton conductivity, and oxidative stability of the composite membranes were investigated. Compared with the recast Nafion^® 212, the composite membrane shows better mechanical properties and improved dimensional stability. The tensile strength of the composite membranes ranges from 39.0 MPa to 80.0 MPa, which is higher than that of the recast Nafion^® 212 membrane (26.6 MPa). The dimensional stability of the composite membranes increases with increasing FPI content in the membranes, whereas the proton conductivity decreases. The composite membranes show considerable proton conductivity from 2.0 × 10⁻² S cm⁻¹ to 8.9 × 10⁻² S cm⁻¹ at a temperature from 30 °C to 100 °C, depending on the FPI contents. The composite membranes with semi-IPN from FPI and Nafion^®212 have considerable high proton conductivity, excellent mechanical properties, thermal and dimensional stabilities.     

A proton-conducting composite membrane: Sn0.95Al0.05P2O7 and polystyrene-b-poly(ethylene/propylene)-b-polystyrene

An anhydrous proton conductor, Sn_0.95Al_0.05P₂O₇ (SAPO), composed of polystyrene-b-poly(ethylene/propylene)-b-polystyrene (SEPS), was developed and characterized using morphological, structural, and electrochemical analyses. In the composite membrane with 20 wt% SEPS, a homogeneous distribution of SAPO particles in the matrix was obtained in the thickness range of 65-90 μm, yielding a proton conductivity of 3.4 × 10⁻³ S cm⁻¹ at 200 °C, tensile strength of 4.6 MPa and an elongation at break of 711.0% at room temperature. Fuel cell tests verified that the open-circuit voltage was maintained at a constant value of approximately 1 V between 100 and 250 °C. The peak power densities achieved with unhumidified H₂ and air were 77.0 mW cm⁻² at 100 °C, 121.0 mW cm⁻² at 150 °C, and 163.1 mW cm⁻² at 225 °C.     

Low temperature performance of graphite electrode in Li-ion cells

We studied low temperature performance of Li/graphite cell. Results show that capacity of the graphite electrode falls significantly in the temperature range of 0 to −20 °C. When lithiation and delithiation are both carried out at −20 °C, graphite only retains 12% of the room temperature capacity. However, delithiation capacity of graphite increases to 92% of the room temperature value if the lithiation is carried out at room temperature. We believe that the poor low temperature performance of the cell is due to slow kinetics of lithium ion diffusion in graphite rather than low ionic conductivity of electrolyte and solid electrolyte interface (SEI) on the graphite surface. During lithiation and delithiation processes, lithium ion has the similar apparent chemical diffusion coefficient of 10⁻⁹-10⁻¹⁰ cm²/s at 20 °C, depending on the state of lithiation of graphite. We observed a dramatic decrease in lithium ion diffusivity in the temperature range of 0 to −20 °C, and that at low temperatures of <−20 °C, lithium ion has higher diffusivity in the delithiated graphite than in the lithiated one. We also observed that temperature dependence of cycling behavior of the Li/graphite cell follows the change of lithium ion diffusivity.     

Radical copolymerization of (−)-menthyl 2-acetamidoacrylate and styrene or methyl methacrylate near ceiling temperature

Radical copolymerization of chiral monomer, (−)-menthyl 2-acetamidoacrylate (1), with low ceiling temperature (T_c = 62.0 °C in [monomer] = 1.0 mol/L) and styrene or methyl methacrylate (MMA) has been studied near ceiling temperature (60 °C) and at the temperature lower than T_c (30 °C). Monomer reactivity ratios and Alfrey-Price Q and e-values of 1 are estimated to be r₁ = 0.27, r₂ = 0.067, Q = 3.0, and e = 1.2 at 30 °C, and r₁ = 0.32 and r₂ = 0.046 at 60 °C for the copolymerization of 1 (M₁) and styrene (M₂), suggesting an alternating tendency at both temperatures, whereas for the copolymerization of 1 (M₁) and MMA (M₂) r₁ and r₂ are estimated to be 2.9 and 0.019 at 30 °C, respectively, indicating longer sequence length of 1. Specific rotation and circular dichroism of the resulting copolymer indicate that styrene, in particular, is effectively incorporated into a helical copolymer structure at 60 °C and even only 25 mol% incorporation of the acetamidoacrylate unit in the copolymer induces the helix formation in solution.     

The use of bimodal blends of vinyl ester monomers to improve resin processing and toughen polymer properties

Vinyl ester (VE) monomers with bimodal molecular weight distributions were prepared by reacting methacrylic acid with blends of monodisperse epoxy resins ranging in molecular weight from 350-7000 g/mol. Monodisperse vinyl ester monomers were prepared from epoxy resins of a single molecular weight. The extent of vinyl ester formation was found to be near complete and side reactions, such as etherification, did not occur to a significant extent. The viscosities of these vinyl ester resins were measured as a function of styrene content. It was found that resin viscosity, η, increased exponentially and predictably as both the styrene content (S) decreased and as the number average molecular weight (M_n) of the vinyl ester monomers increased: η∼exp(M_n)/exp(S). Cure kinetics studies showed that the vinyl ester reactivity ratio decreased to 0.1 from 0.6 for bimodal blends relative to monodisperse resins while the styrene reactivity ratio increased from 0.4 to 0.6. Thus, the microgels in bimodal blends were smaller than in monodisperse resins. Emissions studies proved that decreasing the styrene content reduced the VOC emission rate and total emissions. Higher VE molecular weights decreased the overall emissions due to a reduction in monomer mobility. T_g decreased from 143 to 125 °C as M_n of the VE monomers increased from 540 to 920 g/mol; yet, T_g of these bimodal blends were still equal to or greater than that of commercial VE resins (∼125 °C). The fracture toughness of bimodal blends increased from ∼100 to ∼330 J/m² as VE M_n increased from 540 to 920 g/mol because of matrix toughening. The fracture properties did not improve as the styrene content increased from 35 to 45 wt% because of corresponding changes in the morphology. Yet, there were numerous low VOC bimodal formulations with fracture properties in excess of the low VOC Dow Derakane 441-400 (110 J/m²) and even the industry standard Derakane 411-350 (240 J/m²).     

Formation of soluble hyperbranched polymer through the initiator-fragment incorporation radical copolymerization of ethylene glycol dimethacrylate with N-methylmethacrylamide

The copolymerization of ethylene glycol dimethacrylate (EGDMA) as a divinyl monomer with N-methylmethacrylamide (NMMAm) as a water-soluble monomer was carried out at 70 and 80 °C in N,N-dimethylformamide (DMF) using dimethyl 2,2′-azobisisobutyrate (MAIB) of high concentrations as initiator. When the concentrations of EGDMA, NMMAm and MAIB were 0.15, 0.50 and 0.35 mol/l, the copolymerization proceeded homogeneously with no gelation at 80 °C to give soluble copolymer in a yield of 50%. EGDMA was polymerized more rapidly than NMMAm as shown by Fourier-transform near infrared spectroscopy. The copolymer formed for 8 h consisted of 20 mol% of EGDMA unit, 47 mol% of NMMA unit and 33 mol% of methoxycarbonylpropyl group unit as MAIB-fragment. The copolymer formed at 80 °C for 30 min showed an upper critical solution temperature (34 °C on cooling) in methanol. The intrinsic viscosity of the copolymer formed for 2 h was very low (0.11 dl/g) at 30 °C in DMF despite high weight-average molecular weight [3.1×l0⁶ by multi-angle laser light scattering (MALLS)]. The copolymer exhibited a very low second virial coefficient (4.2×l0⁻⁶) as determined at 25 °C in DMF by MALLS. The individual copolymer molecules were observed as nanoparticles of 7-20 nm diameter by a transmission electron microscope. These results show that the resulting copolymers are of hyperbranched structure.     

Sulfonation and characterization of poly(styrene-isobutylene-styrene) triblock copolymers at high ion-exchange capacities

In this study, a triblock copolymer, poly(styrene-isobutylene-styrene), was sulfonated to eight different levels ranging from 0.36 to 2.04 mequiv./g (13 to 82 mol% of styrene; styrene is 19 mol% of the unsulfonated block copolymer). These sulfonated polymers were characterized with elemental analysis and infrared spectroscopy to confirm sulfonation and determine accurate sulfonation levels. Infrared analysis revealed four additional stretching vibrations as a result of sulfonation. Also, a linear relationship between absorbance at 1006 cm⁻¹ (stretching of the aromatic ring in styrene caused by the para-substituted sulfonic acid) and sulfonation level (measured by elemental analysis) was found. The density and water solubility of all the sulfonated polymers were measured and increased with increasing sulfonation level, as high as 1.31 g/cm³ and 351 wt%, respectively. In addition, a sulfonated triblock copolymer at 79 mol% sulfonation was neutralized with a cesium cation and revealed an increase in density, but a reduction in water solubility. This study demonstrates the resulting unique properties of sulfonated styrene-based block copolymers at higher ion-exchange capacities than previously reported.     

Preparation and curing of alkyd based on ricinoleic acid/melamine coatings

Three alkyd resins of high hydroxyl numbers based on ricinoleic acid, phthalic anhydride and glycerin, trimethylolpropane or ethoxylated pentaerythritol as polyol were prepared. Afterwards synthesized alkyds were made into baking enamels by blending with commercial melamine-formaldehyde resins (weight ratio of 70:30 based on dried mass). Alkyd/melamine resin mixtures were cured in a differential scanning calorimeter (DSC) under non-isothermal mode. Apparent degree of curing as a function of temperature was calculated from the curing enthalpies. Fourier transform infrared spectroscopy (FTIR) was used to identify characteristic peaks of resin mixtures before and after being cured. The gel content, hardness, elasticity and impact resistance of coated film cured at 150 °C for 60 min were measured. The onset of film thermal degradation, determined by thermogravimetric analysis (TGA) was observed at the temperatures from 281 to 330 °C. Based on the results obtained we suppose that the combinations of synthesized alkyds based on ricinoleic acid with used melamine resins could be employed as the compositions for the preparation of baking enamels.     

Effect of zwitterionic salt on the electrochemical properties of a solid polymer electrolyte with high temperature stability for lithium ion batteries

In this study, we prepare a kind of solid polymer electrolyte (SPE) based on N-ethyl-N′-methyl imidazolium tetrafluoroborate (EMIBF₄), LiBF₄ and poly(vinylidene difluoride-co-hexafluoropropylene) [P(VdF-HFP)] copolymer. The resultant SPE displays high thermal stability above 300 °C and high room temperature ionic conductivity near to 10⁻³ S cm⁻¹. Its electrochemical properties are improved with incorporation of a zwitterionic salt 1-(1-methyl-3-imidazolium)propane-3-sulfonate (MIm3S). When the SPE contains 1.0 wt% of the MIm3S, it has a high ionic conductivity of 1.57 × 10⁻³ S cm⁻¹ at room temperature, the maximum lithium ions transference number of 0.36 and the minimum apparent activation energy for ions transportation of 30.9 kJ mol⁻¹. The charge-discharge performance of a Li₄Ti₅O₁₂/SPE/LiCoO₂ cell indicates the potential application of the as-prepared SPE in lithium ion batteries.     

Electrochemical copolymerization of aniline with m-aminophenol and novel electrical properties of the copolymer in the wide pH range

A copolymer, poly(aniline-co-m-aminophenol), has been synthesized using repeated potential cycling. The monomer concentration ratio, acid concentration and applied potential strongly affect the copolymerization rate and the properties of the copolymer. The optimum conditions for the copolymerization are that the scan potential range is controlled between −0.10 and 0.95 V (vs.SCE), and a solution consists of 0.34 M aniline, 0.012 M m-aminophenol and 2 M H₂SO₄. The IR spectra of the copolymers demonstrate that the m-aminophenol units are included in the copolymer chains. The cyclic voltammograms of the copolymers in 0.3 M Na₂SO₄ solution with various pH values were performed at the potential ranges from −0.20 to 0.80 V and at a scan rate of 60 mV s⁻¹. The results indicate that the copolymer still hold 41.7% of the electrochemical activity when the copolymer electrode was transferred from a solution of pH 5.0 to a solution of pH 11.0 in the potential range of −0.20 to 0.80 V. An impedance plot of the copolymer in a solution with pH 12.0 and at 0.40 V is constructed of a semicircle and a Warburg line with a slope of 1. This means that the electrode reaction of the copolymer at pH 12.0 is also under mass transfer control. The conductivity of the copolymer prepared under the optimum conditions is 1.42 S cm⁻¹, and slightly depends on the pH value. Thus, the pH dependence of the electrical properties of the copolymer is improved compared with poly(aniline-co-o-aminophenol), and is much better than that of the parent polyaniline.