Changes During Storage of Electrically Conductive Blends Polyaniline–Poly(Ethylene‐co‐vinyl Acetate)

Abstract

The electrical conductivity behavior of polyaniline–poly(ethylene‐co‐vinyl acetate) (PANI–EVA) blends was variable and dynamic during their storage. It was shown that the apparent concentration of the intrinsically conductive polymer at which a conductivity jump of the blends occurs (Φ _c ) is not a constant value over time. The electrical conductivity of the films of low PANI content (below 2.5 wt.%) increased by several (ca. 5) orders of magnitude. It was found that the PANI phase undergoes a flocculation process subsequently resulting in the formation of conductive pathways and a continuous network. Besides, the shape of percolation curves was found to change during storage of the films. Decreased conductivity deviations were registered for blends of low PANI content (<2.5 wt.%), indicating that an improvement (or decreasing number of defects) of the conductive pathways took place within the bulk of the insulating EVA matrix. These results and observed phenomena are discussed by means of the interfacial model for electrically conductive polymer blends. They supported the dispersion/flocculation phase transition within similar composite materials. The phase separation and conductivity jump are attributed to the interfacial interactions between the polymeric constituents. It was shown that the microstructure of the blends consists of highly ordered PANI paths embedded in the insulating EVA matrix. Long fibrils of PANI and interconnected fractal‐like networks were observed. It was found that the sizes of the PANI domains also varied during storage of the films. Due to the spontaneous flocculation of the primary PANI particles, conductive pathways are formed at extremely low percolation threshold (Φ _c , loading level ca. 5 × 10^?3 wt. fraction). Thus, an important property of the conductive constituent, namely its solid‐state rearrangement, was proved. This PANI self‐organization is also interpreted according to the interfacial model of polymer composites. On the other hand, the competition between self‐organization of the complex of PANI with dodecylbenzenesulfonic acid and crystallization of EVA matrix has resulted in structural changes and formation of continuous conductive networks within the blends, responsible for their significantly increased conductivity.     

Conducting Block Copolymer Nanowires Containing Regioregular Poly(3‐Hexylthiophene) and Polystyrene

Grignard Metathesis polymerization (GRIM) for the synthesis of regioregular poly(3‐alkylthiophenes) proceeds via a “living” chain growth mechanism. Due to the “living” nature of this polymerization regioregular poly(3‐alkylthiophenes) with predetermined molecular weight, narrow molecular weight distributions and desired chain end functionality are now readily available. Allyl terminated poly(3‐hexylthiophene) was successfully used as a precursor for the synthesis of di‐block copolymers containing polystyrene. The addition of “living” poly(styryl)lithium to the allyl terminated regioregular poly(3‐hexylthiophene) generated the di‐block copolymer. Poly(3‐hexylthiophene)‐b‐polystyrene was also synthesized by atom transfer radical polymerization. Integration of poly(3‐hexylthiophene) in di‐block copolymers with polystyrene leads to the formation of nanowire morphology and self‐ordered conducting nanostructured materials.     

Biodegradability of Poly(ester‐ether) and Poly(ester) Obtained from a Radical Ring‐Opening Polymerization of Cyclic Ketene Acetals

2‐Methylene‐1,3,6‐trioxocane (MTC) and 2‐methylene‐1,3‐dioxepane (MD) were synthesized and polymerized via ring‐opening in the presence of a radical initiator. The obtained poly(ester‐ether) (PMTC) and poly(ester) (PMD) were found to be enzymatically degradable by total organic carbon (TOC) analysis using lipase. The enzymatic degradability of PMTC was higher than that of PMD. PMTC and PMD were also found to be biodegradable with a biological oxygen demand (BOD)‐tester using soil. The degradability of PMTC using soil was also higher than that of PMD. The higher degradability of PMTC by enzyme and soil are thought to be due to its higher hydrophilicity.     

Redox Conversions of Polyaniline in Composite Polyaniline–Nafion Polymer Films

Redox processes that occur in composite polyaniline–Nafion films formed on platinum or glassy carbon during the potential cycling are studied by radioisotope and electrochemical methods. Following a change in the conditions and range of potential cycling, the films exhibit a slow relaxation (memory effect).     

Immobilization of Invertase in a Novel Proton Conducting Poly(vinylphosphonic acid) – poly(1-vinylimidazole) Network

A novel proton conducting polymer blend was prepared by mixing poly(vinylphosphonic acid) (PVPA) with poly(1-vinylimidazole) (PVI) at various stoichiometric ratios via changing molar ratio of monomer repeating unit to achieve the highest protonation. The polymer network having the most suitable stoichiometric ratio for substantial proton conductivity was prepared and characterized by FT-IR spectroscopy and proton conductivity measurements. The network was used for immobilization of invertase and some important kinetic parameters such as the maximum reaction rate (V_max) and Michaelis-Menten constant (K_m) were investigated for the immobilized invertase. Additionally, optimum temperature and pH were determined to acquire the best conditions for the highest enzyme activity. Operational stability of the entrapped enzyme was also examined. The results reveal that the most stable and highly proton conducting polymer network may play a pioneer role in the biosensors applications as given by FT-IR, elemental analysis, impedance spectroscopy and storage stability experiments.     

The Preparation and Biodegradable Properties of Poly(L‐lactic acid)‐Poly(ϵ‐caprolactone) Multiblock Copolymers

Multi‐block copolymers of PLLA and PCL were prepared by a coupling reaction between PLLA and PCL prepolymers with –NCO end groups. FTIR proved that the products were PLLA‐PCL copolymers. The weight‐average molecular weight of the copolymers was up to 180,000 at a composition of 60% PLLA and 40% PCL. The degradation properties of PLLA and PLLA‐PCL copolymers were studied by a soil burial test and a hydrolysis test in a phosphate‐buffer solution. The degradation rate was estimated by the mass loss, molecular weight reduction, pH value changes and swelling index; the degradation rates of the copolymers were a function of the composition of PLLA and PCL. Increasing PCL content in the copolymers resulted in lower degradation rate.     

Development and Characterization of Liposome‐Based Formulation of Amiloride Hydrochloride

Amiloride hydrochloride, a generally used diuretic recently has been found effective in the treatment of epilepsy. The side effects of the drug, such as hyperkalemia, hypertension, and hyperaldosteronism were controlled by reducing the dose and targeting the drug to the brain. The objective of this study was to determine the factors influencing encapsulation of amiloride hydrochloride in liposomes and to demonstrate the anti‐epileptic potential of liposomal drug. A series of liposomal formulations of amiloride hydrochloride were prepared by varying the compositions of the formulations. The optimized formulation consisted of 10 mg/mL of amiloride hydrochloride, L‐phosphatidyl choline, lecithin, cholesterol, and butylated hydroxy toulene. The percentage entrapment efficiency in the optimized formulation was 44%. The drug to lipids ratio and L‐phosphatidyl choline: lecithin: cholesterol: butylated hydroxy toulene ratios were 2.0:3.0 and 5:5:5:2, respectively. The formulation showed an in vitro release of 98.17% in 8 hours, and the best fit kinetic model was Peppas model. Treatment with amiloride hydrochloride liposomes resulted in a significant increase in seizure threshold as compared to free drug in increasing current electroshock seizures in mice, which indicated an increase in CNS uptake of drug in liposome formulation.     

Structure – Directing Effect of Renewable Resource Based Amphiphilic Dopants on the Formation of Conducting Polyaniline-Clay Nanocomposite

Summary: The structure-directing effect of two amphiphilic dopants on the nucleation and growth mechanism during the formation of micro/ nanostructured polyaniline (PANI) and polyaniline-clay nanocomposites (PANICNs) is described. PANIs and PANICNs were prepared by in-situ intercalative emulsion polymerization of aniline using the amphiphilic dopants, 3-pentadecyl phenyl phosphoric acid (3-PDPPA) and 3-pentadecyl phenol–4-sulphonic acid (3-PDPSA), derived from cashew nut shell liquid, a renewable resource. These molecules act as intercalating agents, dopants and also as structure-directing agents. X- ray diffraction (XRD) and scanning electron microscopic (SEM) studies revealed the formation of lamellar/fibrillar – network in PANI- PDPPA and cylinder/rod morphology in PANI-PDPSA. Experimental data reveal that fibrillar morphology arises from the heterogeneous nucleation followed by an indefinite growth mechanism. On the other hand rod-like structures are formed from the self-assembled rod-like micelle guided polymerization through homonucleation followed by an anisotropic growth mechanism. Electrical conductivity measurement revealed lower conductivities for PANICNs than that of PANIs.     

The Determination of Salbutamol Sulfat Based on a Flow‐Injection Coupling Irreversible Biamperometry at Poly(aminosulfonic acid)‐Modified Glassy Carbon Electrode

Abstract

The present work describes the development of a simple and efficient method for electrochemical analysis determination of SBS using polymer film coated modified electrode. A glassy carbon electrode (GCE) is successfully modified with electropolymerized film of aminosulfonic acid (ASA) in pH 6.8 phosphate buffer solution (PBS). Cyclic voltammetry (CV) were used to study the electrochemical properties of the polymer film and the appropriate condition for electropolymerization process. The voltammetric behavior of SBS at the PASA GC CMEs has been investigated, the results suggest that the PASA GC CMEs have good effect of electrocatalytic oxidation action to SBS, also propose the mechanism toward SBS. The flow‐injection irreversible biamperometry analysis method was studied under the applied potential difference of 0 V to determinate SBS. In 0.1 mol l^?1 (pH 6.80) phosphate buffer solution, a sensitive and irreversible oxidation peak was obtained at the PASA GC CMEs. Under the optimum conditions, SBS can be determined from the range 2.0×10^?6 to 1.0×10^?3 mol · 1^?1 with the sampling frequency of 100 samples per hour. The detection limit for SBS is 6.5×10^?7 mol l^?1 and the RSD for 20 replicate determinations of 4.0×10^?5 mol l^?1 SBS is 1.85%. The method is simple, with high selective rapid and sensitive. The method is applied to the determination of SBS in the drug with satisfactory results. Moreover, the physiologically common interferents (i.e., sucrose, lactose, citric acid, and citrate) negligibly affected the response of SBS. The PASA GC CMEs film‐coated electrode exhibited a stable and sensitive response to salbutamol sulfat in the presence of electrocatalysis oxidation.     

Synthesis and Properties of Poly(AAm‐KMA‐MA) Hydrogels

In this investigation, poly(acrylamide‐co‐potassium methacrylate‐co‐maleic acid) hydrogels, poly(AAm‐KMA‐MA) were synthesized by redox copolymerization in aqueous solution. The effect of reaction parameters, such as concentration of maleic acid, crosslinking agent, initiator and activator, on the swelling behavior was investigated in detail. The swelling/diffusion characteristics were also evaluated for 1,4‐butanediol diacrylate (BDDA) and 1,2‐ethyleneglycol dimethacrylate (EGDMA) crosslinked hydrogels having different amounts of maleic acid. The results indicate that the water diffusion of hydrogels was of a non‐Fickian type. The hydrogels were characterized by IR spectroscopy and thermogravimetric analysis (TGA). Their surface characteristics were observed by using scanning electron microscopy (SEM). Furthermore, their swelling phenomena in different pH and salt solutions and simulated biological fluids was also studied.     

Compressive Elastic Moduli of Poly(N‐Isopropylacrylamide) Hydrogels Crosslinked with Poly(Dimethyl Siloxane)

Hydrophobically modified and thermally reversible neutral and ionic copolymer hydrogels were prepared from N‐isopropylacrylamide (NIPAAm), vinyl terminated poly (dimethylsiloxane) (VTPDMS) and itaconic acid (IA) by free radical solution polymerization, and their properties such as swelling ratio and compression modulus were studied at the 25°C. The incorporation of VTPDMS as a hydrophobic macrocrosslinker into the structures of neutral NIPAAm hydrogels increased their mechanical strength around 10 times than those of the ones crosslinked with conventional tetra functional monomer, i.e., N,N′‐methylene bisacrylamide (BIS). Compression modulus decreased with an increase in IA content for ionic samples and increased with increasing molecular weight and content of VTPDMS for neutral samples. It was assumed that in the first case, electrostatic repulsive forces resulting from the ionized carboxyl groups of IA were responsible for decreasing mechanical strength, while in the second case, hydrophobic interactions between dimethylsiloxane units of VTPDMS chains enhanced the compression moduli. According to the results presented in this work, it can be said that the right balance of hydrophobic and hydrophilic constituents and adjustment of the number of ionized groups, as well as crosslinking degree, change the structure and physical properties of NIPPAAm hydrogels.     

Swelling Behavior of Semi‐Interpenetrating Polymer Network Hydrogels Based on Chitosan and Poly(acryl amide)

Semi‐interpenetrating polymer networks (semi‐IPNs) composed of chitosan and polyacrylamide (PAAm) hydrogels have been prepared, and the effect of changing pH, temperature, ionic concentration, and applied electric fields on the swelling of the hydrogels was investigated. The swelling kinetics increased rapidly, reaching equilibrium within 60 min. The semi‐IPN hydrogels exhibited a relatively high swelling ratios of 385%–569% at T=25°C. The swelling ratio increased with decreasing pH below pH=7 due to the dissociation of ionic bonds. The swelling ratio of the semi‐IPN hydrogels was pH, ionic concentration, temperature, and electric field dependent. Differential scanning calorimetry (DSC) was used to determine the volume of free water in the semi‐IPN hydrogels, which was found to increase with increasing PAAm content.     

Determination of Poly(3‐Hydroxybutyrate) using a Combination of Enzymatic Spectrophotometry and Alkaline Hydrolysis

Abstract

A combination of enzyme‐based spectrophotometric analysis and alkaline hydrolysis was developed for the measurement of poly(3‐hydroxybutyrate) (PHB). The principle of the determination is as follows: alkaline hydrolysis decomposes PHB into its monomer product 3‐hydroxybutyrate, which is followed with enzymatic reaction catalyzed by 3‐hydroxybutyrate dehydrogenase in the presence of nicotinamide adenosine dinucleotide (NAD). The product, nicotinamide adenosine dinucleotide with hydrogen (NADH) results in a spectrophotometric signal at 340 nm. This method shows high performance characteristics with simple operations.     

Mechanism for Base Hydrolysis of Poly(N‐vinylformamide)

The industrial production of poly(N‐vinylformamide), PNVF, was started a few years ago, making the desired polyvinylamine, PVAm, accessible on a large scale via hydrolysis of PNVF. According to the literature, the key to achieving a 100% conversion of PNVF into PVAm is to employ basic hydrolysis conditions. However, results disclosed in the present note contradict such statements. A radically obtained PNVF polymer, assigned further on as PNVF‐000 with M¯_w=2.63×10⁵ g/mol, was submitted to a stepwise hydrolysis in aq. NaOH solution with periods lasting 0, 5 20, 40, 90, 175, and 240 min. Aliquots ware taken, neutralized, precipitated and purified. For each polymer thus obtained the ¹³C NMR spectra was recorded, providing evidence for transient formation of amidine rings. These rings while decomposing leave not only primary amine functions attached to the backbone, but also OH groups. Elementary analysis of PNVF‐240, the polymer fully deprived of formaldehyde groups, confirm these findings. From the C/N=3.17 ratio the share of vinyl‐alcohol units present in the chains is estimated to be 42 mol%. Considering all the experimental results, the mechanism of basic hydrolysis was established.     

Synthesis of Poly(para‐phenylene) Containing Imidazolium Cation

A novel poly(para‐phenylene) containing imidazolium cation, poly[2,5‐bis[4‐(3‐methyl‐1‐imidazolium)‐butyloxy)‐1,4‐benzene dihexafluorophosphate] (PPP‐IL), has been synthesized.     

Synthesis and Characterization of Hydroxyl‐Terminated Poly(γ‐benzyl‐L‐glutamate)

In order to provide an active end group of hydroxyl group and improve the hydrophility of poly(γ‐benzyl‐L‐glutamate) (PBLG), ethanolamine (EA) was utilized as the initiator to initiate N‐carboxy‐γ‐benzyl‐L‐glutamate anhydride (Bz‐L‐Glu‐NCA) polymerization. The prepared hydroxyl‐terminated PBLG (HO‐PBLG) was fully characterized by FTIR, ¹H‐NMR, XPS, XRD, DSC, and GPC. The results of FTIR and XRD indicated that the chain conformation of HO‐PBLG predominantly presented α‐helix. The water contact angle was measured to confirm that the hydrophilicity was improved by the introduction of hydroxyl group. Chondrocytes studies showed that the cells attachment efficiency on the HO‐PBLG film was good and the cells grew well.     

Disorder Effects in “Plastic” and Highly Conducting Compounds of Poly(aniline)

Numerical methods of molecular dynamics have been combined to measurements of X-ray and neutron scattering in order to obtain a realistic view of structural and dynamical disorder properties of conducting compounds of so called “plastdoped” poly(aniline)s. This combination allowed us to propose for the whole family of these compounds one generic model of a layered structure in which exist statistical fluctuations of the electronic density along the stacking direction of alternating molecular layers. The most part of the dynamics in the 10⁻¹³–10⁻⁹ s time range concerns the motions of protons borne by the flexible tails of doping counter-ions contained in the structure. We found that the molecular dynamics is characterized by both broad time and spatial distributions. These experimental facts coupled to those obtained with electrical conductivity measurements indicate that the high mobility of the counter-ion sublattice seems to be a prerequisite to promote a global metal like electronic behaviour of the polymer films.     

Characterization of Poly(ethyleneoxyethylene terephthalate‐co‐adipate) using NMR Spectroscopy

Comonomer sequence distribution and ¹H‐NMR chemical shifts were determined for poly(ethyleneoxyethylene terephthalate‐co‐adipate) (PEOETA) copolyester. The sequence distribution of terephthalate (T) and adipate (A) residues was found to be random, which is typical for copolyesters synthesized via bulk polycondensation. The inner methylene protons of EOE residues appeared as a pair of doublets due to chemical shift differences among the EOE‐centered dyad sequences TT, TA, AT, and AA. The four equivalent phenylene protons of T residues appeared as a triplet due to chemical shift differences among the T‐centered triad sequences TTT, TTA (?ATA), and ATA. Higher‐order tetrad and pentad sensitivity were also observed for the inner methylene and phenylene protons, respectively, especially for TT‐ and TTT‐centered sequences. The sequence sensitivity of the phenylene protons was attributed to unique spatial interactions between themselves and protons within adjacent adipate and EOE units. These spatial interactions were confirmed using Nuclear Overhauser Enhancement Spectroscopy (NOESY).     

Preparation and Characterization of Poly(N‐Vinylpyrrolidone‐co‐Methacrylic Acid) Hydrogels

In this study, N‐vinylpyrrolidone (VP)/methacrylic acid (MAA) copolymers have been prepared at three different mole percents, the methacrylic acid composition being around 5, 10, 15%. MAA and VP monomer mixtures have been irradiated in ⁶⁰Co‐γ source at different irradiation doses and percent conversions have been determined gravimetrically. ～80% conversion of monomers into hydrogels were performed at 3.4 kGy irradiation dose. These hydrogels were swollen in distilled water at pH 4.0, 7.0, and 9.0. P(VP/MAA) hydrogel which contains 5% methacrylic acid showed the maximum % swelling at pH 9.0 in water. Diffusion of water was found to be of non‐Fickian character. Diffusion coefficients of water in P(VP/MAA) hydrogels were calculated. Initial swelling rates of P(VP/MAA) hydrogels increased with increasing pH and MAA content in hydrogels. Swelling kinetics of P(VP/MAA) hydrogels was found to be of second order. Thermal behavior of PMAA, PVP and P(VP/MAA) hydrogel were investigated by thermal analysis. P(VP/MAA) hydrogel gained new thermal properties and the temperature for maximum weight loss and temperature for half‐life of P(VP/MAA) hydrogel were determined.     

Studies on the Miscibility of Poly(2‐hydroxyethyl methacrylate) and Poly(ethylene oxide) Blends

Miscibility characteristics of poly[2‐hydroxyethylmethacrylate] (PHEMA) and poly[ethylene oxide] (PEO) have been investigated by solution viscometry, ultrasonic and differential scanning calorimetric (DSC) methods. The interaction parameters were obtained using the viscosity data. Ultrasonic velocity and adiabatic compressibility vs. blend composition have been plotted and are found to be linear. A single glass transition temperature was observed by differential scanning calorimetry. Variation of glass transition temperature (T_g) with composition follows Garden‐Taylor equation. T_g values have also been calculated from the Fox equation. The results obtained reveal that PHEMA forms a miscible blend with PEO in the entire composition range.