Stability Of Poly Research Articles

Electrochemical Characteristics and Stability of Poly(1,5-diaminoanthraquinone) in Acidic Aqueous Solution

The electrochemical characteristics and stability of poly(1,5-diaminoanthraquinone) (P15DAAQ) has been investigated in different acidic aqueous solution by electrochemical methods and Fourier transform infrared spectroscopy (FTIR). Cyclic voltammetry (CV) analysis suggests that electropolymerization consists of two phasesthe deposition of P15DAAQ from the oxidation of 15DAAQ monomers and the polymer growth process. The CV and chronoamperometry (CA) data provide the evidence that ion transfers are different between oxidation and reduction processes and are profoundly influenced by the sizes of ion radius during the redox process of P15DAAQ in acid solution. The H+ transfer is diffusionless, while the insertion/expulsion of large aqua anions is controlled by diffusion. A model is proposed to describe these ion transfer processes. In further CA research, the calculated diffusion coefficients of aqua anions in P15DAAQ are in the order of Cl- > S > NO3- > P . As a result of stability research, it can be seen t...

Stability of proteins encapsulated in injectable and biodegradable poly(lactide- co-glycolide)-glucose millicylinders

Purpose To characterize protein stability in poly(lactide- co-glycolide) 50/50-glucose star (PLGA-Glu) injectable millicylinders and to compare results with linear PLGA 50/50. Methods Bovine serum albumin (BSA), a model protein, was encapsulated in PLGA-Glu and linear PLGA millicylinders by solvent-extrusion and incubated under physiological conditions. Important system properties were characterized, including: polymer molecular weight distribution, soluble acidic residues, polymer morphology, polymer water uptake, microclimate pH, protein content and release, and protein aggregation. The polymer microclimate late in the release incubation was simulated and protein recovery was analyzed by UV 280, size exclusion chromatography, amino acid analysis, and a modified Bradford assay. Results PLGA-Glu contained higher levels of low molecular weight oligomers, more rapidly biodegraded, and exhibited a lower microclimate pH than the linear 50/50 PLGA, which is the most acidic type in the PLGA family. BSA, when encapsulated in PLGA-Glu millicylinders, underwent extensive noncovalent insoluble aggregation over 2 weeks in vitro release, which was almost completely inhibited upon co-encapsulation of Mg(OH) 2. However, by 5 weeks release for base-containing formulations, although insoluble aggregation was still suppressed, the soluble fraction of protein in the polymer was unrecoverable by the modified Bradford assay. Polymer microclimate simulations with extensive protein analysis strongly suggested that the low recovery was mostly caused by base-catalyzed hydrolysis of the oligomeric fraction of BSA. Conclusions In PLGA-Glu, the acidic microclimate was similarly responsible for insoluble aggregation of encapsulated BSA. BSA aggregation was inhibited in millicylinders by co-incorporation into the polymer an insoluble base, but over a shorter release interval than linear PLGA likely because of a more acidic microclimate in the star polymer.

Enhancement of Field-Effect Mobility and Stability of Poly(3-hexylthiophene) Field-Effect Transistors by Conformational Change

With the aim of enhancing the field-effect mobility and air stability of self-aligned regioregular poly(3-hexylthiophene), P3HT, by promoting two-dimensional molecular ordering, we transformed the chemical structure of the P3HT chain from a benzoid to a quinoid structure by doping the P3HT solution with HAuCl4 prior to film formation. We found that, for the appropriate HAuCl4 concentration, the P3HT nanocrystals adopt a highly ordered molecular structure with a field-effect mobility of 0.03 cm2 V-1 s-1, which is an improvement by a factor of more than 100. This increase in field-effect mobility is due to a significant enhancement of molecular ordering and the perpendicular orientation of the nanocrystals with respect to the insulator substrate. This resulted from the change in the P3HT chain conformation from a benzoid to a quinoid structure due to oxidation by HAuCl4. The quinoid structure favors a linear or expanded-coil conformation, so the thiophene inter-ring bonds have increased double-bond character, which improves the molecular ordering. Furthermore, the electrical properties of a doped P3HT device had highly improved stability to air without encapsulation. These results suggest that the effect of unintentional doping by oxygen on HAuCl4-doped P3HT film is insignificant because the p-type doping effect of HAuCl4 is the major contributor.

Binding of protoberberine alkaloid coralyne with double stranded poly(A): a biophysical study

Recognition of double stranded ribonucleic acid is a critical event in many biological pathways such as trafficking, editing and maturation of mRNA, interferon antiviral response and RNA interference. In the context of probing double stranded RNA binding small molecules, the interaction of the antitumor protoberberine alkaloid coralyne with double stranded poly(A) has been studied by various biophysical techniques. Typical hypochromic and bathochromic shifts in the absorption spectrum and appreciable quenching of the intrinsic fluorescence of coralyne indicated the strong affinity of coralyne to poly(A). The corresponding intrinsic binding constant evaluated from Scatchard analysis was in the order of 10(5) M(-1). The strong binding was further characterized by significant polarization of the alkaloid fluorescence and stabilization of poly(A) helix against thermal strand separation. The binding process was manifested by remarkable perturbation of the intrinsic circular dichroic spectrum of poly(A) with concomitant generation of optical activity in the bound alkaloid molecules that are otherwise achiral. Job plot analysis showed the binding stoichiometry of the interaction process to be two base pairs per alkaloid molecule. The energetics of the strong interaction was studied by isothermal titration and differential scanning calorimetric techniques that suggested the binding to be exothermic and favoured by both negative enthalpy and positive entropy changes. All these results, together with the Stern-Volmer quenching experiment in fluorescence, revealed the molecular details of the intercalation of coralyne into poly(A) duplex leading to its potential use as an agent in gene regulation in eukaryotic cells.

Crystallinity and Stability of Poly(vinyl alcohol)‐Fumed Silica Mixed Matrix Membranes

Mixed matrix membranes (MMMs) containing poly(vinyl alcohol) (PVA) and 10–30% fumed silica (FS) were prepared using a solvent casting method. The FS particles were distributed evenly in the MMMs as revealed in the scanning electron microscopy/energy dispersive X‐ray spectroscopy (SEM/EDX) micrographs. The surface roughness increased with higher FS content. The thermogravimetric analysis (TGA) results showed that the MMM decomposition temperature was slightly improved with increasing FS content. The MMM crystallinity was determined using Fourier‐transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), and differential scanning calorimetry (DSC). All results indicated that the crystallinity was decreased with FS content. This was attributed to the fact that the FS particles restricted the polymer chain mobility during membrane formation. The confined chain mobility also slowed or inhibited crystal unfolding and, therefore, suppressed the membrane dissolution in water. The lower crystallinity drop of the swollen membranes with FS addition confirmed this finding. The incorporation of FS improved the thermal stability and resistance to water dissolution. These MMMs exhibit potential for use in alkaline direct methanol fuel cell applications.

Influence of assembling pH on the stability of poly( l-glutamic acid) and poly( l-lysine) multilayers against urea treatment

Polyelectrolyte multilayers of poly( l-glutamic acid) (PGA) and poly( l-lysine) (PLL) were built up using the layer-by-layer (LbL) technique in low pH (3.6, PM3.6) and in neutral pH (7.4, PM7.4) solutions. The multilayers were then treated with a concentrated urea (one kind of denaturant for proteins and polypeptides) solution (8 M) and rinsed with corresponding buffer. The buildup and treatment processes were investigated by ultraviolet visible spectroscopy and ellipsometry. The surface morphology was observed by scanning force microscopy (SFM). The inner structures were determined by X-ray reflectometry and circular dichroism spectroscopy (CD). An exponential growth of the optical mass and the layer thickness was observed for both PM3.6 and PM7.4. After urea treatment, a significant mass loss for PM3.6 was found, while no mass change was recorded for PM7.4. The dominant driving force for PM7.4 is electrostatic interaction, resulting in multilayers with an abundant β-sheet structure, which has higher stability against urea treatment. By contrast, the dominant driving force for PM3.6 is hydrogen bonding and hydrophobic interaction, which are sensitive to the urea treatment. The mechanism is substantiated by molecular mechanics calculation. This has offered a convenient pathway to mediate the multilayer properties, which is of great importance for potential applications.

Electrical properties and the thermal and photochemical stability of poly(vinyl chloride) films stabilized with some maleyl amide polymers

AbstractSome maleyl amide polymers were prepared and evaluated as thermal and photochemical stabilizers for rigid poly(vinyl chloride) (PVC). Thermal degradation was determined by measuring the rate of dehydrochlorination potentiometrically. Also, the degree of discoloration was measured for both the thermally degraded and the photochemically degraded PVC. Dibutyltin maleate heat stabilizer was used for comparison in thermal and photodegradation. The applied polymers showed stabilizing efficiency in both thermal and photodegradation by decreasing the rate of degradation, degree of discoloration, and percentage weight loss. The amide polymer of melamine gave better stabilizing efficiency than those of p‐phenylenediamine and m‐phenylenediamine. A dielectric study was carried out over a frequency range from 100 Hz to 100 kHz at room temperature (∼22°C). The results revealed that the stabilizing effect of these maleyl amide polymers depends on the type of stabilizer and its concentration. The dielectric data for the investigated systems were found to be fitted by two absorption regions using the Fröhlich function. These regions are ascribed to the Maxwell–Wagner effect and to intramolecular motion involving the rotation of various segments of the side group as the main chain motion is restricted. The study led to a conclusion that the greater stabilizing efficiency of the melamine amide polymer may be due to the presence of a free amino group (NH2) that can participate in the stabilization process. J. VINYL ADDIT. TECHNOL., 13:206–214, 2007. © 2007 Society of Plastics Engineers

Electrochemical Characteristics and Stability of Poly(1,5-diaminoanthraquinone) in Acidic Aqueous Solution

The electrochemical characteristics and stability of poly(1,5-diaminoanthraquinone) (P15DAAQ) has been investigated in different acidic aqueous solution by electrochemical methods and Fourier transform infrared spectroscopy (FTIR). Cyclic voltammetry (CV) analysis suggests that electropolymerization consists of two phasesthe deposition of P15DAAQ from the oxidation of 15DAAQ monomers and the polymer growth process. The CV and chronoamperometry (CA) data provide the evidence that ion transfers are different between oxidation and reduction processes and are profoundly influenced by the sizes of ion radius during the redox process of P15DAAQ in acid solution. The H+ transfer is diffusionless, while the insertion/expulsion of large aqua anions is controlled by diffusion. A model is proposed to describe these ion transfer processes. In further CA research, the calculated diffusion coefficients of aqua anions in P15DAAQ are in the order of Cl- > S > NO3- > P . As a result of stability research, it can be seen that degradation of the polymer exists not only in overoxidation but also in the stable redox reaction. The degradation rates of P15DAAQ in the reversible potential region from −0.2 to 0.75 V obey the apparent first-order kinetic, and the degradation rate constants are 2.04, 4.93, 2.59, and 3.03 × 10-5 s-1 in HCl, H2SO4, HNO3, and H3PO4, respectively. According to FTIR and CV, the quinone-like structure is destroyed, accompanied with conjugation length of the polymer's π-bond being decreased and chains in the polymer being broken and recombined with anions combined to the polymer, when P15DAAQ is potentiodynamically overoxidized at 1.5 V.

The Kinetic Analysis of Thermal Decomposition of PMMA/MMT Nanocomposites

The thermal decomposition kinetics and thermal stability of poly (methyl methacrylate) (PMMA) and PMMA/ montmorillonite (MMT) nanocomposites containing 4 wt% MMT were researched by thermogravimetry (TG). The results show that, because of the barrier behavior of exfoliated MMT layer, the temperature of thermal decomposition of PMMA/ MMT nanocomposites is improved by about 10 °C, and thermal stability is improved by about double. The apparent activation energy of decomposition, calculated by Ozawa equation, of nanocomposites is higher than that of PMMA before 27 % mass loss.

Effect of boric acid on the stabilization of poly(acrylonitrile-co-itaconic acid)

The effect of boric acid on the stabilization of poly(acrylonitrile-co-itaconic acid) (P(AN-co-IA)) was studied in detail by differential scanning calorimetry (DSC) incorporating with thermogravimetry (TG) in air and nitrogen. In nitrogen atmosphere the ionic cyclization of the doped P(AN-co-IA) copolymer was badly retarded by boric acid, however, the free radical cyclization was little influenced. In air atmosphere boric acid was found to weaken the first exothermic peak corresponding to dehydrogenation and cyclization reactions, and enhance the second exothermic peak corresponding to the oxidative reactions resulting in a great expansion of the heat evolved. The activation energy of stabilization was calculated with Kissinger method, the results indicated that boric acid seemed to be effective to reduce the activation energy. TG studies showed that boric acid could reduce the weight loss during stabilization, which could be attributed to the crosslinking of polymer chains caused by the reaction between boric acid and the hydroxyl groups.

Thermal stabilities of poly(vinyl chloride)/magnesium hydroxide (PVC/MH) composites

The effect of the micrometer and nanometer magnesium hydroxide (MH) as fillers on the thermal stability of poly(vinyl chloride) was investigated by the thermogravimetric analysis (TGA) technique. The poly(vinyl chloride)/magnesium hydroxide (PVC/MH) composites were prepared by the solution blending method, respectively. The results showed that the PVC/MH composites with the nanometer MH filler (PVC/nMH) had the better thermal stability than that with the micrometer MH filler (PVC/uMH) with the same amount of MH filler added. And the initiating temperature (Ti) of the dehydrochlorination reaction increased with the amount of MH filler added. A facile chemical analysis method was developed to examine the thermal stabilising mechanism of MH fillers in the PVC/MH composites after the samples pyrolysed.

Hydrolytic degradation and thermal stability of poly(naphthylimides) based on naphthalene-1,4,5,8-tetracarboxylic dianhydride and bis(naphthalic anhydrides)

The molecular properties of a number of new poly(naphthylimides) derived from naphthalene-1,4,5,8-tetracarboxylic dianhydride and bis(naphthalic anhydrides) have been studied. On the basis of hydrodynamic studies of the polymers at various stages of their thermal degradation in 96% H2SO4 and thermogravimetric measurements, the hydrolytic stability and thermooxidative resistance of the polymers have been compared. A correlation between the experimental data and the chemical structure of molecular chains has been established.

Application of conducting poly(aniline‐co‐pyrrole) film to cholesterol biosensor

AbstractCholesterol oxidase (ChOx) has been covalently immobilized onto poly(aniline‐co‐pyrrole), electrochemically deposited onto indium‐tin‐oxide (ITO) glass plates, using glutaraldehyde as a crosslinker. These poly (An‐co‐Py)/ChOx films have been characterized using UV–visible spectroscopy fourier transform infrared spectroscopy, scanning electron microscopy, and photometric and amperometric techniques, respectively. The poly(An‐co‐Py)/ChOx bioelectrodes have been utilized for cholesterol estimation in the range of 1–10 mM. The ChOx activity in poly(An‐co‐Py)/ChOx bioelectrode has been found to be the highest at pH 7.0 at 25°C. The sensitivity and stability of poly(An‐co‐Py)/ChOx bioelectrode have been experimentally determined as 93.35 μA/mM and 10 weeks at 4°C, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Stability of poly(vinylidene fluoride- co-hexafluoropropylene)-based composite gel electrolytes with functionalized silicas

Various aspects of stability of composite polymer gel electrolytes based on poly(vinylidene fluoride- co-hexafluoropropylene) (PVdF/HFP) polymeric matrix and functionalized precipitated silicas have been studied. The silica fillers have been surface modified with methacryloxy or vinyl groups by partially replacing silanol groups, so that bi-functional (hydrophilic/hydrophobic) character of the inorganic fillers was created. Compatibility of the gel electrolytes with lithium electrode has been examined by means of EIS technique. Electrochemical stability window has been studied with the application of cyclic voltammetry technique with fast sweeping rate. Passive layer formation on graphite electrode has been investigated for all the gel electrolytes by means of cyclic voltammetry with slow scan rate and galvanostatic charging/discharging technique. It has been shown that stability of the interface between lithium and gel electrolyte is significantly improved when bi-functional silicas are used as fillers. The phenomenon has been ascribed to more effective scavenging of trace impurities as well as to better shielding of the electrode surfaces. Cyclic voltammetry on platinum has revealed excessive electrochemical redox processes upon prolonged cycling for all the gel electrolytes. It has been demonstrated that stable passive layers are formed on graphite electrodes upon electrochemical reduction in the presence of the studied composite polymer gel electrolytes.

Effect of pyrene and acetophenone on photostability of poly(methylphenylsilane) films

We have used investigations of low-temperature photoluminescence and thermally stimulated luminescence to study the effect of acetophenone and pyrene dopants on the photochemical stability of poly(methylphenylsilane) (PMPS) films. We have established that pure PMPS films and acetophenone-doped PMPS films degrade on exposure to UV radiation due to breaking of Si-Si bonds followed by formation of crosslinks between the macromolecules. At the same time, pyrene inhibits degradation of PMPS to a significant extent. This proves that photoinduced breaking of the Si-Si bond can occur upon excitation of the macromolecule to the first triplet T1(σσ*) state, since acetophenone sensitizes while pyrene quenches the intrinsic phosphorescence of PMPS. So the photochemical stability of PMPS can be improved by introducing a dopant which quenches triplet excitations of the macromolecule.

Role of the RRM domain in the activity, structure and stability of poly(A)-specific ribonuclease

Poly(A) specific ribonuclease (PARN), which contains a catalytic domain and two RNA-binding domains (R3H and RRM), acts as a key enzyme in eukaryotic organisms to regulate the stability of mRNA by degrading the 3′ poly-(A) tail. In this research, the activity, structure and stability were compared between the full-length 74 kDa PARN, the proteolytic 54 kDa fragment with half of the RRM, and a truncated 46 kDa form completely missing the RRM. The results indicated that the 46 kDa one had the lowest activity and substrate binding affinity, the most hydrophobic exposure in the native state and the least stability upon denaturation. The dissimilarity in the activity, structure and stability of the three PARNs revealed that the entire RRM domain not only contributed to the substrate binding and efficient catalysis of PARN, but also stabilized the overall structures of the protein. Spectroscopic experiments suggested that the RRM domain might be structurally adjacent to the R3 H domain, and thus provide a basis for the cooperative binding of poly(A) by the two RNA-binding domains as well as the catalytic domain.

Carboxylate-Induced Degradation of Poly(3-hydroxybutyrate)s

This communication shows that thermal degradation of poly(3-hydroxybutyrate)s (PHBs) is induced by carboxylate groups via a newly proposed E1cB mechanism. In PHBs with end groups in the form of carboxylic acid salts with Na+, K+, and Bu4N+ counterions, the proposed mechanism explains the dependence of thermal stability on the size of the counterion. The degradation via intermolecular alpha-deprotonation by carboxylate is suggested to be the main PHB decomposition pathway at moderate temperatures. The results of the present study show the ability to control the degradation and stability of poly(3-hydroxybutyrate)s as well as of their blends via chemical structure and concentration of the carboxylate polymer end groups.

Discussion on: “Measurable Signal Decoupling with Dynamic Feedforward Compensation and Unknown-input Observation for Systems with Direct Feedthrough”

In the last four decades, ever since the seminal work of Basile and Marro [1] and Wonham and Morse [6], research efforts have been devoted to analysis and synthesis problems for linear state space systems within the well-known context of the geometric approach. The central issue in this approach is to use basic linear algebraic concepts such as linear mapping and linear subspace to investigate the structural properties of linear systems in terms of properties of the mappings A, B, C, D, etc., appearing in the system equations. For example, properties such as controllability, observability, stabilizability, and detectability can be expressed and characterized very effectively in terms of subspaces generated by these system mappings. Also, important notions such as system invertibility, system zeroes, minimum phase, weak observabilty, and strong controllability are analysed most naturally using the geometric approach. In addition, a large number of synthesis problems has been studied in this framework, such as pole placement and stabilization, observer design, disturbance decoupling by static state feedback or dynamic measurement feedback, observer design in the presence of unknown inputs, problems of output decoupling, problems of tracking and regulation, input-output decoupling, and decentralized control problems. Starting with the famous textbook by W.M. Wonham [7], a treatment of most of these synthesis problems can be found in the textbooks [2] and [4]. In the eighties, the ’exact’ versions of many of these control synthesis problems were generalized to their ’approximative’ versions, resulting in ’high gain’ feedback design problems such as almost disturbance decoupling, almost input-output decoupling, etc., see [5]. Around that time research attention within the systems and control community had been shifted to a large extend to H2 and H∞ control. However, also in the context of H2 and H∞ control an important role continued to be played by problems of disturbance decoupling and almost disturbance decoupling, see e.g [4]. Although the intensity of research within the geometric approach has become less, there is still an active community that devotes attention to further developing the area. L. Ntogramatzidis, the author of the paper to be discussed in this note, is clearly an exponent of this community. In this note we intend to explain the contribution of the

Investigating the effects of surfactants on the size and hydrolytic stability of poly(adipic anhydride) particles

The present study investigates the effects of surfactants (<0.01% v/v) on the size and hydrolytic stability of poly(adipic anhydride) (pAA) micro- and nanospheres fabricated using a modified phase inversion technique. Overall, surfactants increased the output yield by roughly 20%. Lecithin produced the greatest reduction in the volumetric particle size (dvol) compared to particles fabricated with no surfactant (dvol = 530 ± 300 nm and 2.2 ± 1.1 µm, respectively). In addition, sorbitan monooleate produced spheres with smaller numeric diameters (dnum) than the control but appeared to induce aggregation (dvol = 7.7 ± 12.5 µm). The dnum and dvol were not dependent on the hydrophobicity of the surfactant (R2 = 0.36 and 0.03, respectively) or the apparent surface tension of the non-solvent (NS) phase (R2 = 0.44 and 0.04, respectively). In addition, quantitative DSC and FT-IR analysis confirmed that altering the particle size could also influence the hydrolytic stability of pAA.

Electrochemical and in situ Raman spectroscopic study on the stability of poly(N-methylaniline)

The stability of poly(N-methylaniline) (PNMA) as electrode material has been studied in aqueous solutions of sulfuric acid with the use of electrochemical and in situ Raman spectroscopic techniques. It has been shown that the electrochemical decomposition of electrodeposited PNMA films follows a first-order reaction kinetics. The decomposition rate constants vary between 1.2 × 10−5 and 2.0 × 10−3 s−1 for electrode potential varying between 0.2 and 1.0 V vs Ag/AgCl, respectively. In situ Raman spectroscopy has been applied in obtaining kinetic data at selected electrode potentials, and good correlation of these data with the corresponding data obtained by cyclic voltammetry has been found. As compared to polyaniline, the decomposition of PNMA proceeds at nearly the same rate at electrode potentials not exceeding 0.5 V. The decomposition of PNMA proceeds faster within the potential limits of 0.5 to 0.8 V and slower at electrode potentials exceeding 0.8 V as compared to polyaniline.