Anion recognition through amide-based dendritic molecule: a poly(vinyl chloride) based sensor for nitrate ion

Poly(vinyl chloride) (PVC)-based membranes of N,N-bis-succinamide-based dendritic molecule with tetrabutyl ammonium bromide (TBAB) as a cation inhibitor and dibutylphthalate (DBP), dioctylphthalate (DOP), dibutyl (butyl) phosphonate (DBBP) and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and used as nitrate ion-selective electrodes. Optimum performance was observed with the membrane having I-PVC-TBAB-DBP in the ratio 1:33:1:65 (w/w). The electrode has a linear response to nitrate with a detection limit of 3.9 × 10⁻⁵ ± 0.07 M and Nernstian compliance (57.0 ± 0.2 mV/decade) between pH 2.8 and 9.6 with a fast response time of about 20 s. The selectivity coefficient values of the order of 0.001 for mono-; bi- and trivalent anions; indicate high selectivity for nitrate ions over these anions. The preparation procedure of the electrode is very easy and inexpensive. The electrodes were used over a period of 45 days with good reproducibility. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of nitrate ions in waste water samples.     

Photodynamic ion sensor systems with spiropyran: photoactivated acidity changes in plasticized poly(vinyl chloride)

We aim to introduce photoactivated optical ion sensors based on a triggered ion exchange process as novel dynamic tools. The quantification of the acidity change upon photoactivation of spiropyran within an organic membrane phase during photoexcitation is described here for the first time, suggesting a large pK(a) change of more than 6 orders of magnitude.     

Modification of poly(vinyl chloride). XXXI. Crosslinking of poly(vinyl chloride) with 2-R-4,6-dithiol-s-triazine and metal activators

Crosslinking of poly(vinyl chloride) (PVC) with 2-R-4,6-dithiol-s-triazine (R-DT) and metal activators has been studied to determine crosslinking rate constants, induction periods, and apparent activation energy and the final efficiency of crosslinking agents. The rate constants were about 1.4–7.5 min^?1 and the induction periods were about 6.8–24.3 min for various kinds of R-DT at 180°C. The activation energy was about 16.6–33 kcal/mol over the temperature range 160–195°C. The rate constants were strongly influenced by 2-substituted groups (R) in R-DT and increased in the order R′O-? R′NH-< (R′)₂N, where R′ is an alkyl or aryl group. Further, the rate constants increased in the order of: metal carboxylates < metal carboxylates < metal oxides for the activators and in the order of: Pb < Mg < Ca < Ba < Na for metal atoms. The final efficiency was about 75–80% for the activators such as MgO, MgCO₃, PbO, and SnO. The activators containing Na, Ca, and Ba atoms, however, gave final efficiency of more than 100%.     

Investigations on poly(vinyl chloride). III. Effects of metal oxides upon thermal decomposition of poly(vinyl chloride)

Thermal decomposition mechanisms of poly(vinyl chloride) (PVC) and the effects of a few metal oxides on the pyrolysis of PVC were previously reported. In the present work, 33 metal oxides were investigated to determine their effects on the thermal decomposition of PVC, by using a pyrolysis gas chromatograph. Most acidic oxides accelerate the recombination of chlorine atoms with double bonds, since PVC containing these metal oxides easily release lower aliphatics, toluene, ethylbenzene, o-xylene, and chlorobenzenes. On the other hand, most basic metal oxides, such as oxides of alkaline earths or silver, inhibit the recombination. These tendencies observed in the thermal decomposition of PVC agree with the contributions of corresponding metal salts to the dehydrochlorination of PVC proposed by other workers. This means that thermal decomposition or dehydrochlorination of PVC is affected by irregularities in head-to-tail linkages formed by the recombination of chlorine atoms during heat treatment of PVC.     

Modification of poly(vinyl chloride) with pendant metal complex for catalytic applications

Poly(vinyl chloride) was modified to develop an alternative support for the preparation of polymer-supported catalysts. Commercially available poly(vinyl chloride) was synthetically modified to a polymer containing pendant primary amino groups. The Schiff-base of salicylaldehyde and the amino polymer were prepared and were used as the ligands in the synthesis of a polymer-supported copper complex. The polymer-supported ligand and catalysts were characterized by various physical methods. The polymer with the pendant copper complex was able to catalyze the one-pot three-component Mannich reaction between aldehydes, ketones and anilines under mild and environmentally friendly conditions. The catalyst can be recovered by simple filtration and is reusable.     

Investigations on poly(vinyl chloride). IV. Effects of metal chlorides on the thermal decomposition of poly(vinyl chloride)

The effects of various metal oxides upon the thermal decomposition of poly(vinyl chloride) (PVC) were previously reported. In this work, 23 metal chlorides were investigated to determine their effects on the thermal decomposition of PVC by pyrolysis–gas chromatography at 500°C. Each metal chloride exhibits influences on the course of thermal decomposition of PVC almost similar to the corresponding metal oxide except for a few elements; the metal chlorides from acidic metal oxides accelerate the thermal decomposition of PVC, but the metal chlorides from basic metal oxides do not. On comparing the effects of metal oxides and metal chlorides on the thermal decomposition of PVC, most metal chlorides were found to accelerate the thermal decomposition of PVC more than the corresponding metal oxides, owing to ease of addition of the chlorine atoms released from metal chloride to the dehydrochlorinated chains. It is concluded from these results that the thermal decomposition of PVC containing metal salts is markedly influenced by the ease with which chlorine atoms are released from the corresponding metal chloride.     

Morphology-driven surface segregation in a blend of poly(epsilon-caprolactone) and poly(vinyl chloride)

A blend of poly(epsilon-caprolactone) (PCL) and poly(vinyl chloride) (PVC) with 90 wt % PCL was prepared. Two films of this blend, which were grown at 35 and 45 degrees C, showed the absence and presence of banded spherulites, respectively. A detailed examination conducted with time-of-flight secondary ion mass spectrometry (ToF-SIMS) found that the surface composition of the film grown at 45 degrees C was related to its structure, which was shown to contain ridges and valleys. Phase images obtained using atomic force microscopy (AFM) indicated that the ridges and valleys consisted of edge-on and flat-on lamellae, respectively. ToF-SIMS imaging revealed that PVC and PCL were located mainly on the surface of the valleys and ridges, respectively. This morphology-driven surface segregation was caused by the difference in the surface energy between the flat-on and edge-on lamellae.     

Photosensitized dehydrochlorination of poly(vinyl chloride). III. Reaction of thermally degraded poly(vinyl chloride) with hydrogen chloride

Films prepared from thermally degraded poly(vinyl chloride) were photolyzed in the presence of hydrogen chloride. When the light was filtered through a Pyrex disk, the absorbance in the region between 270 nm and about 415 nm decreased and reached a minimum value but the absorbance increased at wavelengths shorter than 270 nm and longer than 415 nm. Maximum bleaching occurred at a wavelength which depended on that of the irradiating light. When the Pyrex filter was omitted, an additional slower photodehydrochlorination reaction was superimposed on the photobleaching reaction. Photolysis of hexane or ethanol solutions of 1,8-diphenyloctatetra-1,3,5,7-ene and hydrogen chloride showed a similar reaction involving bleaching of the absorption of the polyene structure. The problems of using absorbance as an indication of the extent of the photodegradation of poly(vinyl chloride) are discussed.     

Detection of parathion methyl using a surface plasmon resonance sensor combined with molecularly imprinted films

An ultra-sensitive and highly selective parathion methyl(PM) detection method by surface plasmon resonance(SPR) combined with molecularly imprinted films(MIF) was developed. The PM-imprinted film was prepared by thermo initiated polymerization on the bare Au surface of an SPR sensor chip.Template PM molecules were quickly removed by an organic solution of acetonitrile/acetic acid(9:1,v/v), causing a shift of 0.58 in SPR angle. In the concentrations range of 10à13–10à10mol/L, the refractive index showed a gradual increase with higher concentrations of template PM and the changes of SPR angles were linear with the negative logarithm of PM concentrations. In the experiment, the minimum detectable concentration was 10à13mol/L. The selectivity of the thin PM-imprinted film against diuron,tetrachlorvinphose and fenitrothion was examined, but no observable binding was detected. The results in the experiment suggested that the MIF had the advantages of high sensitivity and selectivity.     

Optical determination of ionophore diffusion coefficients in plasticized poly(vinyl chloride) sensing films

The knowledge of accurate diffusion coefficients of electrically neutral ionophores in solvent polymeric membranes is important in view of understanding and optimizing important sensor characteristics of ion-selective electrodes (ISEs) and their corresponding optical sensors. A spectroscopic imaging technique is introduced here to determine the diffusion coefficient of the chromoionophore (N,N-diethyl-5-(octadecanoylimino)-5H-benzo[a]phenoxazine-9-amine, ETH 5294) in solvent polymeric membranes with different types of plasticizers and varying polymer-plasticizer ratio. This method is based on following the changes in the absorbance profiles of the chromoionophore as a function of space and time. The desired membrane composition is solvent cast onto a glass slide and placed under a microscope objective. The membrane is then exposed to light from a mercury arc lamp which photobleaches the dye in a circular area, providing an interface from which the time rate of absorbance change is studied. Spectral images are acquired over fixed time intervals with a microscope equipped with a charge-coupled device (CCD) camera providing 0.41 μm nominal resolution. Two plasticizers, ortho-nitrophenyl octyl ether (o-NPOE) and bis(2-ethylhexyl) sebacate (DOS), are examined in poly(vinyl chloride) (PVC) by varying the ratio of polymer to plasticizer content and measuring the diffusion coefficient of the chromoionophore. Corresponding membrane compositions containing 10 wt.% of an inert lipophilic salt (ETH 500) are also examined. Near linear relationships between the logarithmic diffusion coefficients and the PVC content are observed that obey the following relationships: -0.0459 wt.% PVC (for PVC-DOS), -0.0468 wt.% PVC (for PVC-DOS-ETH 500), -0.0508 wt.% PVC (for PVC-NPOE), -0.0473 wt.% PVC (for PVC-NPOE-ETH 500).     

Retardation of discoloration of poly(vinyl chloride) and decolorization of discolored poly(vinyl chloride) with diimide

Retardation of discoloration of poly(vinyl chloride) with diimide was studied in dimethylformamide at 130°C. with the use of p-toluenesulfonylhydrazide (PSH) as a source of diimide. A process was proposed that involved prolonging the induction periods of discoloration by inhibiting the development of conjugated polyene structure. The optimum proportion of PSH was one fourth of the poly(vinyl chloride), the best results. Furthermore, poly(vinyl chloride) discolored by thermal degradation in o-dichlorobenzene or gamma-ray irradiation under vacuum was decolorized in solution at 130°C. by addition of PSH. The decolorized poly(vinyl chloride) thus obtained was thermally stable compared with that obtained by oxidative methods.     

Potentiometric sensor for hydrogen ion based on N,N'-dialkylbenzylethylenediamine neutral carrier in a poly(vinyl chloride) membrane with polyaniline solid contact

Hydrogen ion selective solid contact electrodes based on N,N'-dialkylbenzylethylenediamine (alkyl=butyl, hexyl, octy, decyl) are prepared. Solid contact electrodes and coated wire electrodes have been fabricated from polymer cocktail solutions based on N,N'-dialkylbenzylethylenediamine (alkyl=butyl, hexyl, octy, decyl). We showed that the response range and slopes are influenced by the alkyl chain length. Response ranges and Nernstian slops for solid contact electrodes were slightly better than for coated wire electrodes. Solid contact electrodes were shown linear selective to hydrogen ion in the pH ranges pH 4.5-13.0, 4.2-13.1, 3.4-13.0 and 3.0-13.2. and their Nernstian slopes were 49.7, 50.8, 51.5 and 53.7 mV pH(-1) at 20+/-0.2 degrees C, respectively. Stability is also improved especially when compared with coated wire electrodes. The 90% response time was <2 s and their electrical resistance varied in the range 2.37-2.76 MOmega. Especially solid contact electrodes with N,N'-didecylbenzylethylenediamine have shown the best selectivity and reproducibility of e.m.f..     

In situ sensing of metal ion adsorption to a thiolated surface using surface plasmon resonance spectroscopy

The kinetics of the adsorption of metal ions onto a thiolated surface and the selective and quantitative sensing of metal ions were explored using surface plasmon resonance (SPR) spectroscopy. The target metal ion was an aqueous solution of Pt2+ and a thin-gold-film-coated glass substrate was modified with 1,6-hexanedithiol (HDT) as a selective sensing layer. SPR spectroscopy was used to examine the kinetics of metal ion adsorption by means of the change in SPR angle. The selectivity of the thiolated surface for Pt2+ over other divalent metal ions such as Cu2+, Ni2+, and Cd2+ was evident by the time-resolved SPR measurement. SPR angle shift, deltatheta(SPR), was found to increase logarithmically with increasing concentration of Pt2+ in the range of 1.0 x 10(-5)-1.0 mM. The rate of Pt2+ adsorption on HDT observed at both 0.1 and 1 mM Pt2+ accelerates until the surface coverage reaches approximately 17%, after which the adsorption profile follows Langmuirian behavior with the surface coverage. The experimental data indicated that heavy metal ions were adsorbed to the hydrophobic thiolated surface by a cooperative mechanism. A mixed self-assembled monolayer (SAM) composed of HDT and 11-mercaptoundecanoic acid was used to reduce the hydrophobicity of the thiol-functionalized surface. The addition of hydrophilic groups to the surface enhanced the rate of adsorption of Pt2+ onto the surface. The findings show that the adsorption of metal ions is strongly dependent upon the hydrophilicity/hydrophobicity of the surface and that the technique represents an easy method for analyzing the adsorption of metal ions to a functionalized surface by combining SPR spectroscopy with a SAM modification.     

Structure of chlorinated poly(vinyl chloride). V. Molecular parameters of chlorinated poly(vinyl chloride)

The molecular parameters of samples of chlorinated poly(vinyl chloride) (CPVC) and chlorinated β,β-dideuterated poly(vinyl chloride) (β,β-d₂-CPVC) were determined by gel permeation chromatography (GPC), light scattering, osmometry, and viscometry. Comparison of GPC, light scattering, osmometric, and viscometric data resulted in a discussion of the possibility of degradation and the causes of changes in the solution properties in chlorination of PVC and ββ-dideuterated poly(vinyl chloride) (ββ-d₂-PVC). The results obtained are discussed in relation to the mechanism of chlorination of PVC.     

Thermal decomposition of poly(vinyl chloride) and chlorinated poly(vinyl chloride). II. Organic analysis

A concerted study of poly(vinyl chloride), chlorinated poly(vinyl chloride), and poly(vinylidene chloride) polymers by spectroscopy, thermal analysis, and pyrolysis-gas chromatography resulted in a proposed mechanism for their thermal degradation. Polymer structure with respect to total chlorine content and position was determined, and the influence of these polymer units on certain of the decomposition parameters is presented. Distinguishing differences were obtained for the kinetics of decomposition, reactive macroradical intermediates, and pyrolysis product distributions for these systems. It was determined that chlorinated poly(vinyl chloride) systems with long-chain ? CHCI? units were more thermally stable than the unchlorinated precursor, exhibited increasing activation energy for the dehydrochlorination, and produced chlorine-containing macroradical intermediates and chlorinated aromatic pyrolysis products. The poly(vinyl chloride) polymer was relatively less thermally stable, exhibited decreasing activation energy during dehydrochlorination, and produced polyenyl macro-radical intermediates and aromatic pyrolysis products.     

Reaction of n-butyllithium with poly(vinyl chloride)

The reactions of poly(vinyl chloride) and butyllithium in tetrahydrofuran were investigated. A deep purple color developed at first with addition of butyllithium to the THF–PVC solution, and a spontaneous color change of the misture occurred successively to blue, green, and finally pale vellow. In these reaction stages, the PVC might be butylated, dehydrochlorinated, and partially lithiated by BuLi. These facts were substantiated by the results of successive reactions with various substances such as Michler's ketone, carbon dioxide, and styrene.     

Blends of a chlorinated poly(vinyl chloride) with a polyurethane

Blends of a 67% chlorinated poly(vinyl chloride) with a low-molecular-weight polyurethane are partially miscible over the 0–80% urethane compositional range. A single, composition-dependent glass transition temperature is observed from both DSC and dynamic mechanical measurements. The blends exhibit a cocontinuous morphology with domain sizes varying from 0.15 to 1.5 μm. These results point out that the relation between miscibility characteristics and domain size is a complex one, not only dependent upon the degree of miscibility, but also on the nature of the blend components and the test method used. Thus the domain size for a certain degree of miscibility is not a universal constant as was previously believed. The melt rheology of the blends as a function of composition is strongly “positive deviating” from the log additivity rule and fits a simplified version of the McAllister model. The strongly “positive deviating” rheological behavior of the blends is most likely a result of the cocontinuous morphology which makes the system behave as a highly entangled network.     

Photo-oxidation of poly(vinyl chloride)

Hydrogen chloride is evolved at an increasing rate in the light-induced oxidation of poly(vinyl chloride) films. These accelerated kinetics were shown to result from an increased absorption of light by the polyenes formed, since the quantum yield of dehydrochlorination (Φ_HCl = 0·015) is independent of the extent of the reaction in the dose range investigated. Determination of the quantum yields of the different processes involved indicate that, for each scission of the polymer backbone, 11 molecules of hydrogen chloride are evolved while three carbonyl groups, two hydroperoxides and 0·4 intermolecular crosslinks appear on the polymer chain. A mechanism that involves β-scissions of the tertiary alkoxy radicals, resulting from non-terminating interactions of α-chloro-peroxy radicals, is suggested to explain the observed increase of the polymer degradation in the presence of oxygen.     

Radiolysis of poly(vinyl chloride)

Allyl free-radical intermediates are detected by ultraviolet absorption at 255 mu in poly(vinyl chloride) irradiated at ?196°C and stored at 25°C. In vacuum at 25°C, allyl radicals are converted into polyenyl free radicals and polyenes. From the nature of allyl radical decay in vacuum, radical chain transfer between polyenyl radicals and poly(vinyl chloride) is inferred. Allyl and polyenyl free radicals are scavenged by oxygen on post-irradiation storage in air.     

Pyrolysis of poly(vinyl chloride)

A pyrolysis–gas chromatography–mass spectrometric technique has been developed to study the thermal degradation of poly(vinyl chlorides) polymerized at different temperatures. Hydrogen chloride and benzene evolution during successive stages of pyrolysis have been quantitatively determined and correlated to the tacticity and molecular weight of the polymer. It was found that lowering the temperature of polymerization and molecular weight depresses benzene evolution and increases char weight but does not affect the HCl yield. It is suggested that the syndiotactic trans microstructure favored at low temperature of polymerization yields polyenes which cannot cyclize to form benzene. As the molecular weight decreases, the increase in number of vinyl chain ends facilitates pyrolytic crosslinking and char formation.