Effects of polymerization and hydrolysis degrees of poly(vinyl alcohol) (PVA) on the efficiency of the PVA-solid substrate for room-temperature phosphorimetry.

Several kinds of poly(vinyl alcohols) (PVAs) having different degrees of polymerization and hydrolysis were tested as a material of a solid substrate for room-temperature phosphorimetry (RTP). Effects of these differences on the efficiency of the solid substrate were investigated. Completely hydrolyzed PVAs acquired a luminescence property in the grinding process of substrate preparation, but partially hydrolyzed PVAs did not acquire this property. When the completely hydrolyzed PVA substrates were prepared by drying their aqueous solutions, their luminescence property almost disappeared. However, very weak background emission remained on the surface of a completely dried substrate which had been treated with an analyte aqueous solution. This residual background affected the spectrum of the analyte, especially at low concentrations. Stability of the phosphorescence intensity with the passage of time was superior on the partially hydrolyzed PVAs than on the completely hydrolyzed PVAs. On the other hand, the RTP intensity and reproducibility were superior on the completely hydrolyzed PVAs. Practically, partially hydrolyzed PVAs were more suitable as a material of the substrate because of the stability of its RTP intensity and the weakness of its background emission. The linear dynamic range of the analytical curve for p-aminobenzoic acid on the substrate of partially hydrolyzed PVA having a degree of polymerization of 3,500 was 5-2,000 pmol/spot (20 microL) and its correlation coefficient was 0.963 for 30 data points.     

Surface analysis of tablets by room-temperature phosphorimetry

The feasibility of surface analysis of homogeneous tablets by room-temperature phosphorimetry is studied for propranolol, p-aminobenzoic acid and acetylsalicylic acid as model compounds. Potassium iodide is used to provide the heavy atom; starch or carboxymethylcellulose is used as the excipient. The analytically useful ranges were found to be 3 × 10^?5?3 × 10^?4% for p-aminobenzoic acid, 5 × 10^?4?5 × 10^?2% for propranolol, and ? 10% for acetylsallicylic acid (all by weight in tablets).     

A highly sensitive coupling technique for the determination of trace quercetin based on solid substrate room temperature phosphorimetry and poly (vinyl alcohol) complex imprinting

Al³⁺ could react with quercetin (Q) to form [AlQ]³⁺ complex which could be used as a template for the preparation of poly (vinyl alcohol)–[AlQ]³⁺ complex imprinting (PVA-C-I). The [AlQ]³⁺ not only had good matching ability and selectivity with the cavity of PVA-C-I, but also could react with the fluorescein isothiocyanate anion (FITC⁻) on the outside of cavity by electrostatic interaction to form ion-association complex [AlQ]³⁺·[(FITC)⁻]₃. The ion-association complex could emit strong and stable room temperature phosphorescence (RTP) on polyamide membrane (PAM) and the ΔI_p of the system had linear relationship with the content of Q, showing the highly selective identification of PVA-C-I to Q. Thus, a new coupling technique for the determination of trace Q based on solid substrate room temperature phosphorimetry and poly (vinyl alcohol) complex imprinting (PVA-C-I-SSRTP) was established. The linear range and limit of detection (LOD) of this method were 0.010–2.0 (×10⁻¹² g mL⁻¹) and 2.0 × 10⁻¹⁴ g mL⁻¹, respectively, showing wide linear range and high sensitivity of PVA-C-I-SSRTP. This method was used to determine the content of Q in waste water, and the results are consistent with those by spectrofluorimetry. Meanwhile, the mechanism for the determination of Q using PVA-C-I-SSRTP was also discussed.     

Determination of carbaryl in foods by solid-phase room-temperature phosphorimetry

A phosphorimetric solid phase assay is proposed for the determination of the pesticide carbaryl (CBL) at room temperature. CBL was spotted on filter paper together with Tl(I) as heavy metal, and dried for 3 min, after which the diffuse transmitted phosphorescence was measured using two quartz plates to avoid the quenching effect produced by atmospheric oxygen. The linear dynamic range was 0.5–4.0 μg/mL and the detection and quantification limits were 0.09 and 0.31 μg/mL, respectively. The precision of the method, expressed as relative standard deviation, was 2.3% for a sample containing 2.0 μg/mL of CBL. The method was applied to the determination of CBL residues in cereals, potatoes and waters, obtaining recoveries ranging between 92 and 105%.     

Determination of carbaryl in foods by solid-phase room-temperature phosphorimetry

A phosphorimetric solid phase assay is proposed for the determination of the pesticide carbaryl (CBL) at room temperature. CBL was spotted on filter paper together with Tl(I) as heavy metal, and dried for 3 min, after which the diffuse transmitted phosphorescence was measured using two quartz plates to avoid the quenching effect produced by atmospheric oxygen. The linear dynamic range was 0.5–4.0 μg/mL and the detection and quantification limits were 0.09 and 0.31 μg/mL, respectively. The precision of the method, expressed as relative standard deviation, was 2.3% for a sample containing 2.0 μg/mL of CBL. The method was applied to the determination of CBL residues in cereals, potatoes and waters, obtaining recoveries ranging between 92 and 105%. Received: 10 October 1997 / Revised: 2 February 1998 / Accepted: 7 February 1998     

Heterotactic poly(vinyl alcohol)

Bulky substituents in vinyl trialkylsilyl ethers and vinyl trialkylcarbinyl ethers led to heterotactic polymers (H = 66%). The polymers were converted into poly(vinyl alcohol) (PVA) and further to poly(vinyl acetate), and tacticity was determined as poly(vinyl acetate). Vinyl triisopropylsilyl ether in nonpolar solvents yielded a heterotactic polymer with a higher percentage of isotactic triads than syndiotactic triads (Hetero-I). Vinyl trialkylcarbinyl ethers in polar solvents gave a heterotactic polymer with more syndiotactic triads than isotactic (Hetero-II). Heterotactic PVA was soluble in water and showed characteristics infrared absorptions. Interestingly, Hetero-I PVA showed no iodine color reaction, but Hetero-II showed a much more intense color reaction than a commercial PVA. The mechanism of heterotactic propagation was discussed in terms of the Markóv chain model.     

Determination of vicinal hydroxyl groups in poly(vinyl alcohol) (PVA)

An accurate procedure for the determination of 1,2-diol groups in styrene glycol and poly-(vinyl alcohol) has been demonstrated. The diols are cloven with periodate and the excess of this is determined by means of standard arsenite solution.     

Sorption of water by poly(vinyl alcohol)

The isotherms of water sorption by poly(vinyl alcohol) have been obtained by static sorption methods in a wide range of vapor activities. The properties of poly(vinyl alcohol) at various values of relative humidity have been studied by DSC, X-ray diffraction analysis, and mechanical testing. It has been shown that the correct thermodynamic analysis of sorption isotherms for sorbents with complex organization requires knowledge of their structural features. A method of allowing for the effect of osmotic pressure on the polymer sorption capacity is proposed. The pair interaction parameters estimated in this study are compared with the published data.     

Functionalization of a poly(vinyl alcohol) in the solid state with a swelling agent by methacrylic anhydride

Poly(vinyl alcohol‐co‐vinyl acetate) was functionalized by methacrylic anhydride to introduce functional groups by a new process that consisted of modifying a polymer directly from a powder form in the solid state. To favor the diffusion of the reagents, a swelling agent composed by a mixture of ethylene carbonate and propylene carbonate was used. N‐methylimidazole was used as a basic catalyst of the esterification reaction, adjusting the reaction times. This work presents the process and the effects of the formulation on anhydride conversion. The side reactions were also determined; they all involved N‐methylimidazole. Decarboxylation reactions of the carbonates were characterized, that is, going from ethylene carbonate to ethylene glycol, which is able to react with two anhydride molecules by esterification reactions to, respectively, form 2‐hydroxyethyl 2‐methylpropenoate and ethyl 1,2‐bis(2‐methyl propenoate). The same side reactions are possible with propylene carbonate but are less reactive than the starting ethylene carbonate. Model anhydrides such as hexanoic and heptanoic anhydrides, less reactive than methacrylic anhydride, were used to characterize a new anhydride decarboxylation reaction. The homogeneity of the grafting is also discussed, especially its dependence on the polymer properties, the diffusion modes of the reagents (carbonate mixture and the anhydride), and the competition between the diffusional and chemical kinetics of methacrylic anhydride. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1618–1629, 2004     

Determination of crystallinity of swollen poly(vinyl alcohol) by laser Raman spectroscopy

Laser Raman spectra of atactic poly(vinyl alcohol) (PVA) after heat treatment and/or swelling in water have been obtained. An amorphous Raman band is observed at 1124 cm^?1, while a crystalline Raman band is found at 1147 cm^?1. A new method for crystallinity determination is proposed, in which the amorphous band is used instead of the crystalline band. The method is superior to others for water-swollen PVA samples. Laser Raman spectra of swollen PVA revealed that swelling causes destruction of a major fraction of the crystalline regions and the remaining intact crystalline part increases with increasing temperature of heat treatment.     

Long branching in poly(vinyl acetate) and poly(vinyl alcohol). II. Polymerization of vinyl acetate in the presence of crosslinked poly(vinyl alcohol)

It is a common view that poly(vinyl acetate) has many branches at the acetyl side group, but that the corresponding poly(vinyl alcohol) has little branching. In order to study the branching in poly(vinyl acetate) and poly(vinyl alcohol) which is formed by chain transfer to polymer, the polymerization of ¹⁴C-labeled vinyl acetate in the presence of crosslinked poly(vinyl acetate), which was able to be decrosslinked to give soluble polymers, was investigated at 60°C and 0°C. This system made it possible to separate as well as to distinguish the graft polymer from the newly polymerized homopolymer. Furthermore, the degree of grafting onto the acetoxymethyl group and onto the main chain were estimated. It became clear that, in the polymerization of vinyl acetate, chain transfer to the polymer main chain takes place about 2.4 times as frequently at 60°C as that to the acetoxy group and about 4.8 times as frequently at 0°C.     

Raman spectral study of solid and dissolved poly(vinyl alcohol) and ethylene-vinyl alcohol copolymer

We have measured the Raman spectra of ethylene-vinyl alcohol copolymer (EVOH) and poly(vinyl alcohol) (PVOH). Spectra of 88% hydrolyzed PVOH were examined from the partially crystalline solid, from PVOH dissolved in both H₂O and D₂O, and from films precipitated from these solutions. The spectrum in H₂O differs from that of the starting material by disappearance of sharp bands having Raman shift values of 1146 and 1093 cm^?1, strengthening of a band near 915 cm^?1, decrease in frequency of bands at 480, 1356, and 1441 cm^?1, and increase in frequency of bands at 369, 413, 1023, 1371, and 2910 cm^?1. The spectrum of the film shows partial reversal of these trends. With D₂O as the solvent, the band shifts are slightly different from those listed above and new bands appear. These changes are indicative of loss of crystallinity, change in stereochemistry, and partial deuteration of hydroxyl during dissolution of this PVOH sample at room temperature. © 1994 John Wiley & Sons, Inc.     

Short branching in poly(vinyl alcohol). IV. Determination of the short branches in poly(vinyl alcohol) polymerized under various conditions

The effect of the conditions of polymerization of vinyl acetate on the formation of short branching in the derived poly(vinyl alcohol) (PVA) was studied. ¹H-NMR combined with a CAT technique was employed for the determination of the short branches. It was found that the formation of short branching is favorable at low concentrations of monomer, at high conversions, and at high temperatures. These facts evidently support the idea that the mechanism of the formation of short branching is back-biting. Amounts of short branches in some commercial PVA were also estimated. The observed values lie in the range of 0.12–1.7 mole-%.     

Characterization of poly(vinyl alcohol) during the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier

During the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates from the aqueous phase contributing to the formation of polymer particles. Since particle formation and therefore the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PVA. In this work, the quantitative separation and characterization of the grafted water-insoluble PVA was carried out by a two-step selective solubilization of the PVAc latex, first with acetonitrile to separate PVAc homopolymer, followed by water to separate the water-soluble PVA from the remaining acetonitrile-insoluble material. After the separation, the water-soluble and water-insoluble PVA were characterized by Fourier Transform Infrared (FTIR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, from which the details of the PVA-graft-PVAc structure were obtained. © 1996 John Wiley & Sons, Inc.     

Structural irregularities in poly(vinyl alcohol)

Poly(vinyl alcohols) derived from the product of polymerization of vinyl acetate in methanol have been characterized by various physical and chemical methods before and after NaIO₄ cleavage. The 220-MHz ¹H-NMR spectra confirm the reliability of NaIO₄ titrimetry for estimating 1,2-glycol content and help explain the tendency for viscometry to grossly underestimate the 1,2-glycol content for low molecular weight polymers. The spectra and related chemical evidence indicate that the major endgroups are HOCH₂CH₂? and CH₃CH(OH)CH(OH)CH₂? . ß-Hydroxyethyl groups also occur as short chain branches, mainly attached to α carbon atoms in the normal head-to-tail polymer chain sequence. The concentrations of the branch and endgroups depend on polymerization conditions and help explain polymerization “solvent” effects on physical properties.     

Radiation effects on the thermal degradation of poly(vinyl chloride) and poly(vinyl alcohol)

Radiation effects on the formation of conjugated double bonds in the thermal degradation of poly(vinyl chloride) (PVC) and poly(vinyl alcohol) (PVA) were investigated. Thin films of PVC and PVA were either irradiated with γ-rays at ambient temperature (pre-irradiation) and then subjected to thermal treatment, or irradiated at elevated temperatures (in situ irradiation). An extensive enhancement of the thermal degradation was observed for the pre-irradiation of the PVC films, which was more effective than the effect of the in situ irradiation at the same absorption dose. For the PVA degradation, however, the effect of the in situ irradiation was larger than that of the pre-irradiation. The results were explained and related mechanisms were discussed based on radiation-induced chemical reactions and their individual contributions to the thermal degradation behaviors of the two polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3089–3095, 1998     

The solvation of poly(vinyl alcohol)

The possible incorporation of water molecules within the crystal structure of poly(vinyl alcohol) is discussed. Modelling of the crystal structure suggested that water could be incorporated without severe disruption, and the effect on the X-ray powder diffraction trace was simulated. The effect of variation in tacticity is discussed in terms of the nature of the hydrogen bonding. Simulated traces are compared with experimental data from atactic samples in which a change in the diffraction peak intensities is observed for samples crystallised with water present. This is compared with samples produced from nonaqueous solutions.