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.     

Preparation of poly(vinyl alcohol) hydrogels with radiation grafted citric and succinic acid groups

Ternary mixtures of PVA/Citric acid (CA)/water and PVA/Succinic acid (SA)/water were gamma irradiated to various doses in air at ambient temperature. Gelation % vs dose curves were constructed and swelling behavior of gels with maximum conversions was studied. In maximum gelled systems 80% of CA used in the feed composition was retained in the gel structure whereas this was only 20% for SA. The volume of swelling of ionic PVA gels increased from 230% to 530% for PVA/CA systems when pH was increased from 2.6 to 7.5. Less significant increase in swelling was observed for PVA/SA gels, from 250% to 330% in the same pH interval. The incorporation of SA and CA groups onto PVA networks improved remarkably the affinity of these structures for Co²⁺ and Ni²⁺ ion uptake.     

Photosensitive poly(vinyl alcohol) bearing N-(1-pyridinio)benzamidate groups

Poly(vinyl alcohol) (PVA) bearing N-(1-pyridinio)benzamidate (PB) was synthesized through acetalization of PVA and 4-dimethoxymethyl-N-(1-pyridinio)benzamidate (DMPB) in water. The PB groups in PVA–PB had almost the same proportion of DMPB to the starting PVA. The UV spectrum of PVA–PB shows an absorption band of pyridinium ylide as a shoulder around 300 nm in water, and as a maximum at 315 nm in a film on a quartz plate. These absorption bands decreased on irradiation at 313 nm. The photoreaction of the PVA–PB film proceeds much faster than that of PVA–PB in water. The solution, of PVA-bearing high-PB content, became slightly turbid during irradiation. After irradiation the film became insoluble in water, and the soluble fraction of polymer (P? = 1700) was 3% at a PB content of 1 mol% and less than 1% at that of more than 2 mol%. This polymer can be applied as a water-soluble negative photoresist.     

Chemical modification of hydroxyl groups of poly(vinyl alcohol) by a glycosidation reaction

A new procedure for chemical modification of poly(vinyl alcohol) (PVA) was established by a glycosidation reaction of hydroxyl groups in PVA with triacetylated sugar oxazoline 1 . ¹H and ¹³C NMR analyses indicated that triacetylated N‐acetyl‐D‐glucosamine (GlcNAc) was introduced onto a PVA backbone selectively via a β‐O‐glycoside linkage. Deacetylation of triacetylated GlcNAc‐substituted PVA 2 resulted in GlcNAc‐substituted PVA 3 in good yield. These modified PVAs 2 and 3 exhibited solubilities and thermal properties different from the original PVA.     

CE of poly(amidoamine) succinamic acid dendrimers using a poly(vinyl alcohol)-coated capillary

Various generations (G1-G8) of negatively charged poly(amidoamine) (PAMAM) succinamic acid dendrimers (PAMAM-SAH) were analyzed by CE using a poly(vinyl alcohol)-coated capillary. Due to its excellent stability and osmotic flow-shielding effect, highly reproducible migration times were achieved for all generations of dendrimer (e.g., RSD for the migration times of G5 dendrimer was 0.6%). We also observed a reverse trend in migration times for the PAMAM-SAH dendrimers (i.e., higher generations migrated faster than lower generation dendrimers) compared to amine-terminated PAMAM dendrimers reported in the literature. This reversal in migration times was attributed to the difference in counterion binding around these negatively charged dendrimers. This reverse trend allowed a generational separation for lower generation (G1-G3) dendrimers. However, a sufficient resolution for the migration peaks of higher generations (G4-G5) in a mixture could not be achieved. This could be due to their nearly identical charge/mass ratio and dense molecular conformations. In addition, we show that dye-functionalized PAMAM-SAH dendrimers can also be analyzed with high reproducibility using this method.     

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.     

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.     

Large edge-excitation red shift for a merocyanine dye in poly(vinyl alcohol) polymer matrix

The observed large edge-excitation red shift of the fluorescence of a merocyanine dye in a polyvinyl alcohol polymer matrix is explained in terms of a matrix that is rigid enough at room temperature to prevent complete equilibration between different solvation sites.     

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.     

Connection of poly(methyl methacrylate) microgel particles dispersed in poly(vinyl alcohol) matrix by seed polymerization

Poly(methyl methacrylate) microgels covered with poly(hydroxyethyl methacrylate) thin layer was dispersed in poly(vinyl alcohol) matrix. Homogeneous and regular arrangement of the microgel particles was suggested by Bragg diffraction for the films prepared by varying the PVA/microgel ratio (from 6/4 to 3/7 (w/w)). It was proved that the regular arrangement and connection of the microgels by seeded polymerization in poly(vinyl alcohol) were possible. © 1996 John Wiley & Sons, Inc.     

Study of the miscibility of poly(vinyl pyridines) with poly(vinyl acetate), poly(vinyl alcohol) and their copolymers

Miscibility of poly(4-vinyl pyridine) (P4VP) and poly(2-vinyl pyridine) (P2VP) with poly(viny acetate) (PVAc), poly(vinyl alcohol) PVA and poly(vinyl acetate-co-alcohol) (ACA copolymers) has been investigated over a wide composition range. Differentiaal scanning calorimetry (DSC) results indicate that P2VP is immiscible with PVAC, PVA, and their copolymers over the whole composition range. In turn, P4VP appears to be immiscible with PVAC and PVA, but miscible with some ACA copolymers in certain range of composition. The P4VP-ACA phase diagram for different copolymer compositions has been determined. The variation of the glass transition temperature with composition for miscible mixtures was found to follow the Gordon-Taylor equation, with the parameter κ dependent upon copolymer composition. FTIR analysis of blends reveal the existence of specific interactions via hydrogen bonding between hydroxyl groups and the nitrogen of the pyridinic ring, which appear to be decisive for miscibility. © 1994 John Wiley & Sons, Inc.     

Electrically controlled separation of maleic acid and fumaric acid through a poly(vinyl alcohol)/poly(acrylic acid) composite membrane

The separation of maleic acid (MA) from a mixture of MA and fumaric acid (FA) was studied using an electrically activated polyelectrolyte gel membrane. The membrane was prepared through the iterative freezing-thawing of an aqueous solution containing poly(vinyl alcohol) and poly(acrylic acid). The separation of MA from an equimolar mixture (5 mM) of MA and FA using the membrane was performed under different conditions of pH (1–8) and electric fields (2–6 V). It was found that MA was separated from the mixture at pH 2 under an applied electric field of greater than 2 V because only the COOH groups of MA were dissociated at pH 2 and the MA⁻ ions were transported through the membrane toward the electrode opposite in sign to their charge.     

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.     

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     

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

In order to clarify the grafting behavior of vinyl trimethylacetate (VTMAc) onto poly-(vinyl acetate) (PVAc), the polymerization of a radioactive VTMAc in the presence of a crosslinked PVAc gel was studied in accordance with the experimental technique described in the previous papers. It was found that, at 60°C, the grafting onto the main chain of PVAc takes place about 2.8 times as readily as that onto the acetyl side group on PVAc.     

Miscibility and orientation behavior of poly(vinyl alcohol) / poly(vinyl pyrrolidone) blends

The miscibility of poly(viny1 alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) blends is investigated by differential scanning calorimetry (DSC) and wide-angle x-ray diffraction (WAXD). The molecular orientation induced by uniaxial stretching of the blends is also examined by WAXD and birefringence measurements. It is shown by the DSC thermal analysis that the polymer pair is miscible, since a single glass transition temperature (T_g) is situated between the T_gs of the two homopolymers at every composition. The T_g versus composition curve does not follow a monotonic function but exhibits a cusp point at a PVP volume fraction of a little under 0.7, as in a case predicted by Kovacs' theory. The presence of a specific intermolecular interaction between the two polymers is suggested by an observed systematic depression in the melting point of the PVA component. A negative value of the polymer-polymer interaction parameter, χ₁₂ = 0.35 (at 513 K), is estimated from a thermodynamic approach via a control experiment using samples crystallized isothermally at various temperatures. The extent of optical birefringence (Δn) of the drawn blends decreases drastically with increasing PVP content up to 80 wt %, when compared at a given draw ratio, and ultimately Δn is found to change from positive to negative at a critical PVP concentration of a little over 80 wt %. Discussion of the molecular orientation behavior takes into consideration a birefringence compensation effect in the miscible amorphous phase due to positive and negative contributions of oriented PVA and PVP, respectively.     

Study of the effect of poly(vinyl alcohol) concentration on the gelation point of poly(vinyl alcohol) poly(acrylic acid) semi‐IPN systems as determined by viscoelastic measurements

We report on the determination of the gelation point of semi‐interpenetrating polymer networks (semi‐IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) formed by a sequential method. The evolution of the viscoelasticity during the gelation reaction of acrylic acid (AAc) in solutions of PVA has been monitored through the sol‐gel transition with dynamic mechanical experiments. The gelation time of the system increased with PVA concentration; however, the molecular structure of the gel, composed of swollen clusters, is rather independent of the presence of PVA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1944–1949, 2005     

Synthesis,polymerization, and copolymerization of multimethacrylate in matrix of poly(vinyl alcohol)

By reacting poly(vinyl alcohol) (PVA) with methacryloyl chloride, multimethacrylate in PVA matrix has been obtained. Free-radical polymerization of multimethacrylate and copolymerization of two multimethacrylates in PVA and p-cresol-formaldehyde matrices in diluted solutions occurs probably along ordered methyl methacrylate units in the matrix and results mainly in ladder-type homopolymer and copolymer. The structures of multimethacrylate, homopolymer, and copolymer have been found on the basis of elemental analysis, IR, and ¹H NMR spectra, and examination of the products of hydrolysis.     

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.