Structure of poly(vinyl alcohol)-iodine complex formed in the amorphous phase of poly(vinyl alcohol) films

The effect of syndiotactivity of poly(vinyl alcohol) (PVA) both on the formation and thermal stability of the complex formed in the amorphous phase of PVA films is investigated, and then a model of the complex is presented. The amount of the complex formed in syndiotacticity-rich PVA is much larger than that formed in atactic PVA under a given iodine-soaking condition, and the former complex has a higher thermal stability in the soaking solution than the latter. The complex formed in the amorphous phase is proposed to have such a structure as that in which a linear polyiodine I₅^? or I₅^? with a 3.1 A? periodicity is enveloped by four PVA segments of syndiotactic configuration with extended conformation. In this model, these four PVA chains participating in a complex are supposed to be fixed by interchain hydrogen bonds. The observed X-ray meridional intensity curve of iodinated PVA film can be explained by a series of two I₅^?. © 1993 John Wiley & Sons, Inc.     

On the poly(vinyl alcohol)–iodine complexes

The color development due to the complex formation of poly(vinyl alcohol) (PVA) with iodine increased with increasing syndiotacticity of PVA. Isotactic PVA showed no color development. The color development of syndiotacticity-rich PVA film decreased with increasing annealing temperature for films before complexization, whereas that of atactic (commercial) PVA increased with it. Lower temperatures, the elongation of complex film, and the presence of boric acid enhanced the absorbance at 600 nm due to I^?₅. The complexes are assumed to be made by incorporation of polyiodines into aggregates of syndiotactic sequences in PVA. The polarizability and electric conductivity of complex films are investigated. © 1993 John Wiley & Sons, Inc.     

Transient currents in poly(vinyl alcohol)–poly(vinyl pyrrolidone) polymer blend films

Transient currents (charging and discharging currents) in poly(vinyl alcohol) (PVA)–poly(vinyl pyrrolidone) (PVP) polymer blend films were measured over the temperature range 30–150°C at field strengths of 2.32–23.2 × 10⁶ Vm^?1. Polymer films were prepared by the isothermal immersion technique. Activation energies were evaluated from quasi-steady-state currents. A single relaxation peak was observed both from isochronal currents and low frequency dielectric relaxation. Activation energies evaluated from these two methods are found to be in fairly good agreement. The polarization is considered to be due to space charge origin along with some contribution from dipolar groups. The maximum loss was observed in Sample I (PVA: PVP = 25:75), suggesting maximum heterogeneity in this blend ratio.     

Formation of poly(vinyl alcohol)–iodine complex in aqueous solution: a SEM study of the freeze-dried substances

The freeze-dried samples prepared from dilute PVA aqueous solutions and PVA–iodine complex aqueous solutions have been examined using a scanning electron microscope. The samples prepared from syndiotacticity-rich PVA (S-PVA) solutions were found to have a network structure due to the formation of intermolecular hydrogen bonds, whereas in the case of atactic PVA (A-PVA) a network structure was not found. The network structure became more finely structured with increasing syndiotacticity. The structure of the freeze-dried sample of the complex solution prepared from S-PVA having a syndiotactic diad content of 63·8%, and iodine, was coarse in comparison with that of the freezedried sample of the S-PVA solution. In addition, the formation of spherical bulges, which are considered to correspond to microgels in the aqueous solution, were observed in several places. In the S-PVA having a syndiotactic diad content of 57·8%, the spherical bulges were not observed, whereas the absorbance of the aqueous solution was the highest. Although A-PVA did not form a PVA– iodine complex at 30°C in solution, the frozen solution turned blue due to the formation of aggregates. These phenomena were confirmed by the degree of crystallinity estimated from IR spectra, and the amount of iodine estimated from X-ray microanalysis of the freeze-dried samples. The PVA–iodine complexes are formed by the interaction of the aggregates of PVA molecules with iodine molecules. However, the PVA microgels do not interact with iodine. © 1998 Society of Chemical Industry     

Poly(acrylic acid)–poly(vinyl alcohol) copolymers with superabsorbent properties

Biodegradable polyacrylates were produced by a series of novel copolymerization and/or crosslinking techniques using poly(vinyl alcohol) (PVA) moieties modified by the incorporation of olefinic structures. PVA was modified by a tosylation and/or detosylation reaction. The functionalized PVA was copolymerized and/or crosslinked with acrylic acid or its partially neutralized form to give crosslinked polyacrylates that could swell in water. Their swelling behavior was determined under load. Degradation studies were performed in α-chymotrypsin, trypsin, and papain solutions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 817–829, 1998     

Permeation characteristics of poly(vinyl alcohol)–poly(vinyl acetate) composite porous membranes

Poly(vinyl alcohol) (PVAc) composite porous membrane has been prepared from PVAc latex film by extraction with acetone. The PVAc latex was prepared by emulsion polymerization of vinyl acetate in the presence of PVA, employing the hydrogen peroxide–tartaric acid systemm as an initiator. The extraction degree of PVAc could be controlled in a wide range by changing the addition method of the initiator, and, acoordingly, PVA–PVAc omposite porous membranes which had variosu void volumes were obtained. The maximum void volume attained was ca. 90%. Permation characteristics of organic solvents wre investigated on the membranes whose extraction degrees were 95.6% and 80.7%. Thge feeds were benzene, n-hexane, cyclohexane, and their mixtures. neither swelling nor shrinkage in tje appearance size of the while benzene hardly permeated even at 20 kg/cm². The grafted PVAc in the mebrane was removed or converted into grafted PVA by treatment with sodium methylate, and then the depression of benzene permeation was lost. The grafted PVAc was suggested to be localizd on the cell wall and was found to function as a valve which closes with nenzene or a good solvent for PVAc and opens with n-haxane or a poor solvent for PVAc.     

Preparation and structure of poly(vinyl alcohol)–poly(vinyl acetate) composite porous membrane

The preparation of poly(vinyl alcohol) (PVA)–poly(vinyl acetate) (PVAc) composite porous membrane was investigated by extracting PVAc with solvent from films of PVAc lattices which were obtained by the emulsion polymerization of vinyl acetate (VAc) in the presence of PVA. The formation of the porous membrane depended upon whether or not PVAc in the latex film was easily extracted with solvent. In the case of using hydrogen peroxide (HPO)–tartaric acid (TA) as an initiator, in the film of the latex which was produced from the batch method in which all ingredients of the batch were put into the reaction vessel before starting polymerization, PVAc could be extracted over 90% of total PVAc with common organic solvents. In the film of the latex which was produced from the dropwise addition method of VAc and initiator, the PVAc extraction was about 20-30%. On the other hand, in the case of using ammonium persulfate as an initiator, the desired porous membrane was not obtained. The structure of the porous membrane obtained from the latex of the batch method by using HPO—TA consisted of spherical cells which were made up of PVA and grafted PVAc or insoluble PVAc like microgels, which were not extracted with organic solvent and were connected by small pores. The PVA—PVAc composite porous membrane is permeated by n-hexane with 5.58 × 10² mL/cm²·s at 0.5 kg/cm², by benzene with only 1.33 × 10^?3mL/cm²·s even at 60 kg/cm².     

Dynamic mechanical properties of photopolymerizable poly(vinyl alcohol)–acrylate monomer blends

Dynamic mechanical properties of photopolymerizable poly(vinyl alcohol) (PVA)–monoacrylate blends were investigated by measuring dynamic shear modulus G′ and loss tangent, tan δ. The dynamic mechanical properties of the blends before being exposed to UV irradiation were governed by the weight percent of the monomers which act as plasticizers. On the other hand, the UV-irradiated blends seemed to be typical two-phase materials since they revealed two tan δ maxima whose positions were independent of the monomer content. Those two maxima were assigned to PVA and photopolymerized acrylates with reference to the dynamic mechanical data of PVA and a PVA-polyacrylamide polyblend. Those dynamic mechanical data suggested that insolubilization of the blend type photopolymers should be caused by a decrease in solubility due to graft polymerization of acrylate monomers onto PVA.     

Microstructure and mechanical properties studies of poly(vinyl alcohol)–lead salts complexes

Poly(vinyl alcohol) (PVA) was found to form complexes with PbCl₂, Pb(NO₃)₂, and Pb(CH₃COO)₂. Different complex compositions were prepared by casting technique. Microdomains were observed in the case of the PbCl₂-PVA system. Complexes of PbCl₂-PVA system are somicrystalline over the entire composition range. PbCl₂-PVA complexes are stable to temperatures greater than 350°C in comparison to 225°C of pure PVA. The general features of the microdomains depends upon the temperature and the salt concentration. The hardness properties of the binary mixture were found to change in a nonlinear mode exhibiting a maximum value with the increase of the PbCl₂ content and in a linear mode for the other salts. © 1995 John Wiley & Sons, Inc.     

Sorption and permeation of iodine in water-swollen poly(vinyl alcohol) membranes and iodine complex formation

The sorption and the permeation of iodine in water-swollen poly(vinyl alcohol) (PVA) membranes and the formation of PVA–iodine complexes were studied. The logarithms of the permeability and the diffusion coefficient decreased approximately linearly with the increase in polymer volume fraction. When the membrane was soaked in an aqueous I₂–KI solution, it contracted and Young's modulus increased. These findings were explained in terms of the formation of extra junction points due to the PVA–iodine complexes. These changes were reversible and could be recovered by replacing the solution with water. The length of the polyiodine chain increased with the increase in the degree of hydration of the membrane. At a fixed degree of hydration, Young's modulus of an iodine-sorbed membrane was much greater than that of a membrane soaked in pure water. This finding was explained on the basis of a double-network structure. The extension of the membrane promoted the complex formation, and the complex disappeared when the tension was released. The critical strain necessary for the complex formation was independent of the degree of hydration. The length of polyiodine chain increased with strain and became constant at higher strains.     

Structural properties of CrF3‐ and MnCl2‐filled poly(vinyl alcohol) films

Poly(vinyl alcohol) (PVA) films filled with different amounts of CrF₃ and MnCl₂ were prepared by the casting method. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) analysis were used to study the changes in the structure properties that occurred because of filling. The changes occurring in the measured parameters with increasing filler contents were interpreted in terms of the structural modification of the PVA matrix. All the studied samples had a main melting temperature due to the main crystalline phase of PVA. The intensity and position of this peak depended on the filling level. However, the samples of CrF₃‐filled PVA films with a filling level greater than or equal to 10 wt % revealed another melting temperature, which indicated the presence of a new crystalline phase in addition to the main crystalline phase. The changes that occurred in the degree of crystallinity of the studied samples were examined. The calculated degree of crystallinity was formulated numerically to be an exponential function of the filling level. The XRD patterns of the studied samples confirmed the DSC results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1115–1120, 2003     

Structure and properties of poly(vinyl alcohol)/κ‐carrageenan blends

Blends of a commercial atactic poly(vinyl alcohol) (a‐PVA) derived from vinyl acetate and κ‐carrageenan were prepared by mixing the aqueous solutions of both samples. Blend films prepared by casting were transparent. In the DSC curves of the blend films, the endothermic peaks shifted to lower temperature with an increase of the content of κ‐carrageenan. The Young's modulus and the strength at break increased with an increase of the content of a‐PVA. As the standing temperature of the blend solutions decreased, the gelation region increased also at high content of carrageenan. In the amorphous regions of blend films, a‐PVA and κ‐carrageenan were miscible. © 2001 Society of Chemical Industry     

Several reactions of poly(vinyl alcohol)–type acetaldehyde polymer

The preparation of the acetaldehyde polymers (PACH) having a poly(vinyl alcohol)-type structure and the thermal degradation of PACH have been reported previously. This paper will describe detailed aspects of several reactions of PACH. Copolymerization of PACH with toluene diisocyanate (TDI) was performed both thermally and catalytically. When piperidine was used as catalyst, the rate of reaction between PACH and TDI was found to depend on the concentration of both the active hydrogen of PACH and the isocynante group TDI. Acid and alkali treatment of PACH were carried out. On treatment with sulfuric acid, white polymers with good spinnability were obtained. The copolymerization of acetaldehyde with n-butylaldehyde were performed in the presence of sodium amalgam as catalyst. The reaction products were colorless, viscous liquids and assumed from the infrared and NMR spectra, elemental analyses, molecular weight and solubility tests to be aldol condensation-type copolymers.     

Mechanical properties of films of poly(vinyl alcohol) derived from vinyl trifluoroacetate

In order to study the influence of the stereoreguralities of polymer chains on the mechanical properties of films of poly(vinyl alcohol) (PVA)_(VTFA) derived from vinyl trifluoroacetate, the strength of the film was measured. In the case of undrawn PVA_(VTFA) films, Young's modulus and strength at break were the smallest at the annealing temperature of about 100°C. It is considered to be due to the melt of small microcrystals and the increase in mobility of chains in amorphous parts. Young's moduli of undrawn PVA_(VTFA) films were in the range of 1.50–3.75 GPs and the values were higher than that (0.17–0.36 GPa) of undrawn film of commercial PVA with the low concentration of syndiotacticity and the high concentration of head-to-head bounds. In the case of drawn, annealed PVA_(VTFA) films, the maximum Young's modulus was about 20 GPa.     

Mechanical properties of oriented poly(vinyl chloride)–poly(caprolactone) blends

Blends of poly(vinyl chloride) (PVC) with polycaprolactone (PCL) of different compositions were prepared from solutions in tetrahydrofuran (THF). The dried blends were stretched at different temperatures above the glass transition, and the birefringence and mechanical properties were studied. It is shown that the birefringence of PVC and the 75/25 PVC/PCL blend follows an affine deformation scheme with a decreasing number of segments with deformation. The 50/50 PVC/PCL blend shows a complex orientation behavior because of the presence of crystallinity in the PCL phase. The mechanical properties of the blends are shown to increase with orientation, and the aggregate model is acceptably followed by the amorphous oriented blends.     

Study of dynamic mechanical properties of poly(vinyl chloride)–ethylene vinyl acetate copolymer and poly(vinyl chloride)–chlorinated ethylene vinyl acetate copolymer mixtures

The compatibility of the mixtures poly(vinyl chloride)—ethylene vinyl acetate copolymer and poly(vinyl chloride)—chlorinated ethylene vinyl acetate copolymer was studied by the method of dynamic mechanical testing. The character of G′ and G″ was confronted with the Takayanagi model. In all cases a limited compatibility of the components was observed.     

Morphology and properties of poly(vinyl chloride)–polyurethane blends

The objective of this research was to study the morphology and properties of PVC–polyurethane blends. Studies on blends of a segmented polyether polyurethane with PVC were carried out utilizing differential scanning calorimetry, Rheovibron, stress–strain, infrared peak position studies, and infrared dichroism experiments. This thermodynamically incompatible system was made kinetically compatible by precipitation from tetrahydrofuran (THF) solutions. THF–dioxane solution casting and melt processing produced an incompatible system. The compatible polyurethane–PVC system contains a well-mixed PVC–polyether matrix phase as evidenced by T_g shifts, orientation characteristics, and infrared peak position changes. The aromatic urethane segments which exhibit microphase separation in the pure polyurethane are not solubilized by blending with PVC by any of sample preparation methods used in this study.     

Bending of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel in electric fields

Bending of poly(vinyl alcohol) hydrogel mixed with poly(sodium acrylate) chains, PVA–PAA gel, under the influence of dc electric fields was studied. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixture of PVA and polyacrylic acid aqueous solutions. The PVA–PAA gel was a hydrogel with the PAA chains, which were entangled with the PVA polymer network and were fixed in the gel. The PVA–PAA gel bent toward the negative electrode in electrolyte solutions under dc electric fields as did the polyelectrolyte gel with negatively charged polyions. The PVA gel, free of PAA, was insensitive to dc electric fields. The deflection of the bending and the bending speed were influenced by the filed intensity, the concentration of the polyion in the gel, and the thickness of the gel. The bending of the PVA–PAA gel was qualitatively explained by a bending theory of polyelectrolyte gel, based upon the change of the osmotic pressure due to the ion concentration difference between the inside and the outside of the gel.     

Phosphorescence and fluorescence of poly(vinyl alcohol) films

Luminescence properties of poly(vinyl alcohol) (PVA) films were investigated at room and low (103 K) temperatures. It was estimated that the PVA films can be regarded as luminescentless matrices when excited by radiation of wavelengths greater than 420 nm (λ_exc ≥ 420 nm).     

Dielectric and mechanical properties of poly(vinyl chloride)–dioctylphthalate systems

The mechanical properties, tensile strength, and elongation were investigated for poly(vinyl chloride) (PVC) samples mixed with dioctylphthalate (DOP) at concentrations from 0 to 100 parts per hundred parts PVC at 23°C. It was found that the tensile strength decreased with the increase of concentration, and the elongation was increased until a concentration of 30 DOP content, and then decreased. This leads to the suggestion that intermolecular plasticization is dominant until 30 DOP content, while interstructural plasticization is prevailing for higher concentrations. The permittivity ε′ and the dielectric loss factor ε″ of the same samples have been measured in the frequency range 10²–10⁵ Hz at temperatures from 3 to 96°C. Results show that as the DOP content increases in PVC, the dielectric absorption becomes broader, and the glass transition temperature T_g is lowered. The magnitude of the loss peak decreases with an increase of DOP content to a minimum at concentrations from 40 to 60 DOP content. At higher concentrations the loss peak is increased and T_g is unaltered. Another absorption was observed at 100 Hz and at high temperatures, which was attributed to Maxwell–Wagner effect or direct current conductivity or both of them. It was found that the sample containing 40 parts DOP in 100 parts PVC possesses the best mechanical and electrical properties.