Novel method for preparation of photocrosslinkable poly(vinyl alcohol)

A convenient procedure to prepare photosensitive poly(vinyl alcohol) by acetalization with 1-methyl-4-(p-formylstyryl)pyridinium methosulfate in heterogeneous condition is described. The reaction of fully saponified poly(vinyl alcohol) was carried out in suspension in acidic aqueous solution, while partially saponified poly(vinyl alcohol) was acetalized in acidic aqueous organic solvent. The photosensitive poly(vinyl alcohol) thus prepared was purified by filtration and successive washing out with methanol. The effect of the preparative condition on the electronic absorption spectra of the styrylpyridinium group attached to poly(vinyl alcohol) is discussed.     

Carbon-13 spin-lattice relaxation study of linear polymers in solution

Proton-decoupled, partially relaxed, Fourier-transform NMR of ¹³C in natural abundance was used to determine spin-lattice relaxation times of individual carbons of polyisobutylene, polyacrylonitrile, poly(vinyl chloride), and poly(vinyl alcohol) in solution. It is shown that the relaxation times are independent of the difference in stereochemical configuration. From the values of the nuclear Overhauser enhancement factor it is shown that the relaxation times are independent of the difference in stereochemical configuration. From the values of the nuclear Overhauser enhancement factor it is shown that the excess spin energy from equilibration of all the ¹³C, even of quaternary carbons, in the polymers dealt with here is transferred to the lattice mainly through ¹³C-¹H dipolar interactions. It is shown that the segmental motions responsible for the spin-lattice relaxation of the polymer skeleton in solution can be described by the isotropic model within a good approximation, except for poly(vinyl alcohol) at low temperature. The activation energies of skeletal and internal methyl motions are estimated from the temperature dependence of the correlation time. Differences in the ¹³C line widths for individual carbons of polyisobutylene are discussed briefly.     

NMR study of model compounds of vinyl polymers

Complicated NMR spectra of vinyl polymers provide conformational and configurational knowledge of the polymers in solution. Explicit expressions for the spectral frequencies and intensities are obtained by the analysis of vinyl polymers and their model compounds as weakly coupled systems. The classified spectra expected for common vinyl polymers are presented by using the results of the analysis. The analysis is applied to model compounds of poly(vinyl alcohol) and poly(vinyl acetate) in solution. The results show that conformations of poly(vinyl alcohol) are determined by the intramolecular hydrogen bonding so that the syndiotactic isomer forms a helical structure, the isotactic one a planar zigzag structure. The poly(vinyl acetate) produces a helical structure for isotactic isomer by the repulsion of side chains and a planar zigzag for the syndiotactic isomer.     

Detection and quantitative determination of the crystalline phase in poly(vinyl alcohol) cryogels by ATR FTIR spectroscopy

The molecular structure of poly(vinyl alcohol) in its cryogels obtained via a single freeze-thaw cycle of aqueous solutions of the polymer is investigated by ATR FTIR spectroscopy. By means of Fourier deconvolution and spectral subtraction, methods, it is found that the spectra of cryogels contain a hidden crystallinity band at 1144 cm^?1 due to poly(vinyl alcohol). For poly(vinyl alcohol) films crystallized at different temperatures, a quantitative relationship is established between the relative intensity of absorption at a frequency of 1144 cm^?1 in the spectra of the polymer and its degree of crystallinity estimated via wide-angle X-ray diffraction. In terms of this relationship, the degree of crystallinity of poly(vinyl alcohol) in the cryogels is determined from their ATR FTIR spectra. This parameter is found to be 6, 10, and 14% for the cryogels with PVA concentrations of 9, 17, and 29%, respectively. The obtained data suggest that the formation of the cryogels is accompanied not only by the appearance of polymer crystallites but also by a change in the system of hydrogen bonds between the polymer and water.     

Thermal properties and flammability performance of poly (vinyl alcohol)/α-zirconium phosphate nanocomposites

Nanocomposites of poly (vinyl alcohol) with ethylamine modified zirconium phosphate (ZrP-EA) were prepared by solution blending. Their morphologies were elucidated with X-ray diffraction and transmission electron microscopy, while the thermal stability and flammability performance were characterized by thermogravimetric analysis, Fourier transform infrared spectra and microscale combustion calorimetry. It was established that the morphology of the nanocomposites evolved as ZrP-EA content increased. In the nanocomposites, catalytic degradation of the acetate groups remaining in poly (vinyl alcohol) occurred and catalytic carbonization was observed. Microscale combustion calorimetry revealed that the flammability performance of poly (vinyl alcohol) was improved by the introduction of zirconium phosphate nanoplatelets.     

High-resolution proton magnetic resonance and infrared spectra of poly(vinyl formal) and its model compounds

High-resolution proton magnetic resonance and infrared spectra of poly(vinyl formal) were studied in comparison with those of the model formals obtained from stereoisomers of pentane-2,4-diol and heptane-2,4,6-triol in order to learn spectral changes due to differences of the steric structures of the polymer. In the NMR spectrum of transformal obtained from dl diol or dl,dl (syndiotactic) triol, all proton signals were well interpreted by assuming a rapid chair-chair inversion of the formal ring. On the other hand, no such inversion was observed spectroscopically in cis-formal obtained from the meso diol or meso,meso (isotactic) triol, and the cis-formal ring was supposed to take a diequatorial form preferentially. Consequently, dioxymethylene protons gave a single peak (equivalent) in trans-formal and an AB quartet (nonequivalent) in cis-formal. In the spectra of poly(vinyl formal), the dioxymethylene signal was an overlap of the singlet and quartet in dimethylsulfoxide solution. Observations of the spectra of various poly(vinyl formals) obtained from poly(vinyl alcohols) of different tacticities and study of temperature dependence of the signal have shown that the singlet and quartet are attributed to trans- and cis- formals, respectively, in the polymer spectrum also. In the infrared spectra of poly(vinyl formals), the 800 and 785 cm^-1 bands were found to be related to cis- and trans-formal rings respectively. A linear relationship was confirmed between D₇₈₅/D₈₀₀ and trans/cis ratios determined from the peak intensities of the dioxymethylene proton signals.     

Complex refractive indexes for polymers over the infrared spectral region: Specular reflection IR spectra of polymers

A dispersion analysis is used to determine the complex refractive indexes over the infrared for the following polymeric systems: isotactic poly(methyl methacrylate), syndiotactic poly(methyl methacrylate), poly(2-methyl-1-pentene)sulfone, poly(perfluoropropylene oxide), poly(pyromellitimide), poly(styrene), and poly(vinyl alcohol). These were combined with solutions of Maxwell's equations for electromagnetic radiation at interfaces in a FORTRAN computer code to model specular relection infrared spectra. Calculations and experimental data are compared to demonstrate the complicated nature of specular reflection and the ability of the modelling to simulate the observed spectra.     

Grafting of 4-vinyl pyridine onto poly(vinyl alcohol) initiated by potassium diperiodatocuprate(III)

In this article, the graft copolymerization of 4-vinyl pyridine onto poly(vinyl alcohol) via the potassium diperiodatocuprate(III)-poly(vinyl alcohol) redox system as an initiator was investigated in an alkaline medium. The graft copolymer was characterized with Fourier-transform infrared spectra analysis. A mechanism is proposed to explain the generation of radicals and the initiation. The effects of reaction variables, such as the initiator concentration, the ratio of monomer to poly(vinyl alcohol), pH, and reaction temperature and time, are investigated, and the grafting conditions are optimized. Graft copolymers with high grafting efficiency are obtained, thus indicating that potassium diperiodatocuprate(III)-PVA redox system is an efficient initiator for this graft copolymerization. Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. B, 2006, Vol. 48, No. 7, pp. 1190–1194. This text was submitted by the authors in English.     

Effect of drawing on the α relaxation of poly(vinyl alcohol)

The α relaxation of isotropic and drawn poly(vinyl alcohol) dried gel films was studied using dynamic mechanical analysis. The temperature of the relaxation T_α increased from 160°C in the isotropic gel to 220°C in a fiber drawn 19 ×. The relaxation, which is associated with the crystalline regions of the material, also decreased continuously in magnitude as drawing proceeded, although crystallinity increased. At draw ratios over 12 ×, the relaxation became difficult to resolve, and no relaxation was observed in fibers drawn over 19 ×. The melting points of the fibers increased with draw ratio, but not enough to account for the large change in T_α. Crystal thickness in the fiber direction also increased with draw ratio. An analogy is drawn to the case of polyethylene where crystal thickness has been found to control T_α. The absence of a resolvable α relaxation is one reason why it is difficult to draw poly(vinyl alcohol) gels to extremely high ratios.     

Noncontact dielectric friction

Dielectric fluctuations are shown to be the dominant source of noncontact friction in high-sensitivity scanning probe microscopy of dielectric materials. Recent measurements have directly determined the friction acting on custom-fabricated single-crystal silicon cantilevers whose capacitively charged tips are located 3-200 nm above thin films of poly(methyl methacrylate), poly(vinyl acetate), and polystyrene. Differences in measured friction among these polymers are explained here by relating electric field fluctuations at the cantilever tip to dielectric relaxation of the polymer.     

Dynamic structure of poly(vinyl pyrrolidone)/ethyl alcohol mixtures studied by time domain reflectometry

Dielectric studies of poly(vinyl pyrrolidone)/ethyl alcohol (PVP–E) binary mixtures with concentration variations were carried out in the frequency range of 10 MHz to 10 GHz by time domain reflectometry at 15, 25, 35, and 45 °C. One relaxation process, corresponding to ethyl alcohol molecules in the poly(vinyl pyrrolidone) (PVP) matrix, was observed in this frequency range for all the mixtures. The static dielectric constant of the PVP–E mixtures decreased linearly with an increase in the weight fraction of PVP. The observed anomalous increase in the value of the relaxation time (τ) of these mixtures was interpreted by the consideration of the variation in the local structure of self‐associated ethyl alcohol molecules and also the PVP behavior as a geometric constraint for the rotational motion of ethyl alcohol molecules. Furthermore, the τ values of these mixtures were independent of the viscosity. The energy parameters for the dielectric relaxation process (the free energy, enthalpy, and entropy of activation for the dipolar orientation) were determined to confirm the transient behavior of the heterogeneous species due to the breaking and re‐forming of hydrogen bonds with the internal rotation of ? OH groups in the ordered structure of the PVP–E mixtures. On the basis of the evaluated dielectric parameters, the formation of supermolecular structure in the PVP–E mixtures in dynamic equilibrium was sketched and examined by the consideration of the hydrogen bonding between the terminal hydroxyl groups of self‐associated ethyl alcohol flexible chains and the carbonyl groups of monomer units of PVP coiled chains. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1134–1143, 2005     

Preparation and characterization of poly(vinyl alcohol)/organo-modified cloisite Na+ with chiral L-leucine amino acid/TiO2 nanocomposites

Poly(vinyl alcohol)/organo-clay/TiO₂ nanocamposites films were prepared with 10 wt % of organo-nanoclay and various amount of TiO₂ nanoparticles. Cloisite Na⁺ has been modified via cation exchange reaction using ammonium salt of natural L-leucine amino acid as a cationic surfactant. After that poly(vinyl alcohol)/organo-nanoclay/TiO₂ nanocomposites were synthesized by dispersion of TiO₂ on the surfaces of organo-nanoclay in poly(vinyl alcohol) matrix by using ultrasonic energy. Three nanocomposites with different loading of TiO₂ were prepared and characterized by X-ray diffraction, fourier transform infrared spectroscopy, field emission type scanning electron microscope, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis and ultraviolet-visible transmission spectra. The results showed that the organo-nanoclay and TiO₂ were dispersed homogeneously in poly(vinyl alcohol) matrix and also showed improvement in their thermal properties compared with the pure poly(vinyl alcohol).     

高选择性透过二氧化硫气体分离膜的研究(Ⅲ)──乙烯基亚砜与聚乙烯醇的Michael加成反应及其结构表征

本文合成了4种烷基乙烯基亚砜。研究了其与聚乙烯醇在碱催化下的Michael加成反应,制备了不同亚砜含量的聚合物。研究了其溶解性能,用IR及¹HNMR法对聚合物进行了表征。     

Dynamics in disordered block copolymers and miscible blends composed of poly(vinyl ethylene) and polyisoprene

We investigated the segmental and terminal relaxation dynamics of a well‐characterized disordered diblock copolymer, poly(isoprene‐b‐vinyl ethylene) (PI‐PVE), and miscible blends of polyisoprene (PI)/poly(vinyl ethylene) (PVE), using dielectric and viscoelastic spectroscopies. Generally, the concentration fluctuation (CF) amplitude of a disordered diblock copolymer is smaller than that of the miscible blend, especially in a length scale longer than the size of the whole block chain. To test whether the difference in the CF amplitudes causes the difference in the segmental relaxation spectra, we compared the shape of the dielectric loss curves between PI‐PVE and PI/PVE with the same composition (PI/PVE ratio = 17:83). However, no appreciable difference was observed, indicating that the CF amplitudes in PI‐PVE and PI/PVE are not so different in the length scale of the segmental motions. We also examined the effect of distinct friction coefficients of the PI and PVE chains on the terminal relaxation dynamics by comparisons of the viscoelastic and dielectric normal mode relaxations in PI‐PVE. The former probes the whole chain motion and the latter probes motions of the PI block. Shift factors (a_T) for the viscoelastic and dielectric relaxations were compared. The dielectric normal mode a_T was found to have weaker temperature dependence than the viscoelastic a_T, which indicates that the friction for the PI block chain is lower than the average friction for the PI‐PVE chain. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4084–4094, 2004     

NMR study of poly(vinyl formate)

The high resolution nuclear magnetic resonance spectrum of poly(vinyl formate), yielded, upon examination at 100 Mc./sec., and under the conditions of decoupling, information on the three tactic forms present. The normal and decoupled spectra indicate that only the CHO resonance is sensitive to the stereochemical configuration. The three components of the CHO resonance are tentatively assigned to isotactic (i), heterotactic (h), and syndiotactic (s) triads with increasing field strength, respectively. This assignment was made on the basis of poly(vinyl alcohol) and poly(vinyl acetate) derived from poly(vinyl formate). The results show that the tacticity is slightly dependent upon the temperature of free-radical polymerization.     

The effect of annealing on the structure and relaxation processes of vinyl alcohol–ethylene copolymers

An annealing process has been applied to three samples of vinyl alcohol–ethylene (VAE) copolymers, richer in the former comonomer. The effect of such a process on the structure and on the relaxation mechanisms is studied. The structure of the three VAE copolymers has changed slightly. Nevertheless, the viscoelastic relaxation processes have been significantly affected for the thermal treatment. Two additional relaxations have appeared: one of them at temperatures above the relaxation associated to the glass transition, and the other at temperatures below the β mechanism of these copolymers. The temperature location, intensity, and apparent activation energy of the distinct relaxations found are discussed and compared with those in the original copolymers and the homopolymers, poly(vinyl alcohol) and polyethylene. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1–12, 2001     

Dynamics of water in partially crystallized polymer/water mixtures studied by dielectric spectroscopy

The dielectric relaxation process of water was investigated for polymer/water mixtures containing poly(vinyl methyl ether), poly(ethyleneimine), poly(vinyl alcohol), and poly(vinylpyrrolidone) with a polymer concentration of up to 40 wt % at frequencies between 10 MHz and 10 GHz in subzero temperatures down to -55 degrees C. These polymer/water mixtures have a crystallization temperature TC of water at -10 to -2 degrees C. Below TC, part of the water crystallized and another part of the water, uncrystallized water (UCW), remained in a liquid state with the polymer in an uncrystallized phase. The dielectric relaxation process of UCW was observed, and reliable dielectric relaxation parameters of UCW were obtained at temperatures of -26 to -2 degrees C. At TC, the relaxation strength, relaxation time, and relaxation time distribution change abruptly, and their subsequent changes with decreasing temperature are larger than those above TC. The relaxation strength of UCW decreases, and the relaxation time and dynamic heterogeneity (distribution of relaxation time) increase with decreasing temperature. These large temperature dependences below TC can be explained by the increase in polymer concentration in the uncrystallized phase C(p,UCP) with decreasing temperature. C(p,UCP) is independent of the initial polymer concentration. In contrast to the relaxation times above TC, which vary with the chemical structure of the polymer and its concentration, the relaxation times of UCW are independent of both of them. This indicates that the factor determining whether the water forms ice crystals or stays as UCW is the mobility of the water molecules.     

Synthesis of poly(vinyl acetate)‐b‐polystyrene and poly(vinyl alcohol)‐b‐polystyrene copolymers by cobalt‐mediated radical polymerization

Well‐defined poly(vinyl acetate) macroinitiators, with the chains thus end‐capped by a cobalt complex, were synthesized by cobalt‐mediated radical polymerization and used to initiate styrene polymerization at 30 °C. Although the polymerization of the second block was not controlled, poly(vinyl acetate)‐b‐polystyrene copolymers were successfully prepared and converted into amphiphilic poly(vinyl alcohol)‐b‐polystyrene copolymers by the methanolysis of the ester functions of the poly(vinyl acetate) block. These poly(vinyl alcohol)‐b‐polystyrene copolymers self‐associated in water with the formation of nanocups, at least when the poly(vinyl alcohol) content was low enough. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 81–89, 2007     

Statistical Chain Dimensions of Poly (vinyl acetal)-Type Molecules

Acetalization of poly(vinyl alcohol) molecules results in acetal ring formation between two successive hydroxyl groups. This will dominate the chain stiffness of poly(vinyl acetal) in different ways, depending on the stereospecificity of poly(vinyl alcohol) used as the starting material. The present paper first deals with calculations of statistical dimensions of hypothetical poly(vinyl acetal) chains with a 100% degree of substitution and different stereospecificities (isotacticity and syndiotacticity). The calculations are essentially identical with those made by Wall and Markovitz, but recent stereochemical knowledges of the acetal ring and poly(vinyl alcohol) are taken into account. The results show that the chain dimension of poly-(vinyl acetal) chain derived from isotactic poly(vinyl alcohol) is much larger than that of poly(vinyl acetal) derived from the syndiotactic one. The treatment used above is extended to more realistic chains that have any degree of stereoregularity and of substitution. As has been anticipated intuitively, it is ascertained that the chain dimensions increase with increase in the degree of substitution for each stereospecificity.     

Broadband dielectric study of dynamics of polymer and solvent in poly(vinyl pyrrolidone)/normal alcohol mixtures

Broadband dielectric measurements of poly(vinyl pyrrolidone) (PVP)-monohydroxyl alcohol mixtures of various normal alcohols with the number of carbon atoms per molecule ranging from 1 to 9 were made in the frequency range of 20 Hz to 20 GHz at 25 degrees C. Two relaxation processes due to the reorientation of dipoles on the PVP and alcohol molecules were observed. The relaxation process at frequencies higher than 100 MHz is the primary process of alcohols, and that at frequencies lower than 10 MHz is attributed to the local chain motion of PVP. For mixtures of alcohol molecules that are smaller than propanol, the relaxation time of the alcohol increases with increasing PVP concentration, whereas for mixtures of alcohol molecules larger than butanol, the relaxation time of the alcohol decreases with increasing PVP concentration. The increase in the density of hydrogen-bonding sites upon the addition of PVP reduces the relaxation time of alcohol in the mixture, and vice versa. The relaxation time of the local chain motion of PVP increases with PVP concentration and solvent viscosity. Different time scales of the molecular motions of polymer and solvent coexist in homogeneous mixtures with hydrogen-bonded polar solvent and polymer.