IR investigation of hydrogen bonds in weakly hydrated films of poly(vinyl alcohol)

A system of hydrogen bonds in weakly hydrated PVA films containing up to ≤8.5 wt % water is investigated via IR spectroscopy. It is shown that water molecules bind to only part of the hydroxyl groups of the polymer that are available for hydration and form the first hydrating layer. In a completely dehydrated film, practically every hydroxyl group of PVA forms hydrogen bonds with two other hydroxyl groups and serves as both a proton donor and a proton acceptor. In the hydrated film, one to three water molecules directly bind with one hydroxyl group of PVA.     

The Structure of Water-Swollen Poly(Vinyl Alcohol) and the Swelling Mechanism

The swelling mechanism of poly(vinyl alcohol) (PVA) in a wide range of the equilibrium swelling index, of 7–153% (with H₂O) and of 12-297% (with D₂O), was investigated by IR, Raman, and broad-band NMR spectroscopy. Analysis of the spectral data obtained confirmed the presence of hydration water (bonded with polymer-free hydroxyl groups) and condensation water (not having been bonded with polymer hydroxyl groups) in poly(vinyl alcohol) swollen samples at low (～7%) and high (>23%) equilibrium swelling indexes, respectively. Moreover, it revealed the intra- and inter-molecular hydrogen bonds breaking in the polymer swollen to higher extent (equilibrium swelling index > 85%).     

Structural and dynamical studies of poly(vinyl alcohol) gels by high-resolution solid-state C NMR spectroscopy

The ¹³C CP/MAS NMR spectra of isotactic, syndiotactic and atactic poly(vinyl alcohol) (PVA) gels were measured in order to clarify the structure of the immobile component of PVA gel. In the ¹³C CP/MAS NMR spectra, the three CH carbon peaks I, II and III (at about 77, 71 and 65 ppm) were clearly observed, which originate from the formation of strong intermolecular or intramolecular hydrogen bonds between hydroxyl groups like solid PVA. It has been assigned that these peaks originate from the crosslinked region in the gel state. On the basis of the experimental results, intermolecular hydrogen bonds play an important role in the formation of the crosslinked-region in the gel state. Further, the effect of PVA's tacticity on the amount of the crosslinked regions by intermolecular interactions was discussed. In addition, molecular motion in the immobile and mobile region of PVA gel was discussed through the observation of ¹³C spin-lattice relaxation time T₁.     

Mechanism of proton conductivity in polyvinyl alcohol-phenolsulfonic acid membranes from <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR data

With line narrowing during magic angle spinning in solid-state NMR, molecular mobility and hydration in composite membranes based on polyvinyl alcohol (PVA) and phenol-2,4-disulfonic acid (PSA) were studied as functions of the ratio of the acidic and polymeric components, the degree of cross-linking in the polymeric matrix, and the moisture content. It is shown that at high relative humidity proton transport takes place by means of the network of hydrogen bonds, which are formed by the H⁺ counterions, sulfonate groups, and water molecules. At low moisture content, the hydroxyl groups in PVA play an active role in proton transport.     

The Microwave-assisted Preparation and X-Ray Structure of 3-Bromocarbazole-N-Acetic Acid

Carbazole and its derivatives have attracted the attention due to its photophysical and photochemical properties as well as biological activities1. So far considerable amounts of carbazole derivatives were prepared to probe the nature of electronic states. Among these carbazole derivatives, carbazole-9-carboxylic acids were important intermediates because the carboxylic group is an active function group for further transformation into other functions. The molecular packing modes of carboxylic …     

SYNTHESIS AND CHARACTERIZATION OF HYBRID PROTON CONDUCTING MEMBRANES OF POLY（VINYL ALCOHOL） AND PHOSPHOMOLYBDIC ACID

Hybrid proton conducting membranes of poly（vinyl alcohol） （PVA） and phosphomolybdic acid （PMA） were prepared by solution casting method. The effect of PMA doping and PVA crosslinking density on the membrane properties and proton conductivity were investigated. The crosslinking reaction between the hydroxyl group of PVA and the aldehyde group of glutaraldehyde （GA） was characterized by IR spectroscopy. Proton conductivity of the membranes increases with an increase in concentration of the doped PMA and also with an increase in crosslinking density of the membranes. Proton conductivity results indicate that a significant amount of PMA was maintained in the membranes even after several hours of immersion in water. A maximum conductivity of 0.0101 S cm^-1 was obtained for the membrane with 33.3 wt% PMA and crosslinking density of 5.825 mol%. X-ray diffraction studies were carried out to investigate the influence of PMA doping and crosslinking density on the nature of the membranes. These properties make them very good candidates for polymer electrolyte membranes for direct methanol fuel cell application.     

Solvation structure of hydroxyl radical by Car-Parrinello molecular dynamics

Car-Parrinello molecular dynamics simulations of a hydroxyl radical in liquid water have been performed. Structural and dynamical properties of the solvated structure have been studied in details. The partial atom-atom radial distribution functions for the hydrated hydroxyl do not show drastic differences with the radial distribution functions for liquid water. The OH is found to be a more active hydrogen bond donor and acceptor than the water molecule, but the accepted hydrogen bonds are much weaker than for the hydroxide OH- ion. The first solvation shell of the OH is less structured than the water's one and contains a considerable fraction of water molecules that are not hydrogen bonded to the hydroxyl. Part of them are found to come closer to the solvated radical than the hydrogen bonded molecules do. The lifetime of the hydrogen bonds accepted by the hydroxyl is found to be shorter than the hydrogen bond lifetime in water. A hydrogen transfer between a water molecule and the OH radical has been observed, though it is a much rarer event than a proton transfer between water and an OH- ion. The velocity autocorrelation power spectrum of the hydroxyl hydrogen shows the properties both of the OH radical in clusters and of the OH- ion in liquid.     

Effects of Electron Beam Irradiation on the Structural Properties of PVA/PAM/CMC Ternary Polymer Blends

Ternary miscible blends based on various ratios of poly(vinyl alcohol) (PVA), poly(acrylamide) (PAM) and carboxymethyl cellulose (CMC) were prepared by solution casting in the form of thin films. The structure‐property behavior of the ternary PVA/PAM/CMC blends, before and after they had been exposed to various doses of electron beam irradiation, was investigated by FT‐IR spectroscopy, SEM, XRD and stress‐strain curves. The visual observation showed that the cast films of the individual polymers PVA, PAM, and CMC and their blends over a wide range of composition are clear and transparent indicating the miscibility of PVA/PAM/CMC ternary blends. The FT‐IR analysis of pure polymers or their ternary blends before or after electron beam irradiation proved the formation of hydrogen bonding. In addition, it was found that the intensity of the different absorption bands depends on the ratio of PAM and CMC in the ternary blend. The XRD patterns showed that the peak position for the ternary blends decreases with increasing the ratio of CMC in the blend. However, the peak position for the ternary blend based on equal ratios of pure polymers was not affected by blending and was found in the same position as in the XRD pattern of pure PVA. The SEM micrographs give support to the visual observation indicating the complete miscibility of PVA/PAM/CMC ternary blends. The improvement in morphology leads to improvement in the tensile mechanical properties of the ternary polymer blends.     

Proton conductivity in crosslinked hydrophilic ionic polymer system: Competitive hydration,crosslink heterogeneity,and ineffective domains

High proton conductivity in hydrophobic backbone‐based polymers such as Nafion is known to be due to the formation of organized ionic clusters and channels upon hydration. However, a lower proton conductivity in hydrophilic, ionic polymers and the role played by the microstructure are not well understood. In this work, we demonstrate the importance of heterogeneity in crosslinked ionic polymer networks in explaining proton conductivity. Poly(vinyl alcohol) (PVA) crosslinked with sulfosuccinic acid (SSA) is used as the model polymer system for the study. Evolution of the microstructure with hydration and the effect on proton conductivity are analyzed using ATR‐FTIR spectroscopy, dielectric spectroscopy, and small‐angle neutron scattering. We show that the presence of the two hydrophilic groups in PVA‐SSA (hydroxyl and sulfonic acid), as opposed to Nafion, results in competition for water and a lower proton conductivity. The crosslinked polymer–water system contains heterogeneous domains of crosslink nodes which are conductive. These domains (of size 20–35 Å) interconnect with each other and form tortuous percolating domains through which proton conduction takes place. The presence of hydroxyl groups results in some of the domains being ineffective for proton transport, resulting in a lower conductivity. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1087–1101     

Connecting structure to infrared spectra of molecular and autodissociated HCl--water aggregates

The properties of perdeuterated HCl(H2O)n aggregates with n=1, 2, ..., 6 water molecules are studied by means of ab initio molecular dynamics simulations. The specific focus is on the phenomenon of autodissociation of the acid HCl as a function of the microsolvation environment size. The calculations provide a basis for characterization in terms of autodissociation energetics as well as in terms of the impact of thermal fluctuations on structure including proton fluxionality and in terms of anharmonic infrared vibrational spectra. Structure stabilization is dominated by strong hydrogen bonds resulting in distinct topologies, which, in turn, heavily influence acid dissociation. The latter is favored for the first time when n = 4. In that case, three hydrogen bonds can be donated toward the chlorine while at the same time a hydronium core is perfectly solvated according to the eigencomplex motif. Hydrogen-bonding interactions between DCl and its solvating molecules affect the dynamical behavior of the D-Cl bond significantly. This can be seen by the onset of fluxionality and an emerging tendency toward proton transfer for the larger clusters. Connecting IR spectra to structural information is possible by exploiting the following observations. Zwitterionic species show characteristic differences in the hydronium region, whereas the D-Cl stretching regime is useful to distinguish neutral aggregates. Furthermore, in the case of fluxional protons large-amplitude motion leads to characteristic band shifts and significant band broadening effects.     

Intramolecular easily polarizable charged and non-charged hydrogen bonds: IR continua and hydrogen bond length

Substances with intramolecular, easily polarizable hydrogen bonds of different length are compared. Long hydrogen bonds cause IR continua which show band-like structures in the region 2800–1800 cm^?1, extending with weaker intensity toward smaller wave-numbers over the whole region studied. Medium length bonds cause continua beginning at 3200 cm^?1 and extending over the whole region studied. Very short, easily polarizable hydrogen bonds, such as the bond in the HAuCl₄ salt of NN'-tetramethyl-o-xylildiamine di-N-oxide, cause continua with very great intensity in the region 1500–850 cm^?1. Comparison of the experimental with calculated continua shows very good agreement with regard to wavenumber regions in which easily polarizable hydrogen bonds of different length cause IR continua.By comparing all these intramolecular, easily polarizable hydrogen bonds causing IR continua it is shown that the charge of the hydrogen bonds is not the decisive property for the occurrence of the continua but rather the shape of the proton potentials. Continua may occur only with hydrogen bonds with double minima or broad flat proton potential.     

Classical molecular-dynamics simulation of the hydroxyl radical in water

We have studied the hydration and diffusion of the hydroxyl radical OH0 in water using classical molecular dynamics. We report the atomic radial distribution functions, hydrogen-bond distributions, angular distribution functions, and lifetimes of the hydration structures. The most frequent hydration structure in the OH0 has one water molecule bound to the OH0 oxygen (57% of the time), and one water molecule bound to the OH0 hydrogen (88% of the time). In the hydrogen bonds between the OH0 and the water that surrounds it the OH0 acts mainly as proton donor. These hydrogen bonds take place in a low percentage, indicating little adaptability of the molecule to the structure of the solvent. All hydration structures of the OH0 have shorter lifetimes than those corresponding to the hydration structures of the water molecule. The value of the diffusion coefficient of the OH0 obtained from the simulation was 7.1x10(-9) m2 s(-1), which is higher than those of the water and the OH-.     

Photoinduced shape fixity and thermal-induced shape recovery properties based on polyvinyl alcohol bearing coumarin

In this paper, polyvinyl alcohol (PVA) bearing coumarin with different degrees of substitution (DS) are synthesized by esterifying hydroxyl of PVA with 7-carboxylmethoxycoumarin. The grafted polymer has photosensitive property and presents photocrosslinking due to the photodimerization between pendant coumarin groups, which affords PVA–coumarin sample photoinduced shape fixity properties. PVA–coumarin can be cross-linked after being illuminated under UV light of 360 nm; this provides the possibility that the sample has shape memory properties only if the cross-linking extent is suitable. The shape memory properties were induced by thermal as most shape memory polymer do. In fact, the shape fixity and recovery has strong relationship with DS, irradiation time, and thickness of sample. The effect of DS on the grafted polymer structure and properties has been studied by differential scanning calorimetry, thermogravimetric analysis, and UV spectra.     

Effect of ferrocene on the structures and properties of epoxy-polyurethane composites

Effects of various ferrocene concentrations on the tensile strengths, elongations at break, and glass-transition temperatures of ferrocene-containing epoxy-polyurethane composite materials are studied. As shown by IR spectroscopy and X-ray diffraction analysis, ferrocene affects the structuring of epoxy-polyurethane composites via redistribution of intermolecular hydrogen bonds between amide, hydroxyl, and urethane groups of the polymer basis and formation of metal-polymer complexes between ferrocene and polar groups of the polymer carrier.     

均苯四甲酸与对羟基吡啶超分子聚合物的制备

超分子聚合物(supramolecular polymer)是指单体单元间依靠可逆和高度取向的非共价作用力结合的、在溶液或本体中表现出聚合物特性的一类特殊聚合物[1].其中,氢键结合超分子聚合物因氢键的高度取向性及丰富的结合形式而具有特殊结构与性能,已成为近期关注的热点[2~4].文献中报道的氢键结合超分子聚合物主要有多重氢键结合和基于羧基与吡啶基的氢键结合(其键能可达45kJ·mol-1[5])两类,它们均可表现出和传统聚合物诸多类似的性质,诸如高的溶液粘度、形成凝胶、具有弹性等,同时其结构和性能又随温度等环境条件的变化而发生可逆变化,使得这类…     

About the compatibility of polymer components in polymer complexes based on poly(acrylamide) and poly(vinyl alcohol)

The issue of applying the usual concepts of polymer compatibility to nonstoichiometric PVA/PAA mixtures of chemically complementary poly(vinyl alcohol) and poly(acrylamide), which form in water solution InterPC (intermolecular polymer complex) stabilyzed by H‐bonds, and PAA to PVA graft copolymers (PVA‐PAA_N) with different grafted chains number N, that are IntraPC (intramolecular polymer complexes) is discussed. PVA and PAA are compatible on molecular level. At the same time PVA/PAA mixture (50/50 W/W) is characterized by heterogeneous structure consists of InterPC with ϕ_char=9g_PVA/g_PAA and the excess of unconnected PAA. In the case of IntraPC, yet, only PVA‐PAA_N, where N=25, is characterized by a single glass transition temperature (Tg). At larger values of N separate PAA domains form giving rise to the corresponding Tg. These results are discussed in view of IntraPC structure peculiarities as a function of N investigated by IR spectroscopy.     

Intermolecular Hydrogen Bonds Formed Between Amino Acid Molecules in Aqueous Solution Investigated by Temperature-jump NanosecondTime-resolved Transient Mid-IR Spectroscopy

Carboxyl (COO?) vibrational modes of two amino acids histidine and glycine in D2O solution were investigated by temperature-dependent FTIR spectroscopy and temperature-jump nanosecond time-resolved IR di?erence absorbance spectroscopy. The results show that hydrogen bonds are formed between amino acid molecules as well as between the amino acid molecule and the solvent molecules. The asymmetric vibrational frequency of COO? around 1600-1610 cm?1 is blue shifted when raising temperature, indicating that the strength of the hydrogen bonds becomes weaker at higher temperature. Two bleaching peaks at 1604 and 1612 cm?1 were observed for histidine in response to a temperature jump from 10 ±C to 20 ±C. The lower vibrational frequency at 1604 cm?1 is assigned to the chain COO? group which forms the intermolecular hydrogen bond with NH3+ group, while the higher frequency at 1612 cm?1 is assigned to the end COO? group forming hydrogen bonds with the solvent molecules. This is because that the hydrogen bonds in the former are expected to be stronger than the latter. In addition the intensities of these two bleaching peaks are almost the same. In contrast, only the lower frequency at 1604 cm?1 bleaching peak has been observed for glycine. The fact indicates that histidine molecules form a dimer-like intermolecular chain while glycine forms a relatively longer chain in the solution. The rising phase of the IR absorption kinetics in response to the temperature-jump detected at 1604 cm?1 for histidine is about 30§10 ns, within the resolution limit ofour instrument, indicating that breaking or weakening the hydrogen bond is a very fast process.     

Simultaneous XRD-DSC measurements of water-2-propanol at sub-zero temperatures.

A simultaneous low-temperature X-ray powder-diffractometric (XRD)-DSC technique was applied to the solid state and melting process of frozen aqueous solutions of 2-propanol. 1H NMR spectra were also obtained at low temperatures. The chemical shifts of the CH3 proton and the CH proton can be classified into four temperature regions: higher than -20 degrees C, around -20 degrees C, -50 to -20 degrees C, and lower than -50 degrees C. In the XRD data, five small diffraction peaks for 2 theta at 21.0 degrees, 25.2 degrees, 27.8 degrees, 31.1 degrees and 32.1 degrees can be attributed to the peritectic, while five diffraction peaks at 22.5 degrees, 24 degrees, 25.6 degrees, 33.4 degrees and 39.8 degrees can be attributed to ice; these peaks are due to the hexagonal form of ice, which disappears upon melting. However, the diffraction peak at 33.4 degrees showed a different pattern than the other peaks due to hexagonal ice. These results indicate that the temperature dependence of the diffraction peak at 33.4 degrees for 2 theta is related to the formation of hydrogen bonds between 2-propanol and water. The simultaneous XRD-DSC technique was effective for investigating this water-alcohol mixture at low temperatures.     

Structure and dynamics of methanol in water: a quantum mechanical charge field molecular dynamics study

An ab initio quantum mechanical charge field molecular dynamics simulation was carried out for one methanol molecule in water to analyze the structure and dynamics of hydrophobic and hydrophilic groups. It is found that water molecules around the methyl group form a cage-like structure whereas the hydroxyl group acts as both hydrogen bond donor and acceptor, thus forming several hydrogen bonds with water molecules. The dynamic analyses correlate well with the structural data, evaluated by means of radial distribution functions, angular distribution functions, and coordination number distributions. The overall ligand mean residence time, τ identifies the methanol molecule as structure maker. The relative dynamics data of hydrogen bonds between hydroxyl of methanol and water molecules prove the existence of both strong and weak hydrogen bonds. The results obtained from the simulation are in excellent agreement with the experimental results for dilute solution of CH(3)OH in water. The overall hydration shell of methanol consists in average of 18 water molecules out of which three are hydrogen bonded.     

海藻糖改性聚乙烯醇及其防雾/防霜涂层

以聚乙烯醇和羧基化海藻糖为原料合成了聚乙烯醇-g-海藻糖(PVA-g-Tre), 将接枝物与少量乙二醇二甲基丙烯酸酯混合, 通过光引发聚合制备了亲水性半互穿网络防雾/防霜涂层. 通过核磁共振氢谱和傅里叶变换红外光谱对PVA-g-Tre的化学结构进行了表征, 利用原子力显微镜、 水接触角测试仪、 拉曼光谱等分析了涂层表面的粗糙度、 润湿性及水与大分子之间的氢键作用, 并考察了涂层的透光性和防雾及防霜性能. 结果表明, 含有不同海藻糖接枝率PVA-g-Tre的涂层表面粗糙度较低且透光率好, 与含有PVA的涂层相比, 引入海藻糖提高了PVA-g-Tre涂层的亲水性和润湿性, 使其同时具有良好的防雾和防霜性能.