负离子对紫精光还原和电氧化还原性能的影响

负离子对紫精光还原和电氧化还原性能的影响冯敏辉，刘伟区，梁兆熙（中山大学高分子研究所，广州，５１０２７５）关键词紫精化合物，负离子，电氧化还原，光还原，化学还原合成了不同负离子（Ｆ－、Ｃｌ－、Ｂｒ－、Ｉ－、ＳＣＮ－、ＣｌＯ４－）的芳基紫精聚合物，并研...     

Preparation and photochromic properties of nanocomposites based on chemically cross-linked polyvinyl alcohol and phosphotungstic acid

Nanocomposite films based on cross-linked polyvinyl alcohol (PVA) and phosphotungstic acid (PTA), in which PTA plays the roles of photochromic component and catalyst of the chemical cross-linking of PVA with glutaric aldehyde (GA), were synthesized. The formation of chemical cross-links in a polymer matrix of nanocomposite films occurring during their formation from PVA-PTA-GA aqueous solutions, was confirmed by IR spectroscopy. It was found that the cross-linkage of a polymer matrix imparts water resistance to PVA/PTA nanocomposites and changes their photochromic properties. By analyzing the electronic absorption spectra of photocolored films, it was shown that PTA anions in the matrix of non-cross-linked PVA upon photoreduction receive only one electron, while not only one-electron but the two-electron reduction of PVA anions occurs in a cross-linked PVA matrix. The photocolorabilty of films based on cross-linked PVA is thus two times higher than that of films based on non-cross-linked PVA. It was found that the rate of discoloration of photocolored PVA/PTA films increases with an increase in the degree of cross-linking of a polymer matrix.     

PHOTOREDUCTION OF ALKYL VIOLOGENS AND POLYVlOLOGENS IN 2-PROPANOL AQUEOUS SOLUTION

In order to study the effect ofalkyl chain length and the polymer effect on the photoreduction behavior of some viologens, a series of alkyl viologen, polyviologen and bisviologen compounds have been synthesized. In the presence of excess 2-propanol, the initial photoreduction of alkyl viologens and polyviologens follow the peudo--seeond--order reaction, the calculated rate constants are related to the alkyl chain length: In addition, the intramoleeular association of radical cations of polyviologens has been found even in dilute solution. However the extent of association is varied with the aikyl chain length. The observed polymer effect of polyviologens in the photoreduetion is significant which can be explained in terms of the nature of second order reaction.     

聚乙烯醇对光还原Ni~(2+)制备纳米Ni性能及染料敏化制氢的影响

采用染料曙红-Y(EY)作为敏化剂将Ni~(2+)光还原制备纳米Ni.在该反应体系中,不加入PVA时,光还原所得到的纳米Ni为球状粒子;而加入PVA,由于其模板导向作用,多数纳米镍呈现棒状.吸附在Ni表面的PVA能够促进光生电子从EY向棒状镍转移,从而提高其染料敏化制氢的活性和稳定性.     

PVA/PEG/Mg(OH)_2复合材料体系的非等温结晶行为

采用熔融共混法,以聚乙二醇(PEG)为增塑剂、Mg(OH)2为稳定剂制备了聚乙烯醇(PVA)/PEG/Mg(OH)2复合材料。利用差示扫描量热仪(DSC)考察了PVA/PEG/Mg(OH)2复合体系中PVA的非等温结晶行为。结果表明:在熔融过程中PEG与PVA大分子形成的分子间氢键,破坏了PVA分子内或分子间的氢键,改善了PVA的热塑性能,使研究其熔融结晶行为成为可能。     

山梨醇改性聚乙烯醇体系的氢键作用及对水状态的影响

采用二维相关红外光谱研究了水渗透进入聚乙烯醇(PVA)及其改性基体过程中, 体系的氢键作用及对水状态的影响; 通过差示扫描量热分析(DSC)研究了改性剂山梨醇(S)对改性PVA中水状态的影响. 实验结果表明, S能通过其羟基与水形成较强氢键, 从而显著改变体系中水的状态及其蒸发行为, 使体系自由水含量逐渐减少, 水的蒸发峰温度升高.     

Study on the nonisothermal crystallization behavior of poly(vinyl alcohol)/attapulgite nanocomposites by DSC analysis

Attapulgite (AT)‐reinforced poly(vinyl alcohol) (PVA) nanocomposite films were prepared by solution‐casting technique. The nonisothermal crystallization behaviors of PVA bulk and PVA/AT nanocomposites have been investigated by differential scanning calorimetry (DSC). It has been found that the uniformly dispersed AT nanorods in the matrix have great influence on the glass transition temperature and crystallization behavior of PVA matrix. The Jeziorny method has been employed to analyze the DSC data. The results show that Jeziorny method could describe this system very well. Comparing with the PVA bulk, PVA/AT nanocomposites have higher crystallinity X_t, shorter semicrystallization time t_1/2, and higher crystallization rate constant Z_c. It can be concluded that AT can be used as an effective nucleating agent and has effects on the growth of crystallites in the crystallization process of PVA matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 534–540, 2006     

Preparation and Characterization of Poly Vinyl Alcohol/Poly Vinyl Pyrrolidone/Clay Based Nanocomposite by Gamma Irradiation

A series of PVA/PVP/clay nanocomposite were prepared by gamma irradiation with different clay contents of (0.15, 0.3, 1, 1.5, 3 and 5 wt%). The gelation content and swelling behavior were investigated. The morphology and structure of PVA/PVP/clay nanocomposite and dispersion of the clay nanoparticles in the polymeric matrix were examined by infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The introduction of clay into polymeric matrix was investigated by X-ray diffraction pattern (XRD) and Transmission electron microscope (TEM). It is observed that, the increase of the clay content causes a decrease in the swelling percent. The thermal stability studies confirmed that the introduction of clay lead to an increase in the thermal stability. The TEM results showed that the clay nanoparticles are interchelated or exfoliated in the polymeric matrix. Some desirable characteristics such as relatively good swelling and excellent barrier capability against microbe penetration suggested that PVA/PVP/clay nanocomposite can be a good candidate as a wound dressing.     

Michael Addition Reaction of Vinyl Sulfoxide with Poly(Vinyl Alcohol)

The Michael addition reaction of a series of alkyl vinyl sulfoxides (CH₂[dbnd]CH-SO-R; R = CH₃ (MVSO), C₂H₅ (EVSO), t-C₄H₉ (BVSO)) with poly(vinyl alcohol) (PVA) was carried out after investigating the model reaction with isopropyl alcohol. The addition reaction was found to proceed in the presence of sodium hydroxide as catalyst. This sulfinylation of PVA proceeded more easily with MVSO and EVSO than with BVSO, and a polymer containing up to 60 mol% sulfoxide unit was obtained with MVSO and EVSO. The solution viscosity as well as the solubility behavior of the modified PVA' having various types and contents of sulfoxide group were also examined.     

Polyaniline/poly(vinyl alcohol) (PAN/PVA) composite films: the synergy of film structural stiffening, redox amplification, and mobile species compositional dynamics

In this work, we report an unexpected but significant improvement of the redox behavior of conducting polyaniline (PAN) films by trapping intrinsically nonconducting poly(vinyl alcohol) (PVA) in the matrix of the polymer acting as stiffening and/or cross-linking agents. Film structural stiffening of PAN/PVA inclusion was studied in relation to film compositional dynamics. PAN and PAN/PVA composite films were potentiodynamically deposited using high-frequency electrochemical quartz crystal microbalance under electrochemical potentiodynamic control. From the simultaneously obtained measurements of nanogravimetric and cyclic voltammetric data, it has been found that the presence of PVA in the deposition solution increased the rate of PAN film growth as a function of PVA concentration. Characterization of the resultant composite films in monomer-free acidic electrolyte solutions showed significantly enhanced redox behavior of PAN/PVA composite films (with different PVA contents) compared to pure PAN by a factor of ～2–4. For the study of structure–composition relationships of composite polymer films, fluxes of instantaneous mobile species dynamics (ion/solvent) as a function of film redox conversion and potential cycling were correlated with film structural stiffening and the observed unusual redox enhancement of PAN/PVA composite films. Using various experimental timescales, we were able to resolve bound (associated with ion transfer) and free solvent compositional dynamics (associated with thermodynamic activity balance).     

水溶性高分子对聚紫罗精光致变色性能的影响

用光谱法研究了四种水溶性高分子(聚乙烯吡咯烷酮PVP、聚乙烯醇PVA、明胶、聚丙烯酰胺PAM)对聚丁基紫罗精溴化物(PBV)的光致变色行为的影响。PBV的变色(还原)速率按PVP>明胶>PVA>PAM的顺序递减。在聚乙烯醇介质中,PBV的还原为二级反应。测定了暗回复(退色)速率,发现其服从一级反应规律,用电子顺磁共振法得到同样的结果。     

熔融碳酸盐燃料电池水溶性隔膜的制备和性能

用水溶性粘结剂聚乙烯醇(PVA)和α-LiAlO2粉料等制备熔融碳酸盐燃料电池水溶性隔膜(PVA隔膜).粉料的水合作用导致PVA隔膜的孔隙率和热失重均比PVB(聚乙烯醇缩丁醛)隔膜的大,但前者的最大孔径却比后者的小.当反应气压为0.9MPa,反应气体利用率为20%,分别于300和428.57mA·cm-2下放电时,PVA隔膜电池输出电压分别为0.849和0.739V;输出功率密度分别为254.7和316.7mW·cm-2,高于PVB隔膜电池的.经10次热循环启动,电池性能出现下降—回升—稳定的变化.这可能是PVA隔膜高温失水引起隔膜电导变化所致.     

An investigation on the dispersion of montmorillonite (MMT) primary particles in PP matrix

A novel path of preparing PP/o-MMT nanocomposites, which pay attention to the breaking up of MMT original agglomerates and dispersing of its primary particles, rather than the intercalation or exfoliation degree of o-MMT, was reported. The method of predispersing the o-MMT particles into a polar poly(vinyl alcohol) (PVA) matrix and then melt blending the pre-treated PVA/o-MMT hybrids with PP was studied. 3-Isopropenyl-α,α-dimethylbenzene-isocyanate (TMI) was used as a modifier of PVA to improve the compatibility between PVA and PP matrix. Pre-disperse o-MMT with TMI modified PVA was proved to be an effective way to get a composite with fine o-MMT particles dispersion. But the method, which is pre-dispersing o-MMT with non modified PVA and then using TMI to modify such PVA/o-MMT hybrid, would largely reduce the reaction degree between TMI and PVA because of the relatively lower reaction temperature. Although the latter method also can obtain finer dispersion composites than that with using PP-g-MAH as compatibilizer, the relatively higher degradation degree of PP matrix in this method will limit the use of this nanocomposite.     

Photoreduction des esters car☐yliques dans l'hexamethylphosphortriamide (HMPT)

Use of HMPT as solvent in photochemistry allows efficient photoreductions. Alkyl esters and especially non absorbing alkyl acetates are photoreduced in excellent yields into alkanes. In the latter case, a protonating agent is necessary. Numerous examples illustrate the generality and convenience of the reaction. This photoreduction involves an electron transfer from HMPT to ester.     

PHOTOOXIDATION OF SOME ORGANIC COMPOUNDS CATALYZED BY DECATUNGSTATES

ＰＨＯＴＯＯＸＩＤＡＴＩＯＮ ＯＦ ＳＯＭＥ ＯＲＧＡＮＩＣ ＣＯＭＰＯＵＮＤＳ ＣＡＴＡＬＹＺＥＤ ＢＹ ＤＥＣＡＴＵＮＧＳＴＡＴＥＳ￥ＢｉｎＹＵＥ；ＳｉＳａｎＺＨＵ；ＧａｏＹａｎｇＸＩＥ；ＹｉＤｏｎｇＧＵ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒ...     

Epidermal cellular response to poly(vinyl alcohol) nanofibers containing silver nanoparticles

A heat-treated PVA nanofibrous matrix containing silver (Ag) was prepared by electrospinning an aqueous 10 wt% PVA solution and followed by heat treatment at 150 °C for 10 min. The average diameter of the as-spun and heat-treated PVA nanofibers was 330 nm. The heat-treated PVA nanofibrous matrix containing Ag was irradiated with UV light to transform the Ag ions in the nanofibrous matrix into Ag nanoparticles. The in vitro cytotoxicity of the Ag ions and/or nanoparticles on normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF) cultures was examined. The PVA nanofibrous matrix containing Ag showed slightly higher level of attachment and spreading in the early stage culture (1 h) than the PVA nanofibers without Ag (control). However, compared with the PVA nanofibers without Ag, the heat-treated and UV-irradiated PVA nanofibers, containing mainly Ag ions and nanoparticles, respectively, showed reduced cell attachment and spreading. This shows that both Ag ions and Ag nanoparticles are cytotoxic to NHEK and NHEF. There was no significant difference in cytotoxicity to NHEK and NHEF between Ag ions and Ag nanoparticles. NHEF appeared to be more sensitive to Ag ions or particles than NHEK. In addition, the residual nitrate ions (NO₃⁻) in the PVA nanofibers had an adverse effect on the culture of both cells.     

Matrix polycondensation through hydrogen bonding interaction

Polycondensation of diesters having hydroxyl or pyridine groups was carried out with hexamethylenediamine (HMD) in the presence of (vinyl alcohol/vinyl acetate) copolymers as a matrix polymer. Apparent rates of the polycondensation of dimethyl tartrate (DMT) with HMD increased with increasing contents of PVA units in the copolymers and a strong entanglement between growing polyamide chains and PVA copolymers took place through the adsorption of HMD and DMT on the matrix copolymers. 2,6-Dimethyl pyridine dicarboxylate (2,6-DMP) reacted with HMD in the presence of the PVA copolymers or polysaccharide, while the rate enhancement effect of the matrix polymers was not significantly observed, as in the case of DMT. The effect of the matrix polymers on the polycondensation was discussed in terms of hydrogen bonding interactions.     

Reductive photocyclization of benzo[b]furans and their analogs

The UV irradiation of substituted 2,3-diphenylbenzo[b]furans and of 2,3-diphenyl-5-t-butylfuran in n-propylamine gives 1,4-dihydro derivatives of the corresponding aromatic cyclized compounds. This reaction does not involve a photoreduction. It can be concluded from deuterium labelling experiments that H atoms of the alkyl chain of n-propylamine are incorporated in the product. When the solvent is not an unhindered primary amine, only totally aromatic photocyclized products are obtained. It is proposed that hydrogens eliminated during formation of the isolated compounds are released in a reductive form and not as radicals. This is supported by the fact that acenaphthylene is reduced when irradiated in n-propylamine together with 2,3-diphenylbenzo[b]furan under conditions which do not promote, photoreduction. This seems to be a general finding in that the irradiation of stilbene in n-propylamine to acenaphthylene is the same as that of 2,3-diphenylbenzo[b]furan.     

The mechanism of photoelectrochemical detection of alkyl and aryl ketones and aldehydes

A photoelectrochemical detector for liquid chromatography, which combines photochemistry and electrochemistry to exploit the redox properties of photogenerated excited states, intermediates, and/or products is characterized, and optimized. The photoelectrochemical detector is responsive to alkyl and aryl ketones and aldehydes, and the limits of detection are in the 2–10 ng range. The mechanism of detection is shown to parallel the photoreduction of carbonyl compounds, and the photoreaction sequence proceeds via radical intermediates which are oxidized at the working electrode. The radical intermediates account for ca. 80% of the photocurrent, and the remaining signal is derived from the oxidation of various photoreduction and photohydrolysis products. The proposed mechanism is delineated by using both electrochemical and photochemical techniques, and the mechanism is successfully utilized to predict analyte reactivity. The analytical utility of photoelectrochemistry as the basis of a liquid chromatographic detector is demonstrated.     

Structure and optoelectronic properties of PbSe quantum dots /PVA. Does the polymer molecular weight matter?

Polyvinyl alcohol (PVA) with different molecular weights (8000, 14,000, and 132,000 g/mol) capped lead selenide (PbSe) quantum dots (QDs) are prepared. The nanocomposites are characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM studies show that the particle size of PbSe QDs decrease with the increase in PVA molecular weight and/or PVA amount. This may be due to the increase in molecular weight inhibiting further growth of PbSe into the polymer matrix. Thermogravimetric analysis showed that the introduction of PbSe QDs into PVA decreases the crystallinity of the polymer. The optical absorption spectroscopy of prepared nanocomposites showed that the absorption peaks are strongly shifted to the lower wavelength (blue shift) from near infrared region to visible region by increasing the PVA molecular weight. The (I–V) characteristic curves of the PVA/PbSe nanocomposite films under illumination showed a photovoltaic cell‐like behavior. The results indicated that as the molecular weight of polymer increases, the conversion efficiency increases. Copyright © 2010 John Wiley & Sons, Ltd.