淀粉/丙烯酸反相乳液体系的稳定性研究

以丙烯酸(AA)单体的水溶液为水相,液体石蜡为油相,失水山梨醇三油酸酯(Span 85)和辛基苯基聚氧乙烯醚(Opan 10)为复合乳化剂,合成了淀粉/丙烯酸反相乳液;考察了乳化剂亲水亲油平衡值(HLB值)、油水比、乳化剂用量、单体浓度、温度对乳液稳定性和类型的影响.结果表明,合成淀粉/丙烯酸稳定反相乳液体系的适宜条件...     

Efficient Synthesis of Poly(acrylic acid) in Aqueous Solution via a RAFT Process

The direct polymerization of acrylic acid (AA) in aqueous solution for high molecular weight by means of living radical polymerization is still difficult. Here, AA was polymerized homogeneously in water by a reversible addition-fragmentation transfer polymerization (RAFT) in the presence of a water-soluble trithiocarbonate as a RAFT agent. Various ratios [AA]:[RAFT agent] were investigated to aim at different molecular weights. The polymerization exhibited living free-radical polymerization characteristics at different ratios [AA]: [RAFT agent]: controlled molecular weight, low polydispersity and well-suited linear growth of the number-average molecular weight, M _n with conversion. The chain transfer to solvent or polymer was suppressed during the polymerization process, thus high linear PAA with high molecular weight and low PDI can be obtained. Moreover, using the generated PAA as a macro RAFT agent, the chain extension polymerization of PAA with fresh AA displayed controlled behavior, demonstrated the ability of PAA to reinitiate sequential polymerization.     

Effect of pH on Poly(acrylic acid) Solution Polymerization

The free-radical redox-initiated aqueous solution polymerization of fully and partially neutralized acrylic acid was carried out at room temperature under full exposure to air. The effect of neutralization degree on the polymerization rate and product properties was studied. Increasing neutralization of the reaction mixture with sodium hydroxide resulted in greater conversion of acrylic acid to sodium acrylate. The rate of polymerization, determined from a gravimetric off-line water removal technique, was shown to decrease significantly with decreasing degree of neutralization. Molecular weight also decreased with decreasing degree of neutralization. The glass transition temperature and hydrophilicity of the polymer product decreased with increasing degree of neutralization. In-line infrared monitoring was also used to monitor the reaction progress and was shown to be an effective tool for this purpose.     

Mechanism of carbon nanotube dispersion and precipitation during treatment with poly(acrylic acid)

Carbon nanotubes have been shown to be easily dispersed within an acidic aqueous solution of poly(acrylic acid) but precipitate when the pH is increased. Transmission electron microscopy showed that the nanotubes were more exfoliated under the acidic condition but highly aggregated under the basic condition. Carbon K‐edge NEXAFS spectroscopy showed that the carbon nanotubes did not chemically react with poly(acrylic acid) during the dispersion or precipitation and that the dispersion mainly involved physical adsorption of poly(acrylic acid) onto the nanotubes. Together with the carbon K‐edge NEXAFS spectra, the cobalt L_{3, 2}‐edge NEXAFS spectra suggested that under the basic condition, the cobalt impurity within the nanotubes strongly reacted with poly(acrylic acid) resulting in complex formation. Cobalt reduces the adsorption of poly(acrylic acid) onto the nanotubes, which then reduced the nanotube dispersion and resulted in the precipitation. Copyright © 2008 John Wiley & Sons, Ltd.     

聚醚树枝体－聚丙烯酸嵌段共聚物的水溶液自组装行为

应用UV－Vis、荧光、光物理探针、动态激光光散射和透射电镜(TEM)方法研究了聚醚树枝体与聚丙烯酸两亲嵌段共聚物(Dendr,PE-PAA)在水溶液中分子自组装行为。实验结果表明通过聚醚树枝体嵌段的疏水作用,易缔合形成聚集体,具有很低(10^-6～10^-7mol·L^-1)的临界缔合浓度(cac)。透过电镜观察到聚集体具有双层膜结构的球状、单室囊泡。临界缔合浓度(cac)以及聚集体的大小对枝状体的代数(Gi)及线性体的聚合度(n)具有明显的依赖关系。     

Kinetics of the potassium persulfate-initiated inverse emulsion polymerization of sodium acrylate solutions

The kinetics of the K₂S₂O₈-initiated inverse emulsion polymerization of aqueous sodium acrylate solutions in kerosene with Span 80 as the emulsifier has been studied. The conversion-time curves are S-shaped. The following expressions have been obtained for the maximum rate of polymerization and the molecular weight of the polymers under the experimental conditions investigated: R_max ∞ [K₂S₂O₈]^0.78[sodium acrylate]^1.5[Span 80]^0.1, (OVERLINE)M(/OVERLINE)_u ∞ [K₂S₂O₈]^−0.37[sodium acrylate]^2.9[Span 80]^−0.2. The activation energy for the maximum rate of polymerization is 94.8 kJ mol^−1. The results suggest a monomer–droplet–nucleation mechanism for the system studied. © 1996 John Wiley & Sons, Inc.     

Reaction of the acrylic acid and 1-vinylimidazole copolymer with CuCl2 in aqueous solution

The reaction of acrylic acid—1-vinylimidazole copolymer with CuCl₂ in an aqueous medium was investigated by potentiometric titration and UV and ESR spectroscopy. The complex formation involves both the azole units and the carboxy groups. The Cl^– ions are also incorporated in the inner sphere of the complexes, their removal by dialysis resulting in an increase in the coordination capacity of the carboxylate groups.     

Self-assembly of hydrophobic associating polyacrylamide prepared by aqueous dispersion polymerization

Abstract

Hydrophobic associating polyacrylamide (PDH) was prepared via aqueous dispersion polymerization in the presence of ammonium sulfate. In order to dissolve the polymer at high salt solution concentration, a hydrophobic precursor monomer with two cationic heads was synthesized. Upon polymerization, spherical PDH polymer particles were obtained with an average size of about 9.1?µm. The PDH was fully dispersed in water in twenty seconds, leading to a transparent gel. PDH demonstrated superior properties compared to the partially hydrolyzed polyacrylamide, for instance, regarding salt tolerance and shear resistance. Addition of a small amount of an anionic surfactant significantly affected the PDH dispersion viscosity due to the formation of mixed micelles. The viscosity slightly decreased after strong shearing (>500?s^?1), showing excellent shear resistance. These features indicate that the synthesized PDH offers a great potential for application in hydraulic fracturing and enhanced oil recovery.     

丙烯酸/2-丙烯酰胺基-2-甲基丙磺酸高吸水树脂的反相悬浮聚合及其性能

采用反相悬浮聚合法,通过均匀实验设计,制备了聚(丙烯酸(AA)/2-丙烯酰胺基-2-甲基丙磺酸(AMPS)）(PAAMPS)高吸水树脂,探讨了单体摩尔分数及其中和度、引发剂及交联剂摩尔分数（相对于单体总量）对蒸馏水、质量分数0.9%NaCl水溶液中吸液性能的影响,并经实验数据拟合,得到了二次回归方程,比较了优化配方、单因素实验的模拟值和实验值,结果表明,模拟值与优化值基本接近,其优化工艺参数为：AMPS占单体的摩尔分数8%,中和度为75%,交联剂、引发剂用量与单体的摩尔分数分别为0.035%和0.17%,单体总质量浓度为30%,分散剂用量为单体质量分数的0.5%,反应温度70 ℃,反应时间1.5 h。 此条件下合成的PAAMPS在蒸馏水、0.9%NaCl水溶液中的吸液倍率分别为1.600和130 g/g。     

Organic acid doped polythiophene nanoparticles as electrode material for redox supercapacitors

An organic acid doped electronically conducting polymer nanomaterial, polythiophene‐tartaric acid (PTh‐TA) nanoparticles, was prepared by cationic surfactant‐assisted dilute polymerization method. The physical properties of the synthesized polymer were characterized by FT‐IR, UV‐visible spectroscopy, X‐ray diffraction, SEM, and electrical conductivity studies. The symmetric type redox supercapacitor performances were studied in PVdF‐HFP in 1 M LiPF₆ containing EC&PC (1:1 v/v) based microporous polymer electrolyte. The specific capacitance of the capacitor was found to be 156 F g^?1. The energy and power densities were calculated as 14 Wh kg^?1 and 522 W kg^?1, respectively. The value of capacitance was found to be almost stable up to 1000 cycles and even more. Copyright © 2009 John Wiley & Sons, Ltd.     

Copper(I)-mediated radical polymerization of methacrylates in aqueous solution

α-Methoxypolyethylene oxide methacrylate was polymerized by copper(I)-mediated living radical polymerization in aqueous solution to give polymers with controlled number-average molecular masses and narrow polydispersities. When equimolar quantities of initiator with respect to copper(I) bromide were used, the reaction was extremely fast with quantitative conversion achieved in less than 5 min at ambient temperature. However, the molecular weight distribution was broad, and control over the number-average molecular weight (M_n) growth was extremely poor; this is ascribed to an increase in termination because of the increased rate as a result of the coordination of water at the copper center. The complex formed between copper(I) bromide and N-(n-propyl)-2-pyridylmethanimine, bis[N-(n-propyl)-2-pyridylmethanimine]copper(I), was demonstrated to be stable in aqueous solution by ¹H NMR over 10 h at 25 °C. However, on increasing the temperature to 50 °C, decomposition occurred rapidly. Thus, polymerization temperatures were maintained at ambient temperature. When longer alkyl chains were utilized in the ligand, that is, pentyl and octyl, the complex acted as a surfactant leading to heterogeneous solutions. When the catalyst concentration was reduced by two orders of magnitude, the rate of polymerization was reduced with 100% conversion achieved after 60 min with the M_n of the final product being higher than that predicted and the polydispersity equal to 1.43. Copper(II) was added as an inhibitor to circumvent these problems. When 10% of Cu(I) was replaced by Cu(II) {[Cu(I)] + [Cu(II)]/[I] = 1/100}, the mass distribution showed a bimodal distribution, and the rate of polymerization decreased significantly. With a catalyst composition [Cu(I)]/[Cu(II)] = 0.5/0.5 {[Cu(I)] + [Cu(II)]}/[I] = 1/100, polymerization proceeded slowly with 80% conversion reached after 22 h. Thus, the concentration of Cu(I) was further reduced with [Cu(I)]/[Cu(II)] = 10/90, {[Cu(I)] + [Cu(II)]}/[I] = 1/100. The system then contained [Initiator]/[Cu(I)] = 1000/1 and [I]/[Cu(II)] = 1000/9. Under these conditions, the reaction reached 50% after 5 h with the polymer having both an M_n close to the theoretical value and a narrow polydispersity of PDi = 1.15. Optimum results were obtained by increasing the amount of catalyst. When a ratio of [Cu(I)]/[Cu(II)] = 10/90 with a ratio of [Cu]/[I] = 1/1, a conversion of 100% was achieved after less than 20 h, leading to a product having M_n = 8500 and PDi = 1.15. Decreasing the amount of Cu(II) relative to Cu(I) to [Cu(I)]/[Cu(II)] = 0.5/0.5 (maintaining the overall amount of copper) led to 100% conversion after 75 min: M_n = 9500, PDi = 1.10. Block copolymers have been demonstrated by sequential monomer addition with excellent control over M_n and PDi. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1696–1707, 2001     

Kinetics of the liquid phase esterification of acrylic acid withn-octanol and 2-ethylhexanol catalyzed by sulfuric acid

Kinetics of the liquid phase esterification of acrylic acid withn-octanol and 2-ethylhexanol catalyzed by sulfuric acid has been studied in an isothermal semibatch reactor. The reaction appears to be second order. The kinetic parameters have been determined.     

Kinetics of hydrolysis of xylometazoline (XYL) in aqueous solution

The effect of pH (over the range of 2.10 - 11.90) and temperature (from 353 K to 363 K) on the stability of xylometazoline (XYL) has been studied by high performance liquid chromatography (HPLC). Using the dependence of log k vs pH, the hydrolysis of both the undissociated and dissociated XYL-molcules has been described by micro rate constants k₁ and k₂. Thermodynamic parameters (activation energy, enthalpy and entropy) of the composition reaction were calculated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Study on aqueous polymerizations of vinyl monomers initiated by metal oxidant–chelating agent redox initiators

In this study, a series of chelating type reductants containing redox pairs were tested as the initiator for aqueous polymerizations. The redox pairs consist of Ce(IV) or several first-row transition metals coupled with chelating agents of amino acids, dibasic acids, or diamine. The initial rates and limiting conversions of acrylamide polymerization initiated by those redox pairs were determined. The reductive reactivity of the chelating agents with Ce(IV) and the oxidative half-wave potential of Ce(III)-chelating agent/Ce(IV)-chelating agent were measured to evaluate the feasibility of these redox pairs as initiators. After the evaluation, the redox pairs other than Ce(IV)-amino acid type chelating agent were precluded to be promising initiators for aqueous polymerizations. Those Ce(IV)-amino acid type chelating agent redox pairs which could form at least two five- or six-membered rings were found to be potential initiators. The Ce(IV)-NTA pair was the most promising one. The mechanism of initiation of the redox pairs was proposed and further confirmed by the ¹³C- and ¹H-NMR spectra of NTA-terminated polyacrylamide. The complex formation constants (K) and disproportionation constants (k_d) of the Ce(IV)-amino acid type chelating agent redox initiators for acrylamide polymerization were evaluated. The factors governing the parameters of chelated complexes and the performance of polymerizations were discussed. These redox pairs were also used as the initiators for aqueous polymerizations of acrylic acid and acrylonitrile. © 1993 John Wiley & Sons, Inc.     

Synthesis of stable aqueous dispersion of graphene/polyaniline composite mediated by polystyrene sulfonic acid

A facile method of producing stable aqueous dispersion of graphene/polyaniline (PANI) composite is described, which involves the in situ polymerization of aniline on the surface of graphene with the aid of polystyrene sulfonic acid (PSS). The prepared aqueous graphene/PANI composite dispersion was very stable and no aggregation or precipitation was observed for several weeks. The excellent aqueous dispersibility and stability of the graphene/PANI composite is attributed to the cooperative interactions of π stacking interaction between PSS, PANI, and the graphene basal planes, and the electrostatic repulsions between negatively charged PSS bound on graphene/PANI composite. Fourier transform‐infrared spectrometry (FTIR), ultraviolet‐visible spectra (UV–vis), and Raman spectra confirmed the interaction of PANI and graphene in the composite, which effectively delocalize the electrons. In addition, the composite showed three orders of magnitude of conductivity increase compared with pure PANI. This new approach is simple, fast, and straightforward, representing a significant improvement in the processing of graphene/PANI composites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

在水溶液中电化学反应制备大面积聚吡咯膜

以不锈钢为电极,在吡咯水溶液中,经电化学聚合制备了大面积的聚吡咯薄膜。研究了反应电流密度、反应温度、对阴离子种类和浓度等因素对成膜性能及电导率的影响。选择合适的反应条件,可得到电导率为120Scm~(-1)、抗拉强度46MPA、模量为1.75GPA的聚吡咯膜。     

The synthesis and characterization of monodisperse poly(acrylic acid) and poly(methacrylic acid)

A number of polyacrylic (PAA) and polymethacrylic (PMAA) acids have been synthesized by living anionic polymerization of the monomeric tert-butyl esters followed by subsequent hydrolysis of the corresponding polyesters. The necessary precautions were taken in order to assure good molecular weight control, as well as high yields in the polymerization reactions. The intermediate and final polymers were characterized by gel permeation chromatography and NMR-H¹ spectrometry.     

Electrosteric stability of styrene/acrylic acid copolymer latices under emulsion polymerization reaction conditions

Acrylic acid (AA) is used in many emulsion polymerization formulations to improve the colloidal stability during and after the production of latex products. Theoretically, the improved stability originates from electrostatic repulsion complemented with steric repulsion. The objective of this work was to study the contribution of AA to the colloidal stability of polystyrene and styrene/AA copolymer latices under simulated reaction conditions. The strength of electrostatic and steric repulsion forces as a function of the electrolyte concentration, pH, and temperature was investigated via coagulation experiments with monomer‐swollen latices in stirred tank reactors. Transmission electron microscopy pictures and dynamic light scattering measurements provided an understanding of the conditions and mechanisms leading to coagulation. The experiments demonstrated that the presence of surface‐bound carboxylic groups only improved the colloidal stability if the carboxylic groups were charged, that is, at a high pH. At a low pH, the copolymer latices were even less stable than the homopolymer latex, and this indicated that the addition of AA did not improve the colloidal stability of a growing polystyrene latex. With respect to emulsion polymerization process operations, insufficient mixing and a highly concentrated electrolyte feed were found to be sources of fouling and enhanced macroscopic coagulation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 726–732, 2005     

磁性壳聚糖-聚丙烯酸微球的制备及表征

壳聚糖通过与丙烯酸接枝共聚制得壳聚糖聚丙烯酸悬浮液,在铁磁流体(Fe3O4)与聚乙二醇(分散剂)存在下通过与戊二醛交联,制备了磁性壳聚糖聚丙烯酸微球。用扫描电镜、红外光谱对合成的高分子微球进行形貌观察和结构表征,并进行了元素分析和磁性能测试,研究了磁性微球对牛血清白蛋白(BSA)的吸附效果。结果表明,合成的磁性微球外表呈球形,粒径为100～400nm;当Fe含量为2.47%时,磁性微球的饱和磁化强度约为1.30emug,磁矫顽力为280Oe,磁化率为2.16×10-4(常温下),属于顺磁性材料;其对BSA有较好的吸附效果,饱和吸附量约为400mgg。