Electrochemical study of lithium insertion into carbon-rich polymer-derived silicon carbonitride ceramics

This paper presents the lithium insertion into carbon-rich polymer-derived silicon carbonitride (SiCN) ceramic synthesized by the thermal treatment of poly(diphenylsilylcarbodiimide) at three temperatures, namely 1100, 1300, and 1700 °C under 0.1 MPa Ar atmosphere. At lower synthesis temperatures, the material is X-ray amorphous, while at 1700 °C, the SiCN ceramic partially crystallizes. Anode materials prepared from these carbon-rich SiCN ceramics without any fillers and conducting additives were characterized using cyclic voltammetry and chronopotentiometric charging/discharging. We found that the studied silicon carbonitride ceramics demonstrate a promising electrochemical behavior during lithium insertion/extraction in terms of capacity and cycling stability. The sample synthesized at 1300 °C exhibits a reversible capacity of 392 mAh g⁻¹. Our study confirms that carbon-rich SiCN phases are electrochemically active materials in terms of Li inter- and deintercalation.     

Enhanced piezoresistivity of polymer-derived SiCN ceramics by regulating divinylbenzene-induced free carbon

In-situ formed free carbon nanodomain is an unique feature of polymer-derived ceramics (PDCs), which plays a significant role to affect the properties of PDCs, especially for the electoral property and piezoresistivity. In this study we report an enhanced piezoresistive properties of amorphous silicon carbonitrides (SiCN) ceramics derived by divinylbenzene (DVB)-modified polysilazane. Microstructure analysis indicated that the free carbon phase in SiCN ceramics is gradually increasing in order degree and concentration with increasing content of DVB. The average spacing between the conducting particles decreases with increasing concentration of free carbon, resulting in an enhanced internal electric field. The effects of DVB concentration on the piezoresistive properties of SiCN ceramics are also discussed, finding that the DVB has a significant effect on the piezoresistive properties.     

Enhanced electric conductivity of polymer‐derived SiCN ceramics by microwave post‐treatment

The effect of microwave treatment on the electric conductivity and structure of a polymer‐derived SiCN ceramic is studied. It is found that the conductivity of the microwave‐treated sample is about 40 times higher than that of the conventional heat‐treated one at the same temperature and dwell time conventionally. The X‐ray diffraction patterns show that both samples are amorphous without obvious crystallization. Raman analysis reveals that the microwave‐treated sample exhibited a narrower full width at half maximum and upper‐shift of G peak. X‐ray photoelectron spectroscopy spectra show that there is a significant sp³‐to‐sp² transition of free carbon in the microwave‐treated sample. These results suggest that the microwave‐treatment can induce a distinct structure evolution of the free carbon, which contributes to the remarkable enhancement of the conductivity of the sample.     

丙烯酸系高吸水树脂的改性与应用

介绍了丙烯酸系吸水树脂的制备及其在农业、石油、建筑、医疗卫生等领域的应用。     

乳化体系对氟硅改性丙烯酸酯乳液性能的影响

采用不同的乳化体系来制备氟硅改性丙烯酸酯乳液,主要探讨了乳化体系对预乳化液稳定性、聚合稳定性、储存稳定性、转化率、粒径大小与分布以及吸水率的影响。结果表明,在所采用的乳化体系中,由聚氧乙烯-4-酚基醚硫酸铵盐(CO436)与1-丙烯基-α-羟基烷基磺酸钠(COPS-1)组成的复合乳液体系,可制得转化率高达98.85%的稳定乳液,乳液粒径呈单分散分布,乳胶膜的吸水率只有4.31%。     

Dehydration of lactic acid to acrylic acid in high temperature water at high pressures

Reaction of lactic acid was investigated with a flow apparatus in water at high temperatures (450 °C) and high pressures (40–100 MPa). The major products obtained from the reaction of lactic acid were acrylic acid, acetaldehyde, and the minor products were acetic acid and propionic acid. The maximum selectivity of acrylic acid was 44% at 23% lactic acid conversion that was obtained at 450 °C, 100 MPa and a residence time of 0.8 s. The reaction kinetics could be modeled by considering two pathways defined as a dehydration pathway to acrylic acid and a combined reaction pathway that consisted of decarboxylation and decarbonylation to acetaldehyde. The data and the kinetic analysis consistently show that both dehydration and the combined decarboxylation and decarbonylation reactions continue to be promoted in supercritical water as pressure (water density) increases. However, high water densities increase the selectivity of the dehydration reaction.     

Cross-linking polymerization of acrylic acid in supercritical carbon dioxide

Cross-linking polymerization of acrylic acid in supercritical carbon dioxide (scCO₂) was studied in a batch reactor at 50 °C and 207 bar with either triallyl pentaerythritol ether or tetraallyl pentaerythritol ether as the cross-linker and with 2,2′-azobis(2,4-dimethyl-valeronitrile) as the free radical initiator. All polymers were white, dry, fine powders. Scanning electron microscopy showed that the morphology of the polymer particles was not affected by cross-linking. As the cross-linker concentration was increased, the polymer glass transition temperature first decreased, then increased. Water-soluble and water-insoluble polymers were synthesized by adjusting the cross-linker concentration. Viscosity measurements showed that the polymer thickening effect strongly depended on the degree of cross-linking. Finally, cross-linking polymerization of acrylic acid in scCO₂ was carried out in a continuous stirred tank reactor. The use of cross-linker decreased the monomer conversion in this system.     

Electrical conductivity of poly(acrylic acid)–polyacrylamide complexes

The conduction mechanism in the interpolymer complex resulting from the interaction between poly(acrylic acid) (PAA) and polyacrylamide (PAAm) was investigated. The characteristic features of the relation between the logarithm of conductivity, log σ, and 1/T are different from those corresponding to the individual components of the complex. The value of σ for the complex was found to be less than its corresponding values for PAA or PAAm. The effects of the weight fraction of each polymer and the ionic strength of the solutions on the conductivity of the complex were also studied. The data showed that the σ of the complex depends on the weight fraction of the polymers. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2049–2055, 1998     

氧化还原引发淀粉与丙烯酸接枝共聚研究

研究了马铃薯淀粉与丙烯酸的接枝共聚反应,以过硫酸钾-亚硫酸氢钠为氧化还原引发体系,考察了不同引发剂浓度、单体浓度、反应温度、反应时间等对单体转化率、接枝率和接枝效率的影响;用红外光谱对共聚物进行了表征。结果表明,采用氧化还原引发体系可使聚合反应低温快速进行,并确定反应较佳条件。     

正交设计在合成玉米淀粉接枝丙烯酸共聚物中的应用

以过硫酸铵为引发剂,N,N’-亚甲基双丙烯酰胺为交联剂,在玉米淀粉上接枝丙烯酸制备高吸水性树脂。用正交实验,采用L16(45)正交表,考察了丙烯酸的中和度、淀粉与单体比例、引发剂、交联剂等对高吸水性树脂吸水率的影响。制得的树脂吸纯水率可达1 300 g/g,吸质量分数为0.9%NaCl溶液90倍,有较好的热稳定性。     

Tailoring bulk and surface grafting of poly(acrylic acid) in electron-irradiated PVDF

Endowing conventional hydrophobic poly(vinylidene fluoride) (PVDF) films with hydrophilic properties was conducted using electron beam irradiation. Grafting of acrylic acid (AA) in/onto pre-irradiated PVDF films was investigated. Reaction parameters, monomer concentration and inhibitor concentration were examined. Radiation grafted films (PVDF-g-PAA) were synthesized with various grafting yields ranging from 12 to 130 wt % in presence of Mohr's salt (25 wt %). Below 80 wt % of monomer concentration, the degree of swelling was found to increase with the grafting yield. The PAA was arranged randomly in all PVDF matrix (grafting through). Above 80 wt % of monomer concentration, the PAA was grafted only onto the surface of PVDF films leading to a highly dense layer of PAA. Grafting through or surface grafting processes were achieved by varying the water fraction in the initial monomer solution. Water molecule acts not only as a carrier for the monomer but also as a plasticizer expanding the film in the three dimensions. Evidences of grafting through and surface grafting were produced using FTIR in ATR mode, SEM coupled to X-ray detection and XPS. An accurate quantification of AA units was possible up to the micromole via a Cu²⁺–EDTA complex analyzed by UV–vis spectroscopy.     

Propagation rate coefficient of acrylic acid: theoretical investigation of the solvent effect

The free-radical polymerization propagation rate coefficient (k_p) of acrylic acid (AA) was calculated using transition state theory and ab initio quantum chemistry in order to shed light on the very strong solvent effects observed experimentally. Calculations were performed using a gas-phase reaction simulation, and the contribution of solvent then taken into account using the Polarizable Continuum Model for two solvents—water and toluene. The frequency factor (A) for AA propagation was insensitive to both varying the level of quantum theory applied as well as introducing a solvent field into the calculations. The activation energy (E_a) decreased substantially (∼10 kJ mol⁻¹) upon introduction of the water solvent field relative to the gas phase; however, the toluene solvent field had little impact on E_a. From analyzing transition state (TS) bond lengths and angles, as well as electronic density, this variation in E_a was attributed to greater resonance stabilization of the TS in the polar solvent, as well as more substantial mixing of reactant molecular orbitals, assisting in the transfer of electrons from the alkene to the radical. This provides a partial explanation to the marked variation in aqueous-phase k_p of water-soluble monomers seen experimentally with changes in monomer and electrolyte concentrations, which alters the hydrogen bonding patterns in solution.     

The thermal degradation of acrylic pressure-sensitive adhesives based on butyl acrylate and acrylic acid

The thermal degradation of acrylic pressure-sensitive adhesives at 250 °C was investigated using pyrolysis-gas chromatography. Knowledge of the types and amounts of pyrolysis products will provide important information on the thermal degradation of acrylic adhesives and the mechanisms involved. Unsaturated monomers including butyl acrylate and butyl methacrylate were formed during thermal degradation of butyl acrylate–acrylic acid copolymers. As a result of side chain reactions in the thermal destruction of the butyl acrylate–acrylic acid-based self-adhesives, a remarkable amount of butyl alcohol was produced. The unsaturated monomers formed as a result of thermal degradation could potentially be used in a new polymerization process.     

低温氧等离子体引发ES纤维接枝丙烯酸的研究

利用低温氧等离子体对ES纤维进行预处理,经与空气接触后接枝丙烯酸。探讨了等离子体处理时间、放电功率、气体压强及接枝单体浓度、接枝反应时间、温度等各因素对接枝率的影响规律。     

Experimental evidence of a relationship between monomer plasma residence time and carboxyl group retention in acrylic acid plasma polymers

Decreasing carboxyl retention in deposits from the glow region of an acrylic acid plasma was measured by X-ray photoelectron spectroscopy and chemical derivatisation as the collection distance from the monomer vapour inlet was increased. Volatilisation of plasma polymerised acrylic acid was detected after trifluoroethanol derivatisation; this is correlated with evaporation of low molecular weight components observed previously.     

天然胶乳的挥发脂肪酸值与电导率关系的探索

通过改变挥发脂肪酸含量、无机盐浓度、外界温度，探索天然胶乳的挥发脂肪酸值与电导率的关系。     

Liquid phase esterification of acrylic acid with 1-butanol catalyzed by solid acid catalysts

Esterification of acrylic acid with 1-butanol has been studied in a heterogeneous solid–liquid reaction system using a variety of solid acids including an acidic salt of H₃PW₁₂O₄₀, Cs_2.5H_0.5PW₁₂O₄₀. The catalytic activity (per proton) of liquid acids such as heteropolyacids, H₂SO₄, and para-toluenesulfonic acid increased as the acid strength of the solution increased, but the difference in the activity among them was not significant. In the solid–liquid reaction system, Cs_2.5H_0.5PW₁₂O₄₀ exhibited the highest catalytic activity in the unit of catalyst weight among the solid oxide catalysts, while the activity of Cs_2.5H_0.5PW₁₂O₄₀ was less than those of organic resins such as Nafion and Amberlyst 15. Contrary to the liquid acids, the specific activity values (per proton) of solid acids were significantly different. It was demonstrated that the activity of Cs_2.5H_0.5PW₁₂O₄₀ was almost retained after the addition of water, while the activities of the organic resins greatly decreased. The water-tolerant property of Cs_2.5H_0.5PW₁₂O₄₀ is presumed to be due to the hydrophobic nature of the surface.     

小麦秸秆接枝丙烯酸制备高吸水性树脂

以N,N'-亚甲基双丙烯酰胺为交联剂,过硫酸钾一硫代硫酸钠为引发剂,采用水溶液聚合法合成了小麦秸秆接枝丙烯酸系列高吸水树脂。研究了单体配比、丙烯酸中和度、引发剂及交联剂用量对吸去离子水的影响。结果表明,该树脂具有良好的吸水性能,吸收去离子水达617 g/g。     

Influence of operating parameters on plasma polymerization of acrylic acid in a mesh-to-plate dielectric barrier discharge

Plasma polymerization of acrylic acid is an interesting research subject, since the obtained coatings can have significant biomedical applications due to their high surface density of carboxylic acid groups. In this work, plasma-polymerized acrylic acid (PPAA) films are synthesized using a mesh-to-plate dielectric barrier discharge operated at medium pressure (10.0 kPa). Results clearly show that this reactor setup is able to deposit uniform PPAA films in contrast to the commonly used parallel plate reactor. Moreover, carefully planned experiments are conducted to study the influence of discharge power and monomer concentration on the chemical composition and thickness of the PPAA films. Results clearly show that input power strongly influences the properties of the deposited films: with increasing discharge power, monomer fragmentation in the discharge increases leading to a decrease in carboxylic acid functional groups and a lower polymer deposition rate. The effect of monomer concentration is less pronounced: only at very low monomer concentration (0.1 g/h), a decrease in carboxylic acid functional groups can be observed. The chemical composition and thickness of the PPAA films can thus be tailored by adjusting the operational parameters of the discharge.     

Effect of matrix graft modification using acrylic acid on the PP/Mg(OH)2 composites and its possible mechanism

The matrix graft modification using an acrylic acid (AAc) was employed on the polypropylene/Mg(OH)₂ flame-retardant composite. The graft modification of PP matrix was carried out via an in-situ reactive extrusion by a twin-screw extruder. The tensile strength of the composites was analyzed using an equation developed by Pukanszky from which both matrix tensile strength σ₀ and interfacial adhesion strength were found to be increased. The enhancement of σ₀ is due to the intermolecular crosslinking of PP by AAc grafting. This crosslinking causes increases of tensile strength, Young’s modulus, impact resistance, and thermal resistance, but decreases the elongation at break of the composites.