Grafting vinyl monomers on silk fibres—I. Graft copolymerization of methyl methacrylate on silk by tetravalent cerium ion

The use of tetravalent cerium to initiate graft copolymerization of methyl methacrylate on to silk fibres has been investigated. The extent of grafting was determined while varying Ce(IV) and monomer concentrations, temperature and nature of the fibre. The graft yield increased on increasing Ce(IV) concentration up to 0.015 M and monomer concentration up to 0.469 M; thereafter it decreased. The effect of an inorganic salt (copper sulphate) on grafting has also been studied. Chemical modification of the silk prior to grafting noticeably affected graft yield.     

Water-soluble copolymers. VII. Cerium (IV) induced graft copolymerization of acrylamide and sodium-2-acrylamido-2-methylpropane sulfonate onto dextran

Studies were conducted on grafting of acrylamide (AM) and sodium-2-acrylamido-2-methylpropane sulfonate (NaAMPS) comonomers onto dextran utilizing Ce(IV) induced initiation. The effects of reaction temperature, the Ce(IV)/dextran ratio, and the AM/NaAMPS ratio on grafting yield were investigated. The graft copolymerization behavior can be explained by exchange of the AMPS anion with one of the ligands on the Ce(IV) initiator. Oxidative modification of the dextran substrate improved the yield of graft copolymer. The dextran-g-poly(acrylamido-co-sodium-2-acrylamido-2-methylpropane sulfonate) samples prepared by this method were characterized as to copolymer composition and molecular weight utilizing elemental analysis, dilute solution viscometry, and aqueous size exclusion chromatography. Relationships of molecular weight and charge density to kinematic viscosity and salt sensitivity are discussed.     

Effects of toluene on thiophene adsorption over NaY and Ce(IV)Y zeolites

Zeolites NaY and Ce(IV)Y were employed as adsorbents to remove organic sulfur compounds from model gasoline(MG) solutions with and without toluene in static adsorption experiments at room temperature(RT) and atmospheric pressure.The adsorbents were characterized by XRD,XRF and pyridine infrared spectrum(IR).The adsorption experiments show that the desulfurization performance of Ce(IV)Y is much better than that of NaY.The sulfur removal over both NaY and Ce(IV)Y decreases with the increase of toluene concentration in MG,however,the decline tendency on Ce(IV)Y is smooth,and it is steep on NaY.FT-IR spectra of thiophene adsorption indicate that thiophene molecules are mainly adsorbed on NaY via π electron interaction,but on Ce(IV)Y,in addition to the π electron interaction,both Ce4+-S direct interaction and protonation of thiophene also play important roles.Toluene molecules are adsorbed on NaY also via π electron interaction.Although the amount of Brnsted acid sites is increased due to the introduction of Ce4+ ions into NaY zeolite,it is not found to influence the adsorption mode of toluene over Ce(IV)Y.Compared with NaY zeolite,the improved desulfurization performance over Ce(IV)Y for removing organic sulfur compounds from MG solution,especially those containing large amount of aromatics,may be ascribed to the direct Ce(IV)-S interaction,which is much resistant to the influence resulted from toluene adsorption.     

Graft copolymerization onto jute fiber: Ceric ion-initiated graft copolymerization of methyl methacrylate

Graft copolymerization of methyl methacrylate (MMA) was carried out on both defatted and bleached jute fibers using ceric ammonium sulfate (CAS) as the initiator. In order to obtain the optimum condition for grafting, the effects of initiator concentrations, temperature, time of reaction, lignin content of jute, and the monomer concentration were studied. The maximum percent grafting and grafting efficiency were found to be 132% and 0.71, respectively. Kinetic studies showed that at 0.03M CAS, the reaction appeared to obey the second-order process. The activation energies were found to be 7.74 and 5.12 kcal/mole for defatted (lignin content, 15.7%) and chlorite-bleached jute (lignin content 10%), respectively. The activation energies of graft copolymerization of MMA onto jute fiber are compared with the energies of activation of graft copolymerization of acrylonitrile (AN).     

Characterization of methyl methacrylate grafting onto preirradiated biodegradable lignocellulose fiber by gamma-radiation

Gamma-radiation-induced graft copolymerization of methyl methacrylate onto natural lignocellulose (jute) fiber was carried out by the preirradiation method in an aqueous medium by using octylphenoxy-polyethoxyethanol as an emulsifier. The different factors that influenced the graft copolymer reaction process were investigated. In the case of radiation-dose-dependent grafting, samples irradiated in the presence of air produced up to 73% graft weight compared to 53% obtained in the case of irradiation in a nitrogen environment. By assuming Arrhenius reaction kinetics, the activation energy (E(a)) of the grafting reaction process was evaluated for different reaction temperatures. Moreover, the graft copolymer reaction was controlled by incorporating a homopolymer-inhibiting agent and three different chain-transfer agents in the reaction medium. The mechanical and thermal properties of jute fiber 'as received' and jute-graft-poly(methyl methacrylate) were also investigated. The results showed that the percentage of grafting with jute fiber has a significant effect on the properties. The kinetic parameters were evaluated from TGA thermograms by using Broido's method in the temperature range 240-350 degrees C. Scanning electron micrographs show that the structural changes on the surface of jute fibers were induced by graft copolymerization of methyl methacrylate monomer. Fiber-fiber surface friction was measured in terms of the average maximum load and the kinetic friction. SEM of jute-graft-poly(methyl methacrylate).     

The preparation,characterization, and application of cellulose–MMA graft copolymers. I. The aqueous-based preparation of cellulose–MMA graft copolymers

Cellulose-MMA graft copolymers have been produced using aqueous-based, Ce(IV)-initiated and periodate-initiated systems and also photochemical initiation. The reaction variables studied include the effect on grafting of varying the MMA monomer concentration, the initiator type and concentration, and also the reaction time. Of the three initiator types examined, the Ce (IV)-initiated and the photochemically-initiated systems are comparable in their effects on graft copolymer formation. Concurrent homopolymer formation was in the region of 50% by weight. Periodate-initiation leads to less efficient grafting of MMA onto cellulose, although homopolymer formation is also lower (typically <20% by weight). The characterization of the copolymeric products through their properties as solids and, as their carbanilated derivatives, through their solution properties has been undertaken. Values of the activation onergy of decomposition (E_A) of the cellulose-MMA graft copolymers decrease with increasing MMA content, ranging between 227 and 155kJ mol^?1. There is also a dependence on initiator type and grafting reaction conditions used (E_A (cellulose wood pulp) = 239 kJ mol^?1; E_A (PMMA) = 115 kJ mol^?1). Quantitative zeta-potential (ζ) determinations for cellulose-MMA graft copolymer samples produce negative surface charge density (σ) values. At a comparable MMA grafting level of 70–80%, values are of the order: photochemical (?730 esu/cm²) > periodate (?470 esu/cm²) > Ce (IV)-initiation (?351 esu/cm²). Characterization of carbanilate solutions (by rheological examination) and of dry, carbanilate films (by study of surface wetting behavior) highlighted differences in the physical conformation of copolymers prepared by the different initiation routes. The highly degradative effect on cellulose of a periodate initiator, in comparison with the Ce (IV)-initiation system, is reflected in significantly reduced molar mass values (typically, M_n 65,000 as opposed to 130,000 for Ce (IV)-initiated graft copolymer carbanilates).     

Oxidative polymerization of acrylamide in the presence of thioglycolic acid

Chemical polymerization of acrylamide at room temperature was examined by using thioglycolic acid-cerium (IV) sulfate and thioglycolic acid-KMnO₄ redox systems in acid aqueous medium. Water soluble polyacrylamides containing thioglycolic acid end groups were synthesized. The effects of the molar ratio of acrylamide to Ce(IV) n _AAm /n _Ce(IV) , the polymerization time, the temperature, the monomer concentration, the molar ratio of cerium (IV) sulfate to thioglycolic acid and the concentration of sulfuric acid on the yield and molecular weight of polymer were investigated. Lower molar ratios of acrylamide/Ce(IV) at constant monomer concentration resulted in an increase in the yield but a decrease in molecular weight of polymer. The increase of reaction temperature from 20 to 70°C resulted in a decrease in the yield but generally resulted in a constant value for the molecular weight of polymer. With increasing polymerization time, the yield and molecular weight of polymer did not change substantially. Ce(IV) and Mn(VII) ions are reduced to Ce(III) and Mn(II) ions respectively in the polymerization reaction. The existence of Ce(III) ion bound to polymer was investigated by UV-visible spectrophotometry and fluoresce measurements. The amount of Mn(II) incorporated into the polymer was determined using graphite furnace atomic absorption spectrometry. The mechanism of this phenomenon is discussed.     

Graft copolymerization of cellulose initiated by ceric salts: Effect of reaction conditions on the consumption of ceric ion

A soluble monomer [methyl acrylate (MA)] and an insoluble monomer [butyl methacrylate (BMA)] were grafted onto cellulose by three types of ceric salts under both oxygen-free conditions and in the presence of oxygen. For comparison, Ce(IV) consumption during cellulose oxidation was also determined under similar reaction conditions. Slightly more Ce(IV) was consumed during cellulose oxidation in the presence of oxygen. During graft copolymerization of MA under oxygen-free conditions, the consumption of Ce(IV) was much lower than during cellulose oxidation regardless of the type of ceric salt employed. The opposite was observed in the presence of oxygen: much more Ce(IV) was consumed during grafting than during cellulose oxidation. The consumption of Ce(IV) in the graft copolymerization of BMA by ceric sulfate was nearly independent of reaction conditions and it was approximately the same as in cellulose oxidation. In the reaction initiated by ceric ammonium nitrate under oxygen-free conditions, less Ce(IV) was once again used up during grafting than during cellulose oxidation. However, the difference was much smaller than in the case of MA.     

Cu(I)-Ce(IV)-Y吸附剂的制备及其脱硫性能研究

采用液相离子交换Cu、Ce离子制备了Cu(I)-Y、Ce(IV)-Y和Cu(I)-Ce(IV)-Y吸附剂,利用XRD、BET等技术对吸附剂进行了表征。通过静态实验考察了制备条件对Cu(I)-Ce(IV)-Y吸附剂脱硫性能的影响,通过固定床实验研究了吸附剂的穿透硫容,同时,在含噻吩与苯并噻吩的正辛烷模拟油中,分别加入甲苯、环己烯、吡啶配成新的模拟油,探究了吸附剂的脱硫选择性。结果表明,离子交换时间48 h,焙烧温度550℃,Cu/Ce物质的量比1∶1下制备的Cu(I)-Ce(IV)-Y吸附剂具有适宜的脱硫活性。在含甲苯、环己烯模拟油中,Cu(I)-Ce(IV)-Y吸附剂具有最好的脱硫性能,相同浓度的甲苯、环己烯和吡啶对各吸附剂脱硫性能的影响顺序为吡啶环己烯甲苯。引入Cu+可改善吸附剂的脱硫活性,引入Ce4+可改善吸附剂对硫化物的选择性,Cu+和Ce4+的协同作用使Cu(I)-Ce(IV)-Y兼具有高的硫容和抗芳烃、烯烃能力。     

Electroinduced polymerization of acrylonitrile in the presence of Ce(IV)

Polymerization of acrylonitrile (AN) initiated by Ce(IV) was performed in an electrolytic cell. The precipitated polymer was formed in the cathodic compartment, and the reduced initiator was reoxidized in the anode, thus allowing for the continuation of the process. The effects of concentrations of the monomer, Ce(IV), and sulfuric acid (the electrolyte) were investigated as well as the potential and the temperature. The yield of the process, proceeding under mild conditions, was high. The study was augmented by voltametric and spectrophotometric investigation. The resulting polymer was characterized by FTIR and optical spectrometry, and its m.w. was determined by viscometric method. A possible mechanism of polymerization is suggested. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2319–2327, 1999     

Deep adsorptive desulfurization over Cu,Ce bimetal ion-exchanged Y-typed molecule sieve

In this paper, Ce(IV)–Y, Cu(II)–Y and Cu(II)–Ce(IV)–Y adsorbents were prepared by the liquid-phase ion-exchange Y zeolites with combined Cu and Ce ions at low temperature and room pressure. The adsorbents were characterized by means of X-ray diffraction, N₂-adsorption specific surface area measurements (BET), X-ray photoelectron spectroscopy, Pyridine adsorption infrared spectroscopy and Fourier transform infrared. The adsorptive desulfurization properties of these three adsorbents were studied in a fixed-bed unit through a model gasoline which made up of 1-octane solution of the refractory sulfur compounds (Such as thiophene and benzothiophene) and a certain amount of toluene or cyclohexene. The results indicate that Cu(II)–Ce(IV)–Y bind the organic sulfur compounds through two types of adsorption modes: π-complexation and direct sulfur–adsorbent interaction. The adsorption selectivity of sulfur compounds onto Cu(II)–Ce(IV)–Y decreased in the order: benzothiophene > 2,5-dimethylthiophene > 3-methylthiophene > thiophene. The effect of competition components on the metal ion-exchanged Y zeolites for sulfur removal in the order: cyclohexene > toluene. The Cu(II)–Ce(IV)–Y possesses the high sulfur adsorption capacity similar to Cu(II)–Y and high selectivity for sulfur compounds similar to Ce(IV)–Y, which can be attributed to the synergistic interaction between Cu²⁺ and Ce⁴⁺.     

Graft Copolymerization of 4-Vinylpyridine Onto Modified Cellulosic Fibers. the Ceric Ion Concentration Effect

The graft copolymerization of 4-vinylpyridine was carried out on mercerized cellulose and partially carboxymethylated cellulose (PCMC) using eerie ammonium nitrate (CAN) as the initiator. the grafting parameters (grafting efficiency (GE), graft yield (G), and total conversion (C¹)) were studied as a function of CAN concentration. It was shown that by increasing the CAN concentration, G and C, reached a maximum. the graft yields for PCMC were significantly higher than those for mercerized cellulose. the largest GE values appeared for PCMC and mercerized cellulose at low and high CAN concentrations, respectively. the Ce(IV) consumption during grafting increased with rising concentration of CAN, and it was greater in the case of PCMC than of mercerized cellulose. After acid hydrolysis of the polysaccharide backbone, the average molecular weight of grafts was determined viscometrically. Molecular weight decreased with initiator concentration. Graft frequency (GF), on the other hand, increased with CAN concentration. GF for PCMC was higher than that for mercerized cellulose. Ce(IV) consumption increased with CAN concentration and it was lower for mercerized cellulose than that consumed during grafting on PCMC. After that, the effect of CAN concentration on the graft copolymerization onto PCMC was examined while the total nitrate ion concentration was maintained constant at 1.59 M by addition of sodium nitrate. Maximum G, C¹ and Ce(IV) consumption were higher than in the previous case.     

Vinyl polymerization of acrylonitrile by the cerium(IV)-propane-1,2-diol system

The polymerization of acrylonitrile (M) initiated by the Ce(IV)-propane-1,2-diol (R) redox system has been studied in aqueous sulphuric acid under nitrogen in the temperature range 30 to 40°. The rate of polymerization is proportional to [M]², [R] and [Ce(IV)]^?1 and the rate of ceric ion disappearance is proportional to [R], [Ce(IV)]. The effects of certain salts, acid, solvent and temperature on both rates have been investigated. A kinetic scheme has been proposed, and various rate and energy parameters evaluated.     

Grafting Vinyl Monomers onto Silk Fibers. V. Graft Copolymerization of Methyl Methacrylate onto Silk with Potassium Permanganate as Initiator

The graft copolymerization of methyl methacrylate onto silk fibers in aqueous solution with the use of manganese (IV) ions as initiator was investigated. The rate of grafting was determined by varying monomer, acidity of the medium, temperature, nature of silk, and the reaction medium. The graft yield increases significantly with increase of manganese (IV) concentration up to 15 meq/liter; with further increase of manganese (IV) concentration, the graft yield decreases. The effect of the increase of monomer concentration brings about a significant enhancement in the graft yield up to 7%, and with further increase of monomer concentration the graft yield decreases. The graft yield is considerably influenced by chemical modification prior to grafting. The effect of some inorganic salts and anionic surfactants on the rate of grafting has been investigated.     

A solid solution theory for matrix modification in electrothermal atomic absorption spectrometry

The kinetics of evaporation of the volatile analytes Pb and Cd in the presence of Ce(IV) introduced as the chemical modifier (NH₄)₂Ce(NO₃)₆ have been studied. The experimental results obtained are found to be in acceptable agreement with the regular solution model applied as a theoretical approach. Comparison with the results from previous investigation on the Pb/W analyte-modifier couple is made. An attempt is also made to explain some effects connected with the application of modifiers as described in the literature within the framework of the present model.     

Thermal stability of poly(methyl methacrylate) as polymerized in aqueous media by using redox systems as initiators

The thermal degradation of poly(methyl methacrylate) as polymerized in aqueous nitric acid solution using Ce(IV) alone and in combination with isobutyl alcohol, isopropyl alcohol, glucose, maltose, and cellobiose as initiator systems has been investigated using differential thermal analysis (DTA) and thermogravimetry (TGA) in dynamic nitrogen. The kinetic parameters E, n, and A have been obtained following several methods of thermogravimetric analysis. The most stable material was found to be the PMMA sample obtained with Ce(IV), and the Ce(IV)–IBA and Ce(IV)–maltose polymerized samples were the least stable. In the pyrolysis of Ce(IV)–IBA and Ce(IV)–maltose polymerized samples it was found that two reactions occurred, while in the case of the PMMA polymerized with Ce(IV), Ce(IV)–IPA, Ce(IV)–glucose, and Ce(IV)–cellobiose three reactions took place.     

A study on sorbitol-ceric ion initiated polymerization of acrylonitrile

The polymerization of acrylonitrile (M) initiated by the sorbitol (R)-Ce(IV) redox system has been studied in sulphuric acid in the range 30–40° under nitrogen. At moderately high concentrations of Ce(IV) (0.00015-0.02 M), the rate of polymerization (R_p) is proportional to $\text{[}\text{M}\text{]}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{[}\text{R}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and the rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. At lower concentration of Ce(IV) (0.00005–0.00015 M) R_p is proportional to [M], [R]^1/2 and [Ce(IV)]^1/2 and rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. The effects of certain salts, acid, solvent and temperature on both rates have been investigated. A kinetic scheme involving mutual termination has been proposed and various rate and energy parameters evaluated. At still higher concentration of Ce(IV) (0.02 M), a linear mode of termination seems to operate.     

Electro‐induced oxidative polymerization of N‐vinylcarbazole

In this study, a novel procedure to increase the yield of the non‐crosslinked, photoconductive, white form of linear poly(N‐vinylcarbazole) (LPVCz) is reported. The yield of LPVCz is increased (up to 53%) by the addition of catalytic amounts of ceric ammonium nitrate as an oxidant during the electrochemical polymerization of N‐vinylcarbazole in a divided electrochemical cell. The concentration of Ce(IV) remained constant during the polymerization since Ce(III) is readily oxidized to Ce(IV) electrochemically. Since the electrochemical oxidation of Ce(III) to Ce(IV) took place simultaneously at the anode, the deposition of dark green crosslinked polyvinylcarbazole on the electrode surface, which hinders the formation of white LPVCz, can be prevented. The Fourier transform infrared, ultraviolet–visible and fluorescence spectra of white LPVCz showed that the structures of polymers are the same as those produced by conventional polymerization. Copyright © 1999 John Wiley & Sons, Ltd.     

Kinetic and mechanistic aspects of metal ion catalysis in cerium(IV) oxidation

This review discusses the kinetic aspects of different metal ion catalysis in Ce(IV) oxidation of different types of organic and inorganic substrates in aqueous acid media. The reactions have been categorised with the metal ions acting as the catalysts. The nature of mechanism of catalysis in Ce(IV) oxidation depends on the nature of substrate for a particular metal ion catalyst and it also largely depends on the nature of acid medium used. The utility and scope of the catalytic oxidation by Ce(IV) in analytical chemistry are discussed.     

A comparative study on chemical treatment of jute fiber: potassium dichromate, potassium permanganate and sodium perborate trihydrate

Studies have been carried out on chemical treatments of jute fibers in order to hinder moisture absorption, which causes incompatibility with a non-polar polymer, and to increase the surface roughness for mechanical interlocking. The objective of this research is to improve the interfacial adhesion between jute fibers and polypropylene by oxidative treatments. On this basis, jute fibers were treated with potassium dichromate (PD), potassium permanganate (PM) and sodium perborate trihydrate (SP). Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy were used to characterize jute fibers. The effects of chemical treatments were also revealed by assessment of moisture absorbability, yarn tensile properties and interfacial shear strength with polypropylene. FTIR and XPS analyses confirmed oxidative modification of jute fibers using any of the surface treatments. It was observed that the proportion of O=C groups increased, whereas that of O–H groups decreased after oxidative modifications. Tensile strength and elasticity modulus results decreased after oxidative treatments, whereas PD, PM and SP enhanced the interfacial shear strength values by 25, 61 and 71 %, respectively. Only SP treatment influenced moisture absorbability results significantly. The surface roughness of untreated jute fibers shows increments after chemical treatments due to partial removal of surface cementings. According to the findings obtained from surface characterization methods and physical tests, the highest interfacial adhesion with better compatibility with polypropylene was achieved after SP treatment by providing the highest surface roughness values and hydrophobic character of jute fiber.