Aqueous polymerization of acrylamide initiated by Ce(IV)-thiomalic acid redox system

Summary The use of a Ce (IV)-thiomalic acid (Ce⁴⁺-TMA) redox system as an initiator in the polymerization of acrylamide (M) in an aqueous medium has been investigated. The Ce⁴⁺ forms a 11 complex with TMA, decomposing through free radical mechanism in an acid medium. From 5 to 15% conversion the rate equation is where Rp is the rate of polymerization and x is 0.5 or 1.0 depending upon the concentration of monomer. The overall energy of activation has been calculated to be 9.12 k cal. deg^–1 mol^–1(38.12 kJ/mol) in the investigated range of temperature (25°–40°C) the degree of polymerization (P) of the polymer is directly proportional to [M]. The number of average molecular weight of the polymer remains unaffected at lower concentration of Ce⁴⁺ and is found to decrease at higher concentrations.In this investigation the kinetics and mechanism of the Ce(IV)-thiomalic acid (TMA) redox system to initiate the polymerization of acrylamide has been studied.Acrylamide (E. Merck) was purified by usual methods. Thiomalic acid and eerie ammonium sulfate were used without purification. All solutions were p repared in twice distilled water.The polymerization procedure adopted was similar to the one used by MISRA et al. [3, 4]. The polymerization was followed by quantitative estimation of the double bonds in acrylamide as described [8]. A small variable induction period was observed perhaps due tothe residual oxygen in the thiol solution. Curves were plotted after eliminating the induction period.The average molecular weights of the p olymers were determined by viscosity measurements at 30°C in an aqueous medium using the relationship of DAINTON et al. [2]. Where []=intrinsic viscosity of the polymer solution and ¯Mn=molecular weight of the sample.     

Acrylonitrile polymerization initiated by Ce(IV)–cyclohexanone redox system in presence of surfactant

The rate of polymerization of acrylonitrile, using the Ce(IV)–cyclohexanone redox system as an initiator, was studied kinetically, in the presence of 0.015M sodium dodecyl sulfate (SDS), over a temperature range of 25–45°C. The rate of polymerization (R_P), percentage of monomer conversion, and rate of Ce(IV) consumption (?R_Ce) were found to increase with the concentration of SDS, above its CMC. The effect of [AN], [Ce(IV)], [H⁺], and the ionic strength were also studied. The overall activation energies for the polymerization processes were computed to be 23.14 and 17.64 kcal/mol in the absence and presence of 0.015M SDS. A suitable kinetic mechanistic scheme for the free‐radical mechanism was proposed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2066–2072, 2003     

Aqueous polymerization of acrylonitrile by Ce(IV)-diacetone alcohol redox system

The kinetics of oxidation of DAA by Ce(IV) in dilute sulphuric acid medium has been studied and the reaction was found to obey a second order rate law. This DAA — Ce(IV) redox system has been used for the polymerization of acrylonitrile and the rate of polymerization was found to be proportional to[Ce(IV)]^0.5, [DAA]^0.5 and [M]^1.5. Based on these results a probable mechanism for initiation and termination has been proposed. The chain lengths of the polymers were found to increase with [M] and decrease with both [Ce(IV)] and [DAA].     

Radical polymerization of acrylamide initiated by ceric ammonium nitrate-methionine redox initiator system

The polymerization of acrylamide, initiated by a cerium (IV) [Ce(IV)] ammonium nitrate-methionine redox initiator system, was carried out in an aqueous solution at different reaction conditions. The dependence of molecular weight and polymerization yield on the concentration of Ce(IV), polymerization time, and temperature was determined. The molecular weight distributions (MWD) of the resulting polymers were examined using the HPLC method. Based on the HPLC results, optimum reaction conditions were determined that provided an opportunity to obtain a polymer that had a narrow MWD. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1643–1648, 1997     

The polymerization of acrylamide initiated with CE(IV) and KMNO4 redox systems in the presence of glycine

Glycine-Ce(IV) salts and −KMnO₄ initiator systems were used for the polymerization of acrylamide, resulting in water-soluble polyacrylamide, which contains amino acid end groups. The dependence of polymerization yields and molecular weights of polymers on the mole ratio of acrylamide monomer to glycine, the polymerization time, the temperature, and the concentration of sulfuric acid were investigated. The decrease in the mole ratio of acrylamide to glycine resulted in a decrese in the molecular weight, and an increase in the yield of acrylamide polymer, which contains a glycine end group. With increasing acid concentration of the polymeric solution, the polymerization yield and the molecular weight of polymer decrease. Ce(IV) and Mn(IV) reduced to Ce(III) and Mn(II) in the polymerization reaction. The amounts of Ce(III) and Mn(II) bound to polymer were determined. The composition of the polymerization product was investigated and a bimodal character of the molecular weight distribution was observed. The mechanism of this phenomena is discussed. © 1996 John Wiley & Sons, Inc.     

Structural definitions for soluble portions of polyacrylamides synthesized with Ce(IV)–chelating agent redox systems

Polymerizations of acrylamide initiated by ceric ammonium nitrate and ceric sulphate in combination with nitrilotriacetic acid, ethylene diamine tetraacetic acid, diethylene triamine pentaacetic acid and 1,2-cyclohexane dinitrilotetraacetic acid were studied in aqueous nitric acid and sulphuric acid solutions at 55°C in the presence of air. The experimental results can be explained by assuming that the complexes of Ce(III) with sulphate and nitrate ions, Ce(SO₄)_n^{x(+ or −}) and Ce(NO₃)_n^{x(+ or −}), have different reactivities in the reactions. FTIR and UV spectra of the polymers, together with conductometric and gravimetric measurements, clearly showed that in the case of sulphato-cerate complexes, there were complexes not only on the end-groups but also on amide groups within the chain. Furthermore, it was observed that the stabilities of the primary radical sources generated by the redox pairs used in this work depend on the anion type and concentration of the acid and oxidation agent.     

Adiabatic polymerization of acrylamide using a persulfate–bisulfite redox couple

The temperature rise during the adiabatic polymerization of acrylamide in water has been used to characterize the kinetic parameters. Based on initial rate data, the following equation is obtained: where concentrations of monomer, persulfate, and bisulfite are in mole/kg, T is in K, and t is in min. The order with respect to monomer is confirmed by an analysis of the entire temperature–time record during polymerization. The persulfate–bisulfite couple was studied also in the absence of monomer. Concentrations were measured by UV absorbance and by permanganate titration. The reaction can be represented by: where concentrations are in mole/liter, T is in K, and t is in min.     

Bulk polymerization of vinyl chloride–commercial initiator systems

The applicability of a model after Talamini for the bulk polymerization of vinyl chloride with several commercial initiators has been examined. The model agrees well with experimental rate data for the initiators: diisopropyl peroxydicarbonate, disecbutyl peroxydicarbonate, t-butyl peroxypivalate, lauroyl peroxide and benzoyl peroxide.     

The manganic hydroxide–hydrazine system as an initiator of vinyl polymerization. IV. The emulsion polymerization of methyl methacrylate

The behavior of the emulsifier sodium dodecyl sulfate and electrolyte sodium hydroxide was studied at the oxidation stage and beyond in the emulsion polymerization of methyl methacrylate initiated by the manganic hydroxide–hydrazine hydrate system. From the rate of polymerization and from the adsorption of hydrazine it was shown that addition of emulsifier is more effective at the oxidation stage than after. But the reverse is obtained with the electrolyte. The effect of hydrazine concentration was also studied. The results are explained on the basis of a surface reaction between hydrazine hydrate and the insoluble manganic hydroxide.     

Effect of toluene on the polymerization of AN initiated by Ce(IV)–sucrose redox system in the presence of surfactants

The effects of toluene on the kinetics of polymerization of acrylonitrile (AN) initiated by the Ce(IV)/sucrose redox system were studied in the presence of an emulsifier, N-cetyl-trimethylammonium bromide (NCTAB) in the temperature range 35–45°C. The effects of concentration of metal ion, monomer, sulfuric acid, substrate (sucrose), emulsifier, toluene, some inorganic salt, and organic solvent on R_p have also been investigated. The remarkable features of the investigation involve the derivation of the rate expression for the above system with the calculation of activation energy. © 1993 John Wiley & Sons, Inc.     

Graft copolymerization of methyl methacrylate onto starch using a Ce(IV)–glucose initiator system

Graft copolymerization of methyl methacrylate onto starch was carried out in aqueous medium using Ce(IV)–glucose initiator in the temperature range 40–60°C. Effects of concentration of Ce(IV), glucose, H₂SO₄, monomer, and starch on grafting were investigated. Percentages of grafting were evaluated and compared. The overall energy of activation was calculated from the effects of time and temperature of polymerization. The reaction mechanism was also discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 981–990, 2004     

Polymerization of acrylamide initiated by the redox system Ce(IV)-4,4′-azobis (4-cyano pentanol)

Summary Acrylamide was polymerized by eeric ion Ce (IV)-4,4-azobis(4-cyano pentanol)(ACP) redox pair in aqueous nitric acid under nitrogen atmosphere. The rate of polymerization is proportional to [M]²,[ACP] and [Ce(IV)]^–1. Termination mechanism which was exclusively linear offered one azo group per polymeric chain. The obtained polyacrylamide can be used as a water soluble initiator for vinyl polymerization.     

The manganic hydroxide–hydrazine hydrate system as an initiator of vinyl polymerization

The reaction of hydrazine hydrate with manganic hydroxide and its application to the solution polymerization of methyl methacrylate has been studied. The kinetic evidence suggests that the hydrazine and the monomer are both adsorbed on the surface of the manganic hydroxide sol and that the decomposition of the hydrazine and the polymerization of the methyl methacrylate follow zero-order kinetics. The rate of polymerization increases slowly with increasing temperature, the activation energy for the polymerization being 4.9 ± 0.2 kcal/mole.     

Kinetic study of aqueous polymerization of methyl methacrylate initiated by Ce(IV)-maltose redox system

Polymerization of methyl methacrylate initiated by ceric ammonium nitrate-maltose has been investigated in aqueous nitric acid under nitrogen in the temperature range 20.5-35°C. The dependence of the initial rate of polymerization and the initial rate of ceric ion consumption on maltose, Ce(IV), and monomer concentrations has been determined. The reaction orders were found to depend on ceric ion concentration. At a moderately high Ce(IV) concentration (1 × 10^?3mol litre^?1) the orders were 1/2 and 3/2 with respect to maltose and monomer concentration, respectively, and independent of Ce(IV) concentration. But at a low Ce(IV) concentration (4 × 10^?4mol litre^?1) the orders with respect to monomer and Ce(IV) changed to 1 and 1/2, respectively. The effect of temperature was also examined. The average molecular weight, as determined by size-exclusion chromacography, was found to depend on maltose, Ce(IV), and monomer concentrations, as well as on temperature.     

A study of the Ce(III)/Ce(IV) redox couple for redox flow battery application

In this study, the electrochemical behavior of the Ce(III)/Ce(IV) redox couple in sulfuric acid medium with various concentrations and the influence of the operating temperature were investigated. A change of the concentration of sulfuric acid mainly produced the following two results. (1) With an increase of the concentration of sulfuric acid the redox peak currents decreased. (2) The peak potential separation for the redox reactions increased with rising concentration of sulfuric acid from 0.1 to 2 M and then decreased with further increase of the concentration. Elevated temperature was electrochemically favorable for Ce(III)/Ce(IV) couple, which caused an increase of the peak currents for the redox reactions and a decrease of the peak potentials separation. Constant-current electrolysis shows that the current efficiency was 73% for the oxidation process of Ce(III) and 78% for the reduction process at 298 K, and could be improved by elevating the temperature. The open-circuit voltage of the Ce-V cell, after full charging, remained constant at 1.870±0.005 V for more than 48 h, and is about 29% higher than that of the all-vanadium batteries. The coulombic efficiency was approximately 87%, showing that self-discharge of the Ce-V battery was small. The preliminary exploration shows that the Ce(III)/Ce(IV) couple is electrochemically promising for redox flow battery (RFB) application.     

Interactions between poly(acrylamide)–poly(itaconic acid) and cerium(IV)–nitrilotriacetic acid redox pair in the synthesis of acrylamide and itaconic acid homo‐ and copolymers

Homopolymers of itaconic acid (PIA) and its copolymers with acrylamide (P(IA‐AAm) were synthesized using ceric ammonium nitrate (NH₄)₂Ce(NO₃)₆ in combination with nitrilotriacetic acid (NTA) as redox initiator, and potassium persulphate at pH 1. The chain structures of the resulting products have been studied by FTIR spectroscopy. It is concluded from a comparison of spectroscopic results with gravimetric and viscometric data that the depressions in the yields and viscosity numbers in the case of Ce(IV)–NTA redox pair result from interactions between the constituents of the redox initiator and IA. Spectra of the insoluble and pale yellow precipitates, which are formed during the first 4 h of the reaction, after addition of Ce(IV) solution to the NTA and NTA–IA homogeneous solutions, also indicate the presence of various oxidation products. Furthermore, it is observed that H‐bonded homopolymer complex obtained from PAAm–PIA blends, prepared from aqueous solutions containing equal unit moles of each polymer, contain both ordered and defective structures. © 2001 Society of Chemical Industry     

Ce(III)/Ce(IV) in methanesulfonic acid as the positive half cell of a redox flow battery

The characteristics of the Ce(III)/Ce(IV) redox couple in methanesulfonic acid were studied at a platinum disk electrode (0.125 cm²) over a wide range of electrolyte compositions and temperatures: cerium (III) methanesulfonate (0.1–1.2 mol dm⁻³), methanesulfonic acid (0.1–5.0 mol dm⁻³) and electrolyte temperatures (295–333 K). The cyclic voltammetry experiments indicated that the diffusion coefficient of Ce(III) ions was 0.5 × 10⁻⁶ cm² s⁻¹ and that the electrochemical kinetics for the oxidation of Ce(III) and the reduction of Ce(IV) was slow. The reversibility of the redox reaction depended on the electrolyte composition and improved at higher electrolyte temperatures. At higher methanesulfonic acid concentrations, the degree of oxygen evolution decreased by up to 50% when the acid concentration increased from 2 to 5 mol dm⁻³. The oxidation of Ce(III) and reduction of Ce(IV) were also investigated during a constant current batch electrolysis in a parallel plate zinc–cerium flow cell with a 3-dimensional platinised titanium mesh electrode. The current efficiencies over 4.5 h of the process Ce(III) to Ce(IV) and 3.3 h electrolysis of the reverse reaction Ce(IV) to Ce(III) were 94.0 and 97.6%, respectively. With a 2-dimensional, planar platinised titanium electrode (9 cm² area), the redox reaction of the Ce(III)/Ce(IV) system was under mass-transport control, while the reaction on the 3-dimensional mesh electrode was initially under charge-transfer control but became mass-transport controlled after 2.5–3 h of electrolysis. The effect of the side reactions (hydrogen and oxygen evolution) on the current efficiencies and the conversion of Ce(III) and Ce(IV) are discussed.     

Graft copolymerization of methyl methacrylate onto jute fiber initiated by cerium(IV)–DMSO redox initiator system

The kinetics of graft copolymerization of methyl methacrylate (MMA) onto chemically modified jute fibers initiated by the Ce(IV)–DMSO redox system was studied in the temperature range of 40–60°C. By studying the effects of the concentration of the monomer, Ce(IV), and DMSO on the rate of grafting, the optimum conditions for grafting were determined. Also, the effect of temperature, time, concentration of the acid, the amount of jute fiber, and some inorganic salts and organic solvents on the rate was investigated. A kinetic scheme was proposed on the basis of the experimental findings. Infrared spectra of chemically modified jute and grafted jute was investigated. More than 120% of grafting could be achieved with the present system. The characterization of MMA-grafted chemically modified jute by TGA and DTA studies was made. The thermal stability of the jute fibers was improved by grafting. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2569–2576, 1998     

Aqueous polymerization of methyl methacrylate initiated by redox pair: Ce(IV)–Azo compounds with methylol functional groups and synthesis of copolymers

Hydroxyl functional azo compounds have been used as reducing agents in redox polymerization of methyl methacrylate (MMA) in conjuction with ceric ammonium nitrate (which acts as an oxidizing agent in aqueous nitric acid at 20°C). Kinetic measurements were followed by gravimetric method, at lower conversions, not exceeding 10% conversion. The dependence of rate of polymerization and average molecular weight, which was determined by gel permeation chromatography (GPC), on azo, Ce(IV), and MMA concentrations, respectively, were investigated. The homopolymers, which contain thermo-and photolabile azo groups, were utilized with different comonomers to give block or graft copolymers depending on termination mechanism of homopolymerization. © 1994 John Wiley & Sons, Inc.     

N,N′-Methylenebisacrylamide polymerization initiated by Ce(IV)—Malic acid redox system—A kinetic study

Free-radical-initiated linear cyclopolymerization of a symmetrical non-conjugated divinyl monomer, viz. N,N'-methylenebisacrylamide, was carried out using cerium sulphate as initiator and malic acid as activator, in an inert atmosphere at 25 ± 0.1°C. A gel-free polymer was formed under the experimental conditions. The order with respect to malic acid and monomer was found to be 1 and 2, respectively. The rate of polymerization was found to be inversely proportional to the concentration of Ce(IV). The overall energy of activation was found to be 25.5 kJ mol^?1. An intramolecular cyclization prior to propagation is proposed in formulating a suitable mechanism to explain the kinetic results.