Effect of amines on the ceric ion-initiated polymerization of vinyl monomers. II. Polymerization of acrylonitrile by ceric ion in presence of various substituted amines

The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate R_p is independent of ceric ion concentration and can be expressed by the equation: R_p = k₁ [amine] [monomer] + k₂[monomer]², where k₁ and k₂ are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.     

Graft polymerization kinetics of acrylamide initiated by ceric nitrate–dextran redox systems

The kinetics of the graft polymerization of acrylamide initiated by ceric nitrate—dextran polymeric redox systems was studied primarily at 25°C. Following an initial period of relatively fast reaction, the rate of polymerization is first-order with respect to the concentrations of monomer and dextran and independent of the ceric ion concentration. The equilibrium constant for ceric ion—dextran complexation K is 3.0 ± 1.6 l./mole, the specific rate of dissociation of the complex, k_d, is 3.0 ± 1.2 × 10^?4 sec.^?1, and the ratio of polymerization rate constants, k_p/k_t, is 0.44 ± 0.15. The number-average degree of polymerization is directly proportional to the ratio of the initial concentrations of monomer and ceric ion and increases exponentially with increasing extent of conversion. The initial rapid rate of polymerization is accounted for by the high reactivity of ceric ion with cis-glycol groups on the ends of the dextran chains. The polymerization in the slower period that follows is initiated by the breakdown of coordination complexes of ceric ions with secondary alcohols on the dextran chain and terminated by redox reaction with uncomplexed ceric ions.     

Mode of initiation in ceric salt initiated aqueous polymerization of methylmethacrylate

Summary The basic reaction for the production of initiating radicals in Ceric salt initiated polymerization of methylmethacrylate is strongly dependent on the acidity of the medium and independent of the nature of the anion associated' with the ceric ion. In moderately acid medium the primary reaction is the formation of hydroxyl radicals by ceric ion oxidation of water. When ceric sulfate is used as the initiator these hydroxyl radicals initiate the polymerization and appear as hydroxyl endgroups in the polymers. On the other hand, when ammonium ions are present, as in case of ceric ammonium sulfate initiator or ceric sulfate initiator in the presence of ammonium sulfate, some of the hydroxyl radicals generated in the primary reaction, react with the ammonium ions producing ammonium radicals and both hydroxyl and ammonium radicals act as the initiator giving rise to both hydroxyl and amine endgroups in the polymers. In strongly acid medium the basic initiating reaction changes into one in which the monomer transfers an electron to the ceric ion producing monomer radicals which initiate the polymerization and polymers with no endgroups are formed.

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Zusammenfassung Die Grundreaktion zur Erzeugung von Startradikalen aus Cersalz-initiierter Polymerisation von Methylmethacrylat ist von der Aciditäat des Mediums stark abhängig und unabhängig von der Natur des Anions, das mit den Cerionen assoziiert ist. Im mäßig sauren Medium besteht die primäre Reaktion in der Bildung von Hydroxylradikalen durch das Cerion auf Basis der Oxidation von Wasser. Wenn Cersulfat als Initiator verwendet wird, starten die Hydroxylradikale die Polymerisation und erscheinen als Kettenendgruppen. Andererseits, bei Gegenwart von Ammonium, wie im Falle des Cerammoniumsulfats oder Cersulfats in Gegenwart von Ammoniumsulfat, reagieren einige der Hydroxylradikale in primärer Reaktion mit den Ammoniumionen und erzeugen Ammoniumradikale, und darn geben beide-Hydroxyl-und Ammoniumradikale - als Initiatoren Anlaß für Hydroxyl-und Aminendgruppen der Hydroxylketten. In stark saurem Medium verändert sich die Startreaktion in eine andere, in der Monomere ein Elektron an das Cerion transferieren und hierdurch Monomerradikale erzeugen, die die Polymerisation starten und Polymere ohne Endgruppen bilden.

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With 5 tables     

Aqueous polymerization of ethyl acrylate initiated by ceric ion-reducing agent system in sulphuric acid medium

Kinetic study of aqueous polymerization of ethyl acrylate (EA) is carried out at 30 °C in dilute sulphuric acid medium by employing ammonium ceric sulphate–methyl ethyl ketone (MEK) as redox initiator system. The ceric ion consumption is found to be first order with respect to ceric ion and half order with respect to reducing agent concentrations. No complex formation between ceric ion and reducing agent is observed. The orders with respect to ceric ion, reducing agent and monomer concentrations are evaluated for the aqueous polymerization of EA by Ce(IV)–MEK redox initiator system, and are found to be 0.5, 0.5 and 1.4, respectively . The overall activation energy, E _overall, for aqueous polymerization of EA in the temperature region of 27–40°C is found to be 20.27 kJ/mol. A kinetic scheme for the aqueous polymerization of EA initiated by Ce(IV)–MEK redox initiator system is presented.This revised version was published online in June 2005 with corrections to figure legends as well as small corrections within text.     

The mechanism of consumption of ceric salt with cellulosic materials

Efforts were made in the present study to elucidate the mechanism of graft copolymerization of cellulose in the presence of a ceric salt as initiator. When cellulose is treated with an aqueous solution of the ceric salt, ceric ion is consumed in a roughly first-order reaction in the oxidation of cellulose and in the adsorption on cellulose, and the ratio of the rate constants of oxidation and adsorption is about 1:3 in the case of sulfite pulp. Ceric ion is adsorbed so strongly on cellulose as not to be readily desorbed by treatment with water, dilute acid, or dilute alkali. The number of moles of adsorbed ceric ion was approximately equal to the number of moles of the total carbonyl groups in the cases of cotton and sulfite pulp, which are low in hemicellulose content, and was several times as large in the cases of kraft pulp and semichemical pulp, which contain about 22% hemicellulose. In these samples, however, it was interesting to note that the amount of the adsorbed ceric ion was roughly equal to the amount consumed in oxidation. Cellulose on which ceric ion is adsorbed reacts with methyl methacrylate to yield graft copolymers; a higher molecular weight of grafts, smaller number of grafts, and lower graft efficiency than in a standard polymerization were observed. Since the stability of the adsorbed ceric ion is high, a contribution of the adsorbed ceric ion to the graft copolymerization appears small, and the oxidation reaction, which proceeds slightly more slowly than adsorption, seems more important to the graft copolymerization.     

Kinetic studies of nonaqueous polymerization of methyl methacrylate initiated by ferric laurate–n-hexyl amine system

The polymerization of methyl methacrylate was studied in carbon tetrachloride medium with ferric laurate, a metal soap, in combination with n-hexyl amine as the initiator system at 60°C. The rate of polymerization was found to be linear with the monomer concentration and proportional to the square root of both ferric ion and amine concentration. A reaction scheme involving initial complex formation between ferric ion and amine and subsequent reaction of the complex with the solvent molecule to produce free radicals responsible for initiation of polymerization has been postulated to account for the observed results.     

Polymerization of acrylamide initiated with pinacol–ceric ion redox system

Polymerization of acrylamide initiated with a pinacol–ceric ion redox system was investigated. The polymer obtained was found to contain one cerium atom in a polymer molecule. It was considered that the cerium atom was introduced into the polymer molecule by the termination reaction as there is no cerium atom in the initiating radical in the present system. A similar termination reaction was attained by ferric ion but not by cerous ion. The metal ion was considered to terminate the polymerization to form a stable polymer. Some considerations on the structure of the reaction product relating to the polymerization mechanism were discussed.     

Relationship between reduction of ceric ion with poly(vinyl alcohol) and graft copolymerization

Various poly(vinyl alcohol) samples were preliminarily subjected to oxidation treatment with sodium hypochlorite, and the reduction of ceric ion and subsequently initiation in the graft copolymerization in the system containing methyl methacrylate were investigated. The reduction behavior of ceric ion could be subdivided into three parts, each of different reaction rate. In the initial stage of the reaction, there was observed rapid cleavage of the backbone chain of poly(vinyl alcohol) with ceric salts. The amount A of cleavage was proportional to the amount of ceric ion reduced at the initial fastest rate for various samples of different extents of oxidation; cleavage of 1 mole required ca. 10 moles of reduction of ceric ion. Higher carbonyl contents of the sample caused increased A. Graft polymerization was carried out in the same system with the addition of the monomer. The amounts of grafted chains produced were determined, and approximately one mole of grafted chains was obtained for per mole of cleavage. The copolymer is concluded to be blocklike in structure. The contribution of the carbonyl groups in poly(vinyl alcohol) sample to the initiation of the polymerization should be emphasized.     

Polymerization of acrylamide with ceric ion–malic acid redox pair

The polymerization of acrylamide (M) in aqueous sulfuric acid medium initiated with ceric ammonium sulfate–malic acid redox pair was investigated at 35 ± 0.2°C under nitrogen atmosphere. The initiation was caused by the free radical generated by the decomposition of the complex formed between ceric ion and malic acid (MA). The rate of monomer disappearance was proportional to the first power of malic acid, ceric ion, and monomer concentrations at lower ceric ion concentrations. However, at higher ceric ion concentrations the rate was independent of [Ce(IV)]. The rate of ceric ion disappearance was proportional to [MA] and [Ce(IV)] but independent of [M] at lower ceric ion concentrations. The activation energy was found to be 57.74 kJ/mol. Sulfuric acid retarded the reaction. Molecular weights increased with increasing [M] and decreasing [Ce(IV)].     

Polymerization of acrylonitrile initiated by ceric ion–citric acid redox system

Heterogeneous polymerization of acrylonitrile initiated by ceric ammonium sulfate–citric acid (C.A.) redox system is reported at 35 ± 0.2°C under nitrogen atmosphere. The rate of monomer disappearance is found to be proportional to [C.A.]⁰, [Ce⁴⁺]^0.63, and [Monomer]^1.59. The rate of ceric ion disappearance is directly proportional to ceric ion concentration but independent of monomer concentration. The initial rate was independent of [H₂SO₄]. The molecular weight of polyacrylonitrile increases with increasing monomer concentration and decreasing ceric ion concentration. Activation energy was found to be 27.9 kJ/mol.     

The role of ceric ion in vinyl polymerization and graft copolymerization

Six kinds of new ceric ion redox initiation systems for vinyl radical polymerization and two kinds of macromolecule graft copolymerization by ceric ion have been briefly reviewed in this paper. The initiators include ceric ion/acetanilide, ceric ion/alkyl phenylcarbamate, ceric ion/4-methoxysuccinyltoluidine, ceric ion/aliphatic aldehyde, ceric ion/aromatic aldehyde, ceric ion/diketone systems. Macromolecules such as poly(ether-urethane) and macromolecules having active pendant groups were selected for graft copolymerization with acrylamide initiated by ceric ion.     

Aqueous polymerization of methyl methacrylate initiated by the redox system Ce(IV)–isopropyl alcohol. Kinetics and molecular weight

Polymerization of methyl methacrylate was carried out in aqueous nitric acid in the temperature range 26–40°C, with the redox initiator system ceric ammonium nitrate–isopropyl alcohol. A short induction period was observed, as well as the attainment of a limiting conversion, and the total ceric ion consumption with reaction time. The reaction orders were 1/2 and 3/2 with respect to the IPA and monomer concentration, respectively, within the range (3–5) × 10^?3M of Ce(IV). But at lower Ce(IV) concentration (≤ 1 × 10^?3M), the order with respect to monomer and Ce(IV) changed to 1 and 1/2, respectively. The rate of ceric ion disappearance was first order with respect to Ce(IV) concentration and (R_Ce)^?1 was proportional to [IPA]^?1. Both the rate of polymerization and the rate of ceric ion consumption increase with rise in temperature. The average-molecular weight can be controlled by variations in IPA, Ce(IV), and monomer concentrations, and in temperature. A kinetic scheme involving oxidation of IPA by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by bimolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included.     

Polymerization of acrylonitrile initiated by ceric ion-organic sulphur compounds reducing agent systems

Polymerization of acrylonitrile was investigated using ceric ion-organic sulfur compounds reducing agent systems. The organic sulphur compounds used as the reductants are, thiourea, thioacetamide, 2-amino ethanethiol, cysteine, and thioglycolic acid. The rates of polymerization were measured within the temperature range of 25 to 40 °C. The initiation was by the radical produced from Ce⁴⁺-sulphur compounds reaction. The rate of monomer disappearance was proportional to [M]^1.5, [S]^0.5 and the rate of ceric disappearance was directly proportional to [S] and [Ce⁴⁺]. A kinetic scheme involving the initiation by the primary radical and termination of the growing polymer radicals by the mutual type has been suggested and the kinetic percentage have been evaluated.     

Polymerization of Acrylonitrile with Ceric lon-2-Propanethiol as Initiator System

The kinetics of the polymerization of arylonitrile with ceric ammonium sulfate in the presence of 2-propanethiol as the redox initiator system in aqueous solution has been investigated. The rate of polymerization was found to be proportional to the square root of both ceric ion and thiol concentrations, and the monomer exponent was close to 1.5. Spectral studies indicated that there is a complex formation between ceric ion and the monomer acrylonitrile. A kinetic scheme, based on initial formation of this complex and its subsequent reaction with the thiol to produce the free radicals (RS.) responsible for initiation has been postulated to account for the observed results. The activation energy and different kinetic and transfer constants for the system have also been evaluated.     

On the oxidation of malonic acid by ceric ions

The oxidation of malonic acid by ceric ions has been investigated in sulfuric acid solution under a variety of conditions. The initial rate at low ceric ion concentrations is first order in each of the two reactants and has an activation energy of 11.6 kcal/mol; the instantaneous rate constant increases somewhat with time during a single run. At higher concentrations of ceric ion, semilogarithmic plots are sigmoid with a reduced rate constant at long times. The rate decreases slightly with increasing sulfuric acid concentration. Rates of carbon dioxide evolution may be much less than rates of ceric ion reduction because of supersaturation effects. The observations can be explained if dissolved oxygen reacts with organic radicals to catalyze the rate of initial attack on malonic acid, but oxygen must also be consumed irreversibly during these reactions. Computations with plausible rate constants have simulated the experimental observations. These oxygen effects can rationalize peculiar almost discontinuous changes in rate when bromomalonic acid is oxidized by ceric ion. These effects may also explain the previously puzzling observation that some Belousov–Zhabotinsky solutions are oscillatory in bulk but become quiescent but excitable when spread in a thin film in contact with air.     

Vinyl polymerization initiated by ceric ion reducing agent systems in sulfuric acid medium

Polymerization of the monomers, methyl acrylate (MA) and methyl methacrylate (MMA) was carried out in sulfuric acid medium at 15°C. With the redox initiator system, ceric ammonium sulfate–malonic acid. There was no induction period, and a steady state was attained in a short time. There was found to be no polymerization even after 1 hr. in the absence of the reducing agent R. The initiation was by the radical produced from the Ce⁴⁺–malonic acid reaction. The rate of monomer disappearance was proportional to [M]^1.5, [R]^0.5, and [Ce⁴⁺]^0.3–0.5, and the rate of ceric disappearance was directly proportional to [R] and [Ce⁴⁺]. Chain lengths of the polymers were directly proportional to [M] and inversely to [R]^1/2 and [Ce⁴⁺]^1/2. The experimental results were explained by a kinetic scheme involving the following steps: (a) oxidation of the substrate to give the primary radical which reacts with Ce⁴⁺ to give the products, (b) initiation by the primary radical, (c) propagation, and (d) termination of the growing polymer radicals by the mutual type. For the polymerization of acrylonitrile (AN) by the redox system, ceric ammonium sulfate–cyclohexanone (CH), in sulfuric acid at 15°C., the scheme was modified to include linear type of termination by Ce⁴⁺, along with the mutual termination to explain the results especially under conditions with [Ce⁴⁺] ≥ [CH].     

Aqueous polymerization of methyl methacrylate initiated by Ce(IV)–alcohol redox systems: Effect of acid concentration and additives

Polymerization of methyl methacrylate (MMA) initiated by ceric ammonium nitrate in combination with alcohols, isopropyl and, isobutyl alcohol, has been studied in aqueous nitric acid. The effect of nitric acid and nitrate ion concentrations on the initial rate of polymerization as well as on that of ceric ion consumption and on polymer molecular weight has been investigated. The rate of polymerization initially rapidly to a maximum with increasing nitric acid concentration at constant nitrate ion concentration, and then, decreased at higher acid concentrations. The rate of ceric ion consumption increased on increasing the acid concentration. A fall in both the rates was observed as the nitrate ion concentration increased, and when acid concentration was kept constant. Average-molecular weights decreased with increasing the acid concentration; whereas they increased with increasing that of nitrate ion. The effect of certain water-miscible organic solvents has also been studied. Both the rates increased in their presence, whereas the molecular weight underwent a decrease     

Studies on the kinetics of ceric-thiourea initiated aqueous polymerization of methyl methacrylate—II. Mechanistic features in strongly acid solutions

The kinetics of ceric-thiourea initiated aqueous polymerization of methyl methacrylate in 1 M H₂SO₄ have been studied. Ceric ion and thiourea initially form an 1:1 complex which then reacts with uncomplexed ceric ion to form the initiating thiocarbamido radicals. The termination is predominantly biomolecular below an initial ceric concentration of 0.66 × 10^?2 M (depending upon the rate of initiation). At higher initial ceric concentrations, polymer radicals are terminated overwhelmingly by ceric ions. Substituted thioureas reduce the rate of polymerization according to the order of increasing electron density on the sulphur atom. The overall activation energy of polymerization is 12.1 kcal/mol in the region of bimolecular termination and 10.2 kcal/mol in the region of metal ion termination.     

Studies of the graft copolymerization of methyl methacrylate by means of the photochemical reduction of ceric ion adsorbed on cellulosic materials

It was observed that the rate of reduction of ceric ion adsorbed on cellulose was remarkably accelerated by irradiation with ultraviolet light, and this behavior depended upon the kind of cellulose. When the graft copolymerization of methyl methacrylate on cellulose with adsorbed ceric ion was carried out by irradiation with ultraviolet light, the percent grafting decreased for softwood, bleached sulfite pulp and increased for hardwood semichemical pulp. The average molecular weight of the grafts was observed generally to decrease. If it is assumed that the ceric ions, which are reduced at an accelerated rate in the early stages of reaction with SCP, do not participate in the graft formation, a relation is observed between the modified amount of reduced ceric ion and the number of grafted chains formed, and the molar ratios of these quantities are 12:1 without irradiation and 75:1 to 100:1 with irradiation. Even when the rate of reduction of ceric ion is accelerated, the increase in the number of grafted chains is found to be very small.     

Grafting vinyl monomers to starch by ceric ion. I. Acrylonitrile and acrylamide

Studies were carried out on the grafting of acrylonitrile (AN) and acrylamide (AA) to starch by ceric ion. The variables affecting the grafting of AN and AA were investigated with granular wheat starch dispersed in aqueous N,N-dimethylformamide and ceric ammonium nitrate as catalyst. Results showed that the concentrations of monomer and catalyst are the major factors influencing the grafting of AN; thus the monomer content of the grafts can be regulated by these variables. The grafting of AA is also influenced by these variables, but to a much less degree. Increasing concentrations of monomer promote homopolymerization and increasing concentration of catalyst inhibit grafting. The extent of grafting of this monomer can best be controlled by reaction time. Under the most favorable conditions, maximum grafting efficiency (ratio of amount of grafted monomer to total amount of monomer converted to polymer) was 87% for AN and 43.8% for AA. Although the monomer content of the AN grafts was higher than that of AA grafts prepared under identical conditions, the number of branches in the grafts was almost the same; only the length of the branches was different. The AN-starch grafts have branches of higher molecular weight.