Study of the morphology of poly(methyl methacrylate) as polymerized by the redox system Ce(IV)–isopropyl alcohol

Methyl methacrylate has been polymerized in aqueous nitric acid at 30°C, with the redox system ceric ammonium nitrate–isopropyl alcohol as initiator. The gravimetric method has been used to follow the reaction. After a short induction period polymerization started, and conversion attained a maximum value with extent of reaction, whereas the ceric ion is exhausted. The size, distribution, and number of PMMA particles formed were measured by scanning electron microscope. From the electron micrographs it was found that the particles are formed over a short period, and that the particle size distribution seems to be determined by flocculation and coagulation of the particles, because these are not stabilized. Average-molecular weight was found to increase at high conversions and the molecular weight distribution became broader as particle size increased. Particle size increased with conversion, whereas the number of particles remained constant.     

Graft Copolymerization of 4-Vinylpyridine Onto Partially Carboxymethylated Cellulose. the Degree of Substitution Effect

The graft copolymerization of 4-vinylpyridine (4-VP) onto partially car-boxymethylated cotton (PCMC), having different carboxymethyl contents, was investigated. Under similar reaction conditions, both the graft yield and eerie ion consumption increased by increasing the degree of substitution of carboxymethyl groups of PCMC up to a value of 0.11, beyond which grafting and Ce(IV) consumption decreased. Proof for grafting onto PCMC was provided through IR analysis. the eerie salt-initiated polymerization of 4-VP in the absence of PCMC was also studied. Three series of homo-polymerization reactions of 4-VP directly initiated by eerie ammonium nitrate were carried out with varying reaction times. Each series was run at a different nitric acid concentration. Both conversion and eerie ion consumption, as well as molecular weight, increased with reaction time. Increasing the nitric acid concentration increased both conversion and eerie ion consumption while the molecular weight decreased.     

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.     

PHOTOSENSITIVITY OF Ce (Ⅳ) INITIATED METHYL ACRYLATE POLYMERIZATION

The influences of UV light irradiation (313 nm) and diffused daylight on the polymerization of methyl acrylate initiated by the ceric ammonium nitrate without any reducing agent have been studied both in aqueous nitric acid and in pure water. The rate of polymerization was found to be accelerated and the overall activation energy and the induction time were found to be decreased sharply by the UV light irradiation. Under UV light, the rate of polymerization is 8 times as high as the rate in dark. The rate of polymerization was found to attain a maximum with the increase of nitric acid concentration and the rate of polymerization became less sensitive to UV light in the presence of nitric acid whereas the induction period reduced outstandingly. Based on the experimental results, the mechanism is proposed.     

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.     

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.     

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.     

Highly branched acrylamide graft copolymer

Acrylamide graft copolymerization onto poly(3-O-methacryloyl D -glucose) (PMG) as a backbone was performed by the ceric ion method. The number of polyacrylamide (PAM) chains grafted was dependent upon the concentration ratio of the redox catalyst system at constant acid concentration and increased in proportion to the ceric ion concentration. A maximum number of grafts obtained, for example, was 29 onto PMG (DP = 244) under the conditions [Ce⁴⁺]/[PMG] = 1/5, [H⁺] = 1.0 × 10^?2 mole/l. In other words, the graft frequency was 12 per 100 monomer units of PMG. Such a high frequency of the grafts was, however, greatly decreased when the acid concentration was increased. Characteristics of the highly branched structure were revealed by the relationship between intrinsic viscosity and graft frequency, which showed a downward curvature with the increasing graft frequency. Influences of acid and ceric ion concentrations on the copolymerization were kinetically evaluated. The rate of polymerization was found to be first-order with respect to ceric ion and proportional to the square of the reciprocal acid concentration. The result suggests that the graft frequency is dependent upon the rate of polymerization.     

Cerium (IV)-2-chloroethanol redox-pair initiated polymerization of acrylamide in aqueous medium

The kinetics of acrylamide polymerization has been investigated by employing cericammoniumnitrate-2-chloroethanol redox pair under nitrogen atmosphere at 30 ± 1°C. The rate of monomer disappearance is directly proportional to the concentration of 2-chloroethanol (1.0 × 10^?2 ? 10.0 × 10^?2 mol. dm^?3) and is inversely proportional to the ceric ion concentration (2.5 × 10^?3 ? 10.0 × 10^?3 mol. dm^?3) but shows square dependence to the concentration of monomer (5.0 × 10^?2 ? 25.0 × 10^?2 mol. dm^?3). The rate of ceric ion disappearance is directly proportional to the initial concentration of ceric ion and 2-chloroethanol but independent of acrylamide concentration. The viscometric average molecular weight (M _v) decreases on increasing the concentration of ceric ion and increases on increasing the concentrations of acrylamide and 2-chloroethanol. A tentative mechanism has been proposed.     

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)].     

Aqueous polymerization of acrylamide initiated by cerium (IV)–ethylenediamine tetraacetic acid redox system

Ethylenediamine tetraacetic acid (EDTA) terminated polyacrylamide was obtained by using the EDTA–cerium(IV) ammonium nitrate [Ce(IV)] redox initiator in the aqueous polymerization of acrylamide. The polymerization behaviors as a function of the concentration of Ce(IV), EDTA, and acrylamide as well as temperature were studied. The consumption rate of cerium(IV) depends a first-order reaction on the ceric ion concentration ([Ce(IV)]). The complex formation constant (K) and disproportionation constant (k_d) of Ce(IV)–EDTA chelated complex are 1.67 × 10⁴ and 3.77 × 10^?3, respectively. The rate dependences of polymerization on monomer concentration and EDTA concentration both follow a second-order reaction in the run of initial monomer concentration ([M]_i) equal to 0.2 mol dm^?3. The number average molecular weight increases linearly with the ratio of [M]_i/[Ce(IV)]_i. The mechanism and kinetics for the polymerization was proposed. The kinetic parameters involved were determined. © 1992 John Wiley & Sons, Inc.     

Vinyl Polymerization Initiated by Ceric Ion–Ethyl Cellosolve Redox System in Aqueous Nitric Acid

Abstract

Polymerizations of methyl methacrylate (MMA) and acrylonitrile (AN) were carried out in aqueous nitric acid at 30°C with the redox initiator system ammonium ceric nitrate-ethyl cellosolve (EC). A short induction period was observed as well as the attainment of a limiting conversion for polymerization reactions. The consumption of ceric ion was first order with respect to Ce(IV) concentration in the concentration range (0.2–0.4) × 10^?2 M, and the points at higher and lower concentrations show deviations from a linear fit. The plots of the inverse of pseudo-first-order rate constant for ceric ion consumption, (k ¹)^?1 vs [EC]^?1, gave straight lines for both the monomer systems with nonzero intercepts supporting complex formation between Ce(IV) and EC. The rate of polymerization increases regularly with [Ce(IV)] up to 0.003 M, yielding an order of 0.41, then falls to 0.0055 M and again shows a rise at 0.00645 M for MMA polymerization. For AN polymerization, R _p shows a steep rise with [Ce(IV)] up to 0.001 M, and beyond this concentration R _p shows a regular increase with [Ce(IV)], yielding an order of 0.48. In the presence of constant [NO^? ₃], MMA and AN polymerizations yield orders of 0.36 and 0.58 for [Ce(IV)] variation, respectively. The rates of polymerization increased with an increase in EC and monomer concentrations: only at a higher concentration of EC (0.5 M) was a steep fall in R _p observed for both monomer systems. The orders with respect to EC and monomer for MMA polymerization were 0.19 and 1.6, respectively. The orders with respect to EC and monomer for AN polymerization were 0.2 and 1.5, respectively. A kinetic scheme involving oxidation of EC by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by biomolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included.     

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.     

Anionic polymerization of 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane

In the first of a two-part series, a study has been made of the anionic polymerization of a five-membered cyclocarbosiloxane, 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane. The polymerization was initiated by lithium n-butyldiphenylsilanolate in the presence of tetrahydrofuran. The chemical shifts of the protons of the cyclic monomer and the polymer were found to be different, and therefore the rate of polymerization was obtained in an NMR spectrometer. The effects of varying the concentrations of THF, initiator, and water upon the rate of polymerization and upon the molecular weight and the molecular weight distribution were investigated. At a constant concentration of monomer and initiator, the rate of polymerization increased when the THF concentration was increased. At a constant concentration of monomer and THF the rate of polymerization reached a constant value when the initiator concentration was varied. The molecular weight and the molecular weight distribution were dependent upon the initiator to water ratio, whereas water concentration had little effect on the rate of polymerization. Essentially monodispersed polymers were obtained when the concentration of initiator was in large excess to that of water or vice versa. A bimodal distribution in molecular weight was obtained when the concentration of initiator was approximately equal to that of water. The apparent activation energy of polymerization was 12.7 kcal/mole.     

Grafting onto wool. I. Ceric ion-initiated grafting of poly(methyl acrylate) onto wool

Poly(methyl acrylate) has been grafted onto wool by using ceric ion as redox initiator in an aqueous medium. Initiation by ceric ammonium nitrate (CAN) was carried out in the presence of nitric acid of varying concentration at 35, 45, and 50°C for a period of 1.5 or 3 hr. Percent grafting was found to be dependent on concentrations of acid and monomer, reaction time, and temperature. Above 45°C, a considerable amount of homopolymer was formed; at 35°C, very little grafting of poly(methyl acrylate) was observed. Nitric acid catalyzed the reaction and a concentration of 0.17–0.19M HNO₃ was found suitable.     

Graft Copolymerizations of Polysaccharides. II. Acrylamide Grafting to Yellow Dextrin

Graft copolymers of acrylamide and yellow dextrin were prepared using cerium(IV) as initiator. The yellow dextrin had a very broad molecular weight distribution but was fractionated utilizing dialysis and ultrafiltration membranes. Initiator efficiencies were determined using size exclusion chromatography and were found to be between 2.4 and 34%. Initiator efficiency increased with acrylamide concentration at constant cerium (IV) and yellow dextrin concentrations, and decreased with increasing cerium(IV) concentration at constant acrylamide and yellow dextrin concentrations. Plots of acrylamide conversion and intrinsic viscosity vs initial acrylamide concentration at constant yellow dextrin and ceric ion concentrations showed a maximum at about 2.0 M.     

Ceric-ion-initiated grafting of methyl methacrylate onto (1 → 5)-α-D-ribofuranan and (1 → 5)-α-D-xylofuranan

We report herein studies of grafting of MMA onto (1 → 5)-α-D -ribofuranan and (1 → 5)-α-D -xylofuranan by ceric ion initiation both in water and in dimethyl sulfoxide (DMSO). In aqueous medium, the graft polymer having high grafting (%) can be obtained easily without adding any nitric acid. The degradation of polysaccharide by the acidic ceric ion solution is not serious; 73–82% of its original molecular weight remained after the polymerization. In DMSO, graft polymers having lower grafting (%) and lower molecular weight of grafts were obtained.     

PHOTOSENSITIVITY OF CERIC ION INITIATED ACRYLAMIDE POLYMERIZATION

Polymerization of acrylamide initiated by ceric ammonium nitrate alone has been studied in aqueous medium. The effects of UV light irradiation on the initial rates of polymerization, the activation energy and on the polymer molecular weights have been investigated. Compared with that in the dark, the rate of polymerization under UV light was accelerated to eleven times higher, and the overall activation energy was lowered markedly.     

Component activities in the system thorium nitrate-nitric acid-water at 25°C

The equilibrium composition of the vapor above thorium nitrate-nitric acid-water mixtures has been studied as a function of the concentrations of thorium nitrate and nitric acid using a transpiration technique. At 25°C, the thorium nitrate concentrations m _T ranged from 0.1 to 2.5 molal and the nitric acid concentrations m _N from 0.3 to 25 modal. The vapor pressure of the nitric acid was found to increase with increasing thorium nitrate concentration for a constant molality of nitric acid in aqueous solution. At constant m _T , the nitric acid vapor pressure was particularly enhanced at low nitric acid concentrations. The water vapor pressures decreased regularly with increasing concentrations of both nitric acid and thorium nitrate. The experimental data were fitted to Scatchard's ion-component model, and to empirical multiparameter functions. From the fitting parameters, and available literature data for the nitric acid-water and thorium nitrate-water systems at 25°C, expressions were calculated for the variation of water and thorium nitrate activities, as functions of the nitric acid and thorium nitrate concentrations, using the Gibbs-Duhem equation. Calculated values for the thorium nitrate activities were strongly dependent on the form of the function originally used to fit the vapor pressure data.Issued as AECL-7461.     

Water-Soluble Copolymers. II. Synthesis and Characterization of Model Dextran-g-Acrylamides by Ce(lV)/HNO3-lnduced Initiation

In order to develop polymers useful as mobility control agents in enhanced oil recovery processes, water-soluble acrylamide grafted polysaccharide copolymers have been synthesized in water at 25° C using a ceric ammonium nitrate/nitric acid system. The effects of varying concentrations of ceric ion, monomer, and substrate on conversion, graft length, and molecular structure of the reaction products have been examined. The crude reaction products were purified by fractional precipitation and then were analyzed for nitrogen content using a micro-Kjeldahl method. The chemical structures of the graft copolymers were studied by selective hydrolysis of the carbohydrate backbones. Intrinsic viscosity and grafting length data were used to predict solution behavior of the graft copolymers prepared under controlled conditions. Aqueous size exclusion and viscosity studies showed direct correlations between hydrodynamic volume and length of the polyacrylamide side-chain grafts.