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].     

Polymerization of Methacrylamide Initiated by Ceric Ion-Citric Acid Redox System

Homogeneous polymerization of methacrylamide initiated by the ceric ammonium sulfate-citric acid (CA) redox pair has been investigated and reported 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 citric acid. The rate of monomer disappearance was found to be proportional to [CA]^0.4, [Ce^0.4+]^0.65, and [Monomer]¹ The rate of ceric ion disappearance was directly proportional to the ceric ion concentration but independent of the monomer concentration. The initial rate was independent of [H₂SO₄]. The activation energy of the system was found to be 21.4 kJ/mol.     

Aqueous Polymerization of Acrylamide Initiated by Glycolic Acid/Ce4+ Redox System

The aqueous polymerization of acrylamide initiated by the glycolic acid/Ce⁴⁺ redox system was studied in sulfuric acid medium at 35 ± 0.2°C under a nitrogen atmosphere. The initiation was carried out by the free radical generated in the decomposition of the complex formed between the oxidant and the reductant. The monomer disappearance was found to be proportional to [GA]^0,89[Ce⁴⁺]^0.57[M]^1.0, and the rate of ceric ion disappearance was found to be directly proportional to [Ce⁴⁺] and [GA] but independent of [M]. The activation energy of the system was found to be 7.21 kcal/deg/mol. The molecular weight of polyacrylamide increased with increasing [monomer] and decreased with increasing [catalyst]. The effect of pH was also studied in the pH range 2.22 to 1.44.     

Aqueous polymerization of methacrylic acid initiated by Ce4+ -glycolic acid redox pair

The aqueous polymerization of methacrylic acid (MAA) initiated by a Ce⁴⁺ -glycolic acid (GA) system was observed in a sulfuric acid medium at 35 ± 0.2°C in a nitrogen atmosphere. The rate of monomer disappearance was proportional to [MAA]¹ and the rate of ceric ion disappearance was proportional to [GA][Ce⁴⁺]. An increase in the reaction temperature from 30 to 45°C raised the rate and the overall activation energy was 63 kJ/mol. The molecular weight increased with a rise in [MAA] and a reduction in [Ce⁴⁺]. The effect of varying [H₂SO₄] was also studied.     

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.     

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.     

Aqueous Polymerization of Methyl Methacrylate Initiated by Ce4+-Glycolic Acid Redox System

The aqueous heterogeneous polymerization of methyl methacrylate (MMA) initiated by the Ce⁴⁺-glycolic acid (GA) redox system was studied at 35 × 0.2°C under a nitrogen atmosphere. The rate of monomer disappearance was proportional to [MMA]¹[GA]¹[Ce⁴⁺]°, and the rate of eerie ion disappearance was found to be directly proportional to [Ce⁴⁺] and [GA] but independent of [MMA]. The activation energy was found to be 34 kJ/mol. The molecular weight of polymethyl methacrylate increased with increasing [MMA] and decreased with increasing [oxidant]. The effect of increasing [H₂SO₄] on polymerization was also studied. The results are compared with those obtained for the aqueous homogeneous polymerization of acrylamide with the same redox pair.     

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)].     

Coordinated radical polymerization and redox polymerization of acrylamide by ceric ammonium nitrate

The ceric salt-initiated polymerization on acrylamide and graft copolymerization of acrylamide onto cellulose were studied. The mechanism of the ceric salt-initiated polymerization of acrylamide in the homopolymerization system can be explained by a radical mechanism based upon Ce⁴⁺-coordinated acrylamide, and the mechanism of the ceric salt-initiated graft copolymerization of acrylamide onto cellulose can be explained in two ways: a free-radical mechanism with the ceric—cerous redox system, and a radical mechanism based upon Ce⁴⁺-coordinated acrylamide. The velocities of initiation, propagation, and termination in the redox mechanism are quite different from those in the coordinated radical mechanism. From the infrared absorption and nuclear magnetic resonance spectra measurements it is concluded that the structure of the ceric-coordinated acrylamide is the π-complex.     

Vinyl polymerization of acrylonitrile by the Ce(IV)-glucose redox system

Aqueous polymerization of acrylonitrile (M) initiated by the Ce(IV)-glucose (R) redox system has been studied under nitrogen in the temperature range of 30–40 °C. The rate of polymerization (Rp) is proportional to [M]², [R] and inversely proportional to [Ce(IV)]. The rate of ceric ion disappearance is proportional to [R] and [Ce(IV)]. The end group in the polymer is characterised by IR spectra. A suitable kinetic scheme has been proposed and explained in the light of these experimental findings.     

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.     

Vinyl polymerization: Kinetics of Ce(IV)–acetophenone-initiated polymerization of acrylonitrile in acetic–sulfuric acid mixtures

The polymerization of acrylonitrile (M) initiated by the Ce(IV)–acetophenone (AP) redox pair has been studied in acetic–sulfuric acid mixtures in a nitrogen atmosphere. The rate of polymerization is proportional to [M]^3/2, [AP]^1/2 and [Ce(IV)]^1/2. The rate of disappearance of ceric ion,–R_Ce, is proportional to [AP], [M], and [Ce(IV)]. The effect of certain salts, solvent, acid and temperature on both the rates have been investigated. A suitable kinetic scheme has been proposed, and the composite rate constants k_p ²(k/k/_t) and k₀/k_i are reported.     

Grafting of Methyl Acrylate onto Cellulose by Ceric Ion

Abstract

Methyl acrylate was grafted onto dissolving pulp by ceric ion in aqueous sulfuric acid under oxygen-free argon. At a low Ce(IV) concentration (up to 1 mmol/L), the rate of polymerization (R_p ) is proportional to [Ce]^0.5 [MA]¹ [cellulose]¹. At higher concentrations of cericion (1–20 mmol/L), R_p is proportional to [Ce]⁰ [M] ^1.5 [cellulose]¹. The mechanism of grafting is consistent with a kinetic scheme involving initiation by primary radicals and termination by growing polymer radicals. Above 20 mmol/L of ceric salt, the data are consistent with the linear termination mode.     

Kinetics of Aqueous Polymerization of Acrylamide Initiated by Ceric Ammonium Sulfate/2-Mercaptoethanol Redox System

Polymerization of acrylamide monomer, initiated by the redox system involving acidified ceric ammonium sulfate and 2-mercaptoethanol (2-ME) was carried out in an aqueous medium at 25° C. White, rigid polyacrylamide, isolated under controlled experimental conditions, showed a molecular weight of 1.5 × 10⁴ from viscosity measurements. The rate of monomer (M) conversion to polymer was found to be proportional to [M]^1.5, [2-ME]^0.5, and [Ce(IV)]^0.4. Further, the rate of disappearance of ceric ion was observed to be directly proportional to [2-ME] and independent of [M] in the range of 0.16–0.48 mole/liter. The explanation of the above proportionalities is given in terms of a proposed reaction mechanism. Values of the usual rate constants, k_r, k₀/k_t and k_t./k_p ^½ have been computed.     

Redox-Initiated Polymerization of Methyl Methacrylate

The redox-initiated polymerization of methyl methacrylate (MMA) by the Ce(IV)-malic acid system has been carried out in aqueous medium under an inert atmosphere. The rate of polymerization was found to be proportional to [MMA]^3/2 [MA]^1/2 [Ce(IV)]^1/2 and the rate of ceric ion disappearance was proportional to [Ce(IV)] but independent of [MMA]. The rate increased linearly up to a certain range of [MA], above which it remained constant. Increasing [H₂SO₄] decreased the rate. The activation energy was found to be 57.44 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.     

Palladium(II) inhibition during cerium(IV) oxidation of aldoses: a kinetic study

Summary The kinetics of oxidation of aldoses, namely xylose, arabinose, galactose and glucose, by Ce^IV have been studied in HClO₄ + H₂SO₄ medium and in the presence of Pd^II. The reactions exhibit a first order rate dependence with respect to oxidant. The rate is inversely dependent on the [HSO _inf4 ^sup– ][H⁺] ratio. The order of reaction with respect to aldose decreases at higher [aldose]. Due to the formation of a complex between Ce^IV and Pd^II, a retarding effect of [Pd^II] on the rate of disappearance of [Ce^IV] has been observed. A mechanism consistent with the observed kinetic data is proposed.     

RADICAL GRAFTING REACTIONS ONTO STARCH AND OTHER WATER-SOLUBLE COPOLYMERS IN ISOLATED GEL DROPLETS

A novel radical grafting copolymerization process has been designed for water-soluble polymers which avoids the problems of conducting grafting reactions in highly viscous polymerization media. A variety of water-soluble graft copolymers having starch or dextran as the backbone chain with grafted side chains of polyacrylamide (—AM—), poly (acrylic acid ) (—AA—), poly (acrylamide-co-acrylic acid) (—AM—NH_4AA—) or poly ( acrylamide-co-2-acryiamido-2-methyl-l-propanesulphinic acid) (—AM—AMPS—) have been synthesized in gel droplets using aceric sulphate redox initiator, and their properties compared. The reaction conditions were optimized taking into account reaction kinetic data and the observed properties of the products produced under different reaction conditions. The effects of the ratios of [backbone]/[graft monomer], [ AM]/[ AA]/[AMPS] , [Ce~(4+)]/[ S_2O_8=] and pH value on the reaction rate , conversion, grafting degree, grafted chain length and the product molecular weight have been investigated.     

Tris-o-phenanthrolineiron(lll) Complex as a Photoinitiator of Acrylamide Polymerization

Abstract

The blue Tris-o-phenanthrolineiron(m) complex, Fe(phen)₃ ³⁺, formed in aqueous solution by oxidation of the red ferrous phenanthroline complex by nitric acid, is found to be a good photo-initiator of acrylamide (A.AM) polymerization. Systematic study of the kinetics of polymerization of acrylamide by Fe(phen) ₃ ³⁺ in aqueous nitric acid solution in the presence of light of Δ = 365 nm at room temperature showed that the rate of polymerization R_p was dependent on [A.AM]^1,5, [C] ^0,5, I^0,5, and [HCOOH], and the rate of Fe(phen) ₃ ³⁺disappearance, -R_c, was found to be proportional to [A.AM], [C], I, and [HCOOH], where [A.AM], [C] and [HCOOH] refer to the concentrations of acrylamide, Fe(phen) ₃ ³⁺, and formic acid, respectively, and I refers to light intensity. The kinetic observations are consistent with the interaction of the excited Fe(phen) ₃ ³⁺ with acrylamide molecule to produce a radical R. capable of initiation and also reduction of Fe(phen) ₃ ³⁺, to the stable Fe(phen) ₃ ²⁺. The results of the present study differ from those reported for photo initiation by ion pairs of the type Fe ³⁺X ^n- where ×= CI^?, Br^?, C₂O₄ ^2- OH^?, etc., which may be attributed to differences in the photo-behavior of the two systems.     

Ce4＋－Ce3＋循环体系引发淀粉与丙烯酰胺接枝共聚合反应动力学研究

The cyclic initiating system of Ce⁴⁺ - Ce³⁺ - Ce⁴⁺, in which the product of reduced ion Ce³⁺ forming from Ce⁴⁺ after initation being oxidized again to the original oxidizing ion Ce⁴⁺ is examined. The characters of process of the graft copolymerisation using the cyclic initiating system is compared with the ones using ceric and persulphate individually. When using the cyclic systerm as initator, it was more effective to graft polymerise acylamide onto starch and a rather high proportion of graft copolymer was made as opposed to using persulphate individually.