Redox Polymerization of Acrylonitrile: Kinetics of the Reaction Initiated by the Redox System 1-Propanol—Chromic Acid

The kinetics of the aqueous polymerization of acrylonitrile initiated by the chromic acid-1-propanol redox system was investigated under a nitrogen atmosphere. The rates of polymerization and the disappearance of Cr(VI) were measured. Chromic acid alone did not initiate the polymerization under deaerated and undeaerated conditions. Water-miscible organic solvents and neutral salts depress both the rate and the conversion. On the basis of the experimental observations of the dependence of the rate of polymerization R_p and the rate of disappearance of Cr(VI)-R_m on various variables, a suitable kinetic scheme was proposed and various rate and energy parameters evaluated.     

Vinyl polymerization initiated by chromic acid–reducing agent systems

A kinetic study of the thermal polymerization of acrylonitrile initiated by chromic acid–reducing agent (n-butanol, ethylene glycol, cyclohexanone, and acetaldehyde) systems was made. Chromic acid alone did not initiate polymerization under deaerated or undeaerated conditions. On the basis of the experimental determination of the dependencies of various variables on the rate of polymerization R_p, the rate of chromium (VI) disappearance ?R_M, the degree of polymerization DP, etc., a reasonable kinetic scheme was arrived at. The mechanism with the reducing agents, n-butanol, cyclohexanone, and ethylene glycol, was found to be similar but different from that with acetaldehyde. Evidence has been presented to prove the formation of radical intermediates formed by the oxidation of the reducing agent by Cr(IV). Rate parameters for oxidation of the reducing agent and polymerization of the monomer were evaluated.     

Kinetic studies on the radical polymerization of acrylamide initiated by Mn3+–ethoxyacetic acid redox system

The kinetics of polymerization of acrylamide (AM) initiated by manganese(III) acetate–ethoxyacetic acid (EAA) redox system in aqueous sulphuric acid was investigated in the temperature range 35–45°C. The effects of variations in [monomer], [Mn³⁺], [EAA], [H⁺], and ionic strength on the rates of monomer disappearance (R_p) and Mn³⁺ disappearance (?R_m) were studied. The polymerization process is initiated by the free radical arising from the oxidation of ethoxyacetic acid by Mn³⁺ and terminated by the mutual combination of growing polymer radicals. Based on the kinetic results, a suitable reaction scheme is proposed and the rate expressions are derived. The study on degree of polymerization supports the proposed scheme for polymerization. The various rate and thermodynamic parameters are evaluated.     

Polymerization of acrylonitrile. Kinetics of the reaction initiated by the Ce(IV)/thioacetamide redox system

Vinyl polymerization of acrylonitrile initiated by the Ce(IV)/thioacetamide redox system has been investigated in aqueous sulfuric acid in the temperature range of 10–20°C. The rate of polymerization (R_p) and the rate of Ce(IV) disappearance (?R_Ce) were measured. The effect of certain water-soluble organic solvents, added electrolytes, and aromatic and heterocyclic organic nitrogen compounds on the rate of polymerization has been investigated. Depending on the experimental results, we have suggested a suitable reaction scheme for the system which involves the production of initiating radicals from the oxidation of thioacetamide (TAm) by ceric ion and the termination of the polymer chain by metal ions.     

Polymerization of N,N′-methylenebis(acrylamide) using potassium peroxydiphosphate–thiocarboxylic acid redox systems: A comparison

The kinetics of aqueous polymerization of the symmetrical nonconjugated divinyl monomer N,N′-methylenebis(acrylamide) (MBA), was studied at 35°C and at constant ionic strength under nitrogen atmosphere involving potassium peroxydiphosphate (PDP) as oxidant with three different activators thiolactic acid (TLA), thiomalic acid (TMA), and thioglycollic acid (TGA). The rate of polymerization, R_P, and rate of disappearance of peroxydiphosphate, –R_PDP have been followed while polymerization was initiated separately by the PDP–TLA/PDP–TMA/PDP–TGA redox systems. R_P for the above three systems showed first-order dependences on both [monomer] and [activator] and zero-order dependence on [PDP]. First-order dependence on [PDP] and zero-order dependences on [monomer] and [activators] were observed with respect to –R_PDP in the above three systems. A reaction mechanism which involves complex formation between PDP and thiocarboxylic acid, propagation through intramolecular–intermolecular reactions, degradative chain transfer reaction of the growing radical with PDP, and linear termination by the interaction of the chain radical with primary radical was proposed. The kinetic parameters for the three polymerization systems were calculated and compared. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 11–20, 1998     

Kinetics of polymerization of acrylonitrile initiated by the Mn3+-thioacetamide redox system

Kinetics of the polymerization of acrylonitrile has been investigated in aqueous sulfuric acid in a temperature range of 25–45°C. The rate of polymerization (R_p) and the rate of managanic ion disappearance, etc., have been measured. The effect of the various additives, such as water-miscible organic solvents, neutral electrolytes, complexing agents, and surfactants, on the rate has been thoroughly studied. A mechanism that involves the initial complex formation between the thiol form of the thioamide and Mn³⁺, whose decomposition yields the initiating free radical with the polymer chain terminated by mutual combination of growing radicals, has been suggested.     

SURFACTANT MEDIATED POLYMERIZATION KINETICS OF ACRYLAMIDE USING CR(VI)-CYCLOHEXANONE REDOX SYSTEM

The effect of organized surfactants on the kinetics of acrylamide (AM) polymerization have been studied over a temperature range of 25–45°C using Cr (VI)-cyclohexanone (CH) redox system as initiator. The rate of polymerization, R_p(obs), as well as, the percentage of the monomer conversio were found to be increased with increasing the concentration of the anionic surfactant (SDS), above its CMC. But the cationic surfactant (CTAB) reduced the rate considerably at higher concentration, while non-ionic surfactant (TX-100) played no role on the rate. The effect of [Cr(VI)], [CH], [AM], [H+], and ionic strength on the rates have also been examined. The presence of 0.015M SDS decreased the overall activation energy of the polymerization by 6.28 k.Cal/ mole as compared to that in the absence of a surfactant. On increasing the SDS concentration, the viscosity average molecular weight was also found to increase. For the polymerization process, a mutable mechanistic scheme has been pro-posed.     

Kinetics of polymerization of acrylic acid initiated by Mn3+–isobutyric acid redox system. II

The kinetics of redox -initiated polymerization of acrylic acid (AA) by the systerm Mn³⁺-isobutyric acid (IBA) in sulfuric acid was studied in the temperature range of 35–50°C. The overall rates of polymerization (R_p), disappearance of manganic ion (?R_m), and degree of polymerization (X _n), were measured with variation in [monomer], [Mn³⁺], [IBA], H⁺, μ, [Mn²⁺], and temperature. The polymerization is initiated by the organic free radical that develops from the Mn³⁺-isobutyric acid oxidation reaction. Two types of termination reactions, one by the metal ion (Mn³⁺) and the other by the MN³⁺-isobutyric acid complex are proposed to explain the kinetic results. The various rate parameters were evaluated an discussed.     

Polymerization of Acrylonitrile Initiated by the Thiourea-Mn3+ Redox System

Kinetics of vinyl polymerization initiated by the redox system thiourea-Mn³⁺ were investigated in the temperature range 30–40°C in sulfuric acid, and the rates of polymerization R_p and disappearance of Mn³⁺ have been measured. The effect of certain water-miscible organic solvents and anionic surfactant on the rates of polymerization was investigated. A mechanism involving the formation of a complex between Mn³⁺ and thiourea whose decomposition yields the initiating free radical with the polymerization terminated by mutual intraction of growing radicals is suggested.     

KINETICS OF POLYMERIZATION OF ACRYLONITRILE INITIATED BY VANADIUM(V)-THIOUREA REDOX SYSTEM

The kinetics of polymerization of acrylonitrile (AN) initiated by quinquevalent vanadium (V~(5+))-thiourea (TU) redox system has been investigated in aqueous nitric acid in the temperature range from 30 to 50℃. The polymerization rate (R_p) can be expressed as follows: In the copolymerization of acryionitrile with methyl acrylate (MA), the reactivity ratios were found to be 1.0 and 1.1, respectively. The experimental observations suggest that the initiating species is probably a complex consisting of a central ion of Lewis acid-VO_2~+ and the ligands of Lewis bases-acrylonitrile, thiourea, and nitrate anions, while the initiating system in lower concentration, the polymerization of acrylonitrile does not occur if the thiourea is acidified prior to its reaction with quinquevalent vanadium. This indicates that the primary radicals (or the monomeric radicals in the present article) are produced by associated thiourea rather than isothlourea.     

Adsorption of Cr(VI) using activated neem leaves: kinetic studies

In the present study, adsorbent is prepared from neem leaves and used for Cr(VI) removal from aqueous solutions. Neem leaves are activated by giving heat treatment and with the use of concentrated hydrochloric acid (36.5 wt%). The activated neem leaves are further treated with 100 mmol of copper solution. Batch adsorption studies demonstrate that the adsorbent prepared from neem leaves has a significant capacity for adsorption of Cr(VI) from aqueous solution. The parameters investigated in this study include pH, contact time, initial Cr(VI) concentration and adsorbent dosage. The adsorption of Cr(VI) is found to be maximum (99%) at low values of pH in the range of 1-3. A small amount of the neem leaves adsorbent (10 g/l) could remove as much as 99% of Cr(VI) from a solution of initial concentration 50 mg/l. The adsorption process of Cr(VI) is tested with Langmuir isotherm model. Application of the Langmuir isotherm to the system yielded maximum adsorption capacity of 62.97 mg/g. The dimensionless equilibrium parameter, R _L, signifies a favorable adsorption of Cr(VI) on neem leaves adsorbent and is found to be between 0.0155 and 0.888 (0<R _L<1). The adsorption process follows second order kinetics and the corresponding rate constant is found to be 0.00137 g/(mg) (min).     

Kinetics of retarded polymerization: Investigation of the retardation of V5+–thiourea initiated polymerization of methyl acrylate by phenol

The kinetics and mechanism of the retarding action of phenol on the V⁵⁺–thiourea initiated polymerization of methyl acrylate (MA) have been studied within the temperature range of 30–50°C. The effects of retarder (phenol), metal ion (V⁵⁺), monomer (MA), sulfuric acid, some organic solvents and inorganic salts on the percentage and rate of polymerization have been studied. The remarkable observation of the present study is the positive intercept obtained from the plot of [M]/R_p vs. 1/[M]. This type of observation is significantly different from previous studies on retarded polymerization. The values of composite rate constants k₀k_t/k_ik_pkK have been calculated from plots of [M]/R_p vs. 1/[M]. On the basis of experimental findings a reaction mechanism has been suggested, and a suitable rate expression has been proposed and explained.     

Polymerization of acrylamide in the presence of ultrasound and peroxomonosulfate

Polymerization of acrylamide (M) in the presence of ultrasound and peroxomonosulfate (PMS) was carried out for the first time for various concentration ranges of monomer and initiator and various temperatures at a constant frequency of 1 Mhz. The rate of polymerization R_p was found to increase with increase in the concentration of monomer and initiator and found to depend on [M] and [PMS]^1/2. The rate of disappearance of initiator (-d[PMS]/dt) was also followed simultaneously under the experimental conditions and found to increase linearly with increase in [PMS]. A probable reaction mechanism was proposed on the basis of the observed results, and the individual rate constant were evaluated. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2715–2719, 1998     

Vinyl polymerization with Fe(III)–thiourea as initiator system. Part II. Kinetics: Predominant primary radical termination

The rate of polymerization R_p of methyl methacrylate initiated by Fe(CIO₄)₃ and thiourea (TU) in tert-butyl alcohol is indepenent of [Fe(III)] and [TU] in the concentration range studied. In contrast to R_p, the degree of polymerization DP changes markedly with the change in the initiator concentration. DP is overwhelmingly lower than is expected in a standard radical polymerization at the same R_p. Further, R_p is proportional to the square of the monomer concentration. Initiation efficiency is less than one. Independent experiments proved that in the azobisisobutyronitrile-initiated polymerization the R_p and DP are negligibly affected by [Fe(CIO₄)₃] or [TU], though high [TU] brings about high induction periods. The results of Fe(III)-TU-initiated polymerization have been interpreted in terms of the predominant termination of polymer radicals by primary radicals.     

Polymerization of methyl methacrylate initiated by Mn(III)–glycerol redox system

The kinetics of thermal polymerization of methyl methacrylate initiated by the redox system Mn(III)–glycerol was studied in aqueous sulfuric acid in the temperature range of 30–40°C, and the rates of polymerization, R_p, and Mn³⁺ disappearance, etc., were measured. The effect of certain water-miscible organic solvents and certain cationic and anionic surfactants on the rates of polymerization has been investigated. A mechanism involving the formation of a complex between Mn³⁺ and glycerol whose decomposition yields the initiating free radical with the polymerization being terminated by the metal ion has been suggested.     

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.     

Aqueous polymerization of acrylonitrile initiated by the bromate–thiourea redox system

The aqueous polymerization of acrylonitrile initiated by an acidified bromate–thiourea redox system has been studied under nitrogen atmosphere. The rate of polymerization is independent of thiourea concentration over the range 2–9 × 10^?3M and reaches maximum at 9 × 10^?3M. The rate varies linearly with [monomer]. The initial rate of polymerization as well as the maximum conversion increases within the range of 4–22.5 × 10^?3M KBrO₃, but beyond 22.5 × 10^?3M the rate of polymerization decreases. The initial rate and the limiting conversion increases with increasing polymerization temperature in the range 30–45°C; and beyond 45°C they decrease. The effect of certain neutral salts, water-soluble solvents, and micelles of cationic, anionic, and nonionic surfactants on the rate of polymerization has been investigated.     

Polymerization of acrylonitrile initiated by thiourea-vanadium(V) redox system

The kinetics of polymerization of acrylonitrile initiated by V⁵⁺-thiourea or V⁵⁺-ethylene thiourea have been studied at 30, 35 and 40°C in nitrogen. The rates of polymerization and V⁵⁺ disappearance, and the chain lengths of polymers were measured. The kinetics are consistent with the formation of an intermediate complex between the thiol form of thiourea or ethylene thiourea and the oxidant decomposition of which leads to the initiating radical. The effects of certain organic solvents (water miscible) and salts on the rate of polymerization have been studied. A kinetic scheme has been proposed and the various rate and energy parameters evaluated.     

Vinyl polymerization initiated by peroxydiphosphate. XII. Polymerization of acrylamide and acrylic acid by peroxydiphosphate–sodium thiosulfate redox system

The aqueous polymerization of acrylic acid and acrylamide initiated by peroxydiphosphate–sodium thiosulfate redox system was investigated within the temperature range of 25–35°C. The rates of polymerization were measured at different concentrations of oxidant, activator and monomer. The monomer and the initiator exponents were evaluated to be 1.12 and 0.51. The rate of polymerization decreases with increasing thiosulfate concentration. On the basis of the experimental observation of the dependence of the rate of polymerization, R_p, on various variables, a suitable kinetic scheme has been proposed and the rate parameters have been evaluated.     

Acidic peroxo salts. A new class of initiators for vinyl polymerization. I. Kinetics of polymerization of acrylonitrile initiated by potassium monopersulfate catalyzed by Ag(I)

The kinetics of polymerization of acrylonitrile initiated by KHSO₅ and catalyzed by Ag(I) have been investigated in an aqueous medium over the temperature range of 35–50°C. The rates of polymerization R_p have been calculated and studied with respect to monomer and initiator. The catalytic activity of various metal ions on the initiator has been determined from a comparison of R_p values. The effects of monomer, catalyst, neutral salts, various amines, and inhibitor (hydroquinone) on the initial rate as well as maximum conversion have been studied. From the kinetics results a suitable reaction scheme has been proposed.