Polymerization of acrylonitrile: Kinetics of the reaction initiated by the Fe2+/BrO3− redox system

The aqueous polymerization of acrylonitrile initiated by the bromate—ferrous redox system in aqueous sulfuric acid was studied under nitrogen atmosphere. The rate of polymerization increased with increasing concentration of ferrous in the range of 0.25-1 × 10^?2M. The percentage of conversion increased with increasing concentration of the catalyst, but beyond 2.5 × 10^?3M there was a decreasing trend in the rate of polymerization. The rate varied linearly with [monomer]. The initial rate of polymerization as well as the maximum conversion increased within the range of 1–2.5 × 10^?3M KBrO₃, but beyond 2.5 × 10^?3M the rate of polymerization decreased. The initial rate and limiting conversion increased with increasing polymerization temperature in the range 30–40°C; beyond 40°C they decreased. The effect of certain neutral salts, water-miscible solvents, complexing agents, and copper sulfate concentration on the rate of polymerization was investigated.     

Aqueous Polymerization of Methyl Methacrylate Initiated by the Bromate-Thiourea Redox System

The aqueous polymerization of methyl methacrylate initiated by the bromate-thiourea redox system in dilute HC1 has been investigated under nitrogen atmosphere. The rate of polymerization increases with increasing concentration of thiourea in the range 5 × 10^?3?10 × 10^?3 M. The percentage of conversion increases with increasing concentration of the catalyst, but beyond 1.5 × 10^?2 M, there is a decreasing trend in the rate of polymerization. The rate of polymerization increases with increasing monomer concentration, but beyond 0.184 M the polymerization rate decreases due to gel effect. The rate of polymerization increases with temperature up to 35°C and beyond 40°C a decreasing trend is noticed. The effect of water miscible organic solvents, certain neutral salts on the rate of polymerization has also been investigated.     

Aqueous Polymerization of Methyl Methacrylate Initiated by the Potassium Bromate-Thiomalic Acid Redox System

The redox system composed of potassium bromate and thiomalic acid was used to initiate the aqueous polymerization of methyl methacrylate under nitrogen atmosphere at 35 ± 0.2°C. The initial rates of polymerization have been found to be approximately proportional to the first power of the initiator concentration in the range of 2.5 to 6.0 ± 10^?3 M and to the first power (1.15) of monomer concentration in the range of 3.72 to 11.16 ± 10^?2 M The overall rate was independent of activator concentration, approaching a maximum at 10 × 10^?3 M. The overall energy of activation was found to be 8.80 kcal/mol. The initial rate and the maximum conversion attained a maximum value at 35°C in the temperature range of 20 to 45°C.     

Polymerization of acrylamide with persulfate–thiomalic acid initiator

The redox system of potassium persulfate–thiomalic acid (I₁–I₂) was used to initiate the polymerization of acrylamide (M) in aqueous medium. For 20–30% conversion the rate equation is where R_p is the rate of polymerization. Activation energy is 8.34 kcal deg^?1 mole^?1 in the investigated range of temperature 25–45°C. M_n is directly proportional to [M] and inversely to [I₁]. The range of concentrations for which these observations hold at 35°C and pH 4.2 are [I₁] = (1.0–3.0) × 10^?3, [I₂] = (3.0–7.5) × 10^?3, and [M] = 5.0 × 10^?2–3.0 × 10^?1 mole/liter.     

Aqueous polymerization of acrylamide initiated by acidic potassium permanganate–ascorbic acid redox system

The polymerization of acrylamide initiated by the acidic permanganate–ascorbic acid redox pair has been studied in aqueous media at 30 ± 0.2°C in nitrogen atmosphere. The initial rate of polymerization has been found to be proportional to nearly the first power of the catalyst KMnO₄ concentration within the range 6.0 × 10^?3–14.0 × 10^?3 mole/l. The rate is proportional to the first power of the monomer concentration within the range 4.00 × 10^?2–12.0 × 10^?2 mole/l. However, the rate of polymerization is independent of ascorbic acid concentration within the range 3.0 × 10^?3–6.0 × 10^?3 mole/l., but the further increase of the concentration depresses the rate of polymerization as well as maximum conversion. The initial rate increases but the maximum conversion decreases as the temperature is increased within the range 20–35°C. The overall energy of activation has been found to be 9.8 kcal/mole. The optimum amount of sulfuric acid is essential to initiate the polymerization but its presence in excess produces no effect either on the rate of reaction or the maximum conversion. Water-miscible organic solvents and salts, e.g., CH₃OH, C₂H₅OH, (CH₃)₂CHOH, KCl, and Na₂SO₄, depress the rate. Slight amounts of MnSO₄ · H₂O and a complexing agent NaF increase the rate of polymerization. Cationic and anionic detergents have been found to decrease and increase the rate, respectively, while nonionic surfactants have no effect on the rate of polymerization.     

Polymerization of acrylamide initiated by the persulfate–thiosulfate redox couple

Conversion–time data were obtained for the polymerization of acrylamide initiated by the redox couple persulfate–thiosulfate by using a dilatometer. A plot of initial rate as a function of thiosulfate concentration shows a well-defined maximum and three distinct regions of behavior. In each region the shape of the conversion–time curves demonstrates the differences in apparent order with respect to monomer arising from changes in initiator concentration during an individual run. A reaction mechanism is proposed to explain the results, and a limiting form of the rate expression is derived for each of the three regions. The ranges of concentration studied are: persulfate, 9.5 × 10^?4?4.7 × 10^?2M; thiosulfate, 2 × 10^?5?2 × 10^?2M; initial monomer, 0.05–1.0M; and temperature, 30–50°C. Within these ranges the initial rate shows a halforder dependence on persulfate and a first-order dependence on initial monomer concentration.     

Studies on the kinetics of ceric–thiourea-initiated aqueous polymerization of methyl methacrylate. I. Mechanistic features in moderately acid solution

The kinetics of the aqueous polymerization of methyl methacrylate by a ceric-thiourea initiator system in moderately acid solution (pH 2.15) was studied. The rate of polymerization was proportional to 0.41 power of ceric concentration, 0.32 power of thiourea concentration, and 1.18 power of monomer concentration. The degree of polymerization was smaller than expected from the rate of polymerization. Initiation efficiency was less than one. There was no evidence of any ceric ion termination in the concentration range of 2.50 × 10^?4–2.00 × 10^?3M studied. The results are explained in terms of partial primary radical termination; the principal mode of termination, however, was bimolecular.     

Precipitation polymerization of acrylamide using vazo-33 as an initiator and acetonitrile/water mixtures as the solvent

Precipitation polymerization of acrylamide initiated by a thermal initiator, Vazo-33 (DuPont Vazo Initiator), was achieved at a solvent composition of acetonitrile/water = 4/6 (vol/vol). The polymerization kinetics were investigated in the acrylamide [M] concentration range 0.86–2.27M, Vazo-33 [I] concentration range 1.4–11.0 × 10^?4M, and temperature range 30–40°C. Polymerization was carried out in reaction ampules and the rate was determined gravimetrically. Number-average molecular weight was obtained from intrinsic viscosity. The precipitation polymerization rate varied as [M]^2.16 and [I]^0.44. Number-average molecular weight was proportional to [M]^1.22 and inversely proportional to [I]^0.31. The overall reaction activation energy was calculated as 17.3 kcal/mol in the temperature range studied. The optimal reaction conditions studied were: acetonitrile/water = 4/6, temperature = 40°C, [M] = 1.95M and [I] = 2.8 × 10^?4M. One hundred percent conversion was achieved in 90 min and a polymer with a number-average molecular weight of 1,200,000 was obtained.     

Aqueous polymerization of acrylamide

The polymerization of acrylamide (I) initiated by a potassium bromate—thioglycollic acid (TGA) redox pair has been studied in aqueous media at 30°C in a nitrogen atmosphere. The reaction order related to the catalyst concentration (KBrO₃) was 0.501, which indicated a bimolecular mechanism for the termination reaction in the range of 1.0?3.0 × 10^?3 mole/liter. The polymerization rate varied linearly with monomer (I) concentration over the range of 1.0?5.0 × 10^?2 mole/liter. A typical behavior is observed, however, by changing the thioglycollic acid concentration. The initial rate of polymerization (Ri), as well as the maximum conversion, increases by increasing the temperature to 30°C, but the initial rate and the maximum conversion falls as the temperature rises above 30°C. The overall energy of activation is 6.218 kcal in the temperature range of 20–40°C. Water-miscible organic solvents, namely, CH₃OH and C₂H₅OH, depress the rate of polymerization.     

Polymerization of acrylamide initiated by the Ce4+/thiourea redox system

The polymerization of acrylamide (M) initiated by the Ce⁴⁺/thiourea (TU) redox system has been studied in an aqueous sulfuric acid medium at 35 ± 0.2°C under nitrogen atmosphere. The rate of polymerization is governed by the expression The activation energy is 5.9 kcal deg^?1 mol^?1 in the investigated temperature range 30–50°C. The molecular weight is directly proportional to the concentration of monomer and inversely proportional to the catalyst concentration. With increasing concentration of DMF molecular weight decreases. The range of concentrations for which these observations hold at sulfuric acid concentration of 2.5 × 10^?2 mol/L are [monomer] = 5.0 × 10^?2–3.0 × 10^?1, [catalyst] = (5.0–15.0) × 10^?4, and [activator] = (1.0–6.0) × 10^?3 mol/L.     

Persulfate-initiated polymerization of acrylamide

A dilatometric technique was used to obtain conversion–time data for the polymerization of acrylamide initiated by potassium persulfate in water. The results are summarized by the empirical rate expression, ?d[M₁]/dt = R_p = k_1.25[K₂S₂O₈]^0.5[M₁]^1.25, and k_1.25 = 1.70 × 10¹¹ exp {?16,900/RT} 1.^0.75/mole^?0.75-min. Persulfate was varied over the range 9.5 × 10^?4 to 5.2 × 10^×2 mole/l., and initial monomer concentration [M₁] was varied from 0.05 to 0.4 mole/l. The temperature range was 30?50°C. Results of analysis of the kinetics and energetics of the polymerization favor a cage-effect theory rather than a complex-formation theory to explain the order with respect to monomer.     

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.     

Degradative chain transfer in vinyl acetate polymerizations using toluene as solvent

In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (C_trs) determined using the Mayo method is equal to 3.8 × 10^?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10^?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the M_n data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007     

Studies of redox polymerization. I. Aqueous polymerization of acrylamide by an ascorbic acid–peroxydisulfate system

The polymerization of acrylamide initiated by an ascorbic acid–peroxydisulfate redox system was studied in aqueous solution at 35 ± 0.2°C in the presence of air. The concentrations studied were [monomer] = (2.0–15.0) × 10^?2 mole/liter; [peroxydisulfate] = (1.5–10.0) × 10^?3 mole/liter; and [ascorbic acid] = (2.84–28.4) × 10^?4 mole/liter; temperatures were between 25–50°C. Within these ranges the initial rate showed a half-order dependence on peroxydisulfate, a first-order dependence on an initial monomer concentration, and a first-order dependence on a low concentration of ascorbic acid [(2.84–8.54) × 10^?4 mole/liter]. At higher concentrations of ascorbic acid the rate remained constant in the concentration range (8.54–22.72) × 10^?4 mole/liter, then varied as an inverse halfpower at still higher concentrations of ascorbic acid [(22.72–28.4) × 10^?4 mole/liter]. The initial rate increased with an increase in polymerization temperature. The overall energy of activation was 12.203 kcal/mole in a temperature range of 25–50°C. Water-miscible organic solvents depressed the initial rate and the limiting conversion. The viscometric average molecular weight increased with an increase in temperature and initial monomer concentration but decreased with increasing concentration of peroxydisulfate and an additive, dimethyl formamide (DMF).     

Trityl salt—initiated polymerization of α-methylstyrene

The initiation reaction of the polymerization of α-methylstyrene by trityl tetrachloroferate and tritylhexachloroantimonate in 1,2-dichloroethane at 20°C was studied. The rate constants were 14 × 10^?3 and 27 × 10^?3 L mol^?1s^?1, respectively. The dissociation constants of tritylterachloroferate (K_d = 0.88 × 10^?4M^?1) and tritylhexachloroantimonate (K_d = 2.64 × 10^?4M^?1) was determined. The effect of electron acceptors and donors on the dissociation equilibrium and initiation rate was investigated. It was shown that in strongly dissociated ion pairs such as stable carbenium salts the electron donors and acceptors have no appreciable effect on the magnitude of the dissociation. The temperature dependence of the rate constants in the ?20–+20°C range yielded the following thermodynamic parameters for trityltetrachloroferate: E_i = 8.54 kcal/mol; A = 3.2 × 10⁴ mol^?1s^?1; ΔH* = 8 kcal/mol; and S* = ?39.8 eu.     

Kinetic model of reversible addition‐fragmentation chain transfer polymerization in microemulsions

A simplified kinetic model for RAFT microemulsion polymerization has been developed to facilitate the investigation of the effects of slow fragmentation of the intermediate macro‐RAFT radical, termination reactions, and diffusion rate of the chain transfer agent to the locus of polymerization on the control of the polymerization and the rate of monomer conversion. This simplified model captures the experimentally observed decrease in the rate of polymerization, and the shift of the rate maximum to conversions less than the 39% conversion predicted by the Morgan model for uncontrolled microemulsion polymerizations. The model shows that the short, but finite, lifetime of the intermediate macro‐RAFT radical (1.3 × 10^?4–1.3 × 10^?2 s) causes the observed rate retardation in RAFT microemulsion polymerizations of butyl acrylate with the chain transfer agent methyl‐2‐(O‐ethylxanthyl)propionate. The calculated magnitude of the fragmentation rate constant (k_f = 4.0 × 10¹–4.0 × 10³ s^?1) is greater than the literature values for bulk RAFT polymerizations that only consider slow fragmentation of the macro‐RAFT radical and not termination (k_f = 10^?2 s^?1). This is consistent with the finding that slow fragmentation promotes biradical termination in RAFT microemulsion polymerizations. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 604–613, 2010     

Direct potentiometric titration of thiosulfate,thiourea, and ascorbic acid with lodate using an iodide ion-selective electrode

A potentiometric method has been developed for the semi-automatic direct titration of thiourea, thiosulfate, and ascorbic acid with potassium iodate in strongly acidic solutions using an iodide ion-selective electrode to monitor the reaction and locate the endpoint. The method is simple, fast, precise, and accurate. Amounts ranging from 0.15–1.5 mg of thiourea (3.9 × 10^?4–3.9 × 10^?3, M), 0.3–3.0 mg of thiosulfate (5.4 × 10^?4–5.4 × 10^?3, M), and 0.5–5.0 mg of ascorbic acid (5.7 × 10^?4–5.7 × 10^?3, M) have been determined with an average error of about 1%. The method has been applied to the determination of ascorbic acid in tablets. Results checked closely with those obtained with a standard titrimetric method.     

Syndiospecific polymerization of styrene. II. Monocyclopentadienyltributoxy titanium/methylaluminoxane catalyst

Syndiospecific polymerization of styrene was catalyzed by monocyclopentadienyltributoxy titanium/methylaluminoxane [CpTi (OBu)₃/MAO]. The atactic and syndiotactic polystyrenes were separated by extracting the former with refluxing 2-butanone. The activity and syndiospecificity of the catalyst were affected by changes in catalyst concentration and composition, polymerization temperature, and monomer concentration. Extremely high activity of 5 × 10⁷ g PS (mol Ti mol S h)^?1 with 99% yield of the syndiotactic product were achieved. The concentration of active species, [C^*], has been determined by radiolabeling. The amount of the syndiospecific and nonspecific catalytic species, [C] and [C] respectively, correspond to 79 and 13% of the CpTi(OBu)₃. The rate constants of propagation for C and C at 45°C are 10.8 and 2.0 (M s)^?1, respectively, the corresponding rate constants for chain transfer to MAO are 6.2 × 10^?4 and 4.3 × 10^?4s^?1. There was no deactivation of the catalytic species during a batch polymerization. The rate constant of chain transfer with monomer is 6.7 × 10^?2 (M s)^?1; the spontaneous β-hydride transfer rate constant is 4.7 × 10^?2 s^?1. The polymerization activity and stereospecificity of the catalyst are highest at 45°C, both decreasing with either higher or lower temperature. The stereoregular polymer have broad MW distributions, M?_w/M?_n = 2.8–5.7, and up to three crystalline modifications. The T_m of the s-PS polymerized at 0–90°C decreased from 261.8 to 241°C indicating thermally activated monomer insertion errors. The styrene polymerization behaviors were essentially insensitive to the dielectric constant of the medium.     

Aqueous Polymerization of Methyl Methacrylate Initiated by Potassium Peroxydisulfate-Ascorbic Acid Redox System

The aqueous polymerization of methyl methacrylate initiated by the redox system K₂S₂O₈-ascorbic acid has been studied at 35°C under the influence of oxygen. The rate of polymerization increases with increasing ascorbic acid concentration at low activator concentration, remains constant within the range 4.375 × 10^?3 to 11.25 × 10^?3 mole/liter, and at higher ascorbic acid concentration again decreases. The rate varies linearly with monomer concentration. The initial rate and the limiting conversion increase with increasing polymerization temperature. Organic solvents (water-miscible only) and small amounts of neutral salts like KC1 and Na₂SO₄ depress the initial rate and the maximum conversion. The addition of small amounts of salts like Cu²⁺ and Mn²⁺ increases the initial rate, but no appreciable increase in the limiting conversion is observed.     

The Effect of Active Carbon on the Kinetics of Polymerization of Methyl Methacrylate

Rates of 2–2¹?azobisisobutyronitrile initiated polymerization of methyl methacrylate in benzene were determined at 77.2, 65.0, and 50.0°C. The variation of molecular weight of the polymer with temperature and conversion was also studied. At a fixed conversion of 2.0%, the molecular weight decreased from 2.05 × 10⁵ at 50°C to 1.4 × 10⁵ at 77.2°C. The ratio of the propagation rate coefficient to the square root of the termination rate coefficient was found to be 0.61, 0.397, and 0.374 at 77.2, 65.0, and 50.0°C, respectively, with an uncertainty of ±0.5°C in temperature. The effect of active carbon on the rates of polymerization at 77.2°C was measured. Rates of polymerization decreased in the presence of active carbon. For example, the initial rate of polymerization decreased from 7.8 × 10^?4 mole/(liter min) to 4.6 × 10^?4 mole/(liter min) when the carbon concentration was varied from 0 to 9.65 g/liter. The molecular weight of the polymer increased from an average of 1.4 × 10⁵ in the absence of carbon to 1.5 × 10⁵ when carbon was present.