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.     

Effect of valence state of vanadium on stereoblock polymerization of methyl methacrylate with VOCl3–AlEt2Br catalyst system

The polymerization of methyl methacrylate with the VOCL₃–ALEt₂Br catalyst system in n-hexane has been studied. The first-order dependence of rate of polymerization on catalyst and monomer concentrations, activation energy of 6.67 kcal/mole, and NMR spectra of polymer lend support to a coordinate anionic mechanism of polymerization. It has been shown that the vanadium in V⁺² oxidation state is less active than V⁺³ oxidation state of active complex.     

Electro-initiated polymerization of acrylonitrile in aqueous acetic acid containing Mn(OAc)2·4H2O and CNCH2COOH

The electro-initiated polymerization of acrylonitrile initiated by the anodic oxidation of an aqueous acid solution (80% HOAc + 20% H₂O) containing Mn(OAc)₂ · 4H₂O/CNCH₂COOH has been investigated in the 30–40°C temperature range. The kinetics and mechanism of the process has been investigated as a function of variables and a suitable mechanism proposed. From the experimental observations the rate of polymerization is seen to be proportional to [An]^1.5I^0.5[Mn⁺²]^0.5 and [CAA]^0.5. The rate of polymerization gradually decreases at a higher applied current. The rate was independent of [CAA]^0.5. The rate of polymerization gradually decreases at a higher applied current. The rate was independent of CAA at high concentration. The average degrees of polymerization (P _n) increases with increasing AN and decreasing [CAA], [Mn⁺²] and applied current, I. The initiation is due to the anodic oxidation of Mn⁺²–CNCH₂COOH complex. Both the initiation of polymerization by the primary radical, viz., CN? C?? COOH as well as the oxidation of the primary radical at the electrode are equally significant reactions and neither can be neglected in comparison with the other. Predominant mutual termination accounts for all the observed data.     

Study on the Kinetics of Polymerization of Tributyltin Methacrylate

The kinetics of polymerization of tributyltin methacrylate (TBTM) has been studied in benzene solution in the temperature range 60–75°C in the presence of azobisisobutyronitrile (AIBN). We have obtained the following polymerization rate equation: R _p = K _p [TBTM]^1.5 [AIBN]^0.5. It shows that the dependence of the polymerization rate on the concentrations of the monomer TBTM and the initiator AIBN are 1.5 and 0.5 order, respectively. The activation energy of polymerization was found to be 18.1 kcal/mol. The activation energy for the degree of polymerization is approximately -12.3 kcal/mol.     

Kinetics and mechanism of polymerization of acrylonitrile by peroxomonosulphate

The kinetics of polymerization of acrylonitrile initiated by peroxomonosulphate (PMS) has been carried out in the temperature range 45–60°C at constant ionic strength of 0.50 mol dm^?3 under deaerated conditions. The rate of polymerization R_p has been investigated at various concentrations of monomer and initiator. The effects of [monomer], [initiator], [H⁺], ionic strength, temperature, and reducing agents (organic and inorganic substrates) on the rate of polymerization have been observed. Activation energy was found to be 15.2 kcal mol^?1.     

Kinetic study of RuIII‐catalyzed polymerization of methylmethacrylate initiated with n‐butylamine in the presence of carbon tetrachloride by a charge‐transfer mechanism

Ruthenium trichloride (RuCl₃ or Ru^III) catalyzed polymerization of methylmethacrylate (MMA) initiated with n‐butylamine (BA) in the presence of carbon tetrachloride (CCl₄) by a charge‐transfer mechanism has been investigated in a dimethylsulfoxide (DMSO) medium by employing a dilatometric technique at 60°C. The rate of polymerization (R_p) has been obtained under the conditions [CCl₄]/[BA] ? 1 and [CCl₄]/[BA] ? 1. The kinetic data indicate the possible participation of the charge‐transfer complex formed between the amine–Ru^III complex and CCl₄ in the polymerization of MMA. In the absence of either CCl₄ or BA, no polymerization of MMA is observed under the present experimental conditions. The rate of polymerization is inhibited by hydroquinone, suggesting a free‐radical initiation. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 70–77, 2011     

Studies on the polymerization of methyl methacrylate activated by azobisisobutyramidine

Kinetic studies on methyl methacrylate polymerization were carried out with watersoluble 2,2′-azobisisobutyramidine (ABA). The rate of polymerization was proportional to the square root of the initiator concentration in the solvents chloroform, methanol, and dimethyl sulfoxide (DMSO), which confirms the bimolecular nature of the termination reaction. The monomer exponent was unity in chloroform but in methanol and DMSO the rate of polymerization passed through a maximum when plotted against the monmer concentration. This behavior in methanol has been attributed to be due to the enhanced rate of production of radical with increasing proportion of methanol. The rate of decomposition of the ABA has been observed to be faster in methanol than in chloroform. The situation becomes more complicated with DMSO, which was found to reduce the value of δ = (2k_t)^1/2/k_p in methyl methacrylate polymerization. The rate of polymerization was observed to be highly dependent on the nature of the solvent, the rate increasing with increased electrophilicity of the solvent. The dependence of R_p on the solvent has been explained in the light of the stabilization of the transition state due to increased solvation of the basic amidine group of the initiator with the increased electrophilicity of the solvent.     

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.     

Vinyl polymerization initiated by peroxydiphosphate. V. Polymerization of acrylonitrile initiated by peroxydiphosphate-cyclohexanol redox system in the presence of silver ion

The polymerization of acrylonitrile was carried out using peroxydiphosphate-cyclohexanol redox system in the presence of silver ion. The rate of polymerization increases with increasing peroxydiphosphate concentration and the initiator exponent was computed to be 0.5. The rate of polymerization increases with increasing monomer concentration and the monomer exponent was computed to be unity. The plot of R_p vs [Ag⁺]^1/2 was linear, indicating 0.5 order with respect to [Ag⁺]. The reaction was carried out at three different temperatures and the overall activation energy was calculated to be 7.60 kcal/mol. The effect of certain surfactants on the rate of polymerization has been investigated and a suitable kinetic scheme has been pictured.     

Cyclic acetal-photosensitized polymerization. II. Photopolymerization of styrene in the presence of various monocyclic acetals

The polymerization of styrene (St) in benzene solution in the presence of 1,3-dioxane (DON), 1,3-dioxepane (DOP), trioxane (TRON), or tetraoxane (TEON) by means of photoirradiation of the system at 40°C has been studied kinetically from the standpoint of photosensitized polymerization. The rate of photosensitized polymerization R_p increased in the order: DOP < DON < TRON < TEON, as shown by the rate constant of decomposition of cyclic acetals, and then could be expressed by R_p = k[monocyclic acetal]^0.5[St]^1.0. The polymerization was confirmed to proceed via a radical mechanism.     

Effect of metal salts on polymerization. Part I. Polymerization of vinylpyridine initiated with cupric acetate

The polymerization of vinylpyridine initiated by cupric acetate has been studied. The rate of polymerization was greatly affected by the nature of the solvent. In general polar solvents increased the rate of polymerization. Polymerization was particularly rapid in water, acetone, and methanol. The initial rate of polymerization of 4-vinylpyridine (4-VP) in a methanol–pyridine mixture at 50°C. is R_p = 6.95 × 10^?6[Cu¹¹]^1/2 [4-VP]² l./mole-sec. The activation energy of initiation by cupric acetate is 5.4 ± 1.6 kcal./mole. Polymerization of 2-vinylpyridine and 2-methyl-5-vinylpyridine with the same initiator was much slower than that of 4-VP. Dependence of R_p on monomer structure and solvent is discussed. Kinetic and spectroscopic studies led to the conclusion that the polymerization of 4-VP is initiated by one electron transfer from the monomer to cupric acetate in a complex having the structure, (4-VP)₂Cu(CH₃COO)₂.     

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.     

Vinyl polymerization of acrylamide initiated by Thallium(III) ions in solution

Kinetics of polymerization of acrylamide initiated by Thallium(III) perchlorate was investigated in aqueous perchloric acid medium in the temperature range of 55–70°C. The rates of polymerization were measured varying the concentration of the monomer, initiator, and perchloric acid. The rate of polymerization was found to increase with increase of temperature, monomer concentration, initiator concentration, and perchloric acid concentration. The effect of additives like different solvents, surfactants, and retarders on the rate of polymerization was studied. Molecular weights of the polymer were determined by viscometry. The chain transfer constants for the monomer (C_M) and that for the solvent dioxan (C_s) were calculated to be 7.33 × 10^?3 and 6.66 × 10^?3, respectively. From the Arrhenius plot, the overall activation energy (E_a) was calculated to be 10.68 kcal/mol. The energy of initiation was calculated to be 12.36 kcal/mol. Depending on the results obtained, a suitable reaction mechanism has been suggested and a rate equation has been derived.     

Kinetics of polymerization of N-tert-butylacrylamide. Part II

The effect of ferric chloride on the kinetics of the radical polymerization of N-tert-butylacrylamide has been investigated in methanol solution at 25°C, with the use of 4,4′-dicyano-4,4′-azodipentanoic acid as initiator. A shrinkage factor of 0.193 mmole polymerized for 1 mm contraction in a capillary of 1 mm diameter has been obtained from density measurements. In the absence of ferric chloride, rates of polymerization were found to be proportional to the concentration of monomer and to the square root of the initiator concentration. With ferric chloride present, the rate of polymerization becomes directly proportional to the initiator concentration and inversely proportional to the concentration of ferric salt. From measurements of the rates of production of ferrous iron, the specific rate constant of the initiation reaction has been found to be (1.8 ± 0.4) × 10^?6sec^?1 at 25°C, compared with a value of 7.63 × 10^?8 sec^?1 calculated from the kinetic data obtained with no ferric salt present. The value of the ratio k_p/k₄. where k_p is the propagation coefficient and k₄ is the velocity coefficient for termination by ferric chloride, has been calculated to be 6.0 × 10^?4 at 25°C, which is considerably smaller than the value found for the ferric chloride-terminated polymerization of acrylamide in water. This markedly lower value of k_p/k₄ has been attributed principally to the steric effect of the tert-butyl group on the magnitude of k_p.     

Thermal polymerization of acrylamide by differential scanning calorimetry

Thermal polymerization of acrylamide was studied by differential scanning calorimetry. Latent heat of fusion ΔH_f and enthalpy of polymerization ΔH_p values were found to be 36 and ?18.0 kcal mol^?1, respectively. The overall activation energy E for the polymerization was calculated to be 19 k cal mol^?1 up to 60% conversion. The added free-radical inhibitor (benzoquinone) was found to desensitize the thermal polymerization of acrylamide suggesting the polymerization to be a free-radical type. The existing rate equation for the heterogeneous bulk polymerization in the presence of initiators has been modified for the thermally initiated bulk polymerization of acrylamide. The experimental overall E value was found to agree well with the calculated E value when considering only the propagation and termination steps, thereby suggesting the process to be similar to postpolymerization of acrylamide.     

Kinetics of the potassium persulfate-initiated inverse emulsion polymerization of sodium acrylate solutions

The kinetics of the K₂S₂O₈-initiated inverse emulsion polymerization of aqueous sodium acrylate solutions in kerosene with Span 80 as the emulsifier has been studied. The conversion-time curves are S-shaped. The following expressions have been obtained for the maximum rate of polymerization and the molecular weight of the polymers under the experimental conditions investigated: R_max ∞ [K₂S₂O₈]^0.78[sodium acrylate]^1.5[Span 80]^0.1, (OVERLINE)M(/OVERLINE)_u ∞ [K₂S₂O₈]^−0.37[sodium acrylate]^2.9[Span 80]^−0.2. The activation energy for the maximum rate of polymerization is 94.8 kJ mol^−1. The results suggest a monomer–droplet–nucleation mechanism for the system studied. © 1996 John Wiley & Sons, Inc.     

Solution polymerization of methyl methacrylate using trioctylmethylammonium persulfate initiator: Kinetics of polymerization and activation parameters for the primary decomposition of the initiator

The kinetics of solution polymerization of methyl methacrylate using trioctylmethylammonium persulfate (aliquat persulfate) at 60°C has been studied in t-butyl alcohol, N,N-dimethyl formamide, acetonitrile, dioxane, acetone, and methyl ethyl ketone. The rate of polymerization depends markedly on the solvent used. The initiator exponent is close to 0.5 in the first three solvents but larger than this value in the other three solvents. The overall activation energy of the polymerization has been determined in all the solvents. The rate constants and activation parameters for the primary decomposition of the initiator have been determined in the first three solvents where ideal polymerization conditions prevail. The activation parameters for the decomposition of AQ₂S₂O₈ in the organic solvents depend on the type of solvent. They are very different from those of the free S₂O^2?₈ ion in water. These differences have been explained taking into consideration the various ionic forms in which the initiator exists in the studied solvents using a previously postulated model of the activated state.     

The effect of organic nitriles on the radiation induced polymerization of styrene

The effect of a range of 10 organic nitriles on the radiation-induced polymerization of styrene was studied. A dose rate of 4.4 rad s^?1 was used. A rate of polymerization of styrene (1.744 mol L^?1 of toluene solution) of 5.0 × 10^?7 mol L^?1 s^?1 was found. With organic nitriles present (styrene:nitrile ratio of 1:0.28) the rate of polymerization increased. Rates in the range of 5.5 × 10^?7 ?5.2 × 10^?6 mol L^?1 s^?1, depending on the nitrile present, were obtained. The polymers were partially characterized and evidence of involvement of each of the nitriles in the polymer chains was revealed. The increase in rate of polymerization has been attributed to the part played by nitrile radicals in the initiation of styrene polymerization. Radical yield values [as G(nitrile radical)] were derived from the relevant rate expressions. Values ranged from 2.7 to 49.5, depending on the particular nitrile. Corresponding values of G(nitrile radical) in the range of 5.1–129.4 were obtained by the manipulation of number-average molar mass data. Values of k_pk_t of approximately 2 × 10^?5 L mol^?1 s^?1 were found. Trommsdorff types of effect are absent from these systems.     

Kinetics and mechanism of the emulsion polymerization of styrene in the aqueous media at 50°C and at low monomer concentration initiated by persulfate. I. Initiation

The mechanism of the water-soluble persulfate-initiated emulsion polymerization of styrene in the aqueous media at 50°C has been investigated kinetically by the conventional dilatometric and gravimetric methods at low concentration of the monomer (5% v/v). It has been found that the initial rate of polymerization V_p is approximately proportional to initiator concentration [I] to the 0.50 power, i.e., V_p ∝ [I]^0.50, and the viscosity-average molecular weight M _v is approximately inversely proportional to the 0.50 power of the initiator concentration, i.e., M _v ∝ [I]^?0.50. With the progress of the reaction, the initiator exponent of the reaction rate equation decreases gradually from 0.50 to 0.25, but that of the molecular weight (1) equation remains constant up to 20% conversion and thereafter begins to decrease. Since the kinetic data at zero conversion satisfy the steady-state kinetics of the free-radical-initiated homogeneous vinyl polymerization, it is suggested that the initiation of emulsion polymerization of styrene is a two-step process. It starts in the aqueous phase by the primary free radicals from the water-soluble initiator or secondary free radicals derived from the soap molecules. The second step occurs in the monomer-leaded micelles by the water-soluble or water-insoluble macroradicals or by radicals derived from the soap molecules. The latter are likely to be produced in the aqueous phase by the oxidation of soap with S₂O₈^2?ions or SO₄^? radicals. It has been noted that the rate of thermal decomposition of persulfate increases by a factor of 6–8 times under different experimental conditions in the presence of soap.     

Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). V. Kinetics of initial template polymerization

The influence of stereoregular poly(methyl methacrylate) (PMMA) as a polymer matrix on the initial rate of radical polymerization of methyl methacrylate (MMA) has been measured between ?11 and +60°C using a dilatometric technique. Under proper conditions an increase in the relative initial rate of template polymerization with respect to a blank polymerization was observed. Viscometric studies showed that the observed effect could be related to the extent of complex formation between the polymer matrix and the growing chain radical. The initial rate was dependent on tacticity and molecular weight of the matrix polymer, solvent type and polymerization temperature. The accelerating effect was most pronounced (a fivefold increase in rate) at the lowest polymerization temperature with the highest molecular weight isotactic PMMA as a matrix in a solvent like dimethylformamide (DMF), which is known to be a good medium for complex formation between isotactic and syndiotactic PMMA. The acceleration of the polymerization below 25°C appeared to be accompanied by a large decrease in the overall energy and entropy of activation. It is suggested that the observed template effects are mainly due to the stereoselection in the propagation step (lower activation entropy Δ S_p^?) and the hindrance of segmental diffusion in the termination step (higher activation energy Δ E_t^?) of complexed growing chain radicals.