Effect of amines on the ceric ion-initiated polymerization of vinyl monomers. II. Polymerization of acrylonitrile by ceric ion in presence of various substituted amines

The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate R_p is independent of ceric ion concentration and can be expressed by the equation: R_p = k₁ [amine] [monomer] + k₂[monomer]², where k₁ and k₂ are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.     

Kinetic Study of Cationic Polymerization of α-Methylstyrene Initiated by BuOTICl3 In Dlchloromethane Solution

The cationic polymerization of α-methylstyrene Initiated by n-BuOTiCl₃ has been studied at -70° C in dlchloromethane solution by using a calorlmetric technique. Polymerizations were performed under high vacuum either in dry conditions for which low monomer conversions were observed (4-12%), or In the presence of added cocatalyst (H₂O or HCl). In these last cases, yields were quantitative, and it was shown that polymerization rate was proportional to added water concentration and first order with respect to catalyst and to monomer. A kinetic scheme is proposed, based on a monomer-Independent initiation step and on a unimolecular termination process. At -70° C, the initiation rate is higher than termination rate during the whole course of the polymerization, and the concentration of active centers increases continuously. The following rate constants were found at -70°C: k_i. = 17 ± 6, k = 2.2 ± 1.1 ± 10⁴,k_trm = 30 ± 15 liter/mole-Sec, and k_t =0 54 ± 0 05 sec^?1. At -50 and -30° C, the concentration of active centers goes through a maximum during the polymerization and incomplete monomer conversions were observed, showing that all the catalyst is consumed. The different rate constants were tentatively estimated at these temperatures by using a simulation method, and this led to a negative value of ca. -7 kcal/mole for the apparent activation energy for propagation, and to a value of ～ 5 kcal/ mole for E_i. The observation of a negative (E_p)_app might be explained either by a shift of the dissociation equilibrium of the growing ends or by a solvation process of these growing ends by monomer prior to the propagation step.     

Kinetics and mechanism of dissolved organic phosphorus (DOP) digestion by the UV/O3 process

In this study, the kinetics and mechanism of UV/O₃ synergistic oxidative digestion of dissolved organic phosphorus (DOP) were investigated, focusing on the ozone direct oxidation and hydroxyl radical oxidation parts of glufosinate and triphenyl phosphate (TPhP). The p-chlorobenzoic acid (p-CBA) was selected as the probe compound, and two kinds of reaction kinetic models were proposed by competitive kinetic method with R_ct according to the different scale of rate constants of hydroxyl radical oxidation. Under the condition of weakly alkaline (pH = 9.0) and weakly acidic environment (pH = 5.0), the second-order rate constants of glufosinate and TPhP was determined indirectly to be ko_{3/glufosinate} = (2.903 ± 0.247)M⁻¹s⁻¹ and ko_3/TPhP = (3.307 ± 0.204) M⁻¹s⁻¹ by ozone direct oxidation, and k_{·OH/glufosinate} = (1.257 ± 1.031) × 10⁹ M⁻¹s⁻¹ and k_·OH/TPhP = (7.120 × 10⁸ ± 0.963) M⁻¹s⁻¹ by hydroxyl radical oxidation, respectively. The comparison of the contribution levels of the two parts to the digestion process showed that the contribution levels in the digestion of glufosinate and TPhP processes both the contribution of ·OH were higher than those of ozone, 86.3% and 72.6%, respectively.     

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.     

Rate constants for the reaction of hydrated electrons and hydroxyl radicals with acrylate monomers

The hydrated electron (e⁻_aq) and hydroxyl radical rate constants with 18 acrylate-, methacrylate-, crotonate-, fumarate- and maleate esters are discussed. The constants approach the diffusion-controlled limit. k(e⁻_aq) and k(OH) change in opposite direction; if k(e⁻_aq) is high then k(OH) is small. This tendency is connected with the nucleophilic character of e⁻_aq and the electrophilic character of OH, although the site of attack of e⁻_aq and OH is different: carbonyl versus vinyl group.     

Solvation effect in the thermal decomposition of 2,2′‐azoisobutyronitrile in the three‐component system

The thermal decomposition rate constant (k_d ) of 2,2′‐azoisobutyronitrile in acrylonitrile (AN; monomer A)–methyl methacrylate (MM; monomer B) comonomer mixtures in N,N‐dimethylformamide (DMF) as a function of the comonomer mixture composition and its concentration in the solvent at 60 °C was studied. The dependences k_d = f(x_A ,C) [x_A (mole fraction of A in the comonomer mixture) = A/(A + B) = A/C, where C is the comonomer mixture concentration] have a different course as a function of C: from a curve k_d = f(x_A ) approaching the straight line (C = 2 mol · dm⁻³) to a convex curve possessing a maximum at a point x_A = 0.7 (C = 4 mol · dm⁻³) to a curve with a flattened wide maximum within the range of x_A = 0.2–0.8 (C = 7 mol · dm⁻³) to a curve with the shape of a lying s (C = 9 mol · dm⁻³). All the courses of the experimental dependences k_d = f(x_A ,C) can be explained with a hypothesis of initiator solvation by the comonomers AN and MM and the solvent DMF. The existing solvated forms, their relative stability constants, the thermal decomposition rate constants, and the relative contents in the system were determined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2156–2166, 2000     

About propagation rate constants in carbocationic polymerizations

Published carbocationic propagation rate constants vary between 2 10³ and 5 10⁹ L·mol⁻¹·s⁻¹, e.g. for k_p^± with styrene in CH₂Cl₂. The low values were deduced from an evaluation of [P_n^±], the high values from competitive experiments assuming diffusion-controlled termination. Recent kinetic and spectrophotometric studies of indene living polymerization have given intermediate values (5 10⁴ to 5 10⁵ L·mol⁻¹·sec⁻¹). An explanation of the high values obtained by the competition method is suggested.     

Synthesis and kinetics of polymerization of hydrophilic monomers: 2,3-dihydroxypropylacrylate and 2,3-dihydroxypropylmethacrylate

Unsaturated monomers containing none, one, or two hydroxyl groups were obtained by the reaction of glycerol (1,2,3-trihydroxypropane) with acrylic and methacrylic chloride. The experimental values of the mole fractions of the different monomers were compared with those theoretically obtained by considering different mechanisms involving two or seven kinetic constants. Agreement between the theoretical and experimental results could only be achieved by assuming that the reactivity of the hydroxyl groups changed with the presence of the substituents. The investigation of the radical polymerizations 2,3-dihydroxypropylacrylate (GA) and 2,3-dihydroxypro- pylmethacrylate (GM) was carried out at several temperatures in water–dioxane solutions. Ultraviolet spectroscopic techniques were used to determine the kinetic constants, and the results were compared with those obtained in the same conditions for methyl acrylate, methyl methacrylate, 2-hydroxyethylacrylate, and 2-hydroxyethylmethacrylate. The values of the ratio k_p/k_t^1/2 for the methacrylic monomer GM were higher than 0.5 L^1/2 mol^−1/2 s^−1/2 at temperatures between 50 and 65 °C. These values exceeded 2 L^1/2 mol^−1/2 s^−1/2 for the acrylic monomer GA, perhaps the highest values reported for this kind of monomer. Electron paramagnetic resonance spectroscopy was also used to study the polymerization of GM. All the polymers were soluble in the reaction mixture until very high conversions, and the gel effect was never detected at monomer concentrations equal to or lower than 1 mol L⁻¹. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1843–1853, 2001     

Free‐radical copolymerization of styrene and itaconic acid studied by 1H NMR kinetic experiments

The free‐radical copolymerization of itaconic acid (IA) and styrene in solutions of dimethylformamide and d₆‐dimethyl sulfoxide (50 wt %) has been studied by ¹H NMR kinetic experiments. Monomer conversion versus time data were used to estimate the ratio k_p · k_t^−0.5 for various comonomer mixture compositions. The ratio k_p · k_t^−0.5 varies from 5.2 · 10⁻² for pure styrene to 2.0 · 10⁻² mol^0.5 L^−0.5 s^−0.5 for pure IA, indicating a significant decrease in the rate of polymerization. Individual monomer conversion versus time traces were used to map out the comonomer mixture–composition drift up to overall monomer conversions of 60%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed can be observed. This depletion becomes more pronounced at higher levels of IA in the initial comonomer mixture. The kinetic information is supplemented by molecular weight data for IA/styrene copolymers obtained by variation of the comonomer mixture composition. A significant decrease in molecular weight of a factor of 2 can be observed when increasing the mole fraction of IA in the initial reaction mixture from 0 to 0.5. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 656–664, 2001     

Thioketone‐Mediated Polymerization of Butyl Acrylate: Controlling Free‐Radical Polymerization via a Dormant Radical Species

It is demonstrated by experiment and simulation that the commercially available thioketone 4,4‐bis(dimethylamino)thiobenzophenone is capable of controlling AIBN‐initiated bulk butyl acrylate polymerization at 80 °C. On the basis of molecular weight data and from monomer conversion versus time curves, the associated rate parameters are estimated. The addition rate coefficient, k_ad, for the reaction of a propagating chain with the thioketone is close to 10⁶ L · mol⁻¹ · s⁻¹ and the fragmentation rate coefficient, k_frag, is around 10⁻² s⁻¹ giving rise to large equilibrium constants in the order of 10⁸ L · mol⁻¹. Furthermore, cross‐ and self‐termination of the dormant radical species are identified to be operational.

     

A laser flash photolysis kinetic study of reactions of the Cl2− radical anion with oxygenated hydrocarbons in aqueous solution

A laser photolysis–long path laser absorption (LP‐LPLA) experiment has been used to determine the rate constants for H‐atom abstraction reactions of the dichloride radical anion (Cl₂⁻) in aqueous solution. From direct measurements of the decay of Cl₂⁻ in the presence of different reactants at pH = 4 and I = 0.1 M the following rate constants at T = 298 K were derived: methanol, (5.1 ± 0.3)·10⁴ M⁻¹ s⁻¹; ethanol, (1.2 ± 0.2)·10⁵ M⁻¹ s⁻¹; 1‐propanol, (1.01 ± 0.07)·10⁵ M⁻¹ s⁻¹; 2‐propanol, (1.9 ± 0.3)·10⁵ M⁻¹ s⁻¹; tert.‐butanol, (2.6 ± 0.5)·10⁴ M⁻¹ s⁻¹; formaldehyde, (3.6 ± 0.5)·10⁴ M⁻¹ s⁻¹; diethylether, (4.0 ± 0.2)·10⁵ M⁻¹ s⁻¹; methyl‐tert.‐butylether, (7 ± 1)·10⁴ M⁻¹ s⁻¹; tetrahydrofuran, (4.8 ± 0.6)·10⁵ M⁻¹ s⁻¹; acetone, (1.41 ± 0.09)·10³ M⁻¹ s⁻¹. For the reactions of Cl₂⁻ with formic acid and acetic acid rate constants of (8.0 ± 1.4)·10⁴ M⁻¹ s⁻¹ (pH = 0, I = 1.1 M and T = 298 K) and (1.5 ± 0.8) · 10³ M⁻¹ s⁻¹ (pH = 0.42, I = 0.48 M and T = 298 K), respectively, were derived. A correlation between the rate constants at T = 298 K for all oxygenated hydrocarbons and the bond dissociation energy (BDE) of the weakest C‐H‐bond of log k_2nd = (32.9 ± 8.9) − (0.073 ± 0.022)·BDE/kJ mol⁻¹ is derived. From temperature‐dependent measurements the following Arrhenius expressions were derived: k (Cl₂⁻ + HCOOH) = (2.00 ± 0.05)·10¹⁰·exp(−(4500 ± 200) K/T) M⁻¹ s⁻¹, E_a = (37 ± 2) kJ mol⁻¹ k (Cl₂⁻ + CH₃COOH) = (2.7 ± 0.5)·10¹⁰·exp(−(4900 ± 1300) K/T) M⁻¹ s⁻¹, E_a = (41 ± 11) kJ mol⁻¹ k (Cl₂⁻ + CH₃OH) = (5.1 ± 0.9)·10¹²·exp(−(5500 ± 1500) K/T) M⁻¹ s⁻¹, E_a = (46 ± 13) kJ mol⁻¹ k (Cl₂⁻ + CH₂(OH)₂) = (7.9 ± 0.7)·10¹⁰·exp(−(4400 ± 700) K/T) M⁻¹ s⁻¹, E_a = (36 ± 5) kJ mol⁻¹ Finally, in measurements at different ionic strengths (I) a decrease of the rate constant with increasing I has been observed in the reactions of Cl₂⁻ with methanol and hydrated formaldehyde. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 169–181, 1999     

Caesium as counter-ion in the anionic polymerization of ethylene oxide—II: Kinetics in hmpt

Results are reported for the kinetics of the anionic polymerization of ethylene oxide in hexamethylphosphoramide using the caesium alkoxide of the monoethylether of diethylene glycol as initiator at 40·0°.The reactions were found to be first order in monomer and 0·5 in initiator; rates are depressed by adding caesium tetraphenyl boride. These results indicate that propagation takes place by free ions and ion pairs; the respective propagation rate constants are k_(?) = 22 and k_(±) = 0·2 M 'sec.     

Absolute rate constants for the gas-phase reaction of OH radicals with cyclohexane and ethane at 295 K

The absolute rate constants for the gas-phase H-atom abstraction by hydroxyl radicals from cyclohexane and ethane have been determined at room temperature. OH radicals were produced by pulse radiolysis of an H₂O-Ar mixture, and the decay of OH was followed by monitoring the transient light absorption around 309 nm. The rate constants were found to be k = (5.24±0.36) × 10⁻¹² and (2.98±0.21) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ for cyclohexane and ethane, res- pectively. These results are compared with literature data.     

Kinetic study of isothermal oil shale pyrolysis: 1. Mathematical model of the evolution of organic pyroproducts

An isothermal fluidized bed reactor was used for a kinetic study of oil shale pyrolysis. The rate of volatile hydrocarbon evolution was monitored by flame ionization detector. An innovative approach to the data obtained, which we adopted in the present study, led us to a simple kinetic model. The rate of volatile hydrocarbon evolution is described as a linear combination of three parallel independent first-order reactions characterized by three rate constants, k₁ = 2.6·10⁶ exp(−23.6 kcal/RT) s⁻¹, k₂ = 2.3·10⁶ exp(−26.0 kcal/RT) s⁻¹ and k₃ = 9.3·10⁵ exp(−28.1 kcal/RT) s⁻¹. The kinetic effect due to the particle size of the sample is probably due to heat transfer effects.     

Kinetics of the reactions of hydroxyl radicals (OH) and of chlorine atoms (Cl) with methylethylether over the temperature range 274–345 K

The rate constants for the gas-phase reactions between methylethylether and hydroxyl radicals (OH) and methylethylether and chlorine atoms (Cl) have been determined over the temperature range 274–345 K using a relative rate technique. In this range the rate constants vary little with temperature and average values of k_MEE+OH = (6.60_−2.62^+3.88) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and k_MEE+Cl= (34.9 ± 6.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ were obtained. The atmospheric lifetimes of methylethylether have been estimated with respect to removal by OH radicals and Cl atoms to be ca. 2 days and ca. 30–40 days, respectively. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 231–236, 1997.     

Effect of imidazole substitution on the dimerization reaction of manganese(III) porphyrin in aqueous environments: Temperature jump study

Equilibrium constants for ligand binding and rate constants for a dimerization reaction in the presence of the ligand imidazole were determined for the manganese(III) porphyrin in 0.1M KNO₃. Imidazole binds to the manganese porphyrin in stepwise equilibria to form the diligated dimer (MnPL)_D and further to the di-imidazole monomer, MnP₂. Analysis of temperature jump kinetic data, supported by spectrophotometric studies, showed that the phenomenon responsible for the relaxation is the dissociation of the ligated dimer. The mechanism proposed involves a self dissociation of the imidazole bound dimer and a ligand induced dimer dissociation viz:

At 302°K, the rate constants evaluated are k₁ = 4.8 × 10⁶ M⁻¹ S⁻¹, k₋₁ = 200 S⁻¹k₂ = 5.4 × 10⁷M⁻¹ S⁻¹ and k₋₂ = 2500 M⁻¹ S⁻¹.     

Determination of Absolute Rate Constants for Radical Polymerization and Copolymerization of Ethyl α-Chloroacrylate: Effects of Substituents on Reaction Rates of Monomer and Polymer Radical

The propagation and termination rate constants (k_p and k_t) for the radical polymerization of ethyl a-chloroacrylate (ECA) were determined by the rotating sector method k_p = 1660 and k_t = 3.33 × 10⁸ L/mol?s at 30° C. The absolute rate constants for cross-propagations in copolymerization were evaluated from the k_p determined for ECA or those for common monomers and the monomer reactivity ratios. The reactivities of ECA and poly-(ECA) radicals estimated as the rate constants of cross-propagations were accounted for by using equations relating these rate constants to the polar and resonance effects of the substituents. ECA was highly reactive toward various polymer radicals as expected from the resonance effects of the carbethoxy and chloro substituents. The poly(ECA) radical was found to be more reactive than common polymer radicals. The reactivity of a polymer radical in cross-propagation seemed to increase with increasing electron-accepting power by facilitating electron transfer from a monomer required for the new C-C bond formation.     

Photolysis of polyphosphate ions in alkaline aqueous solution

Photolysis of pyrophosphate and tripolyphosphate ions in aqueous solution is proposed to produce electron detachment with formation of pyrophosphate and tripolyphosphate radicals (with quantum yields <0.1 at 266 nm), respectively. Formation of P₂O₇^·3− is observed after photolysis of both polyphosphate ions, because the decomposition of P₃O₁₀^·4− yields P₂O₇^·3−. The latter radicals further react with hydroxyl ions (k = 1.4 × 10⁶ M⁻¹s⁻¹) generating HO^· radicals. The reaction of the solvated electrons with molecular oxygen produces O₂^·−. The rate constants for the reaction of SO₄^·− radicals with P₂O₇⁴⁻ and P₃O₁₀⁵⁻ were also measured. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 111–117, 2000     

Solvent effect in the polymerization of e-caprolactone initiated with diethylaluminum ethoxide

Kinetics of ϵ-caprolactone (ϵCL) polymerization initiated with diethylaluminum ethoxide in benzene (C₆H₆) and acetonitrile (CH₃CN) as solvents was studied and compared with the previously studied polymerization conducted in tetrahydrofuran (THF) solvent. Kinetic data were analyzed in terms of the kinetic scheme: “propagation with aggregation,” assuming that actually propagating active species (P_n*) aggregate reversibly into the unreactive (dormant) species . The determined equilibrium constants of deaggregation (K_da) decrease with decreasing solvent polarity, namely K_da (in mol²·L⁻²) = (1.3 ± 0.7)·10⁻² (CH₃CN), (1.8 ± 0.5)·10⁻⁵ (THF), (4.1 ± 0.7)·10⁻⁶(C₆H₆), whereas for the rate constants of propagation the opposite is true, k_p (in mol⁻¹·L·s⁻¹) = (7.5 ± 0.3)·10⁻³ (CH₃CN), (3.87 ± 0.01)·10⁻² (THF), (8.6 ± 0.9)·10⁻² (C₆H₆) (25°C). The latter effect is explained by a specific solvation (the stronger the higher solvent polarity) of the active species already in the ground state in the elementary reaction of the poly(ϵCL) chain growth: C₂H₅[OC(O)(CH₂)₅]_nO(SINGLE BOND)Al(C₂H₅)₂ + ϵCL → C₂H₅[OC(O)(CH₂)₅]_n+1O(SINGLE BOND)Al(C₂H₅)₂. © 1996 John Wiley & Sons, Inc.     

Anion Cryptates: Synthesis,Crystal Structures,and Complexation Constants of Fluoride and Chloride Inclusion Complexes of Polyammonium Macrobicyclic Ligands

Three macrobicyclic octamines 1–3 and the macrotricyclic hexadecamine 14 have been synthesized. The octamines 1–3 bind anionic substrates when protonated. The stability constants of the complexes between the protonated forms of the macrobicyclic polyamines and halide anions have been determined by pH-metric measurements. The stability constants in H₂O are very high; 1 in its hexaprotonated form binds F⁻ with high selectivity (selectivity F⁻/Cl⁻ > 10⁸), while 3 exhibits strong stability constants for both F⁻ and Cl⁻. Three X-ray structures have been obtained, one where F⁻ is held inside the cavity of 1 · 6H⁺, one where Cl⁻ is included in 3 · 6H⁺, and 3 · 6H⁺ where the cavity is empty.