Kinetics and mechanism of the anionic polymerization of acrylamide monomers

The thermodynamics, kinetics, and mechanism of the anionic polymerization of a number of acrylamide monomers has been studied with the use of isothermal and scanning calorimetry, liquid chromatography, ¹H NMR and IR spectroscopy, mass spectrometry, and chemical analysis of functional groups. It has been demonstrated that the polymerization system shows the living character and the interchain exchange reactions are absent. It has been shown that N,N-diethanolacrylamide and N,N-diethanol(meth)acrylamide are uninvolved in anionic polymerization. The causes of this phenomenon have been ascertained. The products of the anionic polymerization of acrylamides are hyperbranched copolymers containing heterochain and carbochain fragments. Macromolecules contain end amide and acrylamide groups; in some macromolecules, end tert-butoxide groups of the used polymerization initiator are detected. For the products of the anionic polymerization of the acrylamide monomers under study, the temperatures of glass transition and melting have been measured.     

Kinetics and mechanism of polymerization of methyl methacrylate initiated by stibonium ylide

Homopolymerization of methyl methacrylate (MMA) was carried out in the presence of triphenylstibonium 1,2,3,4-tetraphenyl-cyclopentadienylide as an initiator in dioxane at 65°C±0·l°C. The system follows non-ideal radical kinetics (R _p ∝ [M]^1·4 [I]^0·44 @#@) due to primary radical termination as well as degradative chain-transfer reaction. The overall activation energy and average value ofk ₂ ^p /k _t were 64 kJmol⁻¹ and 0.173 × 10⁻³ 1 mol⁻¹ s⁻¹ respectively     

Atmospheric oxidation mechanism of naphthalene initiated by OH radical. A theoretical study

The atmospheric oxidation mechanism of naphthalene (Nap) initiated by the OH radical is investigated using density functional theory at B3LYP and BB1K levels. The initial step is dominated by OH addition to the C(1)-position of Nap, forming radical C(10)H(8)-1-OH (R1), followed by the O(2) additions to the C(2) position to form peroxy radical R1-2OO, or by the hydrogen abstraction by O(2) to form 1-naphthol. In the atmosphere, R1-2OO will react with NO to form R1-2O, undergo intramolecular hydrogen transfer from -OH to -OO to form R1-P2O1 radicals, or possibly undergo ring-closure to R1-29OO bi-cyclic radical; while the formation of other bi-cyclic intermediate radicals is negligible because of the extremely high Gibbs energy barriers of >100 kJ mol(-1) (relative to R1+O(2)). The mechanism is different from the oxidation mechanism of benzene, where the bi-cyclic intermediates play an important role. Radicals R1-P2O1 will dissociate to 2-formylcinnamaldehyde, while R1-2O will be transformed to stable products C(10)H(6)O(3) via epoxide-like intermediates. A few reaction pathways suggested in previous experimental studies are found to be invalid.     

Kinetics of surface‐initiated atom transfer radical polymerization

Although atom transfer radical polymerization (ATRP) is often a controlled/living process, the growth rate of polymer films during surface‐initiated ATRP frequently decreases with time. This article investigates the mechanism behind the termination of film growth. Studies of methyl methacrylate and methyl acrylate polymerization with a Cu/tris[2‐(dimethylamino)ethyl]amine catalyst system show a constant but slow growth rate at low catalyst concentrations and rapid growth followed by early termination at higher catalyst concentrations. For a given polymerization time, there is, therefore, an optimum intermediate catalyst concentration for achieving maximum film thickness. Simulations of polymerization that consider activation, deactivation, and termination show trends similar to those of the experimental data, and the addition of Cu(II) to polymerization solutions results in a more constant rate of film growth by decreasing the concentration of radicals on the surface. Taken together, these studies suggest that at high concentrations of radicals, termination of polymerization by radical recombination limits film growth. Interestingly, stirring of polymerization solutions decreases film thickness in some cases, presumably because chain motion facilitates radical recombination. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 386–394, 2003     

Chemiluminescence in the oxidation of phenyl-substituted silole radical anions and dianions

The emittor in the chemiluminescent electron transfer oxidation of the radical anions and dianions of 1,1-dimethyl-2,5-diphenyl- and 1,1-dimethyl-2,3,4,5-tetraphenylsilole is shown to be the parent compound. Chemiluminescence is reported in the oxidation of the radical anions of 1,2,5-triphenylphosphole, 2,3,4,5-tetraphenylthiophene-5-dioxide and 1,1-diphenyldibenzosilole.     

Radiation-induced grafting polymerization by the anionic mechanism

The radiation-induced grafting polymerization of phenylacetylene and 2-methyl-5-vinylpyridine (2M-5VPy) onto low-density polyethylene has been investigated under strict identical conditions, using crude and thoroughly dried monomers. In the case of thoroughly dried monomers, the radiation-induced grafting is performed by the combined (radical + anionic) mechanism. The kinetics of radical and anionic grafting of 2M-5VPy are investigated in detail. The activation energies are 4.8 ± 0.3 and ?2.7 ± 0.3 kcal/mole for the radical and anionic grafting, respectively. The initial rate of grafting is approximately proportional to the dose rate to the 0.47 ± 0.03 and 0.92 ± 0.03 power for the radical and anionic grafting, respectively. The initial rate of grafting is approximately proportional to monomer concentration to the 1.55 ± 0.05 and 2.1 ± 0.05 power for the radical and anionic grafting, respectively. These data conform to the contribution of the anionic mechanism in a thoroughly dried system. The mechanism of radiation-induced anionic grafting is discussed.     

Kinetics and mechanism of emulsion polymerization initiated by oil-soluble initiators. II. Kinetic behavior of styrene emulsion polymerization initiated by 2,2′-azoisobutyronitrile

In order to clarify the general kinetic behavior of emulsion polymerization initiated by oilsoluble initiators, the emulsion polymerization of styrene initiated by 2,2′-azoisobutyronitrile was as a typical example, investigated thoroughly. The variations of the polymerization rate and the number of polymer particles produced with changes in emulsifier (sodium lauryl sulfate), initiator, and monomer concentrations initially charged and the reaction temperature were determined. It is shown from these experimental results that the kinetic behavior of this emulsion polymerization system is quite similar to that of styrene emulsion polymerization initiated by the water-soluble initiator, potassium persulfate despite the difference in the principal loci of radical production in both systems.     

Kinetics and mechanisms in anionic ring-opening polymerization

Recent advances in the anionic ring-opening polymerization (AROP), including covalent (pseudoanionic) polymerization, are reviewed. Thermodynamics, kinetics, and mechanisms of AROP are discussed, covering mostly polymerization of oxiranes, lactones and cyclic siloxanes as monomers. The following general problems of AROP are discussed: anionic polymerizability, thermodynamics - particularly of the monomers exhibiting low ring strain, chemistry of initiation, structures and reactivity of active species. New phenomena, particularly polymerization with reversibly aggregating species are analyzed in more detail. Chain transfer to polymer - the major side reaction - is analyzed quantitatively, by introducing the selectivity parameter β, expressed by the ratio k_p/k_tr. This parameter has been determined for the anionic and pseudoanionic polymerization of ϵ-caprolactone.     

Kinetics of polymerization initiated by peroxides containing heterocyclic groups. I. Kinetics of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide

The rate and degree of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide and, for comparison, by dilauroyl and dibenzoyl peroxides were measured at several temperatures as a function of the initiator concentration. Also the rates of initiation were determined by the inhibition method with Banfield's radicals. The rate of polymerization initiated by difuroyl peroxide appears to be lower than could be expected from the rate of initiation determined by the inhibition method and from the decomposition of difuroyl peroxide. In the case of polymerization of vinyl acetate there are significant deviations from the proportionality between R_p and the square root of the initiator concentration, which follows from the conventional kinetic scheme. The degrees of polymerization are also low, and the plots of P _n^?1 versus R_p are not linear. These deviations can be accounted for by postulating a retardation effect of the furan cycle and chain transfer to difuroyl peroxide.     

Metal chelates in vinyl polymerization: Kinetics and mechanism of acrylonitrile polymerization initiated by Cu(II) imine complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(II) 4-anilino 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(II) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCl₄), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were ≥2 at two different temperatures and in different solvents. The square-root dependence of R_p on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formation was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.     

Kinetics of polymerization of vinyl monomers initiated by lead tetraacetate

A systematic study of the thermal polymerization of α-chloroacrylic acid and α-bromoacrylic acid in aqueous nitric acid was carried out. The effect of variation of monomer concentration lead tetraacetate concentration, hydrogen ion concentration, ionic strength, and temperature on the rate of monomer disappearance was carried out. Based on the experimental observations, suitable reaction schemes were proposed for the polymerization of the above monomers. The rate constants and the thermodynamic parameters were evaluated.     

The free radical initiated polymerization of diethylfumarate

The kinetics of polymerization of diethylfumarate initiated by 1,1′ azo-bis-isobutyronitrile have been studied at temperatures between 60 and 80°. Difficulty in isolating the polymer was overcome by using a petroleum ether-methanol two-phase system to separate the monomer and polymer, and by precipitating the polymer from the methanol phase with an aqueous salt solution. The density of the polymer varied from 1·183 g/cm³ at 80° to 1·211 g/cm³ at 20°, giving volume contractions of approximately 16 per cent for complete conversion of monomer into polymer. The initiator exponent was about 0·45, i.e. slightly lower than normally obtained from free radical initiated vinyl polymerization. The overall energy of activation for the polymerization was 89 ± 2 kJ/mole. Constants for chain transfer with monomer, determined from rate and molecular weight measurements at 60, 70 and 80, were in the region of 0·005 0·017.     

Atom transfer radical polymerization of styrene initiated by triphenylmethyl chloride

Triphenylmethyl chloride (TPMCl) was employed for the first time as the initiator of atom transfer radical polymerization (ATRP) of styrene in the presence of CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst and cyclohexanone as solvent. The kinetic plot was first-order with respect to monomer. A linear increase of number average molecular weight (M_n) vs. monomer conversion was observed, and the molecular weight distribution (MWD) was relatively narrow (M_w/M_n = 1.2-1.5). ¹H NMR spectra revealed the ω-Cl group at the chain end. Another two initiators, benzyl chloride (BzCl) and diphenylmethyl chloride (DPMCl), were also employed in contrast with triphenylmethyl chloride to investigate the influence of phenyl numbers on the polymerization.     

Atom transfer radical polymerization initiated by N‐bromosuccinimide

N‐Bromosuccinimide (NBS) was used as the initiator in the atom transfer radical polymerizations of styrene (St) and methyl methacrylate (MMA). The NBS/CuBr/bipyridine (bpy) system shows good controllability for both polymerizations and yields polymers with polydispersity indexes ranging from 1.18 to 1.25 for St and 1.14 to 1.41 for MMA, depending on the conditions used. The end‐group analysis of poly(MMA) and polystyrene indicated the polymerization is initiated by the succinimidyl radicals formed from the redox reaction of NBS with CuBr/bpy. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5811–5816, 2004     

Kinetics of polymerization by activated monomer mechanism

Polymerization of cyclic ethers by activated monomer mechanism involves consecutive additions of protonated monomer molecules to the growing macromolecules fitted with hydroxyl groups at their ends. For oxirane itself and symmetrically substituted oxiranes there is only one kind of hydroxyl groups and one, unique way of ring-opening. Unsymmetrically substituted oxiranes provide however two sites of attack and two different hydroxyls, resulting from these ring-openings. Kinetics of polymerization of epichlorohydrin (chloromethyloxirane) has been studied and all four rate constants determined, namely rate constants of the primary and secondary alcoholate chain ends with a protonated monomer, opening in result of the attack on substituted or unsubstituted carbon atom. These rate constants are (in mol⁻¹·1·s⁻¹ at 25°C, in CH₂Cl₂ solvent): k₁₁ = 0.055, k₁₂ = = 0.41, k₂₂ = 0.135, and k₂₁ = 0.0011 (e.g. k₁₂ is the rate of reaction of the primary alcohol producing the secondary alcohol). Thus, polymerization proceeds almost exclusively on the secondary alcoholate groups, reproducing themselves (k₂₂).     

Nonsteady-state kinetics for anionic polymerization of polar monomer initiated instantaneously by electron transfer

With the help of the nonsteady-state method, the kinetic differential equations for the anionic polymerization of polar monomer initiated instantaneously by electron transfer with monomer termination are treated rigorously. The expressions for the molecular weight distribution, the number-average and weight-average degrees of polymerization, and the functionality distribution are derived in closed form. A theoretical means is established by which all the molecular parameters of the polymer can be calculated from polymerization conditions, such as the reaction constants, the concentrations of initiator and monomer, and the monomer conversion.     

Kinetics and mechanism of radical polymerization of weak unsaturated acids in aqueous solutions

The behaviour of weak unsaturated acids (such as acrylic and methacrylic) and their salts in radical polymerization in aqueous solutions was studied. A characteristic of these reactions was attributed to change of the effective reactivity of the propagating radicals with the nature of the reaction mixture. The data suggest that the formation of ion pairs may be responsible for a considerable increase in the propagation rate and, in consequence, in the overall polymerization rate. For alkaline values of pH, chain propagation involves only radicals having ion pairs at their ends; the participation of the ion pairs in the propagation can influence the microstructure of the polymer chains. Due to stereochemical control effected by the ion pairs, practically stereospecific polyacids may, in certain cases, be formed. Investigations on the temperature dependence of microtacticity have given values of activation enthalpy and entropy differences greatly exceeding those known up to now for isotactic and syndiotactic radical additions.     

TiCp2Cl-catalyzed living radical polymerization of styrene initiated by oxirane radical ring opening

Epoxides and paramagnetic early transition metal complexes are introduced as two new classes of initiators and catalysts, respectively, for living radical polymerizations. Thus, Ti(III)Cp2Cl synthesized in situ from the reduction of TiCp2Cl2 with Zn catalyzes the radical ring opening of oxiranes to initiate the radical polymerization of styrene. A linear dependence of molecular weight on conversion, low polydispersity, and reinitiation of the polymerization in the presence of fresh monomer indicates that the polymerization is living and that it most likely occurs by the reversible endcapping of the macroradical with Ti(III). Moreover, epoxides provide convenient access to alcohol chain ends, suitable for further transformations.     

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.     

Reactivity indices as a measure of rate constants for protonation of radical anions and dianions

The DFT-based reactivity indices were used to describe protonation reactions of radical anions (RA) and dianions (DA) of aromatic compounds. A correlation between the experimental rate constants for protonation and the global reactivity indices was found. The indices were expressed through the electron affinities and ionization energies computed at the B3LYP level of theory. The protonation reactions of RA and DA of aromatic compounds are correctly described by the reactivity indices calculated as the inverse of the difference between the formal formation potential of RA (or DA) and the formal reduction potential of the proton donor.