Mechanism of N-vinylcarbazole polymerization on Co(II)–13X molecular sieve

Kinetics of polymerization of N-vinylcarbazole over Co(II)-13X molecular sieves in toluene have been studied. The rate of polymerization (R_p) has been found to be second order with respect to percent exchange level of Co(II) and also to the NVC concentration at all the reaction temperatures of 40, 50 and 60°C. The rate increases with decreasing pH of the original exchanging salt solution up to a pH of about 3.5, beyond which it falls. The overall activation energy of polymerization has been found to decrease with increase in monomer concentration, exchange level of Co(II), and the hydrogen ion concentration of the original exchange solution. Average degree of polymerization also follows a similar trend. A mechanism of polymerization involving simultaneous propagation on both metal ion Co(II) and proton on a zeolite surface has been suggested. The two propagation routes are characterized by an average activation energy of 10.36 kcal/mol and 5.40 kcal/mol on the metal ion and proton centers, respectively.     

Photopolymerization initiated by charge–transfer complex. X. Photopolymerization of methyl methacrylate with the use of isoquinoline–sulphur dioxide charge–transfer complex

Aqueous polymerization of methyl methacrylate in visible light was studied using isoquinoline–sulphur dioxide (IQ–SO₂) charge–transfer complex as the photoinitiator. Analysis of kinetic and other data indicate that the polymerization proceed via a radical mechanism and the termination is dependent on the initiator concentration. Chain–termination via degradative chain (initiator) transfer appears to be predominant here.     

Mechanism of charge-transfer polymerization. V. Photopolymerization and photocyclodimerization of N-vinylcarbazole in the N-vinylcarbazole–oxygen–solvent system

Photochemical reactions of N-vinylcarbazole (VCZ), studied in various solvents, were profoundly influenced by the atmosphere. In the deaerated system radical polymerization of VCZ occurred in various solvents, e.g., tetrahydrofuran, acetone, ethyl methyl ketone, acetonitrile, methanol, sulfolane, N,N-dimethylformamide (DMF), or dimethyl sulfoxide (DMSO). By contrast, when dissolved oxygen was present, cyclodimerization of VCZ occurred exclusively to give trans-1,2-dicarbazole-9-yl-cyclobutane in such polar, basic solvents as acetone, ethyl methyl ketone, acetonitrile or methanol. In stronger basic solvents, i.e., sulfolane, DMF, or DMSO, simultaneous radical polymerization and cyclodimerization of VCZ proceeded, the ratio of the cyclodimerization to the radical polymerization decreasing in the order, sulfolane > DMF > DMSO. In dichloromethane, on the other hand, cationic polymerization of VCZ occurred irrespective of the atmosphere. It is suggested that oxygen acts as an electron acceptor to the excited VCZ, electron transfer occurring in polar solvents from the excited VCZ to oxygen to give transient VCZ cation radical. The effect of solvent basicity on the photocyclodimerization of VCZ is discussed.     

Hydrogen effects in propylene polymerization reactions with titanium‐based Ziegler–Natta catalysts. II. Mechanism of the chain‐transfer reaction

Hydrogen is a very effective chain‐transfer agent in propylene polymerization reactions with Ti‐based Ziegler–Natta catalysts. However, measurements of the hydrogen concentration effect on the molecular weight of polypropylene prepared with a supported TiCl₄/dibutyl phthalate/MgCl₂ catalyst show a peculiar effect: hydrogen efficiency in the chain transfer significantly decreases with concentration, and at very high concentrations, hydrogen no longer affects the molecular weight of polypropylene. A detailed analysis of kinetic features of chain‐transfer reactions for different types of active centers in the catalyst suggests that chain transfer with hydrogen is not merely the hydrogenolysis reaction of the Ti? C bond in an active center but proceeds with the participation of a coordinated propylene molecule. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1899–1911, 2002     

Copolymerization of styrene and vinyl acetate by successive photoinduced charge‐transfer polymerization

The synthesis of a diblock copolymer of styrene and vinyl acetate (VAC), PS‐b‐PVAC, was performed by successive photoinduced charge‐transfer polymerization (CTP) under UV irradiation. A novel amphiphilic diblock copolymer of PS‐b‐PVA then was obtained by the hydrolysis of the diblock copolymer PS‐b‐PVAC with sodium ethoxide as a catalyst. Both of them were characterized by Fourier transform infrared, H NMR, and gel permeation chromatography in detail. The effect of the solvents on the CTP and the kinetics of the CTP are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 914–920, 2000     

Mechanism of the three-dimensional polymerization of glycol methacrylates. II. The system glycol monomethacrylate–glycol dimethacrylates–solvents

The three-dimensional polymerization of the system glycol monomethacrylate–glycol dimethacrylates–solvents has been studied. The kinetic dependences thus obtained were interpreted in terms of the dependence of rate constants of the individual reactions on the properties of the medium used. The three-dimensional polymer formed was characterized in the range from medium to the highest conversions.     

Charge transfer spectra of complexes with benzoquinonechlorimides as electron acceptors

Charge transfer absorption maxima have been determined for a number of new complexes between substituted quinonechlorimides and π-donors in cyclohexane. Electron affinity value of the acceptors p-benzoquinone(4)-chlorimide (BC), 2-chloro p-benzoquinone(4)-chlorimide (MCBC), 2,6-dichloro p-benzoquinone(4)-chlorimide (DCBC) and 2,3,6-trichloro p-benzoquinone(4)-chlorimide (TCBC) have been determined from these spectra and compared with those of the corresponding quinones. Results on E_LVMO values for these acceptors as obtained by semi-empirical MO calculations show the same trend. Factors which determine the electron affinity of a quinonoid are discussed.     

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     

Ruthenium(III) catalysis in polymerization of vinyl monomers by charge‐transfer mechanism with aminoalcohols and carbontetrachloride: A kinetic study

The kinetics of ruthenium(III) catalyzed polymerization of vinyl monomers (M) (methyl‐, ethyl‐, and butylacrylates) by charge‐transfer mechanism with aminoalcohols (AA) (namely, ethanol‐, diethanol‐, and triethanol amines) and carbontetrachloride in dimethylsulfoxide medium have been studied. The rate of polymerization depends on the [CCl₄]/[AA] ratio and may be represented as and The rate of polymerization of monomers with each aminoalcohol was found to be in the order R_p (methyl‐)> R_p (ethyl‐)> R_p (butylacrylate) while that of each monomer with different aminoalcohols was found to be in the order of R_p tertiary > R_p secondary > R_p primary aminoalcohol. The suitable mechanism for the polymerization process consistent with kinetic data has been proposed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 585–592, 2006     

Ethylene polymerization reactions with Ziegler–Natta catalysts. III. Chain-end structures and polymerization mechanism

Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit a number of features that differentiate them from polymerization reactions of α olefins: (1) a relatively low ethylene reactivity, (2) markedly higher polymerization rates in the presence of α olefins, (3) a high reaction order with respect to ethylene concentration, and (4) a strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions¹ provided the basis for a new kinetic scheme that postulates the equilibrium formation of Ti C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts several new features of ethylene polymerization reactions, one being that chain initiation via insertion of any α-olefin molecule into the Ti H bond should proceed with an increased probability compared to that via ethylene insertion into the same bond. As a result, a significant fraction of ethylene/α-olefin copolymer chains should contain α-olefin units as the starting units. This article provides experimental data supporting this prediction on the basis of both a detailed structural analysis of co-oligomers formed in ethylene/1-pentene and ethylene/4-methyl-1-pentene copolymerization reactions and a spectroscopic analysis of chain ends in the copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4281–4294, 1999     

Kinetics and mechanism of the cationic polymerization of trioxane. II. Consideration of hydride transfer

The occurrence of hydride-transfer reactions during the cationic polymerization of trioxane was demonstrated, and rate constants were obtained. The donor of hydride ions in the transfer reactions was the monomer. The hydride-transfer reaction was a first-order reaction with respect to the concentration of the monomer, and it was governed, just as polymerization and depolymerization were (Shieh, Y. T.; Chen. S. A. J. Polym. Sci. Part A: Polym. Chem. 1999, 37, 483–492) by morphological changes. The hydride-transfer rate constants were 5 orders of magnitude smaller than those for polymerizations and depolymerizations. The rate constants for the reactions, including the polymerizations, depolymerizations, and hydride transfers, were smaller for the active centers on the solid surface than for those in solution, that is, k^′_p was less than k_p, k^′_d was less than k_d, and k^′_ht was less than k_ht. As a reaction medium, benzene had special effects on the kinetics of the cationic polymerization of trioxane. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4198–4204, 1999     

Enynones in organic synthesis. II. An electron transfer mediated synthesis of methylenecyclopentenones

The electrocyclizaton of enynones to methylenecyclopentenones is markedly accelerated by phenols and catechols having a low oxidation potential.     

Ethylene polymerization reactions with Ziegler–Natta catalysts. I. Ethylene polymerization kinetics and kinetic mechanism

Kinetics of ethylene homopolymerization reactions and ethylene/1-hexene copolymerization reactions using a supported Ziegler–Natta catalyst was carried out over a broad range of reaction conditions. The kinetic data were analyzed using a concept of multicenter catalysis with different centers that respond differently to changes in reaction parameters. The catalyst contains five types of active centers that differ in the molecular weights of material they produce and in their copolymerization ability. In ethylene homopolymerization reactions, each active center has a high reaction order with respect to ethylene concentration, close to the second order. In ethylene/α-olefin copolymerization reactions, the centers that have poor copolymerization ability retain this high reaction order, whereas the centers that have good copolymerization ability change the reaction order to the first order. Hydrogen depresses activity of each type of center in the homopolymerization reactions in a reversible manner; however, the centers that copolymerize ethylene and α-olefins well are not depressed if an α-olefin is present in the reaction medium. Introduction of an α-olefin significantly increases activity of those centers, which are effective in copolymerizing it with ethylene but does not affect the centers that copolymerize ethylene and α-olefins poorly. To explain these kinetic features, a new reaction scheme is proposed. It is based on a hypothesis that the Ti—C₂H₅ bond in active centers has low reactivity due to the equilibrium formation of a Ti—C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4255–4272, 1999     

Ethylene polymerization reactions with Ziegler–Natta catalysts. II. Ethylene polymerization reactions in the presence of deuterium

Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit several features which differentiate them from polymerization reactions of α-olefins: a relatively low ethylene reactivity, higher polymerization rates in the presence of α-olefins, a high reaction order with respect to ethylene concentration, and strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions (see ref. 1 ) provided the basis for a new reaction scheme which explains all these features by postulating the equilibrium formation of a Ti C₂H₅ species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts that the β-agostically stabilized Ti C₂H₅ groups can decompose in the β-hydride elimination reaction with expulsion of ethylene and the formation of a Ti H bond even in the absence of hydrogen in the reaction medium. If D₂ is used as a chain transfer agent instead of H₂, the mechanism predicts the formation of deuterated ethylene molecules, which copolymerize with protioethylene. To prove this prediction, several ethylene homopolymerization reactions were carried out with a supported Ziegler–Natta titanium-based catalyst in the presence of large amounts of D₂. Analysis of gaseous reaction products and polymers confirmed the formation of several types of deuterated ethylene molecules and protio/deuterioethylene copolymers, respectively. In contrast, a metallocene catalyst, Cp₂ZrCl₂ MAO, does not exhibit these kinetic features. In the presence of deuterium, it produces only DCH₂ CH₂ (CH₂ CH₂)_x CH₂ CH₂D molecules. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4273–4280, 1999     

Hydrolytic polymerization of caprolactam. II. Vapor–liquid equilibria

The system water–caprolactam–polymer at equilibrium is regarded as a solution consisting of two solvents (water and caprolactam) and one solute (polymer). The activities of water and caprolactam in equilibrium at 270°C in the range of 2–10 wt-% total water content have been determined by vapor-pressure measurements. Water shows large negative deviations from Raoult's law, as a consequence of the different size of water and polymer molecules. The partial molar free energies of mixing are compared with the expressions derived from the Flory-Huggins theory of polymer solutions; the results are not conclusive, but seem to indicate a qualitative agreement with the theory. The increase in vapor pressure during polymerization in sealed systems and the water dependence of the polycondensation equilibrium are discussed and explained in terms of water activity changes.